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Involvement of older drivers in multivehicle side-impact crashes
Accid. Anal & Prey. Vol. 22. No. 2, pp. 177-188, 1990 Printed in Great Britain.
(1001-4575/90 $3.00+.00 © 1990 Pergamon Press plc
INVOLVEMENT OF OLDER DRIVERS IN MULTIVEHICLE SIDE-IMPACT CRASHES D A V I D C . V I A N O , * C L Y D E C. C U L V E R , * L E O N A R D E V A N S , t MICHAEL FRICK,t *Biomedical Science Department and tOperating Sciences Department, General Motors Research Laboratories, Warren, MI 48090-9055, U.S.A. and R O B E R T SCOTT Safety Research and Development Laboratory, General Motors Proving Ground, Milford, MI 48042, U.S.A.
(Received 22 December 1988; in revised form 3 October 1989) Abstratt--Side impacts were studied using three separate analyses. National Accident Sampling System (NASS) and National Crash Severity Study (NCSS) cases were reviewed on multivehicle crashes involving fatal chest and abdominal injury by interior contact. Twenty-five cases were analyzed and showed an unusually high involvement of older occupants. Analysis of the 19751986 FARS confirmed an overinvolvement. Sixty-four percent of near-side seated occupants were over 50 years old and 36% over 70 in fatal multivehicle side impacts. In contrast, 26% of victims in single-vehicle frontal crashes were over 50 and 8% over 70 years old. Analysis of the 1982-1986 NASS showed that single-vehicle side impacts are not an important injury risk for older drivers, except on icy or wet roads. In contrast, the risk of injury in multivehicle side impacts increases steadily with age and is a major problem for older drivers. The individual NASS and NCSS cases also showed that 88% of the multivehicle side crashes took place at an intersection and that the driver of the struck vehicle frequently caused the crash by driving error (48%) or traffic violation (16%). The majority of the cases occurred in daylight hours, on dry roads, and without alcohol involvement. Changes in visual perception, judgment, and attention of the older driver may he factors in their missing a traffic signal or turning in front of traffic under the right-of-way. In addition, a reduced tolerance to impact force probably contributes to the injury. Although an analysis of photographs of the side-impacted vehicles indicated that 44% had side-structure deformation that was similar to that produced in the National Highway Traffic Safety Administration (NH'I~A) moving deformable barrier test, only 24%-32% of the cases actually addressed the proposed NHTSA dynamic side-impact test. The results of this analysis bear on the agency's preliminary regulatory impact analysis.
INTRODUCTION
One of the next frontiers in automotive safety is the improvement of occupant protection in side-impact crashes. The basis for product improvement is an understanding of crash types and interior contacts that result in serious and fatal injury when the vehicle is struck on the side. This understanding is important because the roadway characteristics and traffic mix for side-impact crashes determine the deformations of the side of the struck vehicle. When a vehicle is struck on the side by another motor vehicle, the frontend shape and orientation of the striking vehicle are important to the side-structure loading and deformation that result in occupant kinematics and contacts in the crash. The higher front-end shapes and heavier mass of trucks make them an important cause of side-impact injuries. The relative speed of vehicles crossing at intersections is another factor. Given a better understanding of the type of crashes and occupant kinematics causing side-impact injury, it is also important to understand the population at risk of crash injury. This generally focuses on the distribution in age of the victims. Next, it is important to develop an understanding of the circumstances of the crash and, in particular, to determine the general categories of why the accident occurred. In many cases, human and environmental factors play an important rQle in crash causation (Viano 1988) and a better understanding in multivehicle side impacts may lead to. specific improvements in driver education and in technologies for accident avoidance. In addition, improvements 177
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can be made in side-impact protection as a better understanding of the cause and control of human impact injury is developed from in-depth research on crash characteristics and injury biomechanics. Part of the present study involved case evaluation of fatal side-impact crashes involving occupants seated on the struck side of the vehicle and experiencing fatal chest or abdominal injury from contact with the side interior. The cases involve multivehicle side impacts and are part of a critical evaluation of the National Highway Traffic Safety Administration's preliminary regulatory impact analysis (NHTSA 1988). NHTSA conducted the analysis to support new dynamic side-impact certification requirements for passenger cars. The dynamic test under consideration involves a moving deformable barrier striking the side of a passenger car. This simulates the crash characteristics of a multivehicle impact and makes it possible to judge safety from responses of anthropomorphic test devices placed on the struck side of the vehicle. Thus, the particular focus of this study is on crashes relevant to the proposed test. MATERIALS
AND METHODS
An analysis was conducted of crashes involving occupants seated on the side of the car struck by another motor vehicle. The initial analysis involved an in-depth evaluation of accidents collected by NHTSA. The study was limited to fatally injured occupants who received their most severe injury by side-interior impact on the chest and abdomen. In subsequent research reported here, general characteristics of side-impact crashes were evaluated by analysis of national data files on fatal and serious injury accidents.
Case study of fatal injuries A search was made of the National Accident Sampling System (NASS) and National Crash Severity Study (NCSS) files to select cases involving nonejected, fatally injured occupants seated on the side of the vehicle struck in a lateral impact. The search was restricted to fatalities in which the most severe injury was to the chest or abdomen because of contact with the side interior. This type of search provided cases which most directly relate to the proposed dynamic side-impact test, as injury assessment in the NHTSA proposed, side-impact dummy was limited to the chest and hip region. The evaluation included a review of postcrash vehicle photographs and of records of occupant and injury data. A typical form contained in the files includes a general description of the crash and specification of both the impacting and case vehicles. Often, there is also information on the extent of side-structure deformation and a determination of crash severity based on the collision deformation classification and CRASH 3 analysis. General information is also included from the police report as well as data on the road type, crash scene, and weather. The files contain slides showing the crash scene and views of the interior and exterior of the involved vehicles. An individual case review was conducted by individuals experienced in accident investigation and analysis. The results of the individual evaluation of the crash circumstances, deformation of the impacted vehicle, and occupant-interior contacts and resulting injuries were provided in an in-depth review of each case and summary information for the aggregate of crashes.
Analysis of FARS data A specific analysis of the 1975-1986 Fatal Accident Reporting System (FARS) data was conducted to determine the age distribution of near-side seated occupants killed in car-to-car side impacts. The investigation examined fatally injured drivers and rightfront passengers seated on the struck side of the vehicle. Side-impact was confined to cars struck by another vehicle,, and single vehicle frontal impacts were evaluated for comparison. Age distributions of fatally injured, nonejected occupants were examined according to the extent of vehicle deformation of the struck vehicle. We limited the cases to those that may be similar to the proposed dynamic side-impact test, so the analysis involved side deformations, classified as moderate, minor, or none, which were combined
Involvement of older drivers in multivehicle crashes
179
for this study. Although the majority of cases in FARS are classified as severe, the side deformation is generally catastrophic, well beyond the severity of the crash test proposed by NHTSA and the type of crash in which the opportunity for fatality prevention exists.
Analysis of NASS crash injury data A parallel analysis of the 1982-1986 NASS data was conducted to determine exposure and injury rates in side-impact crashes. The study was conducted for vehicle-tovehicle and fixed-object impacts involving the front or side of the vehicle. The distribution was weighted to be nationally representative. This allowed an estimate of involvement as a function of the age of the front-seat occupants on the struck side who experience Abbreviated Injury Scale (AIS) 3-6 injury. The analysis of side impacts included occupants on the struck side and excluded cases of rollovers and ejected occupants.
RESULTS
Case study of fatal injuries The regulatory impact analysis (NHTSA 1988) included 31 cases of fatal side-interior contact injury to the chest and abdomen (Table 1). Side-interior contacts accounted for 43% of the assigned cause of fatal injury; and, the chest and abdomen were identified as the body region most seriously injured in 52% of the cases. Only 25 of the original 31 cases (81%) were appropriate to the muitivehicle crash simulation proposed by NHTSA. This excluded single vehicle impacts into such fixed objects as trees, utility poles, or posts, one case of occupant ejection (misclassified in the original analysis), and one file that was not available. A further review of the individual files identified four additional cases that were not relevant to the proposed test procedure or to the original analysis protocol. There were two cases in which the poor health of the occupant prior to the accident was considered a more important factor in the victim's death than the crash. In one case, the occupant was diagnosed as having had a severe brain stem hemorrhage prior to the
Table 1. 1977-1985 NASS and NCSS data on near-side accidents fatal to front-seat passengers in side impacts* Contact
Head
Chest
Abdomen
Front Interior Side Interior Pillars/Rails Exterior
-1 17 10
6 24 2 1
1 7 -1
28 (35%)
33 (41%)
9 (11%)
22
3
Total
Multivehicle cases Excludes: Case 024S - Post impact Case 049S - D o o r opened/ejection
Other 1 3 4 3 11 (13%)
Case Case Case Case
Total 8 35 23 15
(10%) (43%) (28%) (19%)
81t (100%)
158K - Tree impact 257S - Tree impact 329A - Utility pole impact 045 - Not available
Relevant cases 18 3 Excludes: Case 225A - Precrash brain stem h e m o r r h a g e Case 126S - Serious head injury (died after 30 days) Case i17 - Severe skull fracture Case 023 - Died in two weeks from chronic lung and heart condition (crash not the cause of death) * 1973 or later year passenger car, nonejection occupants (summarized from Table IV-3a in the N H T S A regulatory impact analyses (1988). t E x c l u d e s 57 cases listed u n k n o w n and 9 cases listed as noncontact.
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VIANO et al.
crash and another was suffering from a severe chronic lung and heart disease that was considered the cause of death. In two other cases, associated injuries to the head may have been the principal cause of fatality. Therefore, only 21 of the original 31 cases directly relate to the dynamic test procedure proposed for side-impact evaluation of passenger cars. In the remainder, the 25 cases of multivehicle side impact will be used as the basis for statistical review of crash type and causation. A review of the crash circumstances (Table 2) indicated that 88% of the crashes involve side impacts at an intersection. A majority of the cases involved impact as the vehicle was passing through an intersection. Eight of the cases involved the crossing of two-lane roads and five cases involved four-lane intersections. In one case, the car was struck on its side by a turning car while passing on the straight portion of a T-type intersection. In two other cases, two-lane roads crossed obliquely, and in both cases, the struck vehicle was hit from behind at an oblique angle on the side. In these passingthrough crashes, 13 cases involved left-side impact in which the driver was killed (64%) and three cases of right-side impact in which the passenger died (12%). There were three cases each of driver death and passenger-side death as the vehicle turned in front of oncoming traffic. In the cases of passenger deaths, both the driver and passenger were over 60 years of age. There were three cases of loss of control and spinout of the vehicle on a two-lane road and eventual impact on the side of the spinning vehicle. In each of these cases, the crash occurred on an icy road surface. In 16 of the 25 cases (64%), the crash occurred on dry pavement. The remainder of the cases were equally divided among wet and icy road surfaces. A majority of the crashes occurred during daylight hours; very few crashes occurred between 2 A.M. and 4 A.M. In 12 cases (48%) the driver of the struck vehicle was judged to have made a driving error that caused the crash. In four additional cases, the driver's error was sufficient to result in a traffic violation so that driver error was the cause of 64% of the crashes. In three more cases, the driver of the striking vehicle was judged as having made a mistake that caused the crash. There was only one case of alcohol involvement. In 36% of the cases, the side damage of the struck vehicle was considered cata-
Table 2. Case study of 25 fatal nearside impact crashes by type of roadway, road condition, time of day, principal cause, crash severity, and age of victim Type of Roadway
Road Condition and Time of Day
Passing through intersection (64%) 8 2 x 2 Lanes
Dry Wet Ice
16(64%)
5(20%)
5 4x4Lanes 2 2 x 2 Oblique crossing 1 T-section Turning in front of traffic (24%) 2 2x2Lanes t 4 x 4 Lanes 3 T-section
4(16%) 15(60%) 5(20%) 4(16%) 1(4%)
Loss-of-control spin-out (12%) 3 2 Lane Road
6 a.m. - 6 p.m. 6 p.m. - 12 a . m 12a.m.-6a,m.
Unknown
Extent of Vehicle Damage Severe
Extensive
Catastrophic
Total
6 1 2
3 2 2
3 4 2
12(48%) 7(28%) 6(24%)
9 (36%)
7 (28%)
9 (36%)
25 (100%)
Principal Cause 12 (48%) 4 (16%) 4 (16%) 3 (12%) 2 (8%)
Car Pickup/Van Heavy truck
Driver error* Traffic violation Icy road Other driver error
Total
Unknown
Age of Victim 10-20
21-30
31-40
41-50
51-60
61-70
71-80
81-90
18 20
25 28
33
42
54 54 55 57 57 57 59
63 67 68 70 70
73 74 75 76 78 79
83
Involvement of older drivers in multivehicle crashes
181
strophic and involved very severe intrusion and deformation of the side structure (Fig. 1). In an additional seven crashes, the side deformation was considered extensive. Sixtyfour percent of the crashes involved impact energy so severe as to overwhelm the struck vehicle's occupant compartment. This type of side damage is so severe that prevention of the fatality may not be possible by side-structure changes, and crash avoidance may be the only way to save the occupant. Nine of the cases had side-structure damage that was similar to that occurring with NHTSA's crabbed barrier at 33.5 mph. Figure 2 shows typical side-structure damage from barrier crash tests and similar exterior damage to case vehicles. About one-third of the cases have side-structure damage that is relevant to the test protocol proposed by NHTSA. However, some of the crashes involve impact by a heavy truck or pickup with a front structure that is different in geometry and stiffness from the barrier face. Approximately one-fourth of the crashes involve car-to-car impacts in which damage to the case vehicle was similar to the crush caused by the NHTSA barrier. Half of the 25 crashes involved impact by a light truck or van (28%) or by a heavy truck (24%). Nineteen of the fatally injured front-seat occupants (76%) were over 50 years of age and seven (28%) were over 70 years old. This type of age distribution is skewed to older occupants and is in striking contrast to the image of a fatally injured occupant (young, out late at night, and alcohol-involved).
Analysis of FARS data Figure 3 shows the age of all drivers and right-front passengers killed by injury to any body region in side impacts of passenger cars experiencing moderate or less deformation on the side where the passengers were seated. The data contrast with those of victims killed in single-vehicle frontal crashes. Occupants killed in side impacts tend to be substantially older than occupants killed in frontal crashes. Seventy-six percent of the individual cases and 64% of the FARS fatalities involved occupants aged 50 years or older. This fraction compares to only 26% for occupants over 50 killed in frontal crashes. Thirty-six percent of front-seat occupants killed in side impacts were over 70 years of age as opposed to 8% in frontal crashes.
Analysis of NASS crash injury data Serious-to-fatal injury in the 1982-1986 NASS was used to further compare sideimpact crashes with the frontal crashes. The accidents were separated into side impacts (multivehicle or single vehicle crashes) or frontal impacts (also multivehicle or fixedobject impacts). Fifty percent of serious injury in car-to-car side impacts is sustained by occupants over 40 years old (Table 3). In contrast, the risk of serious injury in fixedobject side impacts is extremely low for older occupants. Fixed object side impacts are essentially younger-occupant crashes and are a result of aggressive driving, loss of vehicle control, and skid into a tree or pole. The incidence of frontal impact with fixed objects or other vehicles is relatively constant with age. DISCUSSION
This study has shown the importance of multivehicle side-impact crashes as a risk factor for older drivers and passengers. Contrary to the typical impression of fatal crashes with high involvement of younger drivers, multivehicle side impacts have an overinvolvement of older occupants. Nineteen of 25 cases in the study had a fatally injured occupant over 50 years of age (76%). The average age of those victims was 66.8 -- 9.5 years, indicating that the typical occupant at risk is about 65 years old. This fact is important to design efforts to engineer safety improvements in the side interior. An evaluation of FARS supports the case study conclusion that older occupants are overinvolved in side-impact crashes. In that analysis, 64% of the fatally injured front-seat occupants in side impact crashes are over 50 years old, and 36% are over 70 years of age. NASS data indicate that multivehicle side-impact crashes accounted for one quarter
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Involvement of older drivers in multivehicle crashes
Fig. 2. Structural deformation in laboratory tests using the NHTSA moving deformable barrier crash protocol and comparable crashes for th,: NASS/NCSS case study of accidents (Case No. 021, 222K, 023,049 and 225A).
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Fig. 3. Percentage involvement of occupants in single vehicle frontal crashes and nearside crashes with moderate or less damage as a function of the age of the fatally injured victim (from 1973-1986 FARS).
of the 60-80 year old occupants seriously or fatally injured in car-car or fixed-object impacts involving side or frontal damage. This increases to 28% for occupants over 80 years old. The NASS analysis also provides an estimate of the incidence of serious to fatal injury in this crash configuration. NASS projects that 10,833 occupants over the age of 40 are seriously to fatally injured in multivehide side-impact crashes and that projection represents 50% of all those injured in that type of crash: Applying that fraction to the 1986 FARS indicates 2,730 fatally injured occupants in multivehicle side-impact crashes are over 40 years of age. With 25% seriously-to-fatally injured over 60 years old, fatalities in this crash type are projected at 1,463 for those over 60. The 1986 FARS shows that 31.8% of passenger car fatalities occur in crashes with the principal direction of force lateral on the vehicle (Fig. 4). Two-thirds of the fatalities
Table 3. 1982-1986 NASS passenger car crashes involving serious-fatal injuries (National annual estimate) Side Impact Age
1920-39 40-59 60-79 80+
Car-Car
2,841 (10%) 8,069 (11%) 5,004 (16%) 5,010 (23%) 819 (28%) 21,743 (14%)
Frontal Impact
Fixed Object
Car-Car
Fixed Object
Total
4,829 (17%) 6,827 (9%) 761 (2%) 165 (1%) 46 (2%)
7,738 (27%) 24,056 (33%) 14,229 (45%) 8,286 (38%) 701 (24%)
13,216 (46%) 33,806 (46%) 11,882 (37%) 8,311 (38%) 1,391 (47%)
28,624 72,758 31,876 21,772 2,957
55,010 (35%)
68,606 (43%)
157,987
12,628 (8%)
185
Involvementof older drivers in multivehiclecrashes
SINGLE VEHICLE ACCIDENTS (31.1% SIDE)
MULTI-VEHICLE ACCIDENTS (68.9% SIDE)
333? 34.8%
I 148 e.~'~7~
2,763 20.3%
11,322 TOTAL 2,465 SIDE
13,600 TOTAL 5,458 SIDE
Fig. 4. Incidenceof passenger car fatalitiesas a functionof the principal directionof impact. 32.8% of crashes involvedside-impactloadingon the passengercar (from 1986FARS).
are in multivehicle accidents where the car is struck by a passenger car, truckl or other vehicle, while the other third involves single vehicle accidents primarily with fixed objects. This distribution in single and multivehicle crashes contrasts with the distribution of sideimpact fatalities in the United Kingdom where most occur in collisions with fixed objects (Thomas and Bradford 1989). The reason for the difference in side-impact accident facts between the United Kingdom and the United States is essentially due to the use of roundabouts to connect roads in the United Kingdom. They don't have the perpendicular intersections predominant in the United States that provide the opportunity for high cross speeds. In the United States an inadvertent error by older drivers in an intersection can lead to a side impact if they fail to stop at a red light or if they turn improperly in front of approaching traffic.' This is an intriguing consequence of different roadsystems in the United States and United Kingdom. An equal number of fatalities occur in driver-side and passenger-side lateral-impact crashes. The national loss of human life is 7,923 annually with 5,458 in muitivehicle crashes. Forty percent of fatalities in multivehicle crashes occur with the principal contact lateral on the vehicle. This high level underscores the importance of understanding the causes of fatal intersection crashes in which older occupants are overrepresented as victims. The relatively high incidence of driver error as a cause of these fatal crashes gives support for further in-depth analysis of the driver-vehicle-roadway interactions and evaluation of accident avoidance or warning countermeasures. The involvement of older occupants in intersection crashes has been observed in a study of Foret-Bruno et al. (1983). In the study by Moore et al. (1982), drivers over 65 years old had a higher than average accident involvement rate at intersections for turning maneuvers in urban areas (1.28 times the average for drivers of all ages). The incidence increased in rural intersections (1.5 times) with a particularly high involvement rate for the elderly in rural turning maneuvers (2.59 times). As also observed in this study, older drivers had an appreciably lower than average accident rate involving alcohol use, skidding or loss of control, or darkness (Mourant 1979). Many recent studies suggest that human factors are a principal cause of the overinvolvement of older drivers in intersection side-impacts. In the study by Scialfa et al. (1987), older age was a cause for misjudgment of approaching vehicle velocity and distance. This may le~id to an older driver viewing approaching traffic as relatively safer than do young drivers as they enter intersections and confront approaching traffic. In addition, older drivers are more likely to be involved in accidents in which they receive traffic citations for failure to heed signs, yield the right-of-way, or turn safely (Malfetti and Winter 1987). Recent research by Verhaegen et al. (1988) found that out of 49 drivers 60 years
186
D.C. VIANOet al.
or older and liable in two-car crashes, 24 (49%) were involved in crash types associated with a high risk of side impact. In contrast, only 22 out of 82 (27%) of 30-39-year-old drivers were involved in similar crash types. Given liability for a crash, older drivers are about twice as likely as younger drivers to be involved in a crash with a high risk of side impact. Visual perception (Hills 1980, Kline and Schieber 1985, Bell et al. 1972) and driver attention (Sussman et al. 1982, Yanik 1985) are important factors in safe driving by the elderly. Many studies have shown that an increasing accident rate in older drivers occurs in spite of their vast experience as drivers and that in these accidents, older drivers are very frequently held at fault or blame even though they choose to drive under better operating conditions and in different traffic environments than younger drivers (Ysander and Herner 1976). Age may also be a factor that increases the incidence of injury in multivehicle side impact crashes because of lower tolerances in older occupants. Laboratory tests (Viano et al. 1989a) have demonstrated that human tolerance to impact forces decreases with age over 40. Accident analysis also suggests reduced tolerance with increasing age (Evans 1988a, 1988b). One additional factor was observed in the current case study of the overrepresentation of older occupants in intersection side-impact crashes. Several of the victims were in poor health prior to the crash, and, in at least two cases, the side-impact crash may not have been the principal factor in the ultimate death of the occupant. In addition, a number of the victims survived the side-impact crash for several weeks only to die of a combination of primary and secondary complications. Lower resistance to infection and prolonged bed rest can influence recovery and are significant factors in the outcome of older victims. A projection of the economic cost to society of motor vehicle accidents indicates a total of $74.2 billion dollars (NHTSA 1987). Fatal injuries contribute $16.5 billion. Twelve percent of all fatalities occur in multivehicle side-impact crashes (5,458/46,056) indicating an economic cost to society of $2 billion for the side-impacted victims in this crash type. Based on all crash injuries, the cost to society is $34 billion. With an involvement of passenger car occupants of 54% and assuming an 8.8% incidence of harm related to chest and abdominal contact on the side interior and arm rest (Malliaris et al. 1982) approximately $1.6 billion is the annual societal cost of crash injuries addressed in the proposed NHTSA dynamic test. By either approach of measuring cost to society, it is important to prevent injury in side-impact crashes. The overrepresentation of older occupants as victims must be considered in the design of side-interior padding for optimum crash protection. A safety design that balances protection of low- and high-tolerance victims would provide the maximum societal benefit in injury reductions (Viano 1987a). The balance is between stiff side-padding, which is effective in reducing injury risks in high-severity crashes with higher-tolerance occupants (younger occupants), and soft side-padding, which protects lower-tolerance occupants (older occupants) who may be injured in the more frequent, low-severity crashes. The key is the integration of both the distribution of human tolerance and the distribution in crash severities into the ultimate selection of safety padding. This study suggests favoring lower-stiffness interiors because they are particularly suited for older occupants who have lower thresholds of injury. Improvement of side interiors also requires a humanlike side-impact dummy (Viano 1987b) and a relevant injury criterion, such as the Viscous response (Viano and Lau 1988), to evaluate responses in the dynamic test. Viano et al. (1989d) recently analyzed driving films to determine typical outboard arm positions. As a vehicle proceeds into an intersection, a majority (90%) of drivers have their arm away from their side. Seventy percent have their left hand on the steering wheel. This indicates that side interior padding should emphasize designs improving protection for direct loading of the chest and abdomen. Thus, the determination of chest and abdominal biomechanics of older specimen (Viano 1989c) and injury mechanisms
Involvement of older drivers in multivehicle crashes
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(Viano 1989b) are particularly relevant to the development and evaluation of energyabsorbing materials for side impact protection. In our review of the individual cases, 11 of 25 crashes were identified as having side-structure deformation similar to that produced by the proposed NHTSA moving deformable barrier. Although those 11 cases (44%) were supposed to involve the most severe injury to the chest and abdomen from side interior contact, 3-5 of the cases may be excluded for not satisfying the selection criteria. In several cases, severe head impact injuries may have been the critical factor in the ultimate fatality of the occupant and in several others preexisting medical conditions of the occupant, as opposed to the sideimpact crash, were attributed as being the principal cause of death. Removing those cases leaves 6-8 of the original 25 crashes (24%-32%) as being addressable by sideinterior improvements for chest and abdominal protection. This information has been used by Viano (1989e) to estimate that 140 fatalities (6% of all chest and abdominal fatalities in side-impact crashes) may be prevented by yet-to-be-developed, side-interior padding and structural improvements. REFERENCES Bell, E; Wolf, E.; Bernholz, C. D. Depth perception as a function of age. Aging and Human Development 3:77-81; 1972. Evans, L. Risk of fatality from physical trauma versus sex and age. J Trauma 28:368-378; 1988a. Evans, L. Older driver involvement in fatal and severe traffic crashes. J Gerontology: Social Sciences 43:51865193; 1988b. Foret-Bruno, J. Y.; Hartemann, E; Tarri~re, C.; Got, C.; Patel, A. Conditions required to avoid being killed in cars in side-impact. SAE Technical Paper 830461. Warrendale, PA: Society of Automotive Engineers; 1983. Hills, B. L. Vision, visibility, and driving. Perception 9:183-213; 1980. Kline, D. W.; Schieber, E J. Vision and aging. In: Birren, J. E.; Schaie, K. W. eds. Handbook of the Psychology of Aging. 2nd ed. New York: VanNostrand; 1985. Malfetti, J.; Winter, D. Safe and unsafe performance of older drivers: a descriptive study. Falls Church, VA: AAA Foundation for Traffic Safety; 1987. Malliaris, A. C.; Hitchcock, R.; Hedlund, J. A search for priorities in crash protection. In: Crash Protection, SAE International Congress and Exposition. SAE Technical Paper 820242. Warrendale, PA: Society of Automotive Engineers; 1982; 1-34. Moore, R. L.; Sedgley, I. P.; Sabey, B. E. Ages of car drivers involved in accidents, with special reference to junctions. Supplementary Report 718. Berkshire; U.K.: Transport and Road Research Laboratory; 1982. Mourant, R. R. Driving performance of the elderly. Accid. Anal. Prey. 11:247-253; 1979. National Highway Traffic Safety Administration. Preliminary regulatory impact analysis: New requirements for passenger cars to meet a dynamic side-impact test. FMVSS 214. Washington, DC: NHTSA; 1988. National Highway Traffic Safety Administration, Office of Plans and Policy. The economic cost to society of motor vehicle accidents, 1986 Addendum. Washington, DC: U.S. Department of Transportation; 1987. Scialfa, C. T.; Kline, D. W.; Lyman, B. J,; Kosnik, W. Age differences in judgements of vehicle velocity and distance. In: Proceedings of the Human Factors Society 31st Annual Meeting, 1987: 558-561. Sussman, E. D.; Bishop, H. ; Madnick, B. ; Walter, R. Driver inattention and highway safety. In Transportation Research Record 1047. Transportation Research Board, National Research Council, Washington, DC, 1982: 40-48. Thomas, P.; Bradford, M. Side impact regulations--how do they relate to real world accidents? In: Proceedings of the 1989 Experimental Safety Vehicles Conference, Report #89-5A-0-024, Goteborg, Sweden; 1989. Verhaegen, P. K.; Toebat, K. L.; Delbeke, L. L. Safety of older drivers--a study of their over-involvement ratio. In: Proceedings of the Human Factors Society--32nd Annual Meeting. 1988: 185-188. Viano, D. C. Evaluation of the benefit of energy-absorbing material for side-impact protection: part ii. In Proceedings of the 31st Stapp Car Crash Conference. SAE Technical Paper 872213. Warrendale, PA: Society of Automotive Engineers; November, 1987a: 205-244. Viano, D. C. Evaluation of the SID dummy and "1~I injury criterion for side-impact testing. In Proceedings of the 31st Stapp Car Crash Conference. SAE Technical Paper 872208. Warrendale, PA: Society of Automotive Engineers; 1987b: 143-160. Viano, D. C. Cause and control of automotive trauma. Bull. NY Acad. Med. 2nd Series, 64(5):376-421; 1988. Viano, D. C.; Lau, I. V. A viscous tolerance criterion for soft tissue injury assessment. J. Biomech. 21(5):387399; 1988. Viano, D. C.; Patel, M.; Ciccone, M. Patterns of arm position during normal driving. Human Factors 31(5), 1989d. Viano, D. C. Estimates of fatal chest and abdominal injury prevention by side impact improvements. J. Safety Research 20: 145-152; 1989e.
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Viano, D. C.; King, A. I.; Melvin, J. W.; Weber, K. Injury biomechanics research: an essential element in the prevention of trauma. J Biomech 22(5):403-417; 1989a. Viano, D. C.; Lau, I. V.; Andrezejak, D. V.; Asbury, C. Biomechanics of injury in lateral impacts. Accid. Anal. Prey. 21(6):535-551; 1989b. Viano, D. C.; Lau, I. V.; Asbury, C.; King, A. I.; Begeman, E Biomechanics of the human chest, abdomen, and pelvis in lateral impact. Accid. Anal. Prev. 21(6):553-574; 1989c. Yanik, A. J. What accident data reveal about elderly drivers. SAE Technical Paper 851688. Warrendale, PA: Society of Automotive Engineers; 1985. Ysander, L.; Herner, B. The traffic behavior of elderly male automobile drivers in Gothenburg, Sweden. Accid. Anal. Prey. 8(2-a):81-86; 1976.
(1001-4575/90 $3.00+.00 © 1990 Pergamon Press plc
INVOLVEMENT OF OLDER DRIVERS IN MULTIVEHICLE SIDE-IMPACT CRASHES D A V I D C . V I A N O , * C L Y D E C. C U L V E R , * L E O N A R D E V A N S , t MICHAEL FRICK,t *Biomedical Science Department and tOperating Sciences Department, General Motors Research Laboratories, Warren, MI 48090-9055, U.S.A. and R O B E R T SCOTT Safety Research and Development Laboratory, General Motors Proving Ground, Milford, MI 48042, U.S.A.
(Received 22 December 1988; in revised form 3 October 1989) Abstratt--Side impacts were studied using three separate analyses. National Accident Sampling System (NASS) and National Crash Severity Study (NCSS) cases were reviewed on multivehicle crashes involving fatal chest and abdominal injury by interior contact. Twenty-five cases were analyzed and showed an unusually high involvement of older occupants. Analysis of the 19751986 FARS confirmed an overinvolvement. Sixty-four percent of near-side seated occupants were over 50 years old and 36% over 70 in fatal multivehicle side impacts. In contrast, 26% of victims in single-vehicle frontal crashes were over 50 and 8% over 70 years old. Analysis of the 1982-1986 NASS showed that single-vehicle side impacts are not an important injury risk for older drivers, except on icy or wet roads. In contrast, the risk of injury in multivehicle side impacts increases steadily with age and is a major problem for older drivers. The individual NASS and NCSS cases also showed that 88% of the multivehicle side crashes took place at an intersection and that the driver of the struck vehicle frequently caused the crash by driving error (48%) or traffic violation (16%). The majority of the cases occurred in daylight hours, on dry roads, and without alcohol involvement. Changes in visual perception, judgment, and attention of the older driver may he factors in their missing a traffic signal or turning in front of traffic under the right-of-way. In addition, a reduced tolerance to impact force probably contributes to the injury. Although an analysis of photographs of the side-impacted vehicles indicated that 44% had side-structure deformation that was similar to that produced in the National Highway Traffic Safety Administration (NH'I~A) moving deformable barrier test, only 24%-32% of the cases actually addressed the proposed NHTSA dynamic side-impact test. The results of this analysis bear on the agency's preliminary regulatory impact analysis.
INTRODUCTION
One of the next frontiers in automotive safety is the improvement of occupant protection in side-impact crashes. The basis for product improvement is an understanding of crash types and interior contacts that result in serious and fatal injury when the vehicle is struck on the side. This understanding is important because the roadway characteristics and traffic mix for side-impact crashes determine the deformations of the side of the struck vehicle. When a vehicle is struck on the side by another motor vehicle, the frontend shape and orientation of the striking vehicle are important to the side-structure loading and deformation that result in occupant kinematics and contacts in the crash. The higher front-end shapes and heavier mass of trucks make them an important cause of side-impact injuries. The relative speed of vehicles crossing at intersections is another factor. Given a better understanding of the type of crashes and occupant kinematics causing side-impact injury, it is also important to understand the population at risk of crash injury. This generally focuses on the distribution in age of the victims. Next, it is important to develop an understanding of the circumstances of the crash and, in particular, to determine the general categories of why the accident occurred. In many cases, human and environmental factors play an important rQle in crash causation (Viano 1988) and a better understanding in multivehicle side impacts may lead to. specific improvements in driver education and in technologies for accident avoidance. In addition, improvements 177
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can be made in side-impact protection as a better understanding of the cause and control of human impact injury is developed from in-depth research on crash characteristics and injury biomechanics. Part of the present study involved case evaluation of fatal side-impact crashes involving occupants seated on the struck side of the vehicle and experiencing fatal chest or abdominal injury from contact with the side interior. The cases involve multivehicle side impacts and are part of a critical evaluation of the National Highway Traffic Safety Administration's preliminary regulatory impact analysis (NHTSA 1988). NHTSA conducted the analysis to support new dynamic side-impact certification requirements for passenger cars. The dynamic test under consideration involves a moving deformable barrier striking the side of a passenger car. This simulates the crash characteristics of a multivehicle impact and makes it possible to judge safety from responses of anthropomorphic test devices placed on the struck side of the vehicle. Thus, the particular focus of this study is on crashes relevant to the proposed test. MATERIALS
AND METHODS
An analysis was conducted of crashes involving occupants seated on the side of the car struck by another motor vehicle. The initial analysis involved an in-depth evaluation of accidents collected by NHTSA. The study was limited to fatally injured occupants who received their most severe injury by side-interior impact on the chest and abdomen. In subsequent research reported here, general characteristics of side-impact crashes were evaluated by analysis of national data files on fatal and serious injury accidents.
Case study of fatal injuries A search was made of the National Accident Sampling System (NASS) and National Crash Severity Study (NCSS) files to select cases involving nonejected, fatally injured occupants seated on the side of the vehicle struck in a lateral impact. The search was restricted to fatalities in which the most severe injury was to the chest or abdomen because of contact with the side interior. This type of search provided cases which most directly relate to the proposed dynamic side-impact test, as injury assessment in the NHTSA proposed, side-impact dummy was limited to the chest and hip region. The evaluation included a review of postcrash vehicle photographs and of records of occupant and injury data. A typical form contained in the files includes a general description of the crash and specification of both the impacting and case vehicles. Often, there is also information on the extent of side-structure deformation and a determination of crash severity based on the collision deformation classification and CRASH 3 analysis. General information is also included from the police report as well as data on the road type, crash scene, and weather. The files contain slides showing the crash scene and views of the interior and exterior of the involved vehicles. An individual case review was conducted by individuals experienced in accident investigation and analysis. The results of the individual evaluation of the crash circumstances, deformation of the impacted vehicle, and occupant-interior contacts and resulting injuries were provided in an in-depth review of each case and summary information for the aggregate of crashes.
Analysis of FARS data A specific analysis of the 1975-1986 Fatal Accident Reporting System (FARS) data was conducted to determine the age distribution of near-side seated occupants killed in car-to-car side impacts. The investigation examined fatally injured drivers and rightfront passengers seated on the struck side of the vehicle. Side-impact was confined to cars struck by another vehicle,, and single vehicle frontal impacts were evaluated for comparison. Age distributions of fatally injured, nonejected occupants were examined according to the extent of vehicle deformation of the struck vehicle. We limited the cases to those that may be similar to the proposed dynamic side-impact test, so the analysis involved side deformations, classified as moderate, minor, or none, which were combined
Involvement of older drivers in multivehicle crashes
179
for this study. Although the majority of cases in FARS are classified as severe, the side deformation is generally catastrophic, well beyond the severity of the crash test proposed by NHTSA and the type of crash in which the opportunity for fatality prevention exists.
Analysis of NASS crash injury data A parallel analysis of the 1982-1986 NASS data was conducted to determine exposure and injury rates in side-impact crashes. The study was conducted for vehicle-tovehicle and fixed-object impacts involving the front or side of the vehicle. The distribution was weighted to be nationally representative. This allowed an estimate of involvement as a function of the age of the front-seat occupants on the struck side who experience Abbreviated Injury Scale (AIS) 3-6 injury. The analysis of side impacts included occupants on the struck side and excluded cases of rollovers and ejected occupants.
RESULTS
Case study of fatal injuries The regulatory impact analysis (NHTSA 1988) included 31 cases of fatal side-interior contact injury to the chest and abdomen (Table 1). Side-interior contacts accounted for 43% of the assigned cause of fatal injury; and, the chest and abdomen were identified as the body region most seriously injured in 52% of the cases. Only 25 of the original 31 cases (81%) were appropriate to the muitivehicle crash simulation proposed by NHTSA. This excluded single vehicle impacts into such fixed objects as trees, utility poles, or posts, one case of occupant ejection (misclassified in the original analysis), and one file that was not available. A further review of the individual files identified four additional cases that were not relevant to the proposed test procedure or to the original analysis protocol. There were two cases in which the poor health of the occupant prior to the accident was considered a more important factor in the victim's death than the crash. In one case, the occupant was diagnosed as having had a severe brain stem hemorrhage prior to the
Table 1. 1977-1985 NASS and NCSS data on near-side accidents fatal to front-seat passengers in side impacts* Contact
Head
Chest
Abdomen
Front Interior Side Interior Pillars/Rails Exterior
-1 17 10
6 24 2 1
1 7 -1
28 (35%)
33 (41%)
9 (11%)
22
3
Total
Multivehicle cases Excludes: Case 024S - Post impact Case 049S - D o o r opened/ejection
Other 1 3 4 3 11 (13%)
Case Case Case Case
Total 8 35 23 15
(10%) (43%) (28%) (19%)
81t (100%)
158K - Tree impact 257S - Tree impact 329A - Utility pole impact 045 - Not available
Relevant cases 18 3 Excludes: Case 225A - Precrash brain stem h e m o r r h a g e Case 126S - Serious head injury (died after 30 days) Case i17 - Severe skull fracture Case 023 - Died in two weeks from chronic lung and heart condition (crash not the cause of death) * 1973 or later year passenger car, nonejection occupants (summarized from Table IV-3a in the N H T S A regulatory impact analyses (1988). t E x c l u d e s 57 cases listed u n k n o w n and 9 cases listed as noncontact.
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VIANO et al.
crash and another was suffering from a severe chronic lung and heart disease that was considered the cause of death. In two other cases, associated injuries to the head may have been the principal cause of fatality. Therefore, only 21 of the original 31 cases directly relate to the dynamic test procedure proposed for side-impact evaluation of passenger cars. In the remainder, the 25 cases of multivehicle side impact will be used as the basis for statistical review of crash type and causation. A review of the crash circumstances (Table 2) indicated that 88% of the crashes involve side impacts at an intersection. A majority of the cases involved impact as the vehicle was passing through an intersection. Eight of the cases involved the crossing of two-lane roads and five cases involved four-lane intersections. In one case, the car was struck on its side by a turning car while passing on the straight portion of a T-type intersection. In two other cases, two-lane roads crossed obliquely, and in both cases, the struck vehicle was hit from behind at an oblique angle on the side. In these passingthrough crashes, 13 cases involved left-side impact in which the driver was killed (64%) and three cases of right-side impact in which the passenger died (12%). There were three cases each of driver death and passenger-side death as the vehicle turned in front of oncoming traffic. In the cases of passenger deaths, both the driver and passenger were over 60 years of age. There were three cases of loss of control and spinout of the vehicle on a two-lane road and eventual impact on the side of the spinning vehicle. In each of these cases, the crash occurred on an icy road surface. In 16 of the 25 cases (64%), the crash occurred on dry pavement. The remainder of the cases were equally divided among wet and icy road surfaces. A majority of the crashes occurred during daylight hours; very few crashes occurred between 2 A.M. and 4 A.M. In 12 cases (48%) the driver of the struck vehicle was judged to have made a driving error that caused the crash. In four additional cases, the driver's error was sufficient to result in a traffic violation so that driver error was the cause of 64% of the crashes. In three more cases, the driver of the striking vehicle was judged as having made a mistake that caused the crash. There was only one case of alcohol involvement. In 36% of the cases, the side damage of the struck vehicle was considered cata-
Table 2. Case study of 25 fatal nearside impact crashes by type of roadway, road condition, time of day, principal cause, crash severity, and age of victim Type of Roadway
Road Condition and Time of Day
Passing through intersection (64%) 8 2 x 2 Lanes
Dry Wet Ice
16(64%)
5(20%)
5 4x4Lanes 2 2 x 2 Oblique crossing 1 T-section Turning in front of traffic (24%) 2 2x2Lanes t 4 x 4 Lanes 3 T-section
4(16%) 15(60%) 5(20%) 4(16%) 1(4%)
Loss-of-control spin-out (12%) 3 2 Lane Road
6 a.m. - 6 p.m. 6 p.m. - 12 a . m 12a.m.-6a,m.
Unknown
Extent of Vehicle Damage Severe
Extensive
Catastrophic
Total
6 1 2
3 2 2
3 4 2
12(48%) 7(28%) 6(24%)
9 (36%)
7 (28%)
9 (36%)
25 (100%)
Principal Cause 12 (48%) 4 (16%) 4 (16%) 3 (12%) 2 (8%)
Car Pickup/Van Heavy truck
Driver error* Traffic violation Icy road Other driver error
Total
Unknown
Age of Victim 10-20
21-30
31-40
41-50
51-60
61-70
71-80
81-90
18 20
25 28
33
42
54 54 55 57 57 57 59
63 67 68 70 70
73 74 75 76 78 79
83
Involvement of older drivers in multivehicle crashes
181
strophic and involved very severe intrusion and deformation of the side structure (Fig. 1). In an additional seven crashes, the side deformation was considered extensive. Sixtyfour percent of the crashes involved impact energy so severe as to overwhelm the struck vehicle's occupant compartment. This type of side damage is so severe that prevention of the fatality may not be possible by side-structure changes, and crash avoidance may be the only way to save the occupant. Nine of the cases had side-structure damage that was similar to that occurring with NHTSA's crabbed barrier at 33.5 mph. Figure 2 shows typical side-structure damage from barrier crash tests and similar exterior damage to case vehicles. About one-third of the cases have side-structure damage that is relevant to the test protocol proposed by NHTSA. However, some of the crashes involve impact by a heavy truck or pickup with a front structure that is different in geometry and stiffness from the barrier face. Approximately one-fourth of the crashes involve car-to-car impacts in which damage to the case vehicle was similar to the crush caused by the NHTSA barrier. Half of the 25 crashes involved impact by a light truck or van (28%) or by a heavy truck (24%). Nineteen of the fatally injured front-seat occupants (76%) were over 50 years of age and seven (28%) were over 70 years old. This type of age distribution is skewed to older occupants and is in striking contrast to the image of a fatally injured occupant (young, out late at night, and alcohol-involved).
Analysis of FARS data Figure 3 shows the age of all drivers and right-front passengers killed by injury to any body region in side impacts of passenger cars experiencing moderate or less deformation on the side where the passengers were seated. The data contrast with those of victims killed in single-vehicle frontal crashes. Occupants killed in side impacts tend to be substantially older than occupants killed in frontal crashes. Seventy-six percent of the individual cases and 64% of the FARS fatalities involved occupants aged 50 years or older. This fraction compares to only 26% for occupants over 50 killed in frontal crashes. Thirty-six percent of front-seat occupants killed in side impacts were over 70 years of age as opposed to 8% in frontal crashes.
Analysis of NASS crash injury data Serious-to-fatal injury in the 1982-1986 NASS was used to further compare sideimpact crashes with the frontal crashes. The accidents were separated into side impacts (multivehicle or single vehicle crashes) or frontal impacts (also multivehicle or fixedobject impacts). Fifty percent of serious injury in car-to-car side impacts is sustained by occupants over 40 years old (Table 3). In contrast, the risk of serious injury in fixedobject side impacts is extremely low for older occupants. Fixed object side impacts are essentially younger-occupant crashes and are a result of aggressive driving, loss of vehicle control, and skid into a tree or pole. The incidence of frontal impact with fixed objects or other vehicles is relatively constant with age. DISCUSSION
This study has shown the importance of multivehicle side-impact crashes as a risk factor for older drivers and passengers. Contrary to the typical impression of fatal crashes with high involvement of younger drivers, multivehicle side impacts have an overinvolvement of older occupants. Nineteen of 25 cases in the study had a fatally injured occupant over 50 years of age (76%). The average age of those victims was 66.8 -- 9.5 years, indicating that the typical occupant at risk is about 65 years old. This fact is important to design efforts to engineer safety improvements in the side interior. An evaluation of FARS supports the case study conclusion that older occupants are overinvolved in side-impact crashes. In that analysis, 64% of the fatally injured front-seat occupants in side impact crashes are over 50 years old, and 36% are over 70 years of age. NASS data indicate that multivehicle side-impact crashes accounted for one quarter
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Involvement of older drivers in multivehicle crashes
Fig. 2. Structural deformation in laboratory tests using the NHTSA moving deformable barrier crash protocol and comparable crashes for th,: NASS/NCSS case study of accidents (Case No. 021, 222K, 023,049 and 225A).
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of the 60-80 year old occupants seriously or fatally injured in car-car or fixed-object impacts involving side or frontal damage. This increases to 28% for occupants over 80 years old. The NASS analysis also provides an estimate of the incidence of serious to fatal injury in this crash configuration. NASS projects that 10,833 occupants over the age of 40 are seriously to fatally injured in multivehide side-impact crashes and that projection represents 50% of all those injured in that type of crash: Applying that fraction to the 1986 FARS indicates 2,730 fatally injured occupants in multivehicle side-impact crashes are over 40 years of age. With 25% seriously-to-fatally injured over 60 years old, fatalities in this crash type are projected at 1,463 for those over 60. The 1986 FARS shows that 31.8% of passenger car fatalities occur in crashes with the principal direction of force lateral on the vehicle (Fig. 4). Two-thirds of the fatalities
Table 3. 1982-1986 NASS passenger car crashes involving serious-fatal injuries (National annual estimate) Side Impact Age
1920-39 40-59 60-79 80+
Car-Car
2,841 (10%) 8,069 (11%) 5,004 (16%) 5,010 (23%) 819 (28%) 21,743 (14%)
Frontal Impact
Fixed Object
Car-Car
Fixed Object
Total
4,829 (17%) 6,827 (9%) 761 (2%) 165 (1%) 46 (2%)
7,738 (27%) 24,056 (33%) 14,229 (45%) 8,286 (38%) 701 (24%)
13,216 (46%) 33,806 (46%) 11,882 (37%) 8,311 (38%) 1,391 (47%)
28,624 72,758 31,876 21,772 2,957
55,010 (35%)
68,606 (43%)
157,987
12,628 (8%)
185
Involvementof older drivers in multivehiclecrashes
SINGLE VEHICLE ACCIDENTS (31.1% SIDE)
MULTI-VEHICLE ACCIDENTS (68.9% SIDE)
333? 34.8%
I 148 e.~'~7~
2,763 20.3%
11,322 TOTAL 2,465 SIDE
13,600 TOTAL 5,458 SIDE
Fig. 4. Incidenceof passenger car fatalitiesas a functionof the principal directionof impact. 32.8% of crashes involvedside-impactloadingon the passengercar (from 1986FARS).
are in multivehicle accidents where the car is struck by a passenger car, truckl or other vehicle, while the other third involves single vehicle accidents primarily with fixed objects. This distribution in single and multivehicle crashes contrasts with the distribution of sideimpact fatalities in the United Kingdom where most occur in collisions with fixed objects (Thomas and Bradford 1989). The reason for the difference in side-impact accident facts between the United Kingdom and the United States is essentially due to the use of roundabouts to connect roads in the United Kingdom. They don't have the perpendicular intersections predominant in the United States that provide the opportunity for high cross speeds. In the United States an inadvertent error by older drivers in an intersection can lead to a side impact if they fail to stop at a red light or if they turn improperly in front of approaching traffic.' This is an intriguing consequence of different roadsystems in the United States and United Kingdom. An equal number of fatalities occur in driver-side and passenger-side lateral-impact crashes. The national loss of human life is 7,923 annually with 5,458 in muitivehicle crashes. Forty percent of fatalities in multivehicle crashes occur with the principal contact lateral on the vehicle. This high level underscores the importance of understanding the causes of fatal intersection crashes in which older occupants are overrepresented as victims. The relatively high incidence of driver error as a cause of these fatal crashes gives support for further in-depth analysis of the driver-vehicle-roadway interactions and evaluation of accident avoidance or warning countermeasures. The involvement of older occupants in intersection crashes has been observed in a study of Foret-Bruno et al. (1983). In the study by Moore et al. (1982), drivers over 65 years old had a higher than average accident involvement rate at intersections for turning maneuvers in urban areas (1.28 times the average for drivers of all ages). The incidence increased in rural intersections (1.5 times) with a particularly high involvement rate for the elderly in rural turning maneuvers (2.59 times). As also observed in this study, older drivers had an appreciably lower than average accident rate involving alcohol use, skidding or loss of control, or darkness (Mourant 1979). Many recent studies suggest that human factors are a principal cause of the overinvolvement of older drivers in intersection side-impacts. In the study by Scialfa et al. (1987), older age was a cause for misjudgment of approaching vehicle velocity and distance. This may le~id to an older driver viewing approaching traffic as relatively safer than do young drivers as they enter intersections and confront approaching traffic. In addition, older drivers are more likely to be involved in accidents in which they receive traffic citations for failure to heed signs, yield the right-of-way, or turn safely (Malfetti and Winter 1987). Recent research by Verhaegen et al. (1988) found that out of 49 drivers 60 years
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or older and liable in two-car crashes, 24 (49%) were involved in crash types associated with a high risk of side impact. In contrast, only 22 out of 82 (27%) of 30-39-year-old drivers were involved in similar crash types. Given liability for a crash, older drivers are about twice as likely as younger drivers to be involved in a crash with a high risk of side impact. Visual perception (Hills 1980, Kline and Schieber 1985, Bell et al. 1972) and driver attention (Sussman et al. 1982, Yanik 1985) are important factors in safe driving by the elderly. Many studies have shown that an increasing accident rate in older drivers occurs in spite of their vast experience as drivers and that in these accidents, older drivers are very frequently held at fault or blame even though they choose to drive under better operating conditions and in different traffic environments than younger drivers (Ysander and Herner 1976). Age may also be a factor that increases the incidence of injury in multivehicle side impact crashes because of lower tolerances in older occupants. Laboratory tests (Viano et al. 1989a) have demonstrated that human tolerance to impact forces decreases with age over 40. Accident analysis also suggests reduced tolerance with increasing age (Evans 1988a, 1988b). One additional factor was observed in the current case study of the overrepresentation of older occupants in intersection side-impact crashes. Several of the victims were in poor health prior to the crash, and, in at least two cases, the side-impact crash may not have been the principal factor in the ultimate death of the occupant. In addition, a number of the victims survived the side-impact crash for several weeks only to die of a combination of primary and secondary complications. Lower resistance to infection and prolonged bed rest can influence recovery and are significant factors in the outcome of older victims. A projection of the economic cost to society of motor vehicle accidents indicates a total of $74.2 billion dollars (NHTSA 1987). Fatal injuries contribute $16.5 billion. Twelve percent of all fatalities occur in multivehicle side-impact crashes (5,458/46,056) indicating an economic cost to society of $2 billion for the side-impacted victims in this crash type. Based on all crash injuries, the cost to society is $34 billion. With an involvement of passenger car occupants of 54% and assuming an 8.8% incidence of harm related to chest and abdominal contact on the side interior and arm rest (Malliaris et al. 1982) approximately $1.6 billion is the annual societal cost of crash injuries addressed in the proposed NHTSA dynamic test. By either approach of measuring cost to society, it is important to prevent injury in side-impact crashes. The overrepresentation of older occupants as victims must be considered in the design of side-interior padding for optimum crash protection. A safety design that balances protection of low- and high-tolerance victims would provide the maximum societal benefit in injury reductions (Viano 1987a). The balance is between stiff side-padding, which is effective in reducing injury risks in high-severity crashes with higher-tolerance occupants (younger occupants), and soft side-padding, which protects lower-tolerance occupants (older occupants) who may be injured in the more frequent, low-severity crashes. The key is the integration of both the distribution of human tolerance and the distribution in crash severities into the ultimate selection of safety padding. This study suggests favoring lower-stiffness interiors because they are particularly suited for older occupants who have lower thresholds of injury. Improvement of side interiors also requires a humanlike side-impact dummy (Viano 1987b) and a relevant injury criterion, such as the Viscous response (Viano and Lau 1988), to evaluate responses in the dynamic test. Viano et al. (1989d) recently analyzed driving films to determine typical outboard arm positions. As a vehicle proceeds into an intersection, a majority (90%) of drivers have their arm away from their side. Seventy percent have their left hand on the steering wheel. This indicates that side interior padding should emphasize designs improving protection for direct loading of the chest and abdomen. Thus, the determination of chest and abdominal biomechanics of older specimen (Viano 1989c) and injury mechanisms
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(Viano 1989b) are particularly relevant to the development and evaluation of energyabsorbing materials for side impact protection. In our review of the individual cases, 11 of 25 crashes were identified as having side-structure deformation similar to that produced by the proposed NHTSA moving deformable barrier. Although those 11 cases (44%) were supposed to involve the most severe injury to the chest and abdomen from side interior contact, 3-5 of the cases may be excluded for not satisfying the selection criteria. In several cases, severe head impact injuries may have been the critical factor in the ultimate fatality of the occupant and in several others preexisting medical conditions of the occupant, as opposed to the sideimpact crash, were attributed as being the principal cause of death. Removing those cases leaves 6-8 of the original 25 crashes (24%-32%) as being addressable by sideinterior improvements for chest and abdominal protection. This information has been used by Viano (1989e) to estimate that 140 fatalities (6% of all chest and abdominal fatalities in side-impact crashes) may be prevented by yet-to-be-developed, side-interior padding and structural improvements. REFERENCES Bell, E; Wolf, E.; Bernholz, C. D. Depth perception as a function of age. Aging and Human Development 3:77-81; 1972. Evans, L. Risk of fatality from physical trauma versus sex and age. J Trauma 28:368-378; 1988a. Evans, L. Older driver involvement in fatal and severe traffic crashes. J Gerontology: Social Sciences 43:51865193; 1988b. Foret-Bruno, J. Y.; Hartemann, E; Tarri~re, C.; Got, C.; Patel, A. Conditions required to avoid being killed in cars in side-impact. SAE Technical Paper 830461. Warrendale, PA: Society of Automotive Engineers; 1983. Hills, B. L. Vision, visibility, and driving. Perception 9:183-213; 1980. Kline, D. W.; Schieber, E J. Vision and aging. In: Birren, J. E.; Schaie, K. W. eds. Handbook of the Psychology of Aging. 2nd ed. New York: VanNostrand; 1985. Malfetti, J.; Winter, D. Safe and unsafe performance of older drivers: a descriptive study. Falls Church, VA: AAA Foundation for Traffic Safety; 1987. Malliaris, A. C.; Hitchcock, R.; Hedlund, J. A search for priorities in crash protection. In: Crash Protection, SAE International Congress and Exposition. SAE Technical Paper 820242. Warrendale, PA: Society of Automotive Engineers; 1982; 1-34. Moore, R. L.; Sedgley, I. P.; Sabey, B. E. Ages of car drivers involved in accidents, with special reference to junctions. Supplementary Report 718. Berkshire; U.K.: Transport and Road Research Laboratory; 1982. Mourant, R. R. Driving performance of the elderly. Accid. Anal. Prey. 11:247-253; 1979. National Highway Traffic Safety Administration. Preliminary regulatory impact analysis: New requirements for passenger cars to meet a dynamic side-impact test. FMVSS 214. Washington, DC: NHTSA; 1988. National Highway Traffic Safety Administration, Office of Plans and Policy. The economic cost to society of motor vehicle accidents, 1986 Addendum. Washington, DC: U.S. Department of Transportation; 1987. Scialfa, C. T.; Kline, D. W.; Lyman, B. J,; Kosnik, W. Age differences in judgements of vehicle velocity and distance. In: Proceedings of the Human Factors Society 31st Annual Meeting, 1987: 558-561. Sussman, E. D.; Bishop, H. ; Madnick, B. ; Walter, R. Driver inattention and highway safety. In Transportation Research Record 1047. Transportation Research Board, National Research Council, Washington, DC, 1982: 40-48. Thomas, P.; Bradford, M. Side impact regulations--how do they relate to real world accidents? In: Proceedings of the 1989 Experimental Safety Vehicles Conference, Report #89-5A-0-024, Goteborg, Sweden; 1989. Verhaegen, P. K.; Toebat, K. L.; Delbeke, L. L. Safety of older drivers--a study of their over-involvement ratio. In: Proceedings of the Human Factors Society--32nd Annual Meeting. 1988: 185-188. Viano, D. C. Evaluation of the benefit of energy-absorbing material for side-impact protection: part ii. In Proceedings of the 31st Stapp Car Crash Conference. SAE Technical Paper 872213. Warrendale, PA: Society of Automotive Engineers; November, 1987a: 205-244. Viano, D. C. Evaluation of the SID dummy and "1~I injury criterion for side-impact testing. In Proceedings of the 31st Stapp Car Crash Conference. SAE Technical Paper 872208. Warrendale, PA: Society of Automotive Engineers; 1987b: 143-160. Viano, D. C. Cause and control of automotive trauma. Bull. NY Acad. Med. 2nd Series, 64(5):376-421; 1988. Viano, D. C.; Lau, I. V. A viscous tolerance criterion for soft tissue injury assessment. J. Biomech. 21(5):387399; 1988. Viano, D. C.; Patel, M.; Ciccone, M. Patterns of arm position during normal driving. Human Factors 31(5), 1989d. Viano, D. C. Estimates of fatal chest and abdominal injury prevention by side impact improvements. J. Safety Research 20: 145-152; 1989e.
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Viano, D. C.; King, A. I.; Melvin, J. W.; Weber, K. Injury biomechanics research: an essential element in the prevention of trauma. J Biomech 22(5):403-417; 1989a. Viano, D. C.; Lau, I. V.; Andrezejak, D. V.; Asbury, C. Biomechanics of injury in lateral impacts. Accid. Anal. Prey. 21(6):535-551; 1989b. Viano, D. C.; Lau, I. V.; Asbury, C.; King, A. I.; Begeman, E Biomechanics of the human chest, abdomen, and pelvis in lateral impact. Accid. Anal. Prev. 21(6):553-574; 1989c. Yanik, A. J. What accident data reveal about elderly drivers. SAE Technical Paper 851688. Warrendale, PA: Society of Automotive Engineers; 1985. Ysander, L.; Herner, B. The traffic behavior of elderly male automobile drivers in Gothenburg, Sweden. Accid. Anal. Prey. 8(2-a):81-86; 1976.