- Email: [email protected]
Road accident involvement per miles travelled—IV
ooO1_4575/78/0601_0143/SO2 0010
Accra’ Anal & Prev Vol. IO. pp. 143176 0 Permmon Press Ltd 1978 Pnntcd m Great Bntain
ROAD ACCIDENT INVOLVEMENT TRAVELLED-IV L. A. II
Yongala
Street,
Abstract-This Vehicle-Mile
FOLDVARY
Balwyn.
(Received
PER MILES
3103 Victoria.
23 October
Australia
1973)
paper continues a series (Foldvary 1975. 1976, 1977) reporting on the 1963-64 Performance Survey. The variable treated in this part is age of driver.
Queensland
We first study the total annual mileage of the driver population of Queensland classified according to age of driver, followed by the total accident involvement also classified according to the driver’s age, and compare the variation. We then study the involvement rates for these sets of variables. Table 1 and Fig. 1 show the three corresponding curves, standardized by dividing mileage and accident figures by their respective averages thus making them comparable on the one scale. The regularity of the hyperbolic-type involvement-rate curve which results is striking, but not inconsistent with expectation. One need only consider that the rate-curve is a true expression of the variation of risk according to the effect of driver’s age and experience. The figures do not allow separation of tie effects of these variables, but the resultant risk curve speaks for itself. This involvement rate curve expresses decreasing accident risk with increasing maturity and experience. It clarifies the situation with respect to one of the most controversial issues in the road safety literature-the place of the two extreme age-groups-in road accident involvement. The risk of a driver under 20 is three-and-a-half-times that of the overall risk. It is nearly six-and-a-half-times the risk of a driver over fifty. The next youngest age group, 20-24 shows a substantial improvement over the under 20 group while still having an involvement rate of nearly 2300. The third group on the age scale is also third on the rate scale, and the decreasing Table
I. Male
Age
of
and female
Their vehicle-miles of travel, accident involvement and involvement rates per IO8miles of travel, by age of driver; Queensland, l%l
drivers:
Annual rotal -Tiles
IMveq
of
in Qillion
Tease
kale
Vehicle-
’
Accident
msvel,
~nvDlve?aent
Accident
Miles: Female
All
Xale
Female
Drivers:
All
tivolvemeart
Ratea Ule
Drivers:
Drivers:
(1)
(2)
(3)
(4)
85.9
8.6
94.5
3,224
20 to 24
199.0
26.7
225.7
4,844
25 to 29
249.9
32.5
282.4
3,061
30 to
528.7
83.8
612.6a)
5,191.
525
5,716
982
627
933
752
758
752
Lees
(5)
(6)
1 (7)
(8)
(91
than
20
39
3,449’)
3,751
2,566
3,647
339
5,183
2,431
1,269
2,293
273
3,334
1,224
840
221
I,, 1.00
40 to 49
514.0
57.1
571.. 1
3,866
433
4,299
50 to
429.1.
32.2
461.3
2,404
264
2,668
560
818
520
113
1,561
573
686
580
59
60 4 over Total:
252.7
16.5
269.2
1,448
237t.4b)26t3.1?)2648.70)25,085b)2238b) (a)
Includes
sex unknoun.
(b) (c)
Includes Includes
age unknown. sex unknown,ege
unknowqsnd 143
27,691’)
both
1,056
set
835
aud ege
1,051
unlmorm.
L. A. FOLDVARY
144
!
’
000 <20 XI-S4
25-29
I
1
30-39 Age
Fig.
I. Age
involvement
of rates
driver. per
Vehicle-miles lo* miles
and the annual
40-49
50-59
60+
of driver
of
population performance (I), accident involvements (2). and (3). as ratios of the average performance, average involvement, involvement rate respectively: Queensland. 1%1.
of exposure
over-all
rate rank follows exactly the increasing age rank up to age 60. But beyond this the involvement rate of the 60 and over age group is of statistically the same magnitude as that of the 50-59 age group. Many earlier studies have shown a rate increase for the over 60 age group when compared with the rate of the age group immediately below it. It may be that if the oldest sector of these drivers (say above 70) were shown separately, an increase would appear. This refinement was not possible here because of small sample-size. Nevertheless this may be the first study of its kind where large sample records of actual mileage of a whole driver population were used in calculating the denominator, and a whole year of accident occurrences for the numerator. It may be that this refinement, if compared with earlier methods using estimates of annual total mileage performances, petrol consumption, etc. can explain the difference. Considering first an urban driving environment, where speed is restricted, and drivers may select in many instances parallel routes, the oldest age class of drivers may be expected to be good drivers in spite of their probably reduced sensory capacity and slower reactions. Against these deficiencies stand their experience which is to be expected to be the longest and possibly, their temperament. A tendency to stop driving with deterioration of sensory abilities could also be expected. These considerations apply to some extent in a rural environment also. The aged driver might have a tendency to avoid difficult situations. Being mostly retired people they can avoid periods of commuter traffic, do drive less frequently during night hours, and may not undertake long, exhausting journeys. Our overall rates are more consistent with these logical considerations than some earlier findings, and moreover, are not the first ones of their kind. Munden (1965) has shown similar results in Great Britain; these were, however, based on sampled driver’s estimates of annual total mileage travelled. He concluded that “there may be an unconscious tendency on the part of those responsible to blame the older driver more often than the younger drivers in similar circumstances, and this could account for the higher peak in the blame/not blame rate”. Finally, perhaps the strongest arguments for the validity of the rates obtained, are the inner consistency, and high level of statistical reliability, points which will be discussed in the next section. AGE
OF
DRIVER
AS
THE
MAIN
VARIABLE
The stabilization of risk beyond age 60 is a balance of differing factors. Namely, if the rate for the top age group is further sub-classified according to additional variables, the result is in
Road accident
involvement
145
per miles travelled--IV
some instances a reduction, in other instances an increase. This divergent reaction of the sexagesimals and older drivers and various sub-groups by sex, age and so on, to various conditions of driving is a subject-matter of importance. The subsidiary variables will be type and severity of accident, the type of vehicle used and its level of occupancy, the area, as well as day of week and time of day, and design characteristics of the vehicle. The age of driver, age of vehicles interaction has already been discussed, with the finding that the age specific driver involvement rate retains its hyperbolic shape within each vehicle age class. Age of driver by severity of accident The last but one column of Table 2 presents the rates of casualty and non-casualty involvement for various age groups of drivers relative to exposure and for easier understanding of the nature of these two sequences the last column shows them as percentages of the corresponding overall rate. The two rate series are shown in Fig. 2, while their ratios are given
Age of driver Fig. 2. Age non-casualty
of driver by severity accident involvements accident
of accident involvement. Casualty accident involvements (2) per IO* miles of exposure: the ratio casualty accident involvement rates (Curve 3) Queensland.
(I), and per total
in Fig. 3. [see Foldvary (1%8)]. It is worthwhile to call attention to the striking similarity of casualty and non-casualty involvement except for that part related to the under 25 driver. The sharp decrease of the casualty-rate curve from the teenager class to the (20-24) class is evidenced by a drop in the percentage ratios from 436 to 232. The drop is less sudden although still of considerable magnitude in the non-casualty involvement series, from 316 to 213%. Note the close similarity of the two figures for the 20-24 years group (232 vs 213), and that the corresponding standardized rate-pairs are practically equal in all other age groups. A chi-square partition test was carried out to check this point statistically by using the actual number of accident involvements in the analysis, and the following result was obtained:
Component
of X2 due to:
(i) Difference between the two youngest age groups: (ii) Difference between the two youngest age groups and the rest: (iii) Difference within the five age groups of 25 and over: Total chi-square: AAP Vol IO. No 2-E
X2
Degrees of freedom
Probability level
5.0
I
0 025
s.
99
I
0.005
VHS.
1.9
4
0.750
NS
16.8
6
0.010
HS.
Level of significance
146
L. A. FOLDVARY Table 2. Involvement rates by age of driver, type and severity of accident, per lo* miles of exposure, for all types of vehicles combined Brisbane Metropolitan Area !J?nE
As f DZ; Severity of Accident:
bIultivehicle Rate _Lu
(20
OF
‘$az
Rate
ACCIDENT
Pedestrian
singlevehicle z a)
Casualuccldent_-_--__
Rate
Other wea Rate
Sal
Invclvement
All Za’
types
Rate
Sal
Rates:
1,265
477:
353
654
216
366
13
433
1847
484
20 -
24
543
205
142
263
t19
202
3
100
806
211
25 -
29
301
114
62
115
79
134
3
100
444
1.16
30 -
39
227
86
53
9s
50
85
3
loo
333
87
40 -
49
189
71
25
46
42
71
1
33
257
67
50 -
59
172
65
23
43
46
?B
2
67
242
63
60 %
more
162
61
20
37
26
44
1
33
209
3
a00
265
Werall.: (B.) @
tO0
54
Non-Casualty
100
Accident
59
100
Involvement
55 100
302
Rates
3191
302
630
463
31
206
18
300
3870
319
20 -
24
1872
177
322
237
23
153
6
100
2223
183
25 -
29
1264
119
a52
112
20
133
7
117
l443
119
964
91
121
89
IO
67
6
100
1101
91
757
72
75
55
a5
100
7
117
854
70
669
65
64
47
8
53
2
33
764
63
568
54
52
38
3
20
1.
17
623
51
1058
100
136
100
a5
a00
6
too
1215
ioa
358
X-39 40 -
49
50-59 60 &
more
Werall:
C. ) Weran ( 20
Accident _-
Invclvement
Rates:
4456
337
983
515
2.47
333
31
344
5716
20 -
24
241,4
IS75
464
243
1.42
192
9
100
3029
190
25 -
B
1565
118
213
112
99
133
9
100
1887
aaa
30 -
39
119%
9Q
174
91
60
St
9
a00
1434
9Q
40 -
49
946
72
to1
53
58
78
7
78
1111
70
50 -
59
861
65
87
46
54
73
4
44
1.006
6.3
729
55
72
m
29
39
3
33
832
52
1OQ
74
100
9
IOQ
1597
1oQ
60 &
more Werall Rate:
1323
1DQ
191
Provincial ____ (A.1 2816 _-_-__ Casual.tq_Accident Involvement 610 _;;~~___80s____~;___617---
ho
20
Urbau
tieas
Rates:
22
220
4667
655
-
24
1.247
270
602
336
189
324
30
300
2069
291
25 -
29
489
106
227
127
79
127
9
90
803
113
30 -
39
373
81
151
84
48
77
11
1 IO
583
82
40
-
49
291
63
11
40
51
82
8
80
420
59
50 -
59
338
71
64
36
25
40
5
50
432
61
60 &
more
275
60
77
43
21
34
5
50
377
53
462
100
179
100
62
100
10
100
712
100
Overall
@LNon-Casualty -___...__._
G
_.
Accident Invclvenent __._______ Rates: _________________. I 547 45 643
8998
511
20 -
24
3549
269
1523
361
1.3
186
9
90
5093
289
25 -
29
1498
113
595
141
12
171
27
270
2132
121
30 -
39
1110
84
369
87
4
57
14
140
1496
85
40
-
49
926
70
238
56
7
100
8
80
1179
67
50 -
59
820
62
119
28
5
71
5
50
950
54
764
58
105
25
5
50
873
50
1321
100
422
100
10
100
1760
100
60 & more OPeraI..
6642
503
231
(b) 7
100
(b)
Road accident involvementper milestravelled-IV
147
Table 2 (Coned)
Provincial Urban Areas !cYPS
Zv:Z sever&
-&J. tivehicle
Of
Accident:
RBte
vehicle
a)
F
Rate
A C C I DE N T Other
trian
Rate
:- a)
Involvement - fC.1 -- -__L_____^-l__60 20 - 24
OF Pedes-
Sin&?-
Rates
of
All
All accidents
types
F,a)
Rate
::a)
Rate
a) %
Accident&
9458 4796
530
3758
624
269
2125
353
202
426
616
292
22 39
110 13664
553
1295 7162
290
25 - 29
1987
111
821
1.37
91
1~32
36
180
2935
119
30 - 39
1,483
83
520
87
52
74
25
125
2079
84
40 - 49
1217
68
309
51
58
84
16
80
1599
65
50 - 59
1159
65
183
32
30
44
11
55
1382
56
60 & more
1038
58
182
31
21.
30
9
45
1250
51
t783
100
600
100
69
100
20
100
2472
too
Rural
Areas
Overall Rate:
(A.)
Casualts
Accident
of Queenslend
Involvement
Rates;_
+J
162
337
253
402
22
440
3
150
440
373
20 - 24
98
a04
$76
279
9
w
3
IdO
286
242
25 - 29
57
119
68
108
6
120
3
150
135
I,14
30 - 39 40 - 49
43 35
90 73
50 39
79 62
4 6
80 1.20
2
100
99 81
84
50 - 59
24
50
29
46
1
20
I.
50
56
47
6O&more
39
81
35
56
3
60
77
65
Overall
48
100
63
100
5
100
100
118
TOO
Non-CasualQ _ LB.1 __ ____________
(b) (h) .2
69
Accident Involvement Rates: _______________~._________c__
<20
448
238
586
364
2
200
8
200
1044
296
20 - 24 25 - 29
350 193
186 103
435 21.7
270 135
1 1
100 100
7 6
175 150
792 417
224 118
30 - 39
167
89
151
94
(b)
4
100
322
91
40 - 49
146
78
106
66
(h)
4
100
256
73
50 - 59
116
62
55
34
1
100
2
50
t75
50
60 & more
132
70
58
36 -I--_~-_-
1.
too
1
25 _--_-_-.
192
54
188
100
161
100
1
100
4
1.00
353
100
Overall
&L~Involveruent Rates of Al.1 Accidents. -~-~----_-~~--_----^-----_----~6 1.0 448
258 190
839 6 1.0
375 272
24 10
400 167
11
183
1484
315
10
167
1077
229
25 - 29
250
106
286
128
6
100
30 - 39 40 - 49
210 182
89 77
202 146
90
4
67
9 6
150 100
551 421
117 09
65
6
100
4
67
337
72
50 - 59 60 & more
140 171
59 72
84 93
38 42
2
33
67
230
49
5
83
4 1
17
269
57
236
1.00
224
100
6
100
6
100
471
100
( 20 20 - 24
Overall Rate (a)
Percentages
(b)
IneUfficient
shown exe those aample-adze:
of
rate
the corresponding
overall
has not been calculated.
rate.
148
L. A
FOLDVARY
Table 2 (Contd) Total
Age of
Area
of
TYPB
Driver; Severity
WiLtiRate
Pedestrisn
vehicle
Sal
Rate
ACCIDBHT
OF
Single
vehicle
of Accident:
Queenslaud
$a) --_-_
tspes _ ___~_a,_ _
Rate
Sal
_.
Casuel;Q__Accident -_--_--_-_Involvement
(A.)
All accidents _Gte
Other Rate
-
_- --m-m--
ka--
Rates:
677
413
389
519
103
367
7
233
1176
436
20 -
24
351
214
209
279
60
213
6
200
627
232
25 -
29
1.72
105
85
113
33
118
4
133
294
109
30 -
39
140
85
65
87
23
82
4
133
231
86
40 -
49
118
72
39
52
24
86
1.
33
182
67
50 -
59
102
62
32
43
16
57
2
67
151
56
1.10
67
38
51
12
43
164
100
75
100
<20
60 % more Overall
(a.1 --______ Non-CasuaItg _-_ ( 20
-
1 33 _ _- - -__ _ - -. 100 3 100 I--__
20
Accident Involvement -____w__-l__---___-_
161
60
270
100
--__-
. -
.
___-_
Xates:
1690
289
759
406
13
217
10
200
2471
316
20 -
24
1139
195
512
274
9
150
7
140
1667
213
25 -
29
626
107
244
130
7
117
8
160
886
113
30 -
39
522
89
172
92
3
50
6
120
702
90
40 -
49
445
76
114
61
6
100
5
100
570
73
50 -
59
355
61
65
35
4
75
3
60
426
54
60 8t more 352
60
64
34
1
17
2
40
419
53
100 ..______
5
100 782 -- _____ --___--_-
100
Gverall
584
100 _~
Involvement -CC.) _______ _ -( 20
187 ____
100 6 _^.____.___
-Rates __
of
AlI
Accidents:
2367
327
1148
433
115
338
17
213
3647
347
20 -
24
1490
199
722
276
69
203
12
150
2293
218
25 -
29
797
107
330
126
40
118
12
150
1180
112
jo
-
39
661
88
236
90
26
77
9
113
933
89
40 -
49
563
75
153
58
30
88
6
75
752
71
50 -
59
457
61
98
37
19
56
5
63
578
55
60 & more 462
62
101
39
14
41
3
38
580
55
100
262
100
34
100
8
too
Overall Rate:
747
(a)
Percentsges
(b)
Insufficient
shown are sample-size:
those
of
rate
the
corresponding
has not
been
1052 overall
100 rate.
calculated.
This shows that there is a highly significant difference between the casualty and noncasualty involvement rate series. This difference is, however, primarily due to the difference between the two youngest age groups and the rest; the difference within the two youngest age groups is also significant, while the difference within the five age groups from 25 upwards is statistically insignificant. This finding is added evidence that young drivers are not only often involved in road accidents relative to their exposure but that their involvements significantly more often end in sufferings. disablement and death. Curve No. 3 of Fig. 2 portrays the sequence of ratios of casualty accident to total accident for all age groups. Nearly one third of the total involvements of teenage drivers is of the casualty type, with lower values for the next four older age groups. From 50 on, the ratio starts to increase again at first slightly but the top age group attains a ratio outdone only by the teenage driver. The higher vulnerability of this advanced age is certainly a contributing factor. Age of driver by type of accident We next see how age specific involvement
rates of the two severity groups vary by type of
Road accident
involvement
0!__,1,‘,I,
1
<20 m-2425-29
of driver by severity of overall rates: (1) casualty
,
30-39
Age Fig 3. Age corresponding
149
per mtles travelled--IV
I 40-4s
I
! 50-59
!
I
60+
of driver
accident involvement. accident involvements, Queensland.
Standardized rates being (2) non-casualty accident
ratios of the involvements;
accident. The last page of Table 2 provides the detai1s.t The variation by age of driver for the three main accident types is illustrated in Fig. 4 using standardized rates. (Out of the two severity groups of pedestrian involvements, only the casualty type is plotted; the reason is again small sample-size in non-casualty pedestrian accidents.) The following features of the curves are immediately apparent: (1) their similarity in spite of the significant difference between them in statistical terms, (2) their regular form (hyperbolic, or in some cases parabolic)
I
400
b 'G 0, % P s 8 n
200
100
0
1, I
I ,‘I’
<20 20-2425-29
I !
I
30-39
40-49
50-59
60+
Age of drover Pig. 4. Standardized involvement rates of age of driver by type and severity of accident per IO* miles of exposure, Queensland. The standardized rates are ratios of individual rates to their corresponding overall rate, expressed in percentage form. (1) Multi-vehicle casualty involvements. (2) Single-vehicle casualty involvements. (3) Pedestrian casualty involvements. (4) Multi-vehicle non-casualty involvements. (5) Single-vehicle non-casualty involvements. tout of the four groups of type of accidents, the fourth one termed “the other types” combines those odd kinds of accidents that could not be sorted into the three main groups of multi-vehicle, single-vehicle and pedestrian accidents. Smallness of frequencies in this class, when spread over the seven age-groups of drivers renders it unsuitable for comparative studies.
150
L. A. FOLDVARY
so characteristic of our age specific involvement-rate curves; and in particular: (3) the sharp decrease in the rates from the first to the second to the third age group and the slow decrease thereafter which turns even into increases beyond the age group 50-59 in some cases; (4) that 30 years of driver age is a threshold that separates the greater from the lesser risk. Under that age every curve is above, and above that age every curve is below the line marking average risk. Besides the similarities, there are, however, characteristic differences between the curves, and these must be our main concern. They could provide us with evidence of the differences between the age groups in their level of risk. To attack this problem, we first consider the differences that contribute to the shape of the curves with respect to type and severity. Because severity is a difference of degree it is a secondary consideration in the study of causality. Examining first the type of accident three major types are distinguished: (a) Single-vehicle. No other road user is involved. and no other parties but the vehicle occupants are hurt. (b) Pedestrian. Although either the driver or the pedestrian or both could be responsible, only the pedestrian could be hurt, apart from exceptionally rare cases. (c) Collision. There is another driver or drivers whose actions might contribute to the outcome, and there are at least two groups of parties, occupants of the two (or more) vehicles who could be hurt. In the light of this consideration we examine the differences in the shape of the five curves of Fig. 4. As a first observation we see that involvement rates of the seven age groups vary the least in pedestrian accidents, the range between the two extreme values being 324 in casualty involvements, and 200 in the non-casualty ones. The greatest variation is in single vehicle accidents with values of 476 and 372 respectively. Collisions stand midway with 35 1 and 229 values. For a more detailed consideration, one must start with single-vehicle accidents, because their involvement rates could bring to light the comparative risk of the various age groups of drivers purely, unaffected by actions of other road users. We see the young driver (under 25) has in single-vehicle accidents the highest involvement in both severity groups. He has the second highest involvement in collisions, and the lowest in pedestrian accidents. It might be suggested that this sequence is a clear indication that in many collisions a second young driver could be involved, and that in many other would-be collisions a more mature second driver appears and the so avoided collision contributes to the bringing down the rate. Consequently, on purely theoretical considerations also the involvement ratios for the young driver agree with our figures: highest single-vehicle, mid-value for collisions, and lowest for pedestrian. This situation never reappears in any other age groups. The next two age groups (between 25 and 39) have involvement ratios shifted to other types of accidents notwithstanding that single-vehicle accidents still come out with the second or third top ratios in this comparison. Higher on the age-ladder, the position of the single-vehicle accident drops lower. In the 40-49 age group it occupies the third position with respect to casualty involvements, and the fourth position with respect to non-casualty involvements, and with the 50-59 age group it drops to the lowest, the fourth position in both severity groups. In these latter two age groups of drivers the pedestrian accident involvement achieves the top percentage ratio. This may be due to two reasons: (i) the drivers have proportionally less night driving than those under 30, a major source of accident involvement of the young driver and (ii) consequently they spend proportionally more of their driving time during the day, the period when pedestrians also are more frequent on the roads. The remaining age group (60 and above) presents a picture different form all other age groups. Its percentage involvement ratio is the highest in collisions in both of the severity groups; the single-vehicle accidents come second and pedestrian involvements last. This might perhaps be an indication that a proportion of older drivers has experienced some sensory deterioration or increased reaction-times.
Age of driver by type of area of the accident The involvement rates by age of driver, type and severity of accident are shown on pp. l-2 of Table 2, sub-classified according to metropolitan, provincial urban and rural areas. These pages give both the rates and their transformation into percentages, to facilitate comparisons between types of accidents. The ratios are plotted on Figs. 5-7 showing, however, for simplicity only the two most important types (Multi-vehicle and single-vehicle).
Road accident
involvement
per miles travelled-IV
151
(2)
I
600
I I
4oc
6 = e tk e c 8 & a.
4
2OC
-- c --
_-
IO<
-2 2425-29
3C
9
Age-classes
ITI --7=
4 of
19
.-
L-
50-59
60+
driver
Fig. 5. Brisbane metropolitan area; age of driver by multi-vehicle vs single-vehicle involvements by severity of accident, per IO* miles of exposure. Data shown are ratios of rates to their corresponding overall rate. 0 (I), Multi-vehicle casualty involvements: A (2). Single-vehicle casualty involvements: x (3). Multi-vehicle non-casualty involvements; 0 (4). Single-vehicle non-casualty involvements.
The
24 sets of ratios shown, which represent 4 types of accidents, 2 severity groups, and 3 types of areas, reinforce convincingly the findings of the preceding sub-section. All four basic characteristics of the age-specific involvement rates apply without exception and modification here also, namely their similarity, their shape, their sharp decrease at the start, followed by a slow decrease, ending in some cases with increases at the top age group, and finally, that driver’s age 30 appears to separate the higher from the lower risk. We proceed to examine specific features of these curves. The two youngest age groups of drivers again have the highest involvement in single-vehicle accidents and this applies to all three types of areas of the State, and to each severity group. There is one notable exception, however; the casualty involvements of teenage drivers in rural areas which has its highest involvement in pedestrian accidents. Considering the generally low frequency of pedestrians walking on rural roads, it appears that they could experience a relatively high risk of being hit by an inexperienced teenage driver. The three age groups of drivers between 25 and 50 have in all three areas their highest involvement either in pedestrian, or “other” accidents. Drivers aged 50-59 represent a transitional case, with rank-order of involvement agreeing for some accident types with those of the 4049 age group and in others with the 60 and older drivers. The former is the case with metropolitan casualty involvements, and provincial urban and rural non-casualty involvements, three cases where they have highest involvement ratios in pedestrian accidents. In the other three cases, including the metropolitan non-casualty, and the provincial urban and rural casualty accidents they have highest involvement ratios in collisions with other vehicles. The 60 and older drivers have in all cases but one their highest percentage ratios in collisions with other vehicles. (The significance of this was discussed in the preceding sub-section.) An exception is in rural non-casualty accidents where they have highest involvement ratios in the pedestrian accidents.t tBut this case conclusions.
needs
further
study,
because
the
sample-size
is not quite
large
enough
to allow
drawing
reliable
152
L. A. FOLDVARY I
<20
/
20-2425-29
30-39
40-49
Age -classes
of driver
50-59
60+
Fig. 6. Provincial urban areas of Queensland: age of driver by multi-vehicle vs single-vehicle involvements by severity of accident. per lo* miles of exposure. Data shown are ratios of rates to their correspondmg overall rate. 0 (1). Multi-vehicle casualty involvements: A (2) Single-vehicle casualty involvements: x (3). Multi-vehicle non-casualty involvements: 0 (4). Single-vehicle non-casualty involvements
P
)-
)-
I-
-4
,<20X)-2425-29
30-39
Age-classes
40-49
50-59
60t
of driver
Ftg. 7. Rural area of Queensland; age of driver by multi-vehicle vs single-vehicle involvements and severity of accident. per IO* miles of exposure. Data shown are ratios of rates to their correspondmg overall rate. 0 (1). Multi-vehicle casualty involvements: A (2), Single-vehicle casualty involvements: x (3). Multi-vehicle non-casualty involvements; l (4). Single-vehicle non-casualty involvements.
Road accident involvement per miles travelled--IV
153
We turn now to the involvement rates proper to see what additional information they can provide. It was pointed out that great regularity is observable throughout the 24 curves right up to the top age-class but with this particular class the curve starts in some of the cases to increase, and elsewhere continues its downward trend. If we attack this problem now in detail we see that there are 6 cases where the curve turns upward after reaching age 60; there are five obscure cases because of the smal1 sample-size. and in the other 13 cases the curve continues its downward trend. What is remarkable in this is that each of the curves representing types and severity groups in the rural areas belongs to the bending upwards type. The only remaining bending upwards case is represented by the provincial urban casualty single-vehicle accidents. The hyperbolic nature of the curves in metropolitan and other urban areas, and their parabolic nature in rural areas are well observable also on Figs. 5 (metropolitan), 6 (provincial urban) and 7 (rural). Each of these figures portray the most important groups of their kind, the casualty and non-casualty single-vehicle, and collision involvements. Solomon (1964) produced age-specific involvement rates of drivers per miles travelled, covering 600 miles of main rural highways of the United States. His four curves that cover day and night travel of male and female drivers, are the parabolic type bending upwards at both ends of the age-scale. Apart from the fact that his smaller sample-size did not permit him to obtain such a smooth mathematical form as we obtained, the general shape of his curves for the male driver is quite comparable with our corresponding curves. No earlier published work on the corresponding problem for urban roads is known to the author. Our findings that risk increases beyond age sixty when travelling on rural roads, but does not increase on metropolitan and other urban roads is not inconsistent with expectation. One need only consider the different driving and traffic conditions, the different average speeds and so on, on the rural and urban roads, and the different typical trips an elderly driver probably undertakes on these two kinds of roads. As seen from the detailed account given in this sub-section, there is regularity, a well defined trend in the involvement rates which points to the working of human factors in driver age. Age of driver by type
of vehicle
We have established (Foldvary 1977) that the private vehicle has significantly larger overall risk in each of the two severity classes than either of the two commercial vehicle groups, while these do not differ from each other significantly. The problem turns out to be much more complex when the three main vehicle-types are further sub-classified according to the age of driver. Part (D) of Table 3 and Fig. 8 present the results. Although the private vehicle remains at the top as the riskiest vehicle for three out of seven age groups of drivers, an important change occurs with respect to the teenage driver class. The otherwise high involvement when driving a private vehicle is surpassed in a large commercial (LC) vehicle. The small commerical (SC) vehicle proves on the other hand to be the most reliable vehicle with respect to accident involvement in the hands of drivers of most age groups. Its moderate size and moderate speed combined with the type of driver, are beheved to be the main factors. There are, however, circumstances under which the SC vehicle has the highest involvement rate. The curve for the LC vehicle is somewhat irregular, an unusual feature amongst our curves; for, an increase in the rate appears at the 25-29 age-group. Perhaps it is due to a chance variation, one of those rare occasions, considering that the sample-size does not drop. Figure 9 shows these rates divided according to severity. Its features of importance are that: fa) the teenage driver with high LC involvement retains his highest position in both casualty and non-casualty sub-groups and (b) the irregularity of the LC vehicle curve described above reappears in both severity groups. This suggests that reported mileage performance (a common denominator for the two severity groups) may be responsible for the irregularity. The thin lines hand-drawn on the graphs indicate a possible adjusted curve. A further sub-classification “age of driver by type of vehicle”, in this case by type of accident is given in Table 4 and in the related Fig. 10. The most important result so far obtained is the extraordinarily high risk of the teenage drivel in collision accidents when driving a large commercial vehicle. This is perhaps the only figure on the graph which appears out of place (refer to curve 5 of Fig. 10) indicating its unusually large size. The other curves are more or less parallel to each other, a feature that emphasizes the dominance of the factor “age of driver”.
154
L. A. FOLDVARY
Table 3 Involvement rates by age of driver. type of vehicle, area of involvement and severity of accident. per IO” miles of exposure Age
TYPE
of
Driver;
Private
Area of Involvement.
OF
Vehicleta)
.
All
VEHICLE Small
Casudty
Ccmmercial~bJ
BOW atr
a31
Large CwuaJ-ts
Cornmt~cial~~~
Non-cam atp
,
All
INVOLVEMENTS: (A.1 _--___Briabaue _--_
d
20 2 - 24 25 - 29
t900 859 ;:; 271 212 251
30 r;; 40 E a Zre Overall
Rate _iB.)
$ -
24 29
Overall _LQ
(a) (b) (c) (d)
8718 4750 2095 1.414 1171 583 973
734
1760
;:
‘146 879 395 277 254 1.84 189
120
354
%
Overall
z; - 29 24 30 - 39 40 ;; 50 :: 60 & more Overall
1198
4955 2164 71,5 519 403 440 412
43% 142
-is
104% 845 630 767
Rural Areas -__--__--__
24 29 39 49 59 more
<20
3713 2183
Provincial
z SJ 50 60 & more
( 20 22; ; 60 &
413
)
whole
Metropolitan
1300 555
5632
%
1116 lQl8 841
380 364 236 192 226
I,56 1 1469 869 ;I%
:95:: $833 1105 917 866
1611
300
1182
of
Queensland:
i;:;
Urbsn 1;;;: 2810 11933 1,574 1323 1386 2494 of
Areas
6871 ‘2% 523
21299 2990 2423
44:
1935 1238
zz (d)
1204 810 489
1482
298
1126
1424
8320 ‘2640 3C59 2501 1846 170 1 to47
14274 1523 1145 697 361 233 229
24655 5050 2364 1583
38929
;3?
96%: 2150 1745 1347 1202 716
705
I>818
2586
563
1443
2006
1335
601 275 206 111 76
1501
2102 915 846 481
3275 1836 909 756 499
88;1’: 574
:z ‘%
;zz 2280 1240 to94 804
Queensland. _--____-_
:62:: ;;; :;: 260 474
:;z 129 147 87
97;: 490
Z$ 579
z62 153 147
:;z 217
110
341
451
880 ;z:
:5:74 1017
:;:74 1325
:z 131 162 228
817 522 425 372 731
‘% 556 534 959
;07
107:
22 370 244 1*93 293
128
379
506
1572 381 414 289 169 173 146 224
3297 1225 1242 836 568 523 436 101
% 1656 1125 737 696 582 924
2% 398
al eenslg&
1349
2645
3994
;::
‘3:; 667 g
2484 1214 884 763 603 600 1090
:z 163 163 291
Area:
800
Private vehicles in this Table include cars,station wsggons Panel vans and utilities. Truck-type vehicles of every tjqe not included in the small vehicle @;rcup,and buses of every kind. -yInsufficient sample-size; rate has not been calculated.
and
taxis.
co;merci&
The other factors, type of vehicle and severity of accident, cause minor irregularities observable on the graph-but their basic form remains unaltered. The rates of the age groups are consequently a true measure of the relative risk of being involved in the particular types of accidents studied. The last sub-classification in our analyses is according to area of occurrence. This is given in Table 3. The table brings out some weak points in addition to those already described with respect to the very young and the old driver. The teenager driving a large commercial vehicle produces again some highly significant deviations from rates when driving other types of vehicles. But this feature appears only in the metropolitan and provincial urban areas. In rural areas, interestingly enough, the teenage driver has no significantly higher involvement. Especially the urban casualty involvement rates of this driver-vehicle combination are very large-23times in metropolitan, and 25-times in other urban areas of the corresponding overall rate, while the non-casualty involvement rates are 13-times and 17-times respectively the corresponding average rates. This finding is evidently related to the earlier one demonstrating high risk for this driver-vehicle combination in collisions. The much higher proportion of collisions in urban areas than in rural, is related to the high involvement rates of teenage drivers when driving large
155
Road accident involvement per miles travelled-IV
?9
30-33
40-49
50-5Y
60-t
Age of driver
Fig. 8. Involvement rates by age of driver and type of vehicle, per IO*miles of exposure, Queensland. (I) Small commercial vehicle; (3) E----O, Large commercial vehicle. O--0. Private vehicle; (2) A-A,
commercial vehicles in metropolitan and provincial urban areas. They appear much safer with these vehicies in rural areas. Turning now to the 60 and over drivers, our interest, as in earlier sections, concerns those cases where their involvement rate exceeds the rate of the 50-59 age-group. There are seven cases out of 18 in Table 3 in which this increase occurs, and five of these are rural cases. In fact, all but one of the rural age-specific sets of rates belong to this type, and the increases are significant. They are especialty large with respect to the LC vehicle group, in both severity classifications. Age of driver by hourly variation
We have already (Foldvary 1975, Fig, 1 and Table 3) shown variation in involvement rates broken down into two-hourly periods. The significance of this is that daily variation in risk is composed of two different periods. One is the late night and morning period (from 2 am to 8 am) which could be represented by a third-degree curve with a negative slope throughout while the bulk of the day (from 8 am to 2 am) is best described by a Gompertz-type growth curve. Some additional contribution to this problem is in FoIdvary (1976) subclassifying by day of week, area of occurrence, and severity of accident and by sex of driver. The basic conclusion reached is that every one of the within-day variations is so similar that they represent a single family of curves.
L. A. FOLDVARY 4000
T
-
T
(6) 5 5 h
i
-
3000
6 g I= E
I
(2) (4)
“0
\
s P d F
I
I \
-
2000
E _
i-
hi
z d E5
(5)i I!+ 1 (1)
\
1000 --
iN \\
---A.\
(3)
\ j' I’ 1
I /
~_,
IIt <20 iD-r(25-29
r
I
‘\ Y ‘\
-----. --
/ 0
I
I
I
30-39
40-49
---, 50-59
60
Age of driver Rg.
9. Involvement
rates
exposure, Queensland. volvements. (3) Small casualty involvements.
by age of driver, type of vehicle and severity of accident, per IO’ miles of t I) Private vehicle, casualty involvements. (2) Private vehicie, non-casualty incommerelal vehicle, casualty involvements. (4) Small commercial vehicle, non(St Large ~ommerciai vehicle, casualty involvements (6) Large commercial vehicle, non-casualty involvements
Age of driver is introduced in Table 5 and Fig. 11 to see what changes if any are associated with this factor in hourly variation of risk. The substantial variations are shown by a tree-dimensional surface where the ordinate represents the involvement rate per IO*miles of exposure, and the two abscissae represent age of driver, and two-hourly periods-t Most striking are rates of enormous size that reflect the combination young driver and night driving. From this point the risk surface goes down sharply in every direction, and in the foreground the graph depicts a flat low-risk surface that represents the twelve hours from 4 am to 4 pm and the drivers aged 30 and above. From 4 pm onwards the rates increase sharply, especially for the age-groups under fifty, and this part of the surface, especially before the hours of darkness can be attributed to many factors. From 8 pm to midnight the surface has a sharp slope from its low-point, portraying the risk of the oldest age-group of drivers, upwards. to its top position that portrays the youngest age group. Between midnight and 4 am, the period not shown on the graph, drivers of every age group have high involvement rates (Table 5) and teenage drivers have high rates throughout the day, and highest during the night. It appears worthwhile to examine the table and graph in more detail, and in particular, to study the two factors age of driver and periods of the day separately. Inspecting the individual age groups of drivers, we see that the general shape of the seven curves is that which we observed in earlier sections. It is the shape of the variation in the overall risk with time within a day. It undergoes, however some quite substantial changes with respect to various age groups at various parts of the day. To facilitate comp~isons between the age groups, Table 6 has been prepared: it presents the overall rates of Table 5 Part (Cl in tThe period from midnight to 4 am IS not shown on the graph (the data are available rates would make it too complicated. Table 5 also shows the casualty and non-casualty
in the table), involvement.
because
the very large
157
Road accident involvement per miles travelled--IV Table 4. Involvement
rates by age of driver, type of vehicle. and type and severity of accident per IO* miles of exposure: Queensland” TYPE Private
Ev:f ,,,&
OP
VEHICLB: snail
Vehicle ‘PPPE
OF
Large
Co!nmercial
Commercial
ACCIDENT
Accident
_&I
Casualty
Accident -----_I_-
Involvement
Rates:
786
436
122
456
350
53
1065
305
203
20 - 24
406
241
66
231
152
53
223
to4
34
25 - 29
178
93
38
175
97
32
288
79
37
30 -
39
133
60
23
149
91
25
191
60
25
40 - 49
123
37
26
106
46
16
108
31
23
50 - 59
111
34
18
87
28
12
106
42
(b)
60 & more
115
34
13
94
54
12
135
(b)
(b)
178
80
31
130
73 __--___
22 _ 1_--
145
48
23
(20
All
Drlvere
(BI)on-Casualfq -_----
Accident------ Involvement
Bates:
1801
827
(b)
1740
743
32
1436
863
(b)
20 - 24
1202
548
12
1030
479
4
896
31.1
(b)
25 - 29
648
240
8
696
306
5
862
343
(b)
30 - 39 40 - es
504 456
155 109
4 6
588 393
218 122
2 4
601 439
222 113
(b) 9
50 - 59
372
62
4
335
82
434
82
(b)
60 & more
376
59
(b)
295
74
3 1.0
1t3
(b)
187
6
529
191
4
524
163
6
( 20
All
DArera (C. ) Overall
Accident
InvclvemePlt
A
RateaL
1263
131
2t96
1093
85
3501
20 - 24
1.6cJa
789
78
1261
631
fl
1118
415
34
25 - 29
825
332
46
87i
403
37
1150
422
51
30 - 39
637
21.5
27
738
308
27
793
284
26
20 15 14
547 541 445
144 124 1824
33 24 (b)
zlf‘
-a-
@
2587
40 - 49 579 146 32 498 t67 50-59 4a3 96 21, 422 109 60 b more 491 92 14 12!? DrH8l.a 780 2e? x 264 (a) For details of type of vehicle refer to Table 3. (b) Rate has not been calculated due to insufficient sample-size
standardized
.26--
1107
203
form as ratios to the average rate of each particular age group. The table permits the following inferences: (1) The daily low-point of the various age groups falls without exception on the early morning hours; it is either during the period 4.00-5.59 or 6.00-7.59am. (2) The rate of each age group increases with passable regularity from the morning low-point throughout the day. (3) Two notable deviations are (a) the rate-curves of the two youngest age-groups have a protrusion at about the middle of the day from 10 am to 4 pm, and (b) the rate for every age group of 30-39 and above is larger during the period 2 pm to 4 pm than during the period of 4 pm to 6 pm. (4) As the driver becomes older, the afternoon line of demarcation (drawn on the table) that separates below average from above average rates shifts gradually to earlier hours of the day. Thus for the three age groups under 39 its position is at 6 pm. for the two age groups between 40 and 59 it is at 2 pm, and with respect to the age group 60 and above it is at noon. Now let us inspect the figures by taking the periods of the day as independent variables. Table 7 presents the corresponding standardized rates. The steady decrease with increasing driver age is observable throughout the Table, with the exception of the periods between midnight and 6 am. The variation during this period is rather irregular (and in some cases they are not even available due to the smallness of the sample). Where the sample was theoretically large enough, rates were calculated; but it must be realized that these rates are based on the
158
L.
A. FOLDVARY
Age
of driver
Fig. IO. Involvement rates by age of driver, type of vehicle, type and severity of accident per lo* miles of exposure: (I) Private vehicle invoivement in casualty collisions. (2) Private vehicle involvement in casualty single-vehicle accidents. (3) Small commercial vehicle involvement in casualty collisions. (4) Small commercial vehicle involvement in casualty single-vehicle accidents. (5) Large commercial vehicle involvement in casualty collisions. (6) Large commercial vehicle involvement in casualty single-vehicle accidents. (7) Private vehicle involvement in non-casualty collisions. (8) Private vehicle involvements in non-casualty single-vehicle accidents. (9) Small commercial vehicle involvements in non-casualty collisions. (10) Small commercial vehicle involvements in non-casualty single-vehicle accidents. (1I) Large commercial vehicle involvements in non-casualty collisions. (12) Large commercial vehicle involvements in non-casualty single-vehicle accidents.
smallest samples available and their confidence intervals are rather large. Further studies are therefore necessary to see how these rates vary with age between midnight and 6 am. The steady decrease of rates during the other periods of the day runs through all age groups with, however, three (or possibly four) periods during which an increase is evident at the oldest age group. The six (or eight) hour periods belonging to this group are those from 6 am (or 4 am) to 8 am, from noon to 2 pm, and from 6 pm to 8 pm, Age of driver by day-of-week of accident
Two basic conclusions were made in Part II (Foldvary 1976)while studying the effect of day of week on risk of involvement: (i) The variation in number of accidents by day of week follows closely the variation of vehicle-mile performances, an indication that it is a most important factor, and other factors (as it will be seen later) only under specific conditions have any significant contribution to this variation. This is very different from hourly variations where traffic has a subordinate role and day-night variation is the dominant factor. (ii) Considering the whole State, Saturdays are the worst having 34% higher risk than average followed by Fridays, 21% worse than average. The other days of the week are fairly even in their risk; their rates vary between 898 and 941, representing 86-90% of the average risk. This is in spite of the fact
Road accident involvement
159
Per miles travelled--IV
Table 5. Private vehicles, involvement rates by age of drwer. hour of rnvolvement and severity of accident per IO* miles of exposure: Brisbane metropolitan area’
Hour OS the XV; severity of
AGE 29-24
<"
25-29
DBIVEB _____
OF P-39
40-49
(A.)
__------
xtJ.-
lI.5Qam 3.59am
2.00-
;.;C$oo- ;.;‘,%&
__--_ Casualty Accident InVOlV@JllWnt 10538 28565 13411 127s 3287
8:OO: 9:59am 1%; tO.OO-11.5Qam Noon - L59pm
1723 2831
4.002.006.008.0010.00-l
1281 2882 2846 4277 4404
5.59pIu 3.59pm 7.59~~1 9.59pm 1.59pm
Average tB9d
D&I.y
50-59
237 207 %
z
445 823 ttz t684
z:
857
479
4.006.00-
5.59am 7.59aau
13% ll39l
;;w&
$Yg
‘ls8; :z:
8.0010.00-l
9.59am t .59ma
1971 2338
1.26 1 72;
::R
Noon2004.006.008.0010.00-I
1.59pm 4881 3.59pm 3450 5.59pm 2989 7.59pm 5285 9.59pm I1314 1.99~~ 8024
2936 r591 2666 5282 3465 __l__ 2178
f:: 1308 2658 2682 3502
___--**-_^__ (b)
264 182 157 2t3 %
67 229
:;i? 128 135 143 :;,”
‘:% 226 213 272 366 zz % 1289 413
z:
3;; lO37
627 1196
Es5
285 623 332 324
329
271
250
211
btSS:
13080 “Ez
35541 ‘;;:: 266
2%
Average
3714
1432
13821
1%4
317
55201 5173 z:
811 drivers
R&%3:
Accident _~_~-*---IInVO~VSIImit
_uNon-Caatity -_I-
Daily
6Oarld m0lX
Accident.
939 :;;: 1432 2218 2096 :% __ _ _ __ _ _ _ I _. - _ 1050 845
% 604
573 496
% 1%
g ;z
64% 1129 843 1064 1117 1547 766
773 705 96%
z;z 129g 1105 1844
z$! zz _..________---I 628 1198 -__-
tt xnvo1v0m8nt r&tee: j.C-) Overall Accide~ --I_--
MIS - t.59a 53647 LOO- 3.59am 26822 4.005.5Ysll 4602 6.007.59ma 2239 8.009.59am 3124 ao.oo-11.594361 Noon- 1.59pm 7712 2.0& 3.59pm 5332 4.005.59pm 4270 6.007.59pm 8%31 8.009.5Qpm t5591 iO.OO-11.59pm 12428 Daily Iverage (a) (b)
5610
t3 8E
3035
16194 3448
50368 4u1 333 463 852 859
871 937 1567
733 829 924
:z: 5495 ¶753
1099 949 :g
:z 1.226 1141.
g: 4557
2289 3173 3133
zz 2990
1862 2176
r9st
KS79
11t6
10t6
$2
Ibbj
712 677 708 639
1080
1st t6li --_an& taxi&
839
Private vehicles in this Table include cpzT,ntt9tion T-XL&I Rate ha6 not becahM.ated dtte to tionificiat d#e-r;iee.
that Sundays have the highest traffic volumes. Of course, the percentage of total travel performed on rural roads is much higher during Sundays than other days, and rural travel has generally lower involvement rates. There are various other Sections of this study that enlarged our knowledge of daily variation, treating as variables periods of the day type and severity of accident, type of vehicle, design characteristics and sex of driver. We now turn to the age of driver and day-of-week variations. The analyses for metropolitan and provincial urban areas are shown in Tables 8 and 9. The probability surface method was used as before to illustrate joint variation and Figs. 12-14 present the results. There is similarity between these figures, in that all three show day-of-week as less important than the age of driver. Still, the effect of Saturdays (and to a lesser degree Fridays) comes through cleariy from the surroundings, but do not go through ali age groups. At the oldest group the ridge ebbs away on all three graphs. On the other hand the ridge gets steeper as we progress from this old-age group to younger drivers, and culminates at the teenage driver. At this point, the top-risk age-class of driver combined with the top-risk day (Saturday) produces the high peak of the graphs. Notwithstanding the similarities, there are important differences. We shall study these differences by viewing the distributions of each set of rates from the side of one of the
L. A. FOLDVARY
Fig. 11. Overall involvement rates of private vehicles” by age of driver, and hour of occaston of the accident, per IO* miles of exposure.b The surface is that of the joint function Y = (XI, X2), where Y = involvement rate per IO’ miles travelled (in thousands). X, = the age of driver and X2 = hour of the occurrence of accident. “Including cars, station wagons, taxis and motor-cycles of every kind. bRates for the period between midnight and 4am are not shown: for reason see the text.
variables taken as the independent variable, and then from the other. Considering first the age of driver as independent we see that the various age groups follow diverse patterns in the metropolitan and in provincial urban areas as to the day-of-week variation. While in the metropolitan area the peaks and the second and third highest involvement rates fall on different days for different age groups, there is much uniformity in the provincial urban areas in this respect. Considering the metropolitan area, and the two youngest age groups of drivers, Saturday has the highest risk in both severity groups followed by Sunday (casualty) and Friday or Thursday (non-casualty). This pattern is unique for these age groups. For the driver between 30 and 50, Saturdays are again the most risk-producing days in casualty involvements, and between 40 and 49 also in non-casualty involvements, but between 30 and 39, Fridays has the top risk in non-casualty. For drivers aged N-59, Friday is the worst day with respect to casualty and for drivers 60 and above, Wednesdays in casualty and Thursdays in non-casualty. Another noteworthy fact about this oldest age group is that their third worst day in casualty involvements is Sunday, striking if one considers that this day is the best day for age groups of 40-59. Distinct from this variability is the uniformity in provincial urban areas. The highest risk
161
Road accident involvement per miles travelled-IV Table 6. Standardized overall involvement rates of pwate vehicles by age of driver and time of the accident, per IO’ miles of exposure; Brisbane metropolitan area* Time of the Dsy:
AGB OF DRIVER: M-24 25-29 30-29 40-49
(20
W-59
60 and IllOIW
MN.1.59eJn ?.OO- 3.59em 4.00- 5.59am 6.00- 7.59am 8.00- 9.59nm lO.OO-11.59am
Noon-
9.56 4.78 0.82 0.40 0.56 ro.;jR-
17.55 (b) 4.05 (b) 2.43 0.45 0.51 0.49 0.54 0.82 -1,l:; 0.66 I 11.38 0.73 1 0.77 ;‘; tf1.E_ ;;;1 _ . 0.76 1.82 1.45 1:25 2.76 2.36 1.67 2.20 1.69 2.38
1.59pm
2.00- 3.59pm 4.00- 5.59pm 6.00- 7.59pm 8.00- 9.59pm lO.OO-11.59pm Daily
Awrage (a)
1.00
ii3
t&XSi
(b) Rate has not been
14.50 3.08 0.77 0.54 0.69 0.80 0.86
2.x) 2.27
1.00
1.00
daily
averwe
1.00
For ertpndardisation,the Sg8-groUp
60.30 6.06 0.53 0.60 0.67 0.69 0.80
M
AU drivers
2.36 2.68
49.50 4.28 0.33 0.45 0.64 0.85 0.86 1.47 1.10 1.40 1.83 2.14
(b) (b) 0.85 0.81 0.84 0.76 1.13 1.08 I,.11 1.90 I.29 1.63
30.60 5.13 0.60 0.52 0.64 0.70 0.81 1.00 0.90 1.65 2.28 2.46
1.00
1.00
1.00
1.00
rat% of each partiCul8r
Unit-
calculated due to insufficient
n~plbsize.
Table 7. Standardized overall mvolvement rates of private vehicles by age of driver and period of the day per 10’ miles of exposure; Brisbane metropolitan area’ AGE
Time of the apS
Mi.2.004.006.008.0010.00-I Noon2.004.006.00.. 8.0010.00-t
1.59am 3.59&m 5.59am 7.59aa 9.59= f.5Vam 1. ‘j9pm 3.59pm 5.59pm 7.59pin 9.59gn! 1.59pnl
DpFly Average
@
20-24
25-29
t.09 3.24 4.75 2.70 3.02 3.86 5.93 3.31 2.92 3.06 4.24 3.12
1.08 1.48 7.62 1.87 1.57 3.01 1.70 2.46 E.49 I.43 1.94 1.30
(b) (b) 0.90 c..t3 1.51 1.12 l.l4 0.93 1.20 1.31 0.87 a.15
3.48
1.88
1.19
OF 30-39 1.69
DRIVBB 40-49
50-59
60& more
&U drivers
0.76 1.00 0.89 0.84 0.85 0.85 0.91 0.86 0.86 0.79
0.33 0.42 0.89 0.73 0.75 0.79 0.74 0.75 0.78 0.78 0.72 0.75
1.02 0.52 0.34 0.56 0.82 0.76 0.67 0.93 0.77 0.55 0.51 0.55
(b) (b) 0.74 0.82 0.68 0.57 0.73 0.56 0.64 0.60 0.X 0.34
1.00 1.00
0.86
0.69
0.63
0.52
1.00
1.01
(P) Par staudardieation in this Table,the aver-e
t.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
1.00
rate of each two-h0ur.Q
per&cd haa been taken as unit. fb) Rate
haa
not
been oPlCIikat8d due to insufficient
rample-eise.
days are Saturdays for every age group under 60 with respect to both casualty and non-casualty involvements with some minor variationst For drivers 60 and above, Tuesday had the worst risk in casualty and Friday in non-casualty involvements. It is significant that for these drivers Sundays are the best days in both severity groups of involvements and that the age group 50-59 also fared well on those days. We wilt now turn our attention to the involvement rates of Tables 8 and 9 with day-of-week taken as the independent variable. The interest here concentrates on the shape of the curves of age specific involvement rates for the various days. areas and severity groups. The findings obtained are as follows: (i) As in other cross-analyses of the age-specific rates so far made-this *The 40-49 group in casualty mvolvements, the 2%24 group in non-casualty involvements slipped to the 2nd place. Apart from this minor irregularity. the 2nd and 3rd place occupied in both severtty groups alternately by Fridays or Sundays. AAP Vol
IO. No L-F
162
L. A. FOLDVARI Table
8
Involvement
rates of private vehicles” by age of driver. day of week. and severity miles of exposure; Brisbane metropolitan area DAP
z%:: Sav& Of Accident
konday
-LA.)
l’uesday
CaauPlty
OF
,‘ledneadsy
Accident
of accident,
per IO*
WEBK l’huraday
Involvement -_
Friday
Saturday
Sunday
AL1 dqya
Rates
1376
1237
1407
2229
1571
2895
2395
1900
20
-
24
770
639
725
740
877
Ill32
977
859
25
-
29
402
513
413
593
499
591
385
483
30
-
39
244
357
2 1.2
235
396
516
372
329
40
-
49
210
221
275
228
361
434
184
271
50
-
59
249
214
262
234
368
260
175
251
60
& more
266
160
216
269
147
221
237
212
351
341
349
357
459
616
389
4t3
(20
Overull
(B. ) Non-Caaualtx (20
Accident -I----_--_--__
InVOlvanP3nt
R8tea:
2561
3049
2739
4821
3278
5223
4211
3713
2563
2714
2070
2183
20
-
24
1978
1995
1076
1862
25
-
29
1119
1290
1.136
1971
1748
1532
1300
1434
30
-
39
970
987
752
893
1508
1315
vi3
1050
40
-
49
792
678
899
820
1049
1168
553
845
50
-
59
988
881
979
672
898
694
444
767
60
& more
753
538
1031
559
516
108
508
630
1046
1086
1130
1424
1533
980
18198
Overall
IIt6
-1C.l
Overall
Accident
Involvement
Eateu:
3937
4286
41.46
7050
4849
8118
6606
5613
20
-
24
2756
2634
2601
2602
3440
3896
3047
3042
25
-
29
1521
1803
t549
2564
2247
2i23
1685
1916
30
-
39
121.4
1344
964
112%
1904
183t
1285
1379
40
-
49
1.002
899
1048
1410
1602
737
l.tt6
50
-
59
1237
1095
1241
906
1266
954
620
wia
60
& more
1,020
698
11247
828
663
929
745
841
1467
13886
1435
1487
1882
2149
1369
1611
(20
OIerall (8)
InClUdiUg
CPP8,atUtiOn
tt74
raggOna,
taxin,Pnd
mOtir
CyC.ba
Of
every
kind.
sub-classification produced the familiar hyperbolic curves. The similarity of these curves to one another demonstrates again that age of driver is the dominating factor whilst other factors (day of week and area) are modifying factors effecting minor variations in the individual curves. but not changing their general form significantly. (ii) In consequence, the curves show varying rates for the teenage driver, which are, however, invariably high, then they show sharp decreases through the second age group to the third, and slow decreases thereafter up to the sixties, and either further minor decreases or minor increases thereafter. (iii) The dividing line between the less than average and more than average rate appears to be at about age 30. (iv) A peculiarity with respect to the 60 and above age group is that: (a) in the metropolitan area their rate is higher than that of the age group 51-59 during the two week-end days in both severity groups, but lower than that during the working days in 7 cases out of 10, and inversely: (b) in the provincial urban areas their rate is higher than that of the 51-59 age group during the working days in 8 cases out of 10, but lower than that during the two week-end days. A score of important conclusions could be drawn from the findings in this Section with respect to both the metropolitan and provincial urban situations and their causes, which could include amongst others the effects of social customs, drinking habits, driver’s experience, deterioration of the sense-organs with age and so on. We leave the reader to form his own conclusions.
163
Road accident involvement per miles travelled-IV Table 9. Involvement rates of private vehicles” by age od driver, day of week and severity of accident. per miles of exposure: provincial urban areas of Queensland Age oi Driver ; SeverltJ
DAY Monday
Of
WEEK
OF
Tuesday ledneadag
IO*
Thursday
Friday
Saturday
Sunday All daya
Accident. &&J_Caaualts <20 20 25 30 40 50 60 &
24 29 39 49 59 more
OVerall
Acci_dent Involvement
Rates: --
2832 I713 688 437 377 434 453
3861 1470 451 419 359 290 663
3123 I268 (b) 513 (b) 356 222
4009 1108 534 325 320 286 373
7069 2976 944 515 463 640 455
7166 3625 1790 868 562 690 513
6020 2706 960 501 651 437 336
4955 21164 715 519 403 440 412
599
539
476
470
881
1258
912
734
_(B,1 __-Non-CEUUI Accident P_ 5235 6831 7026 642? 3234 2803 I677 1805 (b) I209 1144 1185
Involvement
Rates:
5690 3030 1467 924
11589 64t6 3630 I802
12040 6236 4890
1,t141
201.1
1515 1509
40 - 49 50 - 59
1 If30 914
I.002 540
(b) 7%
751 697
1555 1073
1773 1518
60 & more
1034
1160
834
849
122E
981
829
8718 4758 2095 1414 II71 883 973
OveralL
1639
1311
1,220
1130
2247
2705
a109
1760
I9206 9861
17161 8790
I3673 6922
(20 20 - 24 25 - 29 30 - 39
&l_‘ferall
Accident -_--__ Involvement
6004 2768
840
Entee:
(20 20 - 24 25 - 29
8067 8136 2365
10692 4104 2256
I0149 407) (b)
9699 4138
I8658 9392
2001
4624
6680
3728
2810
m - 39 40 - 49
1646 1507
1563 136t
1698 (b)
1249 107 1
2317 2018
2879 2335
2016 2t60
1933 1574
50 - 59
1,348
1112
983
1713
2208
127T
1323
Co & sore
1487
te23
83Q
1036
1222
1494
1165
lW5
Overall
2238
la50
t696
tsO0
1683 __--_ 3=3
3963
3021
2494
-
(a) Including cars, station waggcne, taxl8,Pad motor cyclea of evrrg kind. (b) Rate has not been calculated due to inaufflcient aamplcsize.
Age of driver by vehicle occupancy This study has been performed only for the Metropolitan Area, and for cars, station wagons and taxis. It was shown earlier (Foldvary. 1976) that the risk is the highest with the driver’s solo occupancy, and gradually (but not linearly), decreases as occupancy increases. Table 10 presents the variation in rates according to the combination age of driver and vehicle occupancy. In part (A) of the table the involvement incolvement rates are given in part (B) the non-casualty rates, and in part (C) the overall rates. Figures 15 and 16 bring out the nucleus of the Table, the first by classifying the driver age as independent variable and the second one by number of occupants as independent variables. Still more revealing are Figs. 17-19 which present severity rates separately. and in threedimensional form. The effect of the number of occupants and driver age is combined. These Figures and Table 10 tell us: (i) Vehicle occupancy has an effect, on casualty involvement similar to that on non-casualty save for the generally larger figures. (ii) The teenage-driver rates are different from those of the rest of the driver-population. They are not only much higher but they vary differently according to the various levels of occupancy. For the teenage driver. the worst type of occupancy appears to be three persons in
Fig. i-1. Brisbane metropolitan area. casualty accident involvement rates of private vehicles“ by age of driver and day of week of involvement. per 10” miles of exposure The surface is that of the lcnnt function Y = WC,. X:t. where Y = the involvement rate per ldmdes travelled (in thousand\). X, = the age of driver. X? = day of week of involvement a incIuding car<, station wagons, taxis and motor-cycles of every kmd.
1489 1990
Pi All.
I
1514
4
3
2
2 183
1.413
2595 IV01
504%
3666
4
*gfl
including Including
(a) (b)
5613
it902 2769
8353
3
3487
541.2
t9t6
age
of
696
890
1,474
1876
2462
Accidwt
1434
786
1901 1311:
driver
c&rs,atation
X42
2171
2776
5618
1
95
463
not
~mown.
waggoas,and
t379
796
698
1093
1.178
1709
Involvement
to50
604
t354 842
5039
251
271
767
845
tnri8.
1018
797 111.6
580
688
1,003
526
87t
888
778
1252
1369
Rates
437
970 662
516
1 to9 584
Ratea
275
149
219
381 242
209
305 250
282
260
Rates
Accident Involvement _-__c_____________-__
329
259
198
2 1.8
355
355 346
269
40-49
DRIVER
Involvement
30-39
OF
369
565
561
Accident
25-29
liGE
ion-Casualty
859
1347
749
597
Overall _ LC.) _________-_-_-
371’3
4138
3628 3596
892
876
2
ALL
;
2243
3
1
18 1.6
LE.)
1990
Casualty
_(k) 1
2Q-24
(20
2
ixo:Ls
Number
394
841
745
1612
855
958
1246
1348 735
19so 571
1198
699
1538 942
413
304
3t4
385
406
442
1161
630
397
930 389
212
298
121
276
182
232
l&&b)
and severity of accident.
60 & more
vehlcles” by age of dnver, number of occupants per 10s miles of exposure: Bristane metropolitan area
Table 10. Involvement rates of car-class
r
5
? Ln P s
Road accident involvement
per miles travelled-IV
165
Fig. 13. Brisbane metropohtan area. overall accident involvement rates of prrvate vehicies” by age of driver and day of week of involvement. per 10’ mrles of exposure. The surface is that of the joint function Y = F(X,, X2). where Y = the involvement rate of drover per IO8 miles travelled (in thousands). XI = age of “Including cars statton wagons, taxts and motor-cycles of every driver, X, = day of week of involvement kind
the vehicle. The two passengers and the driver all seated in the front compartment in 42% of such cases, as shown in Foldvary (1976). To make comparisons in this and the subsequent paragraphs easy, Table II presents the rates of Table 10 transformed into percentages. The second largest involvement rate of the teenage driver is in solo driving but the one-passenger rate is not much less. With increasing number of passengers, the rate gradually decreases. (iii) For other classes of drivers, the trend of the rate with age and occupancy is remarkably uniform. The rate decreases both with increasing driver age and with increasing occupancy. But while the effect of age produces nearly regular curves the increasing level of occupancy presents some irregular patterns [see Figs. 17-191. (iv) For all ages other than teenagers, the rates are significantly highest when travelling alone. (v) The curves for one and two passengers are similar; parallel with, but on a significantly lower level than the curve of solo occupancy. The curves for four and five or more occupants are lower, than those for two and three occupants, but otherwise similar. (vi) A close study of Figs. 17-19 and Table 11 reveals another interesting relationship: although the three-occupant involvement rate is the highest only for the teenage driver, there is still some adverse effect relative to the other age groups at this level of occupancy.? The point cannot be proved by a statistical significance-test; the rather scattered nature of the low-points tThere are 7 instances in Part (C) of above and below it m the same column appears rn the second row, and the other the three-occupant row would appear to
Table IO where the rate m any one cell is lower than those situated immediately These rates are 5412. 888, 571. 1902. 698, 580 and 394 The first three of them four m the fourth row of the Table. But there IS not a single case where a rate m be lower than Its two verttcal netghbours.
166
L. A. FOLDVARY
Fig. 14. Provincial urban areas of Queensland: casualty accident involvement rates of private vehicles” by age of driver and day of week of involvement, per lo* miles of exposure. The surface is that of the joint function Y = (X,. X2). where Y = the involvement rate per IO* miles travelled (in thousands). X, = the age of driver, X2 = day of week of involvement. “Including cars station waggons. taxis and motor-cycles of every kind.
prevents this. Still it is possible that this peculiarity (reinforced by a visual impression) furnishes evidence that something is “wrong” with the three-persons occupancy. The minor variations of the rates creates a type of ridge and valley-effect at all ages of the same level of occupancy in these figures. AGE OF DRIVER
This section is restricted waggons and taxis.
BY DESIGN
to the Brisbane
CHARACTERISTICS
Metropolitan
OF THE
CAR
Area, and to passenger
cars, station
The effect of brake horsepower variable Variation of the overall involvement rate by brake horsepower was discussed in Foldvary (1977) and detailed rates were presented. Table 12 sub-classifies these rates by age of driver and severity; the accident and exposure figures are also given. Figure 20 illustrates the standardized overall rates where the risk is (Y), and the two independent variables age of driver and B.H.P. of the vehicle by axes (XJ and (X,) respectively (the rates were standardized by taking percentages of the overall rate). The main features of the graph and the three Tables representing the casualty, non-casualty and overall involvement rates may be summarized as follows: (i) The three Tables make a uniform impression. The variations at each of the tables are located at the same classes of each independent variable. (ii) There is an immense variation between the rates within each of the tables; the casualty rate varies by factor 13 (between 138 and 1771) and the non-casualty involvement rate by a factor of 22 (from 346 to 7686). (iii) Both independent variables appear to be of primary importance in road accident causation. This conclusion follows from the fact that the risk surface in all three tables tends in the direction of both independent variables. (iv) In driver age the pattern is the familiar decreasing hyperbolic curve
Road accident Table
Il.
Standardized
involvements
involvement
rates of car-class
per miles travelled-IV
vehicles”
by age of driver
167
and number
of occupants
per 10’
miles of exposure: Brisbane metropolitanareab
NUMBER
Z%S; Severity Of
SO10
LA.) Casualty
OCCUPANTS
3
a
Driver
Accident
OP
4
-*.--Accident
5 or
more
0vereJ.l
Rate _____^_. -
InwlvemeZkt&
0.87
0.93
1.28
1.28
1.36
1.00
20-M
0.95
0.98
0.94
1.21.
1.99
1.00
25 - 29
1.09
1.20
0.81
0.54
0.70
1.00
30 -
39
1.02
1.03
1.27
0.68
0.88
1.00
40 - 49
0.91
1.15
t.51
1.00
0.59
1.00
50 - 59
1.03
0.90
0.97
1.05
1.20
1.00
60 & more
1.05
0.91
1.27
0.58
0.98
0.99
t.12
0.93
1.51 1.00 _IecI_--. 0.88 1.00
El1
-LB. ) Non-Casualtj
Accident
Involvamenta -L------L
0.95
0.95
1.69
1.04
0.69
1.00
1.24
0.87
0.62
0.44
0.68
1.00
25 - 23
1.45
0.63
0.73
0.42
0.73
1.00
30 - 39
1.29
O*aO
0.71
0.48
0.51
1.00
40 - 42
t.3t
0.69
0.74
0.63
0.45
1.00
M, - 59
1.24
Q.87
0.62
0.44
0.68
1.00
60 & more
1.45
0.63
0.73
0.42
0.73
1.00
il.1
1.28
0.78
0.73
0.55
0.46
1.00
20 - 24
( C. 1 Overal~~ent
(20
Inwlvemen2
0.93
0.94
1.71
1.10
0.86
1.00
24
1.14
0.89
0.78
0.70
0.93
1.00
25 - 29 30 - 39
1.26 1.23
0.98 0.85
0.77 0.81
0.50 0.53
0.42 0.59
1.00 1.00
40 - 49
1.22
0.80
0.92
0.72
0.48
1.00
50 - 59 60 & more
1.19 1.35
0.88 0.70
0.70 0.86
0.58 0.46
0.80 0.92
1.00 1.00
All Age-groups
1.21
0.83
0.82
0.64
0.56
1.00
20 -
(a) (b)
-
Including car6, station waggons and taris. In standardization each rate has been related of its particular row.
to the overall.
rate
we met in every sequence of age-specific rates. (v) In power of car the pattern is irregular, with two ridges and one valley. The ridges are formed by the class of 60-70 B.H.P. and by the class under B.H.P. 40. Between them is the valley of B.H.P. 40-59, while the most powerful classes exhibit gradually decreasing rates. (vi) there is a notable exception to this general trend, formed by the youngest age of drivers and top-powered vehicles. This combination, rising high from the low values of the highest B.H.P. class reaches the sky with under 25 drivers. (Teenage and 20-24 years old drivers were combined because of insufficient sample-size). It is instructive to examine the factor which distinguishes the over 60 and the under 25 throughout the range of our B.H.P. values. In the overall series, it is 2.3 for the <40 B.H.P. class, 4.4 for the 4&59 B.H.P. class, 4.2 for the 60-79 B.H.P. class, and 12.2 for the a80 class. Simii~Iy with the non-casualty involvement series, it starts by factor 2.3 for the <40 B.H.P. class, followed by 4.2 for the 40-59 class, 4.3 for the 60-79 B.H.P. class and jumps to 14.0 for the ~80 B.H.P. class. (vii) Thus the upper limit of the rate is formed by the driver-vehicle combination of top-powered vehicles driven by drivers of the youngest age group, while the lowest limit of therange is formed by the second-lowest power-class of cars, driven by the two oldest age-groups. According to these findings, the most powerful cars appear to be less associated with accidents if driven by drivers over 25, but more involved with (possibly less experienced) drivers under 25.
L. A. FOLDVARY
168
Table l?. Vehicle-miles of travel. accident mvolvement and Involvement rates of car-class vehicles” by B car, age of driver and severity of accident. per IO” miles of exposure. Brisbane metropolitan area Age of I&iver
Particulars
BRAKE (40
*E4 25s 30-39
Number of Sample-Cars Making Trips
40-59
1::
7r:
HORSEPOWXR 60-79
E-;;
1:; 196 155
:;;
Z,‘U. ~AJJ
YZ 722
127 32
%
391
1518
1.6.2
11.6
16.5
;;*; 55:o 33.6 26.8 25.0 5.7
36.3 27.2 67.5 65.5 %*'i,
2$24
Annual
25-29 30-39 4049 50-59
Daily Miles Performed by the Car Population,
in 1961
ZKn
(Thousanda).d
TOI'AL
12:3
SO-99
112 46
1:; 116 95
Average
>lOO
1:
3;;
z 106 z
16
49.8 41.0 13a.3 'E 50:1 300.7
Casualty Accidenta, 1961
: 3
E 61
1.:
2;:
:;
i::
%
116 3829
1
399
249
60
1::: 12.1 29.8 37.0 22.8 17.3 4.7
Z:Z 2.2 20.9 19.0 25.2 14.0 3.7
136.5
93.0
16.7
1371.2
51.7 131.4 130.8
Y-Z . 0.8 2.7
;142*; 22413 148.8 57.5
:::
i:;
575.5
90
223
%24 25:29
262 36
:E 15
65
17 11
5 6
126 63
:;z
3@-3g 40-49 50-59
f: 15
;;
152 126 g
22
10
105 :;
:z 204
.
::
86
226
140
;:
40-49 50-59
.COJXJ
&
20-24 Number of Cars $$z in
331 135 327
310.1
Total
Involved All Accidents
Total
239.2
NGn
Number of Cars Involved in Non-Casualty Accidents, 1961
ggn
11 8
14
Number Cars Involved of in
Q-49 Not
Kn.
lxl ‘TATA
19 639
f88
81 49
629
:77
469
1,12 194
1.:;
126 160 11.2 ;44
72 131, 91
10 8
72
:
2:
118 99
107
48
666
1826
21 16
435 283
654
:5
228 420 337 ::z 378
‘% 1383 1074 677 354 551
2463
6569
88 35
z’: 556 475 :z:
1% 80 ;;
97
21
2342
501
:;z
:52 :: 165
1%
33 855
609
2981
608
21 26
z:
877 1499
:93 45 30
291 525 4:
902 17to 137;
::
197 438
z
3129
8395
213
InvolvementRates: -----_-BRAKE (40
40-59
(25 25-29
546 489
:z
Casualty Accident Involvements
30-39 40-49 50-59
294 ::‘:
Non-Casualty
2%9 30139
Accident Involvements
H.P of
50-59 360 4049 Total(c)1
HORSEPOWER: 60-79
%I
1339 523
867 479
149 138
717
:z 232
1652
4466
:6202:631
Total(b) 825 410
T
2731
2113
:;;z
845 762 703 951
614
1586
397 5%
1220 1045 1109
1200 815 810 549
153
663
1784
1272
:z
t Cb)
98;; 707 1312 r
I
Road accident involvement per miles travelled-IV
169
Table 12 (Conrd)
In~lv~~t
Rates:
__I--------_-
Pqtfculsrs
Overall Accident Involvements
BRAKE
%:f
(40
G39
TotaltDJ
60-79
%I
2158 ;z? 546
2636 5804 2009 1539
8553 2425 %
:z:; 1205 t493
%Z 858
1379 1427 2263
‘% 1563
1075 924 1679’ a)
40-59
:::“2 1311 1140
2g9
HORSEPOWER:
>60 E-z; 1012 946 rotill’c11561
t (of
Including cara of every type,s&ion waggons and taxis. Including "Brske Horsepowernot known. category. Including "Age of Driver not known" category. Including "Brake Iforsepowar not known' and *Age of Driver not known' categories. due to insufficiencyof sample-&se. (8) Rate has not been calculated
b” II 6)
P i i
[ I
-
-
\ p
I T\ \
‘\
“a
.
ai
_ L-
c
;7+
-.. -43
m-59 Age of
260
driver
Fig. IS. Overalf accident involvement rates (casuaity and non-casuahy involvements combined) of car-class vehicles, all drivers: age of driver by nom~r of occupants, per IO’ miles of exposure; Brisbane me~o~litan area. f occupant: -2 occupants; A-,-A 3 occupants; C&~-Cl 4 occupants; *.-@ 5 & more occupants. Thin line indicates curve sections based on inadequate sample-size. AAPvol IO.No
Z-G
I
2
3
I
Number of occupants
I
4
>4
Fii. 16. Overall accident involvement rates (casualty and non-casualty involvements combined) of car-class vehiiclts, all drivers; number of occupants by age of driver, per IOsmiles of exposure; Brisbane metropolitan area. (1) -: < 20; (2) o--O: 2W.4; (3) A--.--A: W9; (6) A- - -A: 50-59; (7)S- - -e 3 60.Thin 25-29; (4)D-a*--0: 30-39;(5)r line indicates curve sections based on inadequate sample-size.
I
Fig. f7. Casualty accident invoivement rates of cars by age of driver and number of occupants in the vehicle, per 108miles of exposure; Brisbane metropolitan area.
Road accident
involvement
171
per miles travelled-IV
7
6
5
4
i
--I----
oc
!:
.:
Fig. 18. Non-casualty
accident involvement rates of cars by age of driver and number vehicle, per 10’ miles of exposure; Brisbane metropolitan area.
of occupants
in the
With respect to the other extreme B.H.P. class the lowest powered vehicles which carry a consistently increased accident hazard in the hands of every age group it is possible that some other vehicle factors, possibly connected with the classification of their age and year of manufacture, must materially contribute to their high potential risk.
Weight of car The sub-classification of involvement of cars of various weight groups according to age of driver, and the relevant involvement rates are put forward in Table 13. This sub-classification does not produce involvement rates drastically different from those which characterizes the weight of car classification generally, as described in Foldvary (1977). Thus we do not enlarge on this subject, and turn our attention to the next problem connected with the combined factor B.H.P./Wt. ratio of the car.
172
L. A. FOLDVARY
Fig. 19. Overall accident involvement rates of cars by age of driver and number of occupants, per IO* miles of exposure, Brisbane metropolitan area. The surface is that of the jomt function Y = F(X,,Xz). where Y = accident involvement rate of driver per 10’ miles travelled (in thousands). X, = age of driver, X2 = number of occupants of car.
Age of driver by B.H.P.1 Wt. ratio of vehicle This relationship is shown in Table 14. The near parabolic curve with the inflexion point at its modal value, described [in Foldvary 19771 as being characteristic of the rate curves of the B.H.P./Wt. ratio alters greatly when the sub-curves representing age of driver is taken into consideration. It even loses its parabolic form in some of the subclasses. Let us study first the points of the highest B.H.P./Wt. ratio on all these curves, shown in Fig. 21 and in Table 14. It turns out that this highest B.H.P./Wt. class corresponds to the lowest involvement rate of the whole matrix (and this is for drivers age >60) as well as to the highest involvement rate of the matrix (for drivers under 25). In addition, this highest B.H.P./Wt. ratio group (33.5) produces the lowest involvement rates for every age group of drivers above 29. The situation changes radically, however, with drivers aged 25-29. In their involvement-rate curve, the top B.H.P./Wt. ratio attains the second worst position with its high involvement rate. Further with the youngest (~25) age group of drivers, it occupies the worst position, the highest involvement rate of the whole tabulation. This is another indication that cars of the top B.H.P./Wt. ratio, which serve so well older drivers are less safe with young (perhaps inexperienced) drivers. Other vehicle-design factors The relationship between involvement of cars of various braking surface areas, and the age of driver is presented in Table 15. Similarly, the relationship between the classes of cars having
173
Road accident involvement per miles travelled--IV Table 13. Involvement
rates of car-class vehicles” by weight of car, age of driver and severity of accident, per IO* miles of exposure;
-Severitg Accident
of
Age of Driver
(20
Brisbane metropolitan area
rIJIGH%
OF
20-24
CAR
y5
All 1180
cara
QO
761
1712
(b)
20-24
407
1009
573
686
25-29
313
504
348
4 1.0
30-39
238
3187
205
312
40-49
271
319
154
263
50-59
187
300
188
249
260
208
224
218
218
347
465
261
367
@
2078
5375
2364
3469
20-24
1306
3613
2352
2440
Casualty Accident Involvements
Total
NonC_tY
25-29
888
1976
1277
1479
Accident
30-39
659
1503
944
1181
Involv~ents
4049,
698
1188
613
942
50-59
574
977
684
827
%O
476
794
709
708
1048
1312
Total.
1734
990
2039
8081
3298
4651
20-24
1713
4623
2925
3126
Overill
25-29
1201
2482
1625
1889
Aocident
3Q-39
879
1889
1149
1493
Involvements
40-49
969
1507
767
1205
50-59
761
1275
872
1076
X0
684
tot9
927
926
1337
2199
lzQ9
1679
TOtal
(6)
Including
(b)
Rate
hae
cars not
of been
every
type,rtabion
cahulated
due
waggone to
and
taxl&
insufficient
@8mple_eiaa.
different braking surface area per B.H.P. ratios and the age of driver is studied in Table 16, and that between cars of various B.A./Wt. ratios and the age of driver in Table 17. The most instructive of these is the effect of the B.A./B.H.P. ratio of cars on the age-specific involvement rates of their drivers as shown on Table 16. High involvement rates fill the cells of the first column of this table, amongst them those pertaining to the two youngest age groups of drivers. This column includes cars having the lowest B.A./B.H.P. ratios. Low braking power combined with high driving power is not a car-layout suited to any driver, least of all the young drivers. It appears from our figures that the third B.A./B.H.P. class out of the four (with the ratio of
Table 14. Involvement
Age of Driver
rates of car-class vehicles“ by B.H.P./Wt. ratio of the car and age of driver, per IO* miles of exposure: Brisbane metropolitan area Brake
Eoreepower
(i?.O
per
Weight
Ratio
2.0-2.4
2.5-2.9
3.0-3.4
of
csr . 5
UC-8
05
2708
2893
4694
4174
5909
25.29
1442
1413
1678
3944
1769
1889
30-39 4Q-49
994
1073
l&90
2089
814
1492
SO9
1013
1225
l88S
474
1205
W-59
724
121
1407
1297
570
tO76
$60
705
898
1114
tlta
3t2
925
1333
1435
a39
2281
969
1679
.klJl m-ioel.6 (a)
Including
Oara
Of ewcy
Qpe,ate;tion
waggone
aud
3565
tazie.
174
L. A. FOLDVARY
TableIS.Involvement rates of car-class
vehicles” by area of braking surface, age of driver and severity accident, per IO8 miles of exposure: Brisbane metropolitan area
AREA
CWUalti
OF
BRAKING
so-log
Accident
110-l
39
SURFACE 340 _
Involvqq@&_&&p& 1060 728
All
Care
45
434
815
828
25-29
311
439
332
(b)
450
30-39 40-49
232 182
326 341
316 157
222 292
3x2 263
50-59 960
(b) (b)
321, 26i
142 160
258 235
249 218
295
453
260
368
367
Total
of
(B.1 Non-Casue;Ltg Accident Involvement Rates. _-II_--05
986
3614
2668
25-29
786
1519
1372
2715 2052 807
2737 1479 1181
30-39
471
1123
1227
40-49
569
1143
737
961
942
50-59
513
986
579
972
82’1
YO
446
826
551
788
708
Total
717
1605
11.04
1394
1312
(a)
Including care of every type,atationwaggons end taxis. (b) Rate has not been calculateddue to insufficientsample-size.
Table 16. Involvement rates of car-class vehicles” by braking area per B.H.P. of the car and age of driver, relative to IO8 miles of exposure: Brisbane metropolitan area Age %f
Driver
Breking Area d-5
per Brake Horeeporer Ratio pal 1.5-1.9
2.0-2.4
32.5
CSTe
@
8017
5445
2665
3522
5613
20-24 25w29
6706 2106
3231 2368
1862 1186
2646 1793
3042 1918
X-39 4049
1921
17% 1330
7i9 667
t367
13%
1139
137;9 1116
50-59
1275
11.61
666
738
to 18
878
1090
60-i
936
841
1976
1964
360 All Drivers
_Ratea
il.05
Stsndardiead Relative
1480
16tl
to theoVerall Rate:
20
4.97.
3.38
1.65
2.19
3.49
20-24
4.21.
2.00
1.*6
1.64
1.89
25-29
1.31
1.47
0.74
1.11
1.19
To-39
1. t9
1..09
0.45
0.85
0.85
40-49
0.83
0.82
0.42
O.?l
0.69
50-59
0.7B
0.72
0.41
0.46
0.63
6ct
0.55
0.68
0.43
0.58
0.52
1.23
1.22
0.69
0.92
1.00
All
Drivera
(3
Indluding Car8 of every type,atationwaggons and tads.
Road accident invofvement per miles travelled-IV
175
Fig. 20. Overall accident involvement rates of cars per IO’miles travelled by age of driver by B.H.P. of the car, Brisbane metropolitan area, 1961.
Table 17. ~nvoivemeat rates of car-class vehicles” by braking surface area per weight ratio of car and age of driver. relative to 10’ miles of exposure: Brisbane metropolitan area Ezs
BrzW.ng Surfaoe per Weight Ratio oi: Car 36.0 5.0-5.9 4.0 4.0-4.9
AlA C.SlW 4653 3127 1889 1494
6225 3381 2193 1878 1380 1354 1.052
3640 2883 1859 1353 1344 go2 780
? (Jb)
30-39 40-49 50-59 SO
3389 3167 13ra t026 905 642 733
I))
1016 925
All Drivers
1322
2123
WC!i
752
1679
.& X1-24
444 4$7
1205
(a) Inoludlng cars of everg type,station w~aggona and taris. (b) Rate haa not been calou&eted due IX ineufficiant sampler aise.
176
L. A. FOLDVARY
Fig. 21. Probability surface of the risk of overall accident involvement of cars various B.H.P./Wt. classes driven by drivers of various age classes. Rates per IO* miles of performance: Brisbane, 1961.
between 2.0 and 2.4) includes cars which have the most balanced design in this respect. this column accommodates the lowest involvement rates for each age group.
since
REFERENCES Foldvary L.A. (1968) Vehicle mileage by road, traffic accidents and accident rates. Proc. 4rh Conf. Ausfralian Rood Research Board. 4(l). 1005-1046. Foldvary, L.A. (1975) Road accident involvement per miles traveled-I. Accid. Anal. dl Prev. 7, 191-205. Foldvary L.A. (1976) Road accident involvement per miles traveled-II. Accid. Anal. dt Preu. 8. 97-127. Foldvary L.A. (1977) Road accident involvement per miles traveled--III. Accid. Anal. & Preu. 9. 21-54. Munden J.M. (1%5) The accident rates of car drivers by age. Road Research Laboratory LN/804/JMM. Solomon D. (1964) Accidents on main rural highways related to speed, driver and vehicle. U. S Dept of Commerce, Bureau of Public Roads. U. S. Government Printing Office Washington D. C
Accra’ Anal & Prev Vol. IO. pp. 143176 0 Permmon Press Ltd 1978 Pnntcd m Great Bntain
ROAD ACCIDENT INVOLVEMENT TRAVELLED-IV L. A. II
Yongala
Street,
Abstract-This Vehicle-Mile
FOLDVARY
Balwyn.
(Received
PER MILES
3103 Victoria.
23 October
Australia
1973)
paper continues a series (Foldvary 1975. 1976, 1977) reporting on the 1963-64 Performance Survey. The variable treated in this part is age of driver.
Queensland
We first study the total annual mileage of the driver population of Queensland classified according to age of driver, followed by the total accident involvement also classified according to the driver’s age, and compare the variation. We then study the involvement rates for these sets of variables. Table 1 and Fig. 1 show the three corresponding curves, standardized by dividing mileage and accident figures by their respective averages thus making them comparable on the one scale. The regularity of the hyperbolic-type involvement-rate curve which results is striking, but not inconsistent with expectation. One need only consider that the rate-curve is a true expression of the variation of risk according to the effect of driver’s age and experience. The figures do not allow separation of tie effects of these variables, but the resultant risk curve speaks for itself. This involvement rate curve expresses decreasing accident risk with increasing maturity and experience. It clarifies the situation with respect to one of the most controversial issues in the road safety literature-the place of the two extreme age-groups-in road accident involvement. The risk of a driver under 20 is three-and-a-half-times that of the overall risk. It is nearly six-and-a-half-times the risk of a driver over fifty. The next youngest age group, 20-24 shows a substantial improvement over the under 20 group while still having an involvement rate of nearly 2300. The third group on the age scale is also third on the rate scale, and the decreasing Table
I. Male
Age
of
and female
Their vehicle-miles of travel, accident involvement and involvement rates per IO8miles of travel, by age of driver; Queensland, l%l
drivers:
Annual rotal -Tiles
IMveq
of
in Qillion
Tease
kale
Vehicle-
’
Accident
msvel,
~nvDlve?aent
Accident
Miles: Female
All
Xale
Female
Drivers:
All
tivolvemeart
Ratea Ule
Drivers:
Drivers:
(1)
(2)
(3)
(4)
85.9
8.6
94.5
3,224
20 to 24
199.0
26.7
225.7
4,844
25 to 29
249.9
32.5
282.4
3,061
30 to
528.7
83.8
612.6a)
5,191.
525
5,716
982
627
933
752
758
752
Lees
(5)
(6)
1 (7)
(8)
(91
than
20
39
3,449’)
3,751
2,566
3,647
339
5,183
2,431
1,269
2,293
273
3,334
1,224
840
221
I,, 1.00
40 to 49
514.0
57.1
571.. 1
3,866
433
4,299
50 to
429.1.
32.2
461.3
2,404
264
2,668
560
818
520
113
1,561
573
686
580
59
60 4 over Total:
252.7
16.5
269.2
1,448
237t.4b)26t3.1?)2648.70)25,085b)2238b) (a)
Includes
sex unknoun.
(b) (c)
Includes Includes
age unknown. sex unknown,ege
unknowqsnd 143
27,691’)
both
1,056
set
835
aud ege
1,051
unlmorm.
L. A. FOLDVARY
144
!
’
000 <20 XI-S4
25-29
I
1
30-39 Age
Fig.
I. Age
involvement
of rates
driver. per
Vehicle-miles lo* miles
and the annual
40-49
50-59
60+
of driver
of
population performance (I), accident involvements (2). and (3). as ratios of the average performance, average involvement, involvement rate respectively: Queensland. 1%1.
of exposure
over-all
rate rank follows exactly the increasing age rank up to age 60. But beyond this the involvement rate of the 60 and over age group is of statistically the same magnitude as that of the 50-59 age group. Many earlier studies have shown a rate increase for the over 60 age group when compared with the rate of the age group immediately below it. It may be that if the oldest sector of these drivers (say above 70) were shown separately, an increase would appear. This refinement was not possible here because of small sample-size. Nevertheless this may be the first study of its kind where large sample records of actual mileage of a whole driver population were used in calculating the denominator, and a whole year of accident occurrences for the numerator. It may be that this refinement, if compared with earlier methods using estimates of annual total mileage performances, petrol consumption, etc. can explain the difference. Considering first an urban driving environment, where speed is restricted, and drivers may select in many instances parallel routes, the oldest age class of drivers may be expected to be good drivers in spite of their probably reduced sensory capacity and slower reactions. Against these deficiencies stand their experience which is to be expected to be the longest and possibly, their temperament. A tendency to stop driving with deterioration of sensory abilities could also be expected. These considerations apply to some extent in a rural environment also. The aged driver might have a tendency to avoid difficult situations. Being mostly retired people they can avoid periods of commuter traffic, do drive less frequently during night hours, and may not undertake long, exhausting journeys. Our overall rates are more consistent with these logical considerations than some earlier findings, and moreover, are not the first ones of their kind. Munden (1965) has shown similar results in Great Britain; these were, however, based on sampled driver’s estimates of annual total mileage travelled. He concluded that “there may be an unconscious tendency on the part of those responsible to blame the older driver more often than the younger drivers in similar circumstances, and this could account for the higher peak in the blame/not blame rate”. Finally, perhaps the strongest arguments for the validity of the rates obtained, are the inner consistency, and high level of statistical reliability, points which will be discussed in the next section. AGE
OF
DRIVER
AS
THE
MAIN
VARIABLE
The stabilization of risk beyond age 60 is a balance of differing factors. Namely, if the rate for the top age group is further sub-classified according to additional variables, the result is in
Road accident
involvement
145
per miles travelled--IV
some instances a reduction, in other instances an increase. This divergent reaction of the sexagesimals and older drivers and various sub-groups by sex, age and so on, to various conditions of driving is a subject-matter of importance. The subsidiary variables will be type and severity of accident, the type of vehicle used and its level of occupancy, the area, as well as day of week and time of day, and design characteristics of the vehicle. The age of driver, age of vehicles interaction has already been discussed, with the finding that the age specific driver involvement rate retains its hyperbolic shape within each vehicle age class. Age of driver by severity of accident The last but one column of Table 2 presents the rates of casualty and non-casualty involvement for various age groups of drivers relative to exposure and for easier understanding of the nature of these two sequences the last column shows them as percentages of the corresponding overall rate. The two rate series are shown in Fig. 2, while their ratios are given
Age of driver Fig. 2. Age non-casualty
of driver by severity accident involvements accident
of accident involvement. Casualty accident involvements (2) per IO* miles of exposure: the ratio casualty accident involvement rates (Curve 3) Queensland.
(I), and per total
in Fig. 3. [see Foldvary (1%8)]. It is worthwhile to call attention to the striking similarity of casualty and non-casualty involvement except for that part related to the under 25 driver. The sharp decrease of the casualty-rate curve from the teenager class to the (20-24) class is evidenced by a drop in the percentage ratios from 436 to 232. The drop is less sudden although still of considerable magnitude in the non-casualty involvement series, from 316 to 213%. Note the close similarity of the two figures for the 20-24 years group (232 vs 213), and that the corresponding standardized rate-pairs are practically equal in all other age groups. A chi-square partition test was carried out to check this point statistically by using the actual number of accident involvements in the analysis, and the following result was obtained:
Component
of X2 due to:
(i) Difference between the two youngest age groups: (ii) Difference between the two youngest age groups and the rest: (iii) Difference within the five age groups of 25 and over: Total chi-square: AAP Vol IO. No 2-E
X2
Degrees of freedom
Probability level
5.0
I
0 025
s.
99
I
0.005
VHS.
1.9
4
0.750
NS
16.8
6
0.010
HS.
Level of significance
146
L. A. FOLDVARY Table 2. Involvement rates by age of driver, type and severity of accident, per lo* miles of exposure, for all types of vehicles combined Brisbane Metropolitan Area !J?nE
As f DZ; Severity of Accident:
bIultivehicle Rate _Lu
(20
OF
‘$az
Rate
ACCIDENT
Pedestrian
singlevehicle z a)
Casualuccldent_-_--__
Rate
Other wea Rate
Sal
Invclvement
All Za’
types
Rate
Sal
Rates:
1,265
477:
353
654
216
366
13
433
1847
484
20 -
24
543
205
142
263
t19
202
3
100
806
211
25 -
29
301
114
62
115
79
134
3
100
444
1.16
30 -
39
227
86
53
9s
50
85
3
loo
333
87
40 -
49
189
71
25
46
42
71
1
33
257
67
50 -
59
172
65
23
43
46
?B
2
67
242
63
60 %
more
162
61
20
37
26
44
1
33
209
3
a00
265
Werall.: (B.) @
tO0
54
Non-Casualty
100
Accident
59
100
Involvement
55 100
302
Rates
3191
302
630
463
31
206
18
300
3870
319
20 -
24
1872
177
322
237
23
153
6
100
2223
183
25 -
29
1264
119
a52
112
20
133
7
117
l443
119
964
91
121
89
IO
67
6
100
1101
91
757
72
75
55
a5
100
7
117
854
70
669
65
64
47
8
53
2
33
764
63
568
54
52
38
3
20
1.
17
623
51
1058
100
136
100
a5
a00
6
too
1215
ioa
358
X-39 40 -
49
50-59 60 &
more
Werall:
C. ) Weran ( 20
Accident _-
Invclvement
Rates:
4456
337
983
515
2.47
333
31
344
5716
20 -
24
241,4
IS75
464
243
1.42
192
9
100
3029
190
25 -
B
1565
118
213
112
99
133
9
100
1887
aaa
30 -
39
119%
9Q
174
91
60
St
9
a00
1434
9Q
40 -
49
946
72
to1
53
58
78
7
78
1111
70
50 -
59
861
65
87
46
54
73
4
44
1.006
6.3
729
55
72
m
29
39
3
33
832
52
1OQ
74
100
9
IOQ
1597
1oQ
60 &
more Werall Rate:
1323
1DQ
191
Provincial ____ (A.1 2816 _-_-__ Casual.tq_Accident Involvement 610 _;;~~___80s____~;___617---
ho
20
Urbau
tieas
Rates:
22
220
4667
655
-
24
1.247
270
602
336
189
324
30
300
2069
291
25 -
29
489
106
227
127
79
127
9
90
803
113
30 -
39
373
81
151
84
48
77
11
1 IO
583
82
40
-
49
291
63
11
40
51
82
8
80
420
59
50 -
59
338
71
64
36
25
40
5
50
432
61
60 &
more
275
60
77
43
21
34
5
50
377
53
462
100
179
100
62
100
10
100
712
100
Overall
@LNon-Casualty -___...__._
G
_.
Accident Invclvenent __._______ Rates: _________________. I 547 45 643
8998
511
20 -
24
3549
269
1523
361
1.3
186
9
90
5093
289
25 -
29
1498
113
595
141
12
171
27
270
2132
121
30 -
39
1110
84
369
87
4
57
14
140
1496
85
40
-
49
926
70
238
56
7
100
8
80
1179
67
50 -
59
820
62
119
28
5
71
5
50
950
54
764
58
105
25
5
50
873
50
1321
100
422
100
10
100
1760
100
60 & more OPeraI..
6642
503
231
(b) 7
100
(b)
Road accident involvementper milestravelled-IV
147
Table 2 (Coned)
Provincial Urban Areas !cYPS
Zv:Z sever&
-&J. tivehicle
Of
Accident:
RBte
vehicle
a)
F
Rate
A C C I DE N T Other
trian
Rate
:- a)
Involvement - fC.1 -- -__L_____^-l__60 20 - 24
OF Pedes-
Sin&?-
Rates
of
All
All accidents
types
F,a)
Rate
::a)
Rate
a) %
Accident&
9458 4796
530
3758
624
269
2125
353
202
426
616
292
22 39
110 13664
553
1295 7162
290
25 - 29
1987
111
821
1.37
91
1~32
36
180
2935
119
30 - 39
1,483
83
520
87
52
74
25
125
2079
84
40 - 49
1217
68
309
51
58
84
16
80
1599
65
50 - 59
1159
65
183
32
30
44
11
55
1382
56
60 & more
1038
58
182
31
21.
30
9
45
1250
51
t783
100
600
100
69
100
20
100
2472
too
Rural
Areas
Overall Rate:
(A.)
Casualts
Accident
of Queenslend
Involvement
Rates;_
+J
162
337
253
402
22
440
3
150
440
373
20 - 24
98
a04
$76
279
9
w
3
IdO
286
242
25 - 29
57
119
68
108
6
120
3
150
135
I,14
30 - 39 40 - 49
43 35
90 73
50 39
79 62
4 6
80 1.20
2
100
99 81
84
50 - 59
24
50
29
46
1
20
I.
50
56
47
6O&more
39
81
35
56
3
60
77
65
Overall
48
100
63
100
5
100
100
118
TOO
Non-CasualQ _ LB.1 __ ____________
(b) (h) .2
69
Accident Involvement Rates: _______________~._________c__
<20
448
238
586
364
2
200
8
200
1044
296
20 - 24 25 - 29
350 193
186 103
435 21.7
270 135
1 1
100 100
7 6
175 150
792 417
224 118
30 - 39
167
89
151
94
(b)
4
100
322
91
40 - 49
146
78
106
66
(h)
4
100
256
73
50 - 59
116
62
55
34
1
100
2
50
t75
50
60 & more
132
70
58
36 -I--_~-_-
1.
too
1
25 _--_-_-.
192
54
188
100
161
100
1
100
4
1.00
353
100
Overall
&L~Involveruent Rates of Al.1 Accidents. -~-~----_-~~--_----^-----_----~6 1.0 448
258 190
839 6 1.0
375 272
24 10
400 167
11
183
1484
315
10
167
1077
229
25 - 29
250
106
286
128
6
100
30 - 39 40 - 49
210 182
89 77
202 146
90
4
67
9 6
150 100
551 421
117 09
65
6
100
4
67
337
72
50 - 59 60 & more
140 171
59 72
84 93
38 42
2
33
67
230
49
5
83
4 1
17
269
57
236
1.00
224
100
6
100
6
100
471
100
( 20 20 - 24
Overall Rate (a)
Percentages
(b)
IneUfficient
shown exe those aample-adze:
of
rate
the corresponding
overall
has not been calculated.
rate.
148
L. A
FOLDVARY
Table 2 (Contd) Total
Age of
Area
of
TYPB
Driver; Severity
WiLtiRate
Pedestrisn
vehicle
Sal
Rate
ACCIDBHT
OF
Single
vehicle
of Accident:
Queenslaud
$a) --_-_
tspes _ ___~_a,_ _
Rate
Sal
_.
Casuel;Q__Accident -_--_--_-_Involvement
(A.)
All accidents _Gte
Other Rate
-
_- --m-m--
ka--
Rates:
677
413
389
519
103
367
7
233
1176
436
20 -
24
351
214
209
279
60
213
6
200
627
232
25 -
29
1.72
105
85
113
33
118
4
133
294
109
30 -
39
140
85
65
87
23
82
4
133
231
86
40 -
49
118
72
39
52
24
86
1.
33
182
67
50 -
59
102
62
32
43
16
57
2
67
151
56
1.10
67
38
51
12
43
164
100
75
100
<20
60 % more Overall
(a.1 --______ Non-CasuaItg _-_ ( 20
-
1 33 _ _- - -__ _ - -. 100 3 100 I--__
20
Accident Involvement -____w__-l__---___-_
161
60
270
100
--__-
. -
.
___-_
Xates:
1690
289
759
406
13
217
10
200
2471
316
20 -
24
1139
195
512
274
9
150
7
140
1667
213
25 -
29
626
107
244
130
7
117
8
160
886
113
30 -
39
522
89
172
92
3
50
6
120
702
90
40 -
49
445
76
114
61
6
100
5
100
570
73
50 -
59
355
61
65
35
4
75
3
60
426
54
60 8t more 352
60
64
34
1
17
2
40
419
53
100 ..______
5
100 782 -- _____ --___--_-
100
Gverall
584
100 _~
Involvement -CC.) _______ _ -( 20
187 ____
100 6 _^.____.___
-Rates __
of
AlI
Accidents:
2367
327
1148
433
115
338
17
213
3647
347
20 -
24
1490
199
722
276
69
203
12
150
2293
218
25 -
29
797
107
330
126
40
118
12
150
1180
112
jo
-
39
661
88
236
90
26
77
9
113
933
89
40 -
49
563
75
153
58
30
88
6
75
752
71
50 -
59
457
61
98
37
19
56
5
63
578
55
60 & more 462
62
101
39
14
41
3
38
580
55
100
262
100
34
100
8
too
Overall Rate:
747
(a)
Percentsges
(b)
Insufficient
shown are sample-size:
those
of
rate
the
corresponding
has not
been
1052 overall
100 rate.
calculated.
This shows that there is a highly significant difference between the casualty and noncasualty involvement rate series. This difference is, however, primarily due to the difference between the two youngest age groups and the rest; the difference within the two youngest age groups is also significant, while the difference within the five age groups from 25 upwards is statistically insignificant. This finding is added evidence that young drivers are not only often involved in road accidents relative to their exposure but that their involvements significantly more often end in sufferings. disablement and death. Curve No. 3 of Fig. 2 portrays the sequence of ratios of casualty accident to total accident for all age groups. Nearly one third of the total involvements of teenage drivers is of the casualty type, with lower values for the next four older age groups. From 50 on, the ratio starts to increase again at first slightly but the top age group attains a ratio outdone only by the teenage driver. The higher vulnerability of this advanced age is certainly a contributing factor. Age of driver by type of accident We next see how age specific involvement
rates of the two severity groups vary by type of
Road accident
involvement
0!__,1,‘,I,
1
<20 m-2425-29
of driver by severity of overall rates: (1) casualty
,
30-39
Age Fig 3. Age corresponding
149
per mtles travelled--IV
I 40-4s
I
! 50-59
!
I
60+
of driver
accident involvement. accident involvements, Queensland.
Standardized rates being (2) non-casualty accident
ratios of the involvements;
accident. The last page of Table 2 provides the detai1s.t The variation by age of driver for the three main accident types is illustrated in Fig. 4 using standardized rates. (Out of the two severity groups of pedestrian involvements, only the casualty type is plotted; the reason is again small sample-size in non-casualty pedestrian accidents.) The following features of the curves are immediately apparent: (1) their similarity in spite of the significant difference between them in statistical terms, (2) their regular form (hyperbolic, or in some cases parabolic)
I
400
b 'G 0, % P s 8 n
200
100
0
1, I
I ,‘I’
<20 20-2425-29
I !
I
30-39
40-49
50-59
60+
Age of drover Pig. 4. Standardized involvement rates of age of driver by type and severity of accident per IO* miles of exposure, Queensland. The standardized rates are ratios of individual rates to their corresponding overall rate, expressed in percentage form. (1) Multi-vehicle casualty involvements. (2) Single-vehicle casualty involvements. (3) Pedestrian casualty involvements. (4) Multi-vehicle non-casualty involvements. (5) Single-vehicle non-casualty involvements. tout of the four groups of type of accidents, the fourth one termed “the other types” combines those odd kinds of accidents that could not be sorted into the three main groups of multi-vehicle, single-vehicle and pedestrian accidents. Smallness of frequencies in this class, when spread over the seven age-groups of drivers renders it unsuitable for comparative studies.
150
L. A. FOLDVARY
so characteristic of our age specific involvement-rate curves; and in particular: (3) the sharp decrease in the rates from the first to the second to the third age group and the slow decrease thereafter which turns even into increases beyond the age group 50-59 in some cases; (4) that 30 years of driver age is a threshold that separates the greater from the lesser risk. Under that age every curve is above, and above that age every curve is below the line marking average risk. Besides the similarities, there are, however, characteristic differences between the curves, and these must be our main concern. They could provide us with evidence of the differences between the age groups in their level of risk. To attack this problem, we first consider the differences that contribute to the shape of the curves with respect to type and severity. Because severity is a difference of degree it is a secondary consideration in the study of causality. Examining first the type of accident three major types are distinguished: (a) Single-vehicle. No other road user is involved. and no other parties but the vehicle occupants are hurt. (b) Pedestrian. Although either the driver or the pedestrian or both could be responsible, only the pedestrian could be hurt, apart from exceptionally rare cases. (c) Collision. There is another driver or drivers whose actions might contribute to the outcome, and there are at least two groups of parties, occupants of the two (or more) vehicles who could be hurt. In the light of this consideration we examine the differences in the shape of the five curves of Fig. 4. As a first observation we see that involvement rates of the seven age groups vary the least in pedestrian accidents, the range between the two extreme values being 324 in casualty involvements, and 200 in the non-casualty ones. The greatest variation is in single vehicle accidents with values of 476 and 372 respectively. Collisions stand midway with 35 1 and 229 values. For a more detailed consideration, one must start with single-vehicle accidents, because their involvement rates could bring to light the comparative risk of the various age groups of drivers purely, unaffected by actions of other road users. We see the young driver (under 25) has in single-vehicle accidents the highest involvement in both severity groups. He has the second highest involvement in collisions, and the lowest in pedestrian accidents. It might be suggested that this sequence is a clear indication that in many collisions a second young driver could be involved, and that in many other would-be collisions a more mature second driver appears and the so avoided collision contributes to the bringing down the rate. Consequently, on purely theoretical considerations also the involvement ratios for the young driver agree with our figures: highest single-vehicle, mid-value for collisions, and lowest for pedestrian. This situation never reappears in any other age groups. The next two age groups (between 25 and 39) have involvement ratios shifted to other types of accidents notwithstanding that single-vehicle accidents still come out with the second or third top ratios in this comparison. Higher on the age-ladder, the position of the single-vehicle accident drops lower. In the 40-49 age group it occupies the third position with respect to casualty involvements, and the fourth position with respect to non-casualty involvements, and with the 50-59 age group it drops to the lowest, the fourth position in both severity groups. In these latter two age groups of drivers the pedestrian accident involvement achieves the top percentage ratio. This may be due to two reasons: (i) the drivers have proportionally less night driving than those under 30, a major source of accident involvement of the young driver and (ii) consequently they spend proportionally more of their driving time during the day, the period when pedestrians also are more frequent on the roads. The remaining age group (60 and above) presents a picture different form all other age groups. Its percentage involvement ratio is the highest in collisions in both of the severity groups; the single-vehicle accidents come second and pedestrian involvements last. This might perhaps be an indication that a proportion of older drivers has experienced some sensory deterioration or increased reaction-times.
Age of driver by type of area of the accident The involvement rates by age of driver, type and severity of accident are shown on pp. l-2 of Table 2, sub-classified according to metropolitan, provincial urban and rural areas. These pages give both the rates and their transformation into percentages, to facilitate comparisons between types of accidents. The ratios are plotted on Figs. 5-7 showing, however, for simplicity only the two most important types (Multi-vehicle and single-vehicle).
Road accident
involvement
per miles travelled-IV
151
(2)
I
600
I I
4oc
6 = e tk e c 8 & a.
4
2OC
-- c --
_-
IO<
-2 2425-29
3C
9
Age-classes
ITI --7=
4 of
19
.-
L-
50-59
60+
driver
Fig. 5. Brisbane metropolitan area; age of driver by multi-vehicle vs single-vehicle involvements by severity of accident, per IO* miles of exposure. Data shown are ratios of rates to their corresponding overall rate. 0 (I), Multi-vehicle casualty involvements: A (2). Single-vehicle casualty involvements: x (3). Multi-vehicle non-casualty involvements; 0 (4). Single-vehicle non-casualty involvements.
The
24 sets of ratios shown, which represent 4 types of accidents, 2 severity groups, and 3 types of areas, reinforce convincingly the findings of the preceding sub-section. All four basic characteristics of the age-specific involvement rates apply without exception and modification here also, namely their similarity, their shape, their sharp decrease at the start, followed by a slow decrease, ending in some cases with increases at the top age group, and finally, that driver’s age 30 appears to separate the higher from the lower risk. We proceed to examine specific features of these curves. The two youngest age groups of drivers again have the highest involvement in single-vehicle accidents and this applies to all three types of areas of the State, and to each severity group. There is one notable exception, however; the casualty involvements of teenage drivers in rural areas which has its highest involvement in pedestrian accidents. Considering the generally low frequency of pedestrians walking on rural roads, it appears that they could experience a relatively high risk of being hit by an inexperienced teenage driver. The three age groups of drivers between 25 and 50 have in all three areas their highest involvement either in pedestrian, or “other” accidents. Drivers aged 50-59 represent a transitional case, with rank-order of involvement agreeing for some accident types with those of the 4049 age group and in others with the 60 and older drivers. The former is the case with metropolitan casualty involvements, and provincial urban and rural non-casualty involvements, three cases where they have highest involvement ratios in pedestrian accidents. In the other three cases, including the metropolitan non-casualty, and the provincial urban and rural casualty accidents they have highest involvement ratios in collisions with other vehicles. The 60 and older drivers have in all cases but one their highest percentage ratios in collisions with other vehicles. (The significance of this was discussed in the preceding sub-section.) An exception is in rural non-casualty accidents where they have highest involvement ratios in the pedestrian accidents.t tBut this case conclusions.
needs
further
study,
because
the
sample-size
is not quite
large
enough
to allow
drawing
reliable
152
L. A. FOLDVARY I
<20
/
20-2425-29
30-39
40-49
Age -classes
of driver
50-59
60+
Fig. 6. Provincial urban areas of Queensland: age of driver by multi-vehicle vs single-vehicle involvements by severity of accident. per lo* miles of exposure. Data shown are ratios of rates to their correspondmg overall rate. 0 (1). Multi-vehicle casualty involvements: A (2) Single-vehicle casualty involvements: x (3). Multi-vehicle non-casualty involvements: 0 (4). Single-vehicle non-casualty involvements
P
)-
)-
I-
-4
,<20X)-2425-29
30-39
Age-classes
40-49
50-59
60t
of driver
Ftg. 7. Rural area of Queensland; age of driver by multi-vehicle vs single-vehicle involvements and severity of accident. per IO* miles of exposure. Data shown are ratios of rates to their correspondmg overall rate. 0 (1). Multi-vehicle casualty involvements: A (2), Single-vehicle casualty involvements: x (3). Multi-vehicle non-casualty involvements; l (4). Single-vehicle non-casualty involvements.
Road accident involvement per miles travelled--IV
153
We turn now to the involvement rates proper to see what additional information they can provide. It was pointed out that great regularity is observable throughout the 24 curves right up to the top age-class but with this particular class the curve starts in some of the cases to increase, and elsewhere continues its downward trend. If we attack this problem now in detail we see that there are 6 cases where the curve turns upward after reaching age 60; there are five obscure cases because of the smal1 sample-size. and in the other 13 cases the curve continues its downward trend. What is remarkable in this is that each of the curves representing types and severity groups in the rural areas belongs to the bending upwards type. The only remaining bending upwards case is represented by the provincial urban casualty single-vehicle accidents. The hyperbolic nature of the curves in metropolitan and other urban areas, and their parabolic nature in rural areas are well observable also on Figs. 5 (metropolitan), 6 (provincial urban) and 7 (rural). Each of these figures portray the most important groups of their kind, the casualty and non-casualty single-vehicle, and collision involvements. Solomon (1964) produced age-specific involvement rates of drivers per miles travelled, covering 600 miles of main rural highways of the United States. His four curves that cover day and night travel of male and female drivers, are the parabolic type bending upwards at both ends of the age-scale. Apart from the fact that his smaller sample-size did not permit him to obtain such a smooth mathematical form as we obtained, the general shape of his curves for the male driver is quite comparable with our corresponding curves. No earlier published work on the corresponding problem for urban roads is known to the author. Our findings that risk increases beyond age sixty when travelling on rural roads, but does not increase on metropolitan and other urban roads is not inconsistent with expectation. One need only consider the different driving and traffic conditions, the different average speeds and so on, on the rural and urban roads, and the different typical trips an elderly driver probably undertakes on these two kinds of roads. As seen from the detailed account given in this sub-section, there is regularity, a well defined trend in the involvement rates which points to the working of human factors in driver age. Age of driver by type
of vehicle
We have established (Foldvary 1977) that the private vehicle has significantly larger overall risk in each of the two severity classes than either of the two commercial vehicle groups, while these do not differ from each other significantly. The problem turns out to be much more complex when the three main vehicle-types are further sub-classified according to the age of driver. Part (D) of Table 3 and Fig. 8 present the results. Although the private vehicle remains at the top as the riskiest vehicle for three out of seven age groups of drivers, an important change occurs with respect to the teenage driver class. The otherwise high involvement when driving a private vehicle is surpassed in a large commercial (LC) vehicle. The small commerical (SC) vehicle proves on the other hand to be the most reliable vehicle with respect to accident involvement in the hands of drivers of most age groups. Its moderate size and moderate speed combined with the type of driver, are beheved to be the main factors. There are, however, circumstances under which the SC vehicle has the highest involvement rate. The curve for the LC vehicle is somewhat irregular, an unusual feature amongst our curves; for, an increase in the rate appears at the 25-29 age-group. Perhaps it is due to a chance variation, one of those rare occasions, considering that the sample-size does not drop. Figure 9 shows these rates divided according to severity. Its features of importance are that: fa) the teenage driver with high LC involvement retains his highest position in both casualty and non-casualty sub-groups and (b) the irregularity of the LC vehicle curve described above reappears in both severity groups. This suggests that reported mileage performance (a common denominator for the two severity groups) may be responsible for the irregularity. The thin lines hand-drawn on the graphs indicate a possible adjusted curve. A further sub-classification “age of driver by type of vehicle”, in this case by type of accident is given in Table 4 and in the related Fig. 10. The most important result so far obtained is the extraordinarily high risk of the teenage drivel in collision accidents when driving a large commercial vehicle. This is perhaps the only figure on the graph which appears out of place (refer to curve 5 of Fig. 10) indicating its unusually large size. The other curves are more or less parallel to each other, a feature that emphasizes the dominance of the factor “age of driver”.
154
L. A. FOLDVARY
Table 3 Involvement rates by age of driver. type of vehicle, area of involvement and severity of accident. per IO” miles of exposure Age
TYPE
of
Driver;
Private
Area of Involvement.
OF
Vehicleta)
.
All
VEHICLE Small
Casudty
Ccmmercial~bJ
BOW atr
a31
Large CwuaJ-ts
Cornmt~cial~~~
Non-cam atp
,
All
INVOLVEMENTS: (A.1 _--___Briabaue _--_
d
20 2 - 24 25 - 29
t900 859 ;:; 271 212 251
30 r;; 40 E a Zre Overall
Rate _iB.)
$ -
24 29
Overall _LQ
(a) (b) (c) (d)
8718 4750 2095 1.414 1171 583 973
734
1760
;:
‘146 879 395 277 254 1.84 189
120
354
%
Overall
z; - 29 24 30 - 39 40 ;; 50 :: 60 & more Overall
1198
4955 2164 71,5 519 403 440 412
43% 142
-is
104% 845 630 767
Rural Areas -__--__--__
24 29 39 49 59 more
<20
3713 2183
Provincial
z SJ 50 60 & more
( 20 22; ; 60 &
413
)
whole
Metropolitan
1300 555
5632
%
1116 lQl8 841
380 364 236 192 226
I,56 1 1469 869 ;I%
:95:: $833 1105 917 866
1611
300
1182
of
Queensland:
i;:;
Urbsn 1;;;: 2810 11933 1,574 1323 1386 2494 of
Areas
6871 ‘2% 523
21299 2990 2423
44:
1935 1238
zz (d)
1204 810 489
1482
298
1126
1424
8320 ‘2640 3C59 2501 1846 170 1 to47
14274 1523 1145 697 361 233 229
24655 5050 2364 1583
38929
;3?
96%: 2150 1745 1347 1202 716
705
I>818
2586
563
1443
2006
1335
601 275 206 111 76
1501
2102 915 846 481
3275 1836 909 756 499
88;1’: 574
:z ‘%
;zz 2280 1240 to94 804
Queensland. _--____-_
:62:: ;;; :;: 260 474
:;z 129 147 87
97;: 490
Z$ 579
z62 153 147
:;z 217
110
341
451
880 ;z:
:5:74 1017
:;:74 1325
:z 131 162 228
817 522 425 372 731
‘% 556 534 959
;07
107:
22 370 244 1*93 293
128
379
506
1572 381 414 289 169 173 146 224
3297 1225 1242 836 568 523 436 101
% 1656 1125 737 696 582 924
2% 398
al eenslg&
1349
2645
3994
;::
‘3:; 667 g
2484 1214 884 763 603 600 1090
:z 163 163 291
Area:
800
Private vehicles in this Table include cars,station wsggons Panel vans and utilities. Truck-type vehicles of every tjqe not included in the small vehicle @;rcup,and buses of every kind. -yInsufficient sample-size; rate has not been calculated.
and
taxis.
co;merci&
The other factors, type of vehicle and severity of accident, cause minor irregularities observable on the graph-but their basic form remains unaltered. The rates of the age groups are consequently a true measure of the relative risk of being involved in the particular types of accidents studied. The last sub-classification in our analyses is according to area of occurrence. This is given in Table 3. The table brings out some weak points in addition to those already described with respect to the very young and the old driver. The teenager driving a large commercial vehicle produces again some highly significant deviations from rates when driving other types of vehicles. But this feature appears only in the metropolitan and provincial urban areas. In rural areas, interestingly enough, the teenage driver has no significantly higher involvement. Especially the urban casualty involvement rates of this driver-vehicle combination are very large-23times in metropolitan, and 25-times in other urban areas of the corresponding overall rate, while the non-casualty involvement rates are 13-times and 17-times respectively the corresponding average rates. This finding is evidently related to the earlier one demonstrating high risk for this driver-vehicle combination in collisions. The much higher proportion of collisions in urban areas than in rural, is related to the high involvement rates of teenage drivers when driving large
155
Road accident involvement per miles travelled-IV
?9
30-33
40-49
50-5Y
60-t
Age of driver
Fig. 8. Involvement rates by age of driver and type of vehicle, per IO*miles of exposure, Queensland. (I) Small commercial vehicle; (3) E----O, Large commercial vehicle. O--0. Private vehicle; (2) A-A,
commercial vehicles in metropolitan and provincial urban areas. They appear much safer with these vehicies in rural areas. Turning now to the 60 and over drivers, our interest, as in earlier sections, concerns those cases where their involvement rate exceeds the rate of the 50-59 age-group. There are seven cases out of 18 in Table 3 in which this increase occurs, and five of these are rural cases. In fact, all but one of the rural age-specific sets of rates belong to this type, and the increases are significant. They are especialty large with respect to the LC vehicle group, in both severity classifications. Age of driver by hourly variation
We have already (Foldvary 1975, Fig, 1 and Table 3) shown variation in involvement rates broken down into two-hourly periods. The significance of this is that daily variation in risk is composed of two different periods. One is the late night and morning period (from 2 am to 8 am) which could be represented by a third-degree curve with a negative slope throughout while the bulk of the day (from 8 am to 2 am) is best described by a Gompertz-type growth curve. Some additional contribution to this problem is in FoIdvary (1976) subclassifying by day of week, area of occurrence, and severity of accident and by sex of driver. The basic conclusion reached is that every one of the within-day variations is so similar that they represent a single family of curves.
L. A. FOLDVARY 4000
T
-
T
(6) 5 5 h
i
-
3000
6 g I= E
I
(2) (4)
“0
\
s P d F
I
I \
-
2000
E _
i-
hi
z d E5
(5)i I!+ 1 (1)
\
1000 --
iN \\
---A.\
(3)
\ j' I’ 1
I /
~_,
IIt <20 iD-r(25-29
r
I
‘\ Y ‘\
-----. --
/ 0
I
I
I
30-39
40-49
---, 50-59
60
Age of driver Rg.
9. Involvement
rates
exposure, Queensland. volvements. (3) Small casualty involvements.
by age of driver, type of vehicle and severity of accident, per IO’ miles of t I) Private vehicle, casualty involvements. (2) Private vehicie, non-casualty incommerelal vehicle, casualty involvements. (4) Small commercial vehicle, non(St Large ~ommerciai vehicle, casualty involvements (6) Large commercial vehicle, non-casualty involvements
Age of driver is introduced in Table 5 and Fig. 11 to see what changes if any are associated with this factor in hourly variation of risk. The substantial variations are shown by a tree-dimensional surface where the ordinate represents the involvement rate per IO*miles of exposure, and the two abscissae represent age of driver, and two-hourly periods-t Most striking are rates of enormous size that reflect the combination young driver and night driving. From this point the risk surface goes down sharply in every direction, and in the foreground the graph depicts a flat low-risk surface that represents the twelve hours from 4 am to 4 pm and the drivers aged 30 and above. From 4 pm onwards the rates increase sharply, especially for the age-groups under fifty, and this part of the surface, especially before the hours of darkness can be attributed to many factors. From 8 pm to midnight the surface has a sharp slope from its low-point, portraying the risk of the oldest age-group of drivers, upwards. to its top position that portrays the youngest age group. Between midnight and 4 am, the period not shown on the graph, drivers of every age group have high involvement rates (Table 5) and teenage drivers have high rates throughout the day, and highest during the night. It appears worthwhile to examine the table and graph in more detail, and in particular, to study the two factors age of driver and periods of the day separately. Inspecting the individual age groups of drivers, we see that the general shape of the seven curves is that which we observed in earlier sections. It is the shape of the variation in the overall risk with time within a day. It undergoes, however some quite substantial changes with respect to various age groups at various parts of the day. To facilitate comp~isons between the age groups, Table 6 has been prepared: it presents the overall rates of Table 5 Part (Cl in tThe period from midnight to 4 am IS not shown on the graph (the data are available rates would make it too complicated. Table 5 also shows the casualty and non-casualty
in the table), involvement.
because
the very large
157
Road accident involvement per miles travelled--IV Table 4. Involvement
rates by age of driver, type of vehicle. and type and severity of accident per IO* miles of exposure: Queensland” TYPE Private
Ev:f ,,,&
OP
VEHICLB: snail
Vehicle ‘PPPE
OF
Large
Co!nmercial
Commercial
ACCIDENT
Accident
_&I
Casualty
Accident -----_I_-
Involvement
Rates:
786
436
122
456
350
53
1065
305
203
20 - 24
406
241
66
231
152
53
223
to4
34
25 - 29
178
93
38
175
97
32
288
79
37
30 -
39
133
60
23
149
91
25
191
60
25
40 - 49
123
37
26
106
46
16
108
31
23
50 - 59
111
34
18
87
28
12
106
42
(b)
60 & more
115
34
13
94
54
12
135
(b)
(b)
178
80
31
130
73 __--___
22 _ 1_--
145
48
23
(20
All
Drlvere
(BI)on-Casualfq -_----
Accident------ Involvement
Bates:
1801
827
(b)
1740
743
32
1436
863
(b)
20 - 24
1202
548
12
1030
479
4
896
31.1
(b)
25 - 29
648
240
8
696
306
5
862
343
(b)
30 - 39 40 - es
504 456
155 109
4 6
588 393
218 122
2 4
601 439
222 113
(b) 9
50 - 59
372
62
4
335
82
434
82
(b)
60 & more
376
59
(b)
295
74
3 1.0
1t3
(b)
187
6
529
191
4
524
163
6
( 20
All
DArera (C. ) Overall
Accident
InvclvemePlt
A
RateaL
1263
131
2t96
1093
85
3501
20 - 24
1.6cJa
789
78
1261
631
fl
1118
415
34
25 - 29
825
332
46
87i
403
37
1150
422
51
30 - 39
637
21.5
27
738
308
27
793
284
26
20 15 14
547 541 445
144 124 1824
33 24 (b)
zlf‘
-a-
@
2587
40 - 49 579 146 32 498 t67 50-59 4a3 96 21, 422 109 60 b more 491 92 14 12!? DrH8l.a 780 2e? x 264 (a) For details of type of vehicle refer to Table 3. (b) Rate has not been calculated due to insufficient sample-size
standardized
.26--
1107
203
form as ratios to the average rate of each particular age group. The table permits the following inferences: (1) The daily low-point of the various age groups falls without exception on the early morning hours; it is either during the period 4.00-5.59 or 6.00-7.59am. (2) The rate of each age group increases with passable regularity from the morning low-point throughout the day. (3) Two notable deviations are (a) the rate-curves of the two youngest age-groups have a protrusion at about the middle of the day from 10 am to 4 pm, and (b) the rate for every age group of 30-39 and above is larger during the period 2 pm to 4 pm than during the period of 4 pm to 6 pm. (4) As the driver becomes older, the afternoon line of demarcation (drawn on the table) that separates below average from above average rates shifts gradually to earlier hours of the day. Thus for the three age groups under 39 its position is at 6 pm. for the two age groups between 40 and 59 it is at 2 pm, and with respect to the age group 60 and above it is at noon. Now let us inspect the figures by taking the periods of the day as independent variables. Table 7 presents the corresponding standardized rates. The steady decrease with increasing driver age is observable throughout the Table, with the exception of the periods between midnight and 6 am. The variation during this period is rather irregular (and in some cases they are not even available due to the smallness of the sample). Where the sample was theoretically large enough, rates were calculated; but it must be realized that these rates are based on the
158
L.
A. FOLDVARY
Age
of driver
Fig. IO. Involvement rates by age of driver, type of vehicle, type and severity of accident per lo* miles of exposure: (I) Private vehicle invoivement in casualty collisions. (2) Private vehicle involvement in casualty single-vehicle accidents. (3) Small commercial vehicle involvement in casualty collisions. (4) Small commercial vehicle involvement in casualty single-vehicle accidents. (5) Large commercial vehicle involvement in casualty collisions. (6) Large commercial vehicle involvement in casualty single-vehicle accidents. (7) Private vehicle involvement in non-casualty collisions. (8) Private vehicle involvements in non-casualty single-vehicle accidents. (9) Small commercial vehicle involvements in non-casualty collisions. (10) Small commercial vehicle involvements in non-casualty single-vehicle accidents. (1I) Large commercial vehicle involvements in non-casualty collisions. (12) Large commercial vehicle involvements in non-casualty single-vehicle accidents.
smallest samples available and their confidence intervals are rather large. Further studies are therefore necessary to see how these rates vary with age between midnight and 6 am. The steady decrease of rates during the other periods of the day runs through all age groups with, however, three (or possibly four) periods during which an increase is evident at the oldest age group. The six (or eight) hour periods belonging to this group are those from 6 am (or 4 am) to 8 am, from noon to 2 pm, and from 6 pm to 8 pm, Age of driver by day-of-week of accident
Two basic conclusions were made in Part II (Foldvary 1976)while studying the effect of day of week on risk of involvement: (i) The variation in number of accidents by day of week follows closely the variation of vehicle-mile performances, an indication that it is a most important factor, and other factors (as it will be seen later) only under specific conditions have any significant contribution to this variation. This is very different from hourly variations where traffic has a subordinate role and day-night variation is the dominant factor. (ii) Considering the whole State, Saturdays are the worst having 34% higher risk than average followed by Fridays, 21% worse than average. The other days of the week are fairly even in their risk; their rates vary between 898 and 941, representing 86-90% of the average risk. This is in spite of the fact
Road accident involvement
159
Per miles travelled--IV
Table 5. Private vehicles, involvement rates by age of drwer. hour of rnvolvement and severity of accident per IO* miles of exposure: Brisbane metropolitan area’
Hour OS the XV; severity of
AGE 29-24
<"
25-29
DBIVEB _____
OF P-39
40-49
(A.)
__------
xtJ.-
lI.5Qam 3.59am
2.00-
;.;C$oo- ;.;‘,%&
__--_ Casualty Accident InVOlV@JllWnt 10538 28565 13411 127s 3287
8:OO: 9:59am 1%; tO.OO-11.5Qam Noon - L59pm
1723 2831
4.002.006.008.0010.00-l
1281 2882 2846 4277 4404
5.59pIu 3.59pm 7.59~~1 9.59pm 1.59pm
Average tB9d
D&I.y
50-59
237 207 %
z
445 823 ttz t684
z:
857
479
4.006.00-
5.59am 7.59aau
13% ll39l
;;w&
$Yg
‘ls8; :z:
8.0010.00-l
9.59am t .59ma
1971 2338
1.26 1 72;
::R
Noon2004.006.008.0010.00-I
1.59pm 4881 3.59pm 3450 5.59pm 2989 7.59pm 5285 9.59pm I1314 1.99~~ 8024
2936 r591 2666 5282 3465 __l__ 2178
f:: 1308 2658 2682 3502
___--**-_^__ (b)
264 182 157 2t3 %
67 229
:;i? 128 135 143 :;,”
‘:% 226 213 272 366 zz % 1289 413
z:
3;; lO37
627 1196
Es5
285 623 332 324
329
271
250
211
btSS:
13080 “Ez
35541 ‘;;:: 266
2%
Average
3714
1432
13821
1%4
317
55201 5173 z:
811 drivers
R&%3:
Accident _~_~-*---IInVO~VSIImit
_uNon-Caatity -_I-
Daily
6Oarld m0lX
Accident.
939 :;;: 1432 2218 2096 :% __ _ _ __ _ _ _ I _. - _ 1050 845
% 604
573 496
% 1%
g ;z
64% 1129 843 1064 1117 1547 766
773 705 96%
z;z 129g 1105 1844
z$! zz _..________---I 628 1198 -__-
tt xnvo1v0m8nt r&tee: j.C-) Overall Accide~ --I_--
MIS - t.59a 53647 LOO- 3.59am 26822 4.005.5Ysll 4602 6.007.59ma 2239 8.009.59am 3124 ao.oo-11.594361 Noon- 1.59pm 7712 2.0& 3.59pm 5332 4.005.59pm 4270 6.007.59pm 8%31 8.009.5Qpm t5591 iO.OO-11.59pm 12428 Daily Iverage (a) (b)
5610
t3 8E
3035
16194 3448
50368 4u1 333 463 852 859
871 937 1567
733 829 924
:z: 5495 ¶753
1099 949 :g
:z 1.226 1141.
g: 4557
2289 3173 3133
zz 2990
1862 2176
r9st
KS79
11t6
10t6
$2
Ibbj
712 677 708 639
1080
1st t6li --_an& taxi&
839
Private vehicles in this Table include cpzT,ntt9tion T-XL&I Rate ha6 not becahM.ated dtte to tionificiat d#e-r;iee.
that Sundays have the highest traffic volumes. Of course, the percentage of total travel performed on rural roads is much higher during Sundays than other days, and rural travel has generally lower involvement rates. There are various other Sections of this study that enlarged our knowledge of daily variation, treating as variables periods of the day type and severity of accident, type of vehicle, design characteristics and sex of driver. We now turn to the age of driver and day-of-week variations. The analyses for metropolitan and provincial urban areas are shown in Tables 8 and 9. The probability surface method was used as before to illustrate joint variation and Figs. 12-14 present the results. There is similarity between these figures, in that all three show day-of-week as less important than the age of driver. Still, the effect of Saturdays (and to a lesser degree Fridays) comes through cleariy from the surroundings, but do not go through ali age groups. At the oldest group the ridge ebbs away on all three graphs. On the other hand the ridge gets steeper as we progress from this old-age group to younger drivers, and culminates at the teenage driver. At this point, the top-risk age-class of driver combined with the top-risk day (Saturday) produces the high peak of the graphs. Notwithstanding the similarities, there are important differences. We shall study these differences by viewing the distributions of each set of rates from the side of one of the
L. A. FOLDVARY
Fig. 11. Overall involvement rates of private vehicles” by age of driver, and hour of occaston of the accident, per IO* miles of exposure.b The surface is that of the joint function Y = (XI, X2), where Y = involvement rate per IO’ miles travelled (in thousands). X, = the age of driver and X2 = hour of the occurrence of accident. “Including cars, station wagons, taxis and motor-cycles of every kind. bRates for the period between midnight and 4am are not shown: for reason see the text.
variables taken as the independent variable, and then from the other. Considering first the age of driver as independent we see that the various age groups follow diverse patterns in the metropolitan and in provincial urban areas as to the day-of-week variation. While in the metropolitan area the peaks and the second and third highest involvement rates fall on different days for different age groups, there is much uniformity in the provincial urban areas in this respect. Considering the metropolitan area, and the two youngest age groups of drivers, Saturday has the highest risk in both severity groups followed by Sunday (casualty) and Friday or Thursday (non-casualty). This pattern is unique for these age groups. For the driver between 30 and 50, Saturdays are again the most risk-producing days in casualty involvements, and between 40 and 49 also in non-casualty involvements, but between 30 and 39, Fridays has the top risk in non-casualty. For drivers aged N-59, Friday is the worst day with respect to casualty and for drivers 60 and above, Wednesdays in casualty and Thursdays in non-casualty. Another noteworthy fact about this oldest age group is that their third worst day in casualty involvements is Sunday, striking if one considers that this day is the best day for age groups of 40-59. Distinct from this variability is the uniformity in provincial urban areas. The highest risk
161
Road accident involvement per miles travelled-IV Table 6. Standardized overall involvement rates of pwate vehicles by age of driver and time of the accident, per IO’ miles of exposure; Brisbane metropolitan area* Time of the Dsy:
AGB OF DRIVER: M-24 25-29 30-29 40-49
(20
W-59
60 and IllOIW
MN.1.59eJn ?.OO- 3.59em 4.00- 5.59am 6.00- 7.59am 8.00- 9.59nm lO.OO-11.59am
Noon-
9.56 4.78 0.82 0.40 0.56 ro.;jR-
17.55 (b) 4.05 (b) 2.43 0.45 0.51 0.49 0.54 0.82 -1,l:; 0.66 I 11.38 0.73 1 0.77 ;‘; tf1.E_ ;;;1 _ . 0.76 1.82 1.45 1:25 2.76 2.36 1.67 2.20 1.69 2.38
1.59pm
2.00- 3.59pm 4.00- 5.59pm 6.00- 7.59pm 8.00- 9.59pm lO.OO-11.59pm Daily
Awrage (a)
1.00
ii3
t&XSi
(b) Rate has not been
14.50 3.08 0.77 0.54 0.69 0.80 0.86
2.x) 2.27
1.00
1.00
daily
averwe
1.00
For ertpndardisation,the Sg8-groUp
60.30 6.06 0.53 0.60 0.67 0.69 0.80
M
AU drivers
2.36 2.68
49.50 4.28 0.33 0.45 0.64 0.85 0.86 1.47 1.10 1.40 1.83 2.14
(b) (b) 0.85 0.81 0.84 0.76 1.13 1.08 I,.11 1.90 I.29 1.63
30.60 5.13 0.60 0.52 0.64 0.70 0.81 1.00 0.90 1.65 2.28 2.46
1.00
1.00
1.00
1.00
rat% of each partiCul8r
Unit-
calculated due to insufficient
n~plbsize.
Table 7. Standardized overall mvolvement rates of private vehicles by age of driver and period of the day per 10’ miles of exposure; Brisbane metropolitan area’ AGE
Time of the apS
Mi.2.004.006.008.0010.00-I Noon2.004.006.00.. 8.0010.00-t
1.59am 3.59&m 5.59am 7.59aa 9.59= f.5Vam 1. ‘j9pm 3.59pm 5.59pm 7.59pin 9.59gn! 1.59pnl
DpFly Average
@
20-24
25-29
t.09 3.24 4.75 2.70 3.02 3.86 5.93 3.31 2.92 3.06 4.24 3.12
1.08 1.48 7.62 1.87 1.57 3.01 1.70 2.46 E.49 I.43 1.94 1.30
(b) (b) 0.90 c..t3 1.51 1.12 l.l4 0.93 1.20 1.31 0.87 a.15
3.48
1.88
1.19
OF 30-39 1.69
DRIVBB 40-49
50-59
60& more
&U drivers
0.76 1.00 0.89 0.84 0.85 0.85 0.91 0.86 0.86 0.79
0.33 0.42 0.89 0.73 0.75 0.79 0.74 0.75 0.78 0.78 0.72 0.75
1.02 0.52 0.34 0.56 0.82 0.76 0.67 0.93 0.77 0.55 0.51 0.55
(b) (b) 0.74 0.82 0.68 0.57 0.73 0.56 0.64 0.60 0.X 0.34
1.00 1.00
0.86
0.69
0.63
0.52
1.00
1.01
(P) Par staudardieation in this Table,the aver-e
t.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
1.00
rate of each two-h0ur.Q
per&cd haa been taken as unit. fb) Rate
haa
not
been oPlCIikat8d due to insufficient
rample-eise.
days are Saturdays for every age group under 60 with respect to both casualty and non-casualty involvements with some minor variationst For drivers 60 and above, Tuesday had the worst risk in casualty and Friday in non-casualty involvements. It is significant that for these drivers Sundays are the best days in both severity groups of involvements and that the age group 50-59 also fared well on those days. We wilt now turn our attention to the involvement rates of Tables 8 and 9 with day-of-week taken as the independent variable. The interest here concentrates on the shape of the curves of age specific involvement rates for the various days. areas and severity groups. The findings obtained are as follows: (i) As in other cross-analyses of the age-specific rates so far made-this *The 40-49 group in casualty mvolvements, the 2%24 group in non-casualty involvements slipped to the 2nd place. Apart from this minor irregularity. the 2nd and 3rd place occupied in both severtty groups alternately by Fridays or Sundays. AAP Vol
IO. No L-F
162
L. A. FOLDVARI Table
8
Involvement
rates of private vehicles” by age of driver. day of week. and severity miles of exposure; Brisbane metropolitan area DAP
z%:: Sav& Of Accident
konday
-LA.)
l’uesday
CaauPlty
OF
,‘ledneadsy
Accident
of accident,
per IO*
WEBK l’huraday
Involvement -_
Friday
Saturday
Sunday
AL1 dqya
Rates
1376
1237
1407
2229
1571
2895
2395
1900
20
-
24
770
639
725
740
877
Ill32
977
859
25
-
29
402
513
413
593
499
591
385
483
30
-
39
244
357
2 1.2
235
396
516
372
329
40
-
49
210
221
275
228
361
434
184
271
50
-
59
249
214
262
234
368
260
175
251
60
& more
266
160
216
269
147
221
237
212
351
341
349
357
459
616
389
4t3
(20
Overull
(B. ) Non-Caaualtx (20
Accident -I----_--_--__
InVOlvanP3nt
R8tea:
2561
3049
2739
4821
3278
5223
4211
3713
2563
2714
2070
2183
20
-
24
1978
1995
1076
1862
25
-
29
1119
1290
1.136
1971
1748
1532
1300
1434
30
-
39
970
987
752
893
1508
1315
vi3
1050
40
-
49
792
678
899
820
1049
1168
553
845
50
-
59
988
881
979
672
898
694
444
767
60
& more
753
538
1031
559
516
108
508
630
1046
1086
1130
1424
1533
980
18198
Overall
IIt6
-1C.l
Overall
Accident
Involvement
Eateu:
3937
4286
41.46
7050
4849
8118
6606
5613
20
-
24
2756
2634
2601
2602
3440
3896
3047
3042
25
-
29
1521
1803
t549
2564
2247
2i23
1685
1916
30
-
39
121.4
1344
964
112%
1904
183t
1285
1379
40
-
49
1.002
899
1048
1410
1602
737
l.tt6
50
-
59
1237
1095
1241
906
1266
954
620
wia
60
& more
1,020
698
11247
828
663
929
745
841
1467
13886
1435
1487
1882
2149
1369
1611
(20
OIerall (8)
InClUdiUg
CPP8,atUtiOn
tt74
raggOna,
taxin,Pnd
mOtir
CyC.ba
Of
every
kind.
sub-classification produced the familiar hyperbolic curves. The similarity of these curves to one another demonstrates again that age of driver is the dominating factor whilst other factors (day of week and area) are modifying factors effecting minor variations in the individual curves. but not changing their general form significantly. (ii) In consequence, the curves show varying rates for the teenage driver, which are, however, invariably high, then they show sharp decreases through the second age group to the third, and slow decreases thereafter up to the sixties, and either further minor decreases or minor increases thereafter. (iii) The dividing line between the less than average and more than average rate appears to be at about age 30. (iv) A peculiarity with respect to the 60 and above age group is that: (a) in the metropolitan area their rate is higher than that of the age group 51-59 during the two week-end days in both severity groups, but lower than that during the working days in 7 cases out of 10, and inversely: (b) in the provincial urban areas their rate is higher than that of the 51-59 age group during the working days in 8 cases out of 10, but lower than that during the two week-end days. A score of important conclusions could be drawn from the findings in this Section with respect to both the metropolitan and provincial urban situations and their causes, which could include amongst others the effects of social customs, drinking habits, driver’s experience, deterioration of the sense-organs with age and so on. We leave the reader to form his own conclusions.
163
Road accident involvement per miles travelled-IV Table 9. Involvement rates of private vehicles” by age od driver, day of week and severity of accident. per miles of exposure: provincial urban areas of Queensland Age oi Driver ; SeverltJ
DAY Monday
Of
WEEK
OF
Tuesday ledneadag
IO*
Thursday
Friday
Saturday
Sunday All daya
Accident. &&J_Caaualts <20 20 25 30 40 50 60 &
24 29 39 49 59 more
OVerall
Acci_dent Involvement
Rates: --
2832 I713 688 437 377 434 453
3861 1470 451 419 359 290 663
3123 I268 (b) 513 (b) 356 222
4009 1108 534 325 320 286 373
7069 2976 944 515 463 640 455
7166 3625 1790 868 562 690 513
6020 2706 960 501 651 437 336
4955 21164 715 519 403 440 412
599
539
476
470
881
1258
912
734
_(B,1 __-Non-CEUUI Accident P_ 5235 6831 7026 642? 3234 2803 I677 1805 (b) I209 1144 1185
Involvement
Rates:
5690 3030 1467 924
11589 64t6 3630 I802
12040 6236 4890
1,t141
201.1
1515 1509
40 - 49 50 - 59
1 If30 914
I.002 540
(b) 7%
751 697
1555 1073
1773 1518
60 & more
1034
1160
834
849
122E
981
829
8718 4758 2095 1414 II71 883 973
OveralL
1639
1311
1,220
1130
2247
2705
a109
1760
I9206 9861
17161 8790
I3673 6922
(20 20 - 24 25 - 29 30 - 39
&l_‘ferall
Accident -_--__ Involvement
6004 2768
840
Entee:
(20 20 - 24 25 - 29
8067 8136 2365
10692 4104 2256
I0149 407) (b)
9699 4138
I8658 9392
2001
4624
6680
3728
2810
m - 39 40 - 49
1646 1507
1563 136t
1698 (b)
1249 107 1
2317 2018
2879 2335
2016 2t60
1933 1574
50 - 59
1,348
1112
983
1713
2208
127T
1323
Co & sore
1487
te23
83Q
1036
1222
1494
1165
lW5
Overall
2238
la50
t696
tsO0
1683 __--_ 3=3
3963
3021
2494
-
(a) Including cars, station waggcne, taxl8,Pad motor cyclea of evrrg kind. (b) Rate has not been calculated due to inaufflcient aamplcsize.
Age of driver by vehicle occupancy This study has been performed only for the Metropolitan Area, and for cars, station wagons and taxis. It was shown earlier (Foldvary. 1976) that the risk is the highest with the driver’s solo occupancy, and gradually (but not linearly), decreases as occupancy increases. Table 10 presents the variation in rates according to the combination age of driver and vehicle occupancy. In part (A) of the table the involvement incolvement rates are given in part (B) the non-casualty rates, and in part (C) the overall rates. Figures 15 and 16 bring out the nucleus of the Table, the first by classifying the driver age as independent variable and the second one by number of occupants as independent variables. Still more revealing are Figs. 17-19 which present severity rates separately. and in threedimensional form. The effect of the number of occupants and driver age is combined. These Figures and Table 10 tell us: (i) Vehicle occupancy has an effect, on casualty involvement similar to that on non-casualty save for the generally larger figures. (ii) The teenage-driver rates are different from those of the rest of the driver-population. They are not only much higher but they vary differently according to the various levels of occupancy. For the teenage driver. the worst type of occupancy appears to be three persons in
Fig. i-1. Brisbane metropolitan area. casualty accident involvement rates of private vehicles“ by age of driver and day of week of involvement. per 10” miles of exposure The surface is that of the lcnnt function Y = WC,. X:t. where Y = the involvement rate per ldmdes travelled (in thousand\). X, = the age of driver. X? = day of week of involvement a incIuding car<, station wagons, taxis and motor-cycles of every kmd.
1489 1990
Pi All.
I
1514
4
3
2
2 183
1.413
2595 IV01
504%
3666
4
*gfl
including Including
(a) (b)
5613
it902 2769
8353
3
3487
541.2
t9t6
age
of
696
890
1,474
1876
2462
Accidwt
1434
786
1901 1311:
driver
c&rs,atation
X42
2171
2776
5618
1
95
463
not
~mown.
waggoas,and
t379
796
698
1093
1.178
1709
Involvement
to50
604
t354 842
5039
251
271
767
845
tnri8.
1018
797 111.6
580
688
1,003
526
87t
888
778
1252
1369
Rates
437
970 662
516
1 to9 584
Ratea
275
149
219
381 242
209
305 250
282
260
Rates
Accident Involvement _-__c_____________-__
329
259
198
2 1.8
355
355 346
269
40-49
DRIVER
Involvement
30-39
OF
369
565
561
Accident
25-29
liGE
ion-Casualty
859
1347
749
597
Overall _ LC.) _________-_-_-
371’3
4138
3628 3596
892
876
2
ALL
;
2243
3
1
18 1.6
LE.)
1990
Casualty
_(k) 1
2Q-24
(20
2
ixo:Ls
Number
394
841
745
1612
855
958
1246
1348 735
19so 571
1198
699
1538 942
413
304
3t4
385
406
442
1161
630
397
930 389
212
298
121
276
182
232
l&&b)
and severity of accident.
60 & more
vehlcles” by age of dnver, number of occupants per 10s miles of exposure: Bristane metropolitan area
Table 10. Involvement rates of car-class
r
5
? Ln P s
Road accident involvement
per miles travelled-IV
165
Fig. 13. Brisbane metropohtan area. overall accident involvement rates of prrvate vehicies” by age of driver and day of week of involvement. per 10’ mrles of exposure. The surface is that of the joint function Y = F(X,, X2). where Y = the involvement rate of drover per IO8 miles travelled (in thousands). XI = age of “Including cars statton wagons, taxts and motor-cycles of every driver, X, = day of week of involvement kind
the vehicle. The two passengers and the driver all seated in the front compartment in 42% of such cases, as shown in Foldvary (1976). To make comparisons in this and the subsequent paragraphs easy, Table II presents the rates of Table 10 transformed into percentages. The second largest involvement rate of the teenage driver is in solo driving but the one-passenger rate is not much less. With increasing number of passengers, the rate gradually decreases. (iii) For other classes of drivers, the trend of the rate with age and occupancy is remarkably uniform. The rate decreases both with increasing driver age and with increasing occupancy. But while the effect of age produces nearly regular curves the increasing level of occupancy presents some irregular patterns [see Figs. 17-191. (iv) For all ages other than teenagers, the rates are significantly highest when travelling alone. (v) The curves for one and two passengers are similar; parallel with, but on a significantly lower level than the curve of solo occupancy. The curves for four and five or more occupants are lower, than those for two and three occupants, but otherwise similar. (vi) A close study of Figs. 17-19 and Table 11 reveals another interesting relationship: although the three-occupant involvement rate is the highest only for the teenage driver, there is still some adverse effect relative to the other age groups at this level of occupancy.? The point cannot be proved by a statistical significance-test; the rather scattered nature of the low-points tThere are 7 instances in Part (C) of above and below it m the same column appears rn the second row, and the other the three-occupant row would appear to
Table IO where the rate m any one cell is lower than those situated immediately These rates are 5412. 888, 571. 1902. 698, 580 and 394 The first three of them four m the fourth row of the Table. But there IS not a single case where a rate m be lower than Its two verttcal netghbours.
166
L. A. FOLDVARY
Fig. 14. Provincial urban areas of Queensland: casualty accident involvement rates of private vehicles” by age of driver and day of week of involvement, per lo* miles of exposure. The surface is that of the joint function Y = (X,. X2). where Y = the involvement rate per IO* miles travelled (in thousands). X, = the age of driver, X2 = day of week of involvement. “Including cars station waggons. taxis and motor-cycles of every kind.
prevents this. Still it is possible that this peculiarity (reinforced by a visual impression) furnishes evidence that something is “wrong” with the three-persons occupancy. The minor variations of the rates creates a type of ridge and valley-effect at all ages of the same level of occupancy in these figures. AGE OF DRIVER
This section is restricted waggons and taxis.
BY DESIGN
to the Brisbane
CHARACTERISTICS
Metropolitan
OF THE
CAR
Area, and to passenger
cars, station
The effect of brake horsepower variable Variation of the overall involvement rate by brake horsepower was discussed in Foldvary (1977) and detailed rates were presented. Table 12 sub-classifies these rates by age of driver and severity; the accident and exposure figures are also given. Figure 20 illustrates the standardized overall rates where the risk is (Y), and the two independent variables age of driver and B.H.P. of the vehicle by axes (XJ and (X,) respectively (the rates were standardized by taking percentages of the overall rate). The main features of the graph and the three Tables representing the casualty, non-casualty and overall involvement rates may be summarized as follows: (i) The three Tables make a uniform impression. The variations at each of the tables are located at the same classes of each independent variable. (ii) There is an immense variation between the rates within each of the tables; the casualty rate varies by factor 13 (between 138 and 1771) and the non-casualty involvement rate by a factor of 22 (from 346 to 7686). (iii) Both independent variables appear to be of primary importance in road accident causation. This conclusion follows from the fact that the risk surface in all three tables tends in the direction of both independent variables. (iv) In driver age the pattern is the familiar decreasing hyperbolic curve
Road accident Table
Il.
Standardized
involvements
involvement
rates of car-class
per miles travelled-IV
vehicles”
by age of driver
167
and number
of occupants
per 10’
miles of exposure: Brisbane metropolitanareab
NUMBER
Z%S; Severity Of
SO10
LA.) Casualty
OCCUPANTS
3
a
Driver
Accident
OP
4
-*.--Accident
5 or
more
0vereJ.l
Rate _____^_. -
InwlvemeZkt&
0.87
0.93
1.28
1.28
1.36
1.00
20-M
0.95
0.98
0.94
1.21.
1.99
1.00
25 - 29
1.09
1.20
0.81
0.54
0.70
1.00
30 -
39
1.02
1.03
1.27
0.68
0.88
1.00
40 - 49
0.91
1.15
t.51
1.00
0.59
1.00
50 - 59
1.03
0.90
0.97
1.05
1.20
1.00
60 & more
1.05
0.91
1.27
0.58
0.98
0.99
t.12
0.93
1.51 1.00 _IecI_--. 0.88 1.00
El1
-LB. ) Non-Casualtj
Accident
Involvamenta -L------L
0.95
0.95
1.69
1.04
0.69
1.00
1.24
0.87
0.62
0.44
0.68
1.00
25 - 23
1.45
0.63
0.73
0.42
0.73
1.00
30 - 39
1.29
O*aO
0.71
0.48
0.51
1.00
40 - 42
t.3t
0.69
0.74
0.63
0.45
1.00
M, - 59
1.24
Q.87
0.62
0.44
0.68
1.00
60 & more
1.45
0.63
0.73
0.42
0.73
1.00
il.1
1.28
0.78
0.73
0.55
0.46
1.00
20 - 24
( C. 1 Overal~~ent
(20
Inwlvemen2
0.93
0.94
1.71
1.10
0.86
1.00
24
1.14
0.89
0.78
0.70
0.93
1.00
25 - 29 30 - 39
1.26 1.23
0.98 0.85
0.77 0.81
0.50 0.53
0.42 0.59
1.00 1.00
40 - 49
1.22
0.80
0.92
0.72
0.48
1.00
50 - 59 60 & more
1.19 1.35
0.88 0.70
0.70 0.86
0.58 0.46
0.80 0.92
1.00 1.00
All Age-groups
1.21
0.83
0.82
0.64
0.56
1.00
20 -
(a) (b)
-
Including car6, station waggons and taris. In standardization each rate has been related of its particular row.
to the overall.
rate
we met in every sequence of age-specific rates. (v) In power of car the pattern is irregular, with two ridges and one valley. The ridges are formed by the class of 60-70 B.H.P. and by the class under B.H.P. 40. Between them is the valley of B.H.P. 40-59, while the most powerful classes exhibit gradually decreasing rates. (vi) there is a notable exception to this general trend, formed by the youngest age of drivers and top-powered vehicles. This combination, rising high from the low values of the highest B.H.P. class reaches the sky with under 25 drivers. (Teenage and 20-24 years old drivers were combined because of insufficient sample-size). It is instructive to examine the factor which distinguishes the over 60 and the under 25 throughout the range of our B.H.P. values. In the overall series, it is 2.3 for the <40 B.H.P. class, 4.4 for the 4&59 B.H.P. class, 4.2 for the 60-79 B.H.P. class, and 12.2 for the a80 class. Simii~Iy with the non-casualty involvement series, it starts by factor 2.3 for the <40 B.H.P. class, followed by 4.2 for the 40-59 class, 4.3 for the 60-79 B.H.P. class and jumps to 14.0 for the ~80 B.H.P. class. (vii) Thus the upper limit of the rate is formed by the driver-vehicle combination of top-powered vehicles driven by drivers of the youngest age group, while the lowest limit of therange is formed by the second-lowest power-class of cars, driven by the two oldest age-groups. According to these findings, the most powerful cars appear to be less associated with accidents if driven by drivers over 25, but more involved with (possibly less experienced) drivers under 25.
L. A. FOLDVARY
168
Table l?. Vehicle-miles of travel. accident mvolvement and Involvement rates of car-class vehicles” by B car, age of driver and severity of accident. per IO” miles of exposure. Brisbane metropolitan area Age of I&iver
Particulars
BRAKE (40
*E4 25s 30-39
Number of Sample-Cars Making Trips
40-59
1::
7r:
HORSEPOWXR 60-79
E-;;
1:; 196 155
:;;
Z,‘U. ~AJJ
YZ 722
127 32
%
391
1518
1.6.2
11.6
16.5
;;*; 55:o 33.6 26.8 25.0 5.7
36.3 27.2 67.5 65.5 %*'i,
2$24
Annual
25-29 30-39 4049 50-59
Daily Miles Performed by the Car Population,
in 1961
ZKn
(Thousanda).d
TOI'AL
12:3
SO-99
112 46
1:; 116 95
Average
>lOO
1:
3;;
z 106 z
16
49.8 41.0 13a.3 'E 50:1 300.7
Casualty Accidenta, 1961
: 3
E 61
1.:
2;:
:;
i::
%
116 3829
1
399
249
60
1::: 12.1 29.8 37.0 22.8 17.3 4.7
Z:Z 2.2 20.9 19.0 25.2 14.0 3.7
136.5
93.0
16.7
1371.2
51.7 131.4 130.8
Y-Z . 0.8 2.7
;142*; 22413 148.8 57.5
:::
i:;
575.5
90
223
%24 25:29
262 36
:E 15
65
17 11
5 6
126 63
:;z
3@-3g 40-49 50-59
f: 15
;;
152 126 g
22
10
105 :;
:z 204
.
::
86
226
140
;:
40-49 50-59
.COJXJ
&
20-24 Number of Cars $$z in
331 135 327
310.1
Total
Involved All Accidents
Total
239.2
NGn
Number of Cars Involved in Non-Casualty Accidents, 1961
ggn
11 8
14
Number Cars Involved of in
Q-49 Not
Kn.
lxl ‘TATA
19 639
f88
81 49
629
:77
469
1,12 194
1.:;
126 160 11.2 ;44
72 131, 91
10 8
72
:
2:
118 99
107
48
666
1826
21 16
435 283
654
:5
228 420 337 ::z 378
‘% 1383 1074 677 354 551
2463
6569
88 35
z’: 556 475 :z:
1% 80 ;;
97
21
2342
501
:;z
:52 :: 165
1%
33 855
609
2981
608
21 26
z:
877 1499
:93 45 30
291 525 4:
902 17to 137;
::
197 438
z
3129
8395
213
InvolvementRates: -----_-BRAKE (40
40-59
(25 25-29
546 489
:z
Casualty Accident Involvements
30-39 40-49 50-59
294 ::‘:
Non-Casualty
2%9 30139
Accident Involvements
H.P of
50-59 360 4049 Total(c)1
HORSEPOWER: 60-79
%I
1339 523
867 479
149 138
717
:z 232
1652
4466
:6202:631
Total(b) 825 410
T
2731
2113
:;;z
845 762 703 951
614
1586
397 5%
1220 1045 1109
1200 815 810 549
153
663
1784
1272
:z
t Cb)
98;; 707 1312 r
I
Road accident involvement per miles travelled-IV
169
Table 12 (Conrd)
In~lv~~t
Rates:
__I--------_-
Pqtfculsrs
Overall Accident Involvements
BRAKE
%:f
(40
G39
TotaltDJ
60-79
%I
2158 ;z? 546
2636 5804 2009 1539
8553 2425 %
:z:; 1205 t493
%Z 858
1379 1427 2263
‘% 1563
1075 924 1679’ a)
40-59
:::“2 1311 1140
2g9
HORSEPOWER:
>60 E-z; 1012 946 rotill’c11561
t (of
Including cara of every type,s&ion waggons and taxis. Including "Brske Horsepowernot known. category. Including "Age of Driver not known" category. Including "Brake Iforsepowar not known' and *Age of Driver not known' categories. due to insufficiencyof sample-&se. (8) Rate has not been calculated
b” II 6)
P i i
[ I
-
-
\ p
I T\ \
‘\
“a
.
ai
_ L-
c
;7+
-.. -43
m-59 Age of
260
driver
Fig. IS. Overalf accident involvement rates (casuaity and non-casuahy involvements combined) of car-class vehicles, all drivers: age of driver by nom~r of occupants, per IO’ miles of exposure; Brisbane me~o~litan area. f occupant: -2 occupants; A-,-A 3 occupants; C&~-Cl 4 occupants; *.-@ 5 & more occupants. Thin line indicates curve sections based on inadequate sample-size. AAPvol IO.No
Z-G
I
2
3
I
Number of occupants
I
4
>4
Fii. 16. Overall accident involvement rates (casualty and non-casualty involvements combined) of car-class vehiiclts, all drivers; number of occupants by age of driver, per IOsmiles of exposure; Brisbane metropolitan area. (1) -: < 20; (2) o--O: 2W.4; (3) A--.--A: W9; (6) A- - -A: 50-59; (7)S- - -e 3 60.Thin 25-29; (4)D-a*--0: 30-39;(5)r line indicates curve sections based on inadequate sample-size.
I
Fig. f7. Casualty accident invoivement rates of cars by age of driver and number of occupants in the vehicle, per 108miles of exposure; Brisbane metropolitan area.
Road accident
involvement
171
per miles travelled-IV
7
6
5
4
i
--I----
oc
!:
.:
Fig. 18. Non-casualty
accident involvement rates of cars by age of driver and number vehicle, per 10’ miles of exposure; Brisbane metropolitan area.
of occupants
in the
With respect to the other extreme B.H.P. class the lowest powered vehicles which carry a consistently increased accident hazard in the hands of every age group it is possible that some other vehicle factors, possibly connected with the classification of their age and year of manufacture, must materially contribute to their high potential risk.
Weight of car The sub-classification of involvement of cars of various weight groups according to age of driver, and the relevant involvement rates are put forward in Table 13. This sub-classification does not produce involvement rates drastically different from those which characterizes the weight of car classification generally, as described in Foldvary (1977). Thus we do not enlarge on this subject, and turn our attention to the next problem connected with the combined factor B.H.P./Wt. ratio of the car.
172
L. A. FOLDVARY
Fig. 19. Overall accident involvement rates of cars by age of driver and number of occupants, per IO* miles of exposure, Brisbane metropolitan area. The surface is that of the jomt function Y = F(X,,Xz). where Y = accident involvement rate of driver per 10’ miles travelled (in thousands). X, = age of driver, X2 = number of occupants of car.
Age of driver by B.H.P.1 Wt. ratio of vehicle This relationship is shown in Table 14. The near parabolic curve with the inflexion point at its modal value, described [in Foldvary 19771 as being characteristic of the rate curves of the B.H.P./Wt. ratio alters greatly when the sub-curves representing age of driver is taken into consideration. It even loses its parabolic form in some of the subclasses. Let us study first the points of the highest B.H.P./Wt. ratio on all these curves, shown in Fig. 21 and in Table 14. It turns out that this highest B.H.P./Wt. class corresponds to the lowest involvement rate of the whole matrix (and this is for drivers age >60) as well as to the highest involvement rate of the matrix (for drivers under 25). In addition, this highest B.H.P./Wt. ratio group (33.5) produces the lowest involvement rates for every age group of drivers above 29. The situation changes radically, however, with drivers aged 25-29. In their involvement-rate curve, the top B.H.P./Wt. ratio attains the second worst position with its high involvement rate. Further with the youngest (~25) age group of drivers, it occupies the worst position, the highest involvement rate of the whole tabulation. This is another indication that cars of the top B.H.P./Wt. ratio, which serve so well older drivers are less safe with young (perhaps inexperienced) drivers. Other vehicle-design factors The relationship between involvement of cars of various braking surface areas, and the age of driver is presented in Table 15. Similarly, the relationship between the classes of cars having
173
Road accident involvement per miles travelled--IV Table 13. Involvement
rates of car-class vehicles” by weight of car, age of driver and severity of accident, per IO* miles of exposure;
-Severitg Accident
of
Age of Driver
(20
Brisbane metropolitan area
rIJIGH%
OF
20-24
CAR
y5
All 1180
cara
QO
761
1712
(b)
20-24
407
1009
573
686
25-29
313
504
348
4 1.0
30-39
238
3187
205
312
40-49
271
319
154
263
50-59
187
300
188
249
260
208
224
218
218
347
465
261
367
@
2078
5375
2364
3469
20-24
1306
3613
2352
2440
Casualty Accident Involvements
Total
NonC_tY
25-29
888
1976
1277
1479
Accident
30-39
659
1503
944
1181
Involv~ents
4049,
698
1188
613
942
50-59
574
977
684
827
%O
476
794
709
708
1048
1312
Total.
1734
990
2039
8081
3298
4651
20-24
1713
4623
2925
3126
Overill
25-29
1201
2482
1625
1889
Aocident
3Q-39
879
1889
1149
1493
Involvements
40-49
969
1507
767
1205
50-59
761
1275
872
1076
X0
684
tot9
927
926
1337
2199
lzQ9
1679
TOtal
(6)
Including
(b)
Rate
hae
cars not
of been
every
type,rtabion
cahulated
due
waggone to
and
taxl&
insufficient
@8mple_eiaa.
different braking surface area per B.H.P. ratios and the age of driver is studied in Table 16, and that between cars of various B.A./Wt. ratios and the age of driver in Table 17. The most instructive of these is the effect of the B.A./B.H.P. ratio of cars on the age-specific involvement rates of their drivers as shown on Table 16. High involvement rates fill the cells of the first column of this table, amongst them those pertaining to the two youngest age groups of drivers. This column includes cars having the lowest B.A./B.H.P. ratios. Low braking power combined with high driving power is not a car-layout suited to any driver, least of all the young drivers. It appears from our figures that the third B.A./B.H.P. class out of the four (with the ratio of
Table 14. Involvement
Age of Driver
rates of car-class vehicles“ by B.H.P./Wt. ratio of the car and age of driver, per IO* miles of exposure: Brisbane metropolitan area Brake
Eoreepower
(i?.O
per
Weight
Ratio
2.0-2.4
2.5-2.9
3.0-3.4
of
csr . 5
UC-8
05
2708
2893
4694
4174
5909
25.29
1442
1413
1678
3944
1769
1889
30-39 4Q-49
994
1073
l&90
2089
814
1492
SO9
1013
1225
l88S
474
1205
W-59
724
121
1407
1297
570
tO76
$60
705
898
1114
tlta
3t2
925
1333
1435
a39
2281
969
1679
.klJl m-ioel.6 (a)
Including
Oara
Of ewcy
Qpe,ate;tion
waggone
aud
3565
tazie.
174
L. A. FOLDVARY
TableIS.Involvement rates of car-class
vehicles” by area of braking surface, age of driver and severity accident, per IO8 miles of exposure: Brisbane metropolitan area
AREA
CWUalti
OF
BRAKING
so-log
Accident
110-l
39
SURFACE 340 _
Involvqq@&_&&p& 1060 728
All
Care
45
434
815
828
25-29
311
439
332
(b)
450
30-39 40-49
232 182
326 341
316 157
222 292
3x2 263
50-59 960
(b) (b)
321, 26i
142 160
258 235
249 218
295
453
260
368
367
Total
of
(B.1 Non-Casue;Ltg Accident Involvement Rates. _-II_--05
986
3614
2668
25-29
786
1519
1372
2715 2052 807
2737 1479 1181
30-39
471
1123
1227
40-49
569
1143
737
961
942
50-59
513
986
579
972
82’1
YO
446
826
551
788
708
Total
717
1605
11.04
1394
1312
(a)
Including care of every type,atationwaggons end taxis. (b) Rate has not been calculateddue to insufficientsample-size.
Table 16. Involvement rates of car-class vehicles” by braking area per B.H.P. of the car and age of driver, relative to IO8 miles of exposure: Brisbane metropolitan area Age %f
Driver
Breking Area d-5
per Brake Horeeporer Ratio pal 1.5-1.9
2.0-2.4
32.5
CSTe
@
8017
5445
2665
3522
5613
20-24 25w29
6706 2106
3231 2368
1862 1186
2646 1793
3042 1918
X-39 4049
1921
17% 1330
7i9 667
t367
13%
1139
137;9 1116
50-59
1275
11.61
666
738
to 18
878
1090
60-i
936
841
1976
1964
360 All Drivers
_Ratea
il.05
Stsndardiead Relative
1480
16tl
to theoVerall Rate:
20
4.97.
3.38
1.65
2.19
3.49
20-24
4.21.
2.00
1.*6
1.64
1.89
25-29
1.31
1.47
0.74
1.11
1.19
To-39
1. t9
1..09
0.45
0.85
0.85
40-49
0.83
0.82
0.42
O.?l
0.69
50-59
0.7B
0.72
0.41
0.46
0.63
6ct
0.55
0.68
0.43
0.58
0.52
1.23
1.22
0.69
0.92
1.00
All
Drivera
(3
Indluding Car8 of every type,atationwaggons and tads.
Road accident invofvement per miles travelled-IV
175
Fig. 20. Overall accident involvement rates of cars per IO’miles travelled by age of driver by B.H.P. of the car, Brisbane metropolitan area, 1961.
Table 17. ~nvoivemeat rates of car-class vehicles” by braking surface area per weight ratio of car and age of driver. relative to 10’ miles of exposure: Brisbane metropolitan area Ezs
BrzW.ng Surfaoe per Weight Ratio oi: Car 36.0 5.0-5.9 4.0 4.0-4.9
AlA C.SlW 4653 3127 1889 1494
6225 3381 2193 1878 1380 1354 1.052
3640 2883 1859 1353 1344 go2 780
? (Jb)
30-39 40-49 50-59 SO
3389 3167 13ra t026 905 642 733
I))
1016 925
All Drivers
1322
2123
WC!i
752
1679
.& X1-24
444 4$7
1205
(a) Inoludlng cars of everg type,station w~aggona and taris. (b) Rate haa not been calou&eted due IX ineufficiant sampler aise.
176
L. A. FOLDVARY
Fig. 21. Probability surface of the risk of overall accident involvement of cars various B.H.P./Wt. classes driven by drivers of various age classes. Rates per IO* miles of performance: Brisbane, 1961.
between 2.0 and 2.4) includes cars which have the most balanced design in this respect. this column accommodates the lowest involvement rates for each age group.
since
REFERENCES Foldvary L.A. (1968) Vehicle mileage by road, traffic accidents and accident rates. Proc. 4rh Conf. Ausfralian Rood Research Board. 4(l). 1005-1046. Foldvary, L.A. (1975) Road accident involvement per miles traveled-I. Accid. Anal. dl Prev. 7, 191-205. Foldvary L.A. (1976) Road accident involvement per miles traveled-II. Accid. Anal. dt Preu. 8. 97-127. Foldvary L.A. (1977) Road accident involvement per miles traveled--III. Accid. Anal. & Preu. 9. 21-54. Munden J.M. (1%5) The accident rates of car drivers by age. Road Research Laboratory LN/804/JMM. Solomon D. (1964) Accidents on main rural highways related to speed, driver and vehicle. U. S Dept of Commerce, Bureau of Public Roads. U. S. Government Printing Office Washington D. C