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Minimizing inter city transportation risk—A matter of perspective
Accid. Anal. and Pm., Vol. 28, No. 3, pp. 409-413, 1996 Copyright 0 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved Oool-4575/96 S15.00 + 0.00
Pergamon SOOOl-4575(96)00010-3
MINIMIZING RISK-A
INTER CITY TRANSPORTATION MATTER OF PERSPECTIVE PETTERWULFF
Swedish Defence Research Establishment, (Accepted
S-172 90 Stockholm, Sweden
26 November 1995)
Abstract-Car, aeroplane and train travel have different risk characteristics that influence the safety ranking between them. The ranking depends on the range of distances compared. It also depends on what we mean by risk. Three reasonable interpretations of risk are presented. They are applied to Swedish transportation statistics. The results reveal that there is a safety niche for each of the three alternatives. That is, car, aeroplane and train each have a certain claim to being the safest means of transportation. Copyright 0 1996 Elsevier Science Ltd Keywords-Auto
safety, Airline safety, Train safety, Risk measure injured in an accident in Sweden is about one in 200 million car kilometres (Table 1). This can be compared to Sweden’s domestic scheduled air traffic. There have been two accidents in that sector during the last 20 years; both without survivors. These two accidents out of more than 2 million departures since 1975 give a risk level close to the general West European risk level-O.8 per one million departures (Oster et al. 1992). That value will be used here as being statistically more well founded than the Swedish value. The fatality risk per flight will actually often be double the value mentioned, as most flight routes between two places in Sweden will mean double take offs and landings with an intermediate stop at Stockholm/Arlanda. The risk of travelling by air will then correspond to 1.6 per one million trips. This equals the risk of driving about 300 km by car. The train is a third viable contender for Swedish travel customers. During the last 10 years there have been some collisions and derailments with fatalities. The largest accident took the lives of six passengers and three crew members. The risk profile for train travel is similar to that of the car for longer distances. Train travel has a distance-independent risk as well. But that portion of the risk is dominant only for distances shorter than about 25 km. The resulting risk for train travel is therefore rising roughly in proportion to distance travelled. However, the risk level in this case comes out far below car risk level. The safety performance of trains is also better than that of scheduled air traffic for all domestic distances in Sweden (Fig. 1). So far the safety issue seems to be settled beyond
INTRODUCTION As has been shown by Evans et al. (1990) safety comparisons between car and aeroplane can be meaningfully made if the travelling distance is taken into account. Air travel has a risk profile rather independent of distance, while car travel entails a risk rising with distance travelled. That is, air travel is generally the safer mode of travelling for long distances and car for short ones. Sivak et al. (1991) have improved the analysis by distinguishing between nonstop and other flights. The analysis by Evans et al. has pointed to car travel as the safer mode of travelling under certain circumstances. The analysis by Sivak et al. has adjusted the limits, so to speak, of the realm where the private car may be the safer travelling alternative. The aim of this paper, in contrast to the papers mentioned, is to illustrate that there may be no fixed solution to the problem. Different meanings of risk tend to result in different modes of transportation being the safest. The scope is also broadened to three modes of transportation. The setting is West European (Sweden) rather than North American as with the Evans and Sivak papers.
THE
TRAVELLER’S
FATALITY
RISK
Let us first compare the individual traveller’s risk of being killed in an accident. This is the risk measure used in both the Evans and Sivak papers. As in those papers, travelling by car is here taken to mean driving. A car driver’s risk of getting fatally 409
P. WULFF
410
Table 1. Statistical
background
for the traveller’s fatality SJ 1986-94)
Private car Driver fatalities: Distance driven: Resulting risk:
2 (all dead) 2.3 x lo6 0.9 per lo6 departures) 0.8 per lo6 departures
Passenger train (State railways) (1) Fatalities in train accidents, at level crossings and other occasions: Total traffic: Resulting risk: (2) Fatalities; embarkation, disembarkation, fall or jump from train in movement: Number of trips: Resulting risk (distance independent):
TOTAL
of
the
train
RISK OF SERIOUS FATALITY
as
mode
INJURY
Fatality
probability
54 x lo9 passenger-km 1 in 3400 x 10’ passenger-km 4 passengers
524 x lo6 1 per 130 x lo6 trips
of
OR
x lo6
200
300
400
Fig. 1. An individual’s risk of dying in a travel accident as a function of distance travelled.
( 1977-1989)
,
m in Sweden
1985-93) (1985591)
(1985-91)
ented persons, who choose consumers’ goods according to their harm to the environmental system. Here the idea would be to choose a mode of travelling according to its harm done to people. This would, at least in principle, put pressure on the providers of less safe travelling services to improve their safety performance. Further, let the risk measure here be extended also to cover serious injuries. Including victims in transportation personnel raises the risk levels for air and rail alternatives relative to private car travel, where the category does not exist. For car and rail alternatives the risk levels increase substantially when victims (fatalities and serious injuries) among third persons are included. For car traffic third person injuries/deaths are typically represented by a pedestrian hit when crossing a street. Similarly, a person in a car may be hit at a rail crossing, making him a typical third person victim to rail traffic. Air traffic has the smallest proportion of third persons injured or killed. During the last 20 year period in Sweden the number of seriously injured people in scheduled air traffic operations is only about 15% of the number of persons killed in accidents. More extensive statistics from the U.S. indicate the proportion of seriously injured to be less than 50% of the number killed (Oster et al. 1992). Third person fatalities from regular air traffic together with personnel fatalities account for only about one tenth of air passenger fatalities. The low proportion of persons seriously injured and persons fatally injured leads to a very modest rise in the number of persons at risk as compared to our first risk perspective. The risk level will be about 25% higher than for the case “traveller’s fatality risk”.
;~__y____T-=!-;Dz
1975-92) 1975-92)
16 passengers
We have up to this point been dealing with an individual traveller concerned only with his (her) own survival. But, as is well known, there are victims other than travellers. They fall into the categories of personnel and “third persons”. A third person is a person who is not a part of the transportation system considered. Now let “risk” mean the sum of risks incurred by travellers, personnel and third persons together. This is a risk perspective that might be held by a citizen looking at the different transportation systems objectively. It is also a perfectly possible ground for personal decision-making by a traveller. It is reminiscent of the risk perspective held by ecologically ori-
A
1977-93;
281 persons 57 x lo9 km 1 fatality in 200 x lo6 km
Domestic air traffic in scheduled operations Number of fatal accidents: Number of take offs/landings: (Resulting risk: Estimated risk: (Western Europe; Oster et al. 1992)
dispute in favour transportation.
risk (SCB 1994; Luftfartsverket
Minimizing
inter city transportation
With car traffic the risk level increases drastically. It is about 15 times greater than with the former risk perspective. With rail traffic the risk level increase is even more drastic-about 35 times (see Table 2). With this interpretation of risk (and safety), air travel is the safest mode of transportation for all distances of practical interest to regular flights. That is, by changing our measure of what we mean by risk, we have come to a completely different result with regard to transportation safety. TOTAL
FATALITY
RISK
It is also possible for the private car to become a minimum risk alternative. If we subtract the seriously injured from the case above we will have a meaning of risk that is favourable for car travel. This meaning of risk is similar to the meaning above. Only here, considerations are restricted to fatalities. It is an equally possible (although probably not as common) ground for personal decision-making as the two risk perspectives considered earlier. The risk per km of train travel in this case will still fall below the risk of car driving. However, this difference is offset by the fact that the road system is more fine-meshed than the railroad system, which means that a trip by car generally saves travel distance as compared to a trip by train. The private car will on average be quite competitive in relation to train travel over all distances. The car will also have an advantage over nonstop flying up to about 150 km and up to double that distance for flights with an intermediate stop at Arlanda/ Table 2. Statistical
background
411
Stockholm. A middle-aged driver-with only two thirds of the average driver’s risk (SCB, 1989)--may compete with flying risks up to 50% longer distances. RISK CONTRIBUTION TRIPS
OF ACCESS
Points of departure and destination are seldom located at airports or railway stations. Normally you have to go by car or bus to gain access to an airport or a railway station and similarly to reach your point of destination. These access trips at both ends of a main trip will tend to increase the risk for the air and rail alternatives. The length of the access trips is normally only a fraction of the city to city distances considered in the main analysis; typically 20% or less (10% or less for rail). Access trips by car can therefore lead to a risk increase in air and rail travel by up to 20% of the car risk level. If the access trips are undertaken by bus, the risk increase will be even less than that because of the better safety record of buses as compared to cars. Normally you will also have to walk some distance at both ends of a trip to get to your point of destination. Jorgensen (1993) has presented a detailed analysis of access trips for an urban transport situation. He concludes that pedestrian access trips are the dominant risks of “low-risk” travel alternatives like bus and local train. That is, getting to and from a bus or train is by far the riskiest part of such trips. Inter city travel has different characteristics. First, inter city trip distances are about one order of magnitude greater (or more) than distances in the
for total risk of serious injury or fatality (SCB 1994; Luftfartsverket 1977-93; SJ 1986-94)
Private car All serious and fatal injuries: Total driver and passenger distance: Resulting risk: Air trafic in scheduled operations Serious and fatal injuries (including international traffic): Estimated
risk
risk:
Passenger train (State railways) (1) All serious and fatal injuries or fatalities in train accidents, at level crossings and other occasions: Total traffic: Resulting risk: (2) All serious and fatal injuries; embarkation, disembarkation, fall or jump from train in movement: Number of trips: Resulting risk:
4031 persons 91 x lo9 person-km 1 in 14x106km
(1993) (1993)
43 (38 fatal, 5 serious)
(1975-92)
(no “third person” victims) 1.0 per lo6 departures (25% above case l/table 1)
566 persons
(1985-93)
54 x lo9 passenger-km 1 in 95 x lo6 person-km 17 passengers
(1985-93)
524 x lo6 1 per 30x lo6 trips
(1985-91)
(1985-91)
412
P. WULFF
Table 3. Statistical Private car All fatalities: Total driver and passenger Resulting risk:
background
for total fatality
distance:
Air trajic in scheduled operations Estimated risk:
Passenger train (State railways) (1) All fatalities in train accidents, at level crossings and other occasions: Total traffic: Resulting risk: (2) All fatalities; embarkation, disembarkation, fall or jump from train in movement: Number of trips: Resulting risk:
Jorgensen study (5-15 km), but pedestrian access trips are likely to be of about the same length. The relative importance of access trips on foot will therefore be about one order of magnitude smaller (at least) than in the Jorgensen study. Also, Swedish pedestrian risk rates seem to be low in comparison with international rates. The fatality rate is less than half the rate reported for Great Britain (Collings 1994) and close to the lower of two values reported for Denmark (by Jorgensen, assuming a daily walking distance of around 1 km per person). Further, Jorgensen is analyzing routine trips to and from work. Car riders can be expected to have found fairly optimal parking solutions for these kinds of trips. This will generally mean that walking distances are minimized. According to Jorgensen the average walking distance for car riders is only about 10% of the average walking distance for local train passengers. Parking solutions can be expected to be less optimal for car drivers on inter city trips. Therefore, walking distances to end-points in a city visited will tend to be longer than walking distances from car to workplace. That is, access trip lengths-and riskswill be less unevenly distributed between travel modes than in the Jorgensen study. This will lessen the importance of access trip risks with regard to risk ranking. With trip end-points in suburban areas, private car travel will generally leave you with less distance to walk and less pedestrian risks to take than an aeroplane plus bus, or a train plus bus alternative. But with trip end-points in central city areas it may be the other way round because of central area parking problems. Also, if an aeroplane or train trip is complemented with a ride in a taxi, the pedestrian
risk (SCB 1994; SJ 1986-94)
533 91 x lo9 person-km 1 in 170 x lo6 km
(1993) (1993)
0.9 per lo6 departures (10% above case 1)
27 1 persons
(1985-93)
54 x lo9 passenger-km 1 in 200 x lo6 person-km 11 persons
(1985593)
524 x lo6 1 per 50 x lo6 trips
(1985-91)
(1985591)
phase of the total trip and its associated risks will tend to be smaller than for the car driving alternative. Before leaving the access trip problem let us indicate a possibility of quantitative analysis. The critical part of pedestrian movement is the crossing of streets with car traffic. Assuming an average of at least two crossings per person per day, there are more than 6000 million street crossings annually in Sweden. This activity results in less than 100 pedestrian fatalities (94 in 1993; SCB 1994). The fatality risk per crossing would then be below one in 60 million. This is a fairly low figure. A door to door trip with up to 10 pedestrian crossings, which would probably include the majority of all car, air and rail trips undertaken, would entail a pedestrian fatality risk of only a fraction of one in a million. This would only marginally influence the safety ranking between transportation modes. A similar line of reasoning could be employed for the risk perspective where serious injuries are included (580 pedestrian fatalities + serious injuries in 1993; SCB 1994). CONCLUSIONS In the above-mentioned study by Jorgensen (1993) the transportation alternatives were seen to have a risk ranking which is not much influenced by the choice of risk perspective (individual fatality risk, individual risk of injury, total fatality risk, total risk of injury). According to Jorgensen, for trips confined to the central part of a city, risk ranking is independent of the choice of risk perspective (1. bus, 2. car, 3. bicycle). For trips between suburb and centre there are, in the Jorgensen study, some shifts in ranking between train and bus. Either may be the minimum risk alternative
Minimizing
inter city transportation
depending on risk perspective. Car is consistently the last alternative and bicycle the last but one, out of the four alternatives considered. We have arrived at a rather different conclusion regarding inter city travel. When analysing which among car, air and train travel is a risk minimizing alternative, we have found all three to be. Which alternative comes out as the safest depends on the risk perspective chosen and to some extent on distances considered. The three perspectives on the meaning of risk that have been used are similar to those used in the Jerrgensen study. All relate to physical harm, but they differ with respect to who comes to harm and the extent of harm considered. The results are summarized in Fig. 2. For the air and train travel alternatives there has been a more or less complete shift of preference between risk perspectives 1 and 2. For the private car there is a partial shift of preference as we move to the third risk perspective. The only general conclusion to be drawn from these observations is that the private car is not a risk minimizing alternative for long distance travel. A risk comparison between the car and air travel alternatives was made by Sivak et al. (1991). Their conclusion was that flying is always safer than driving for an average driver “for any reasonable combinations of the trip distance and number of flight segments”. The results obtained here do not agree with that conclusion. With the higher Swedish (West European) risk level for flying we find a safety niche for the private car up to 150-300 km with risk perspectives 1 and 3 (although the train is a safer alternative with perspective 1).
IRisk perspective
I Safest mode of transportation I
O-Distance
-
1500 km
Fig. 2. The safest mode of inter city travel changes with risk perspective and distance. (Access trips are assumed to have little impact or cancel out between alternatives.)
risk
413
The influence of access trips on the risk ranking of alternatives seems generally to be limited. This is partly due to the fact that the proportion of access to total trip length is (at least) about an order of magnitude less than for trips within a city. It is also due to the fact that the burden of access trip risk seems to fall less unevenly on the inter city travel alternatives than on the urban ones. Also, Swedish pedestrian risks tend to be low. All this works toward lessening the risk impact of access trips and not upsetting the minimum risk rankings made. The point that can be made with respect to access trips is that they may to some extent be chosen. Debarking from a train at a railway station, for instance, leaves you with a choice of continuing on foot, by bus or by taxi to the point of destination. Taxi would seem to be the preference as that would minimize the relatively high-risk activity of walking (across streets). Therefore, it is not quite fair to add statistical averages of access trip risks when summing up total inter city trip risks. To sum up the main conclusion of this paper; if we as individuals want to minimize transportation risk, we should first decide on what we would mean by risk. Am I as a traveller concerned solely with my own chances of survival or do I want also to avoid being part of situations where others die violently or get seriously injured? Until we have a clear idea of our preferences, the safety race between car, aeroplane and train remains undecided.
REFERENCES Collings, H. Transport Statistics Great Britain. London: HMSO; 1994. Evans, L.; Frick, M. C.; Schwing, R. C. Is it safer to fly or drive? Risk Analysis 10: 239-245; 1990. Jorgensen, N. The safety of different means of transport in urban traffic. Paper given at ISATA Conference; Aachen, September 1993. Luftfartsverket 19xx. (The Civil Aviation Administration 19~~). Official Statistics of Sweden; 1977-1993. (Annual publication) Oster, C. V.; Strong, J. S.; Zorn, C. K. Why airplanes crash: Aviation safety in a changing world. Oxford University Press; 1992. SCB. Risker pi vlg-vlgda risker. (Road risks-weighed risks). Statistics Sweden; 1989. SCB. Trafikskador ‘93. (Traffic injuries ‘93). Statistics Sweden; 1994. Sivak, M.; Weintraub, D. J.; Flannagan, M. Nonstop flying is safer than driving. Risk Analysis 11: 145-148; 1991. SJ. Trafiksgkerheten. (Traffic safety). Swedish State Railways; 1986-94. (Annual publication)
Pergamon SOOOl-4575(96)00010-3
MINIMIZING RISK-A
INTER CITY TRANSPORTATION MATTER OF PERSPECTIVE PETTERWULFF
Swedish Defence Research Establishment, (Accepted
S-172 90 Stockholm, Sweden
26 November 1995)
Abstract-Car, aeroplane and train travel have different risk characteristics that influence the safety ranking between them. The ranking depends on the range of distances compared. It also depends on what we mean by risk. Three reasonable interpretations of risk are presented. They are applied to Swedish transportation statistics. The results reveal that there is a safety niche for each of the three alternatives. That is, car, aeroplane and train each have a certain claim to being the safest means of transportation. Copyright 0 1996 Elsevier Science Ltd Keywords-Auto
safety, Airline safety, Train safety, Risk measure injured in an accident in Sweden is about one in 200 million car kilometres (Table 1). This can be compared to Sweden’s domestic scheduled air traffic. There have been two accidents in that sector during the last 20 years; both without survivors. These two accidents out of more than 2 million departures since 1975 give a risk level close to the general West European risk level-O.8 per one million departures (Oster et al. 1992). That value will be used here as being statistically more well founded than the Swedish value. The fatality risk per flight will actually often be double the value mentioned, as most flight routes between two places in Sweden will mean double take offs and landings with an intermediate stop at Stockholm/Arlanda. The risk of travelling by air will then correspond to 1.6 per one million trips. This equals the risk of driving about 300 km by car. The train is a third viable contender for Swedish travel customers. During the last 10 years there have been some collisions and derailments with fatalities. The largest accident took the lives of six passengers and three crew members. The risk profile for train travel is similar to that of the car for longer distances. Train travel has a distance-independent risk as well. But that portion of the risk is dominant only for distances shorter than about 25 km. The resulting risk for train travel is therefore rising roughly in proportion to distance travelled. However, the risk level in this case comes out far below car risk level. The safety performance of trains is also better than that of scheduled air traffic for all domestic distances in Sweden (Fig. 1). So far the safety issue seems to be settled beyond
INTRODUCTION As has been shown by Evans et al. (1990) safety comparisons between car and aeroplane can be meaningfully made if the travelling distance is taken into account. Air travel has a risk profile rather independent of distance, while car travel entails a risk rising with distance travelled. That is, air travel is generally the safer mode of travelling for long distances and car for short ones. Sivak et al. (1991) have improved the analysis by distinguishing between nonstop and other flights. The analysis by Evans et al. has pointed to car travel as the safer mode of travelling under certain circumstances. The analysis by Sivak et al. has adjusted the limits, so to speak, of the realm where the private car may be the safer travelling alternative. The aim of this paper, in contrast to the papers mentioned, is to illustrate that there may be no fixed solution to the problem. Different meanings of risk tend to result in different modes of transportation being the safest. The scope is also broadened to three modes of transportation. The setting is West European (Sweden) rather than North American as with the Evans and Sivak papers.
THE
TRAVELLER’S
FATALITY
RISK
Let us first compare the individual traveller’s risk of being killed in an accident. This is the risk measure used in both the Evans and Sivak papers. As in those papers, travelling by car is here taken to mean driving. A car driver’s risk of getting fatally 409
P. WULFF
410
Table 1. Statistical
background
for the traveller’s fatality SJ 1986-94)
Private car Driver fatalities: Distance driven: Resulting risk:
2 (all dead) 2.3 x lo6 0.9 per lo6 departures) 0.8 per lo6 departures
Passenger train (State railways) (1) Fatalities in train accidents, at level crossings and other occasions: Total traffic: Resulting risk: (2) Fatalities; embarkation, disembarkation, fall or jump from train in movement: Number of trips: Resulting risk (distance independent):
TOTAL
of
the
train
RISK OF SERIOUS FATALITY
as
mode
INJURY
Fatality
probability
54 x lo9 passenger-km 1 in 3400 x 10’ passenger-km 4 passengers
524 x lo6 1 per 130 x lo6 trips
of
OR
x lo6
200
300
400
Fig. 1. An individual’s risk of dying in a travel accident as a function of distance travelled.
( 1977-1989)
,
m in Sweden
1985-93) (1985591)
(1985-91)
ented persons, who choose consumers’ goods according to their harm to the environmental system. Here the idea would be to choose a mode of travelling according to its harm done to people. This would, at least in principle, put pressure on the providers of less safe travelling services to improve their safety performance. Further, let the risk measure here be extended also to cover serious injuries. Including victims in transportation personnel raises the risk levels for air and rail alternatives relative to private car travel, where the category does not exist. For car and rail alternatives the risk levels increase substantially when victims (fatalities and serious injuries) among third persons are included. For car traffic third person injuries/deaths are typically represented by a pedestrian hit when crossing a street. Similarly, a person in a car may be hit at a rail crossing, making him a typical third person victim to rail traffic. Air traffic has the smallest proportion of third persons injured or killed. During the last 20 year period in Sweden the number of seriously injured people in scheduled air traffic operations is only about 15% of the number of persons killed in accidents. More extensive statistics from the U.S. indicate the proportion of seriously injured to be less than 50% of the number killed (Oster et al. 1992). Third person fatalities from regular air traffic together with personnel fatalities account for only about one tenth of air passenger fatalities. The low proportion of persons seriously injured and persons fatally injured leads to a very modest rise in the number of persons at risk as compared to our first risk perspective. The risk level will be about 25% higher than for the case “traveller’s fatality risk”.
;~__y____T-=!-;Dz
1975-92) 1975-92)
16 passengers
We have up to this point been dealing with an individual traveller concerned only with his (her) own survival. But, as is well known, there are victims other than travellers. They fall into the categories of personnel and “third persons”. A third person is a person who is not a part of the transportation system considered. Now let “risk” mean the sum of risks incurred by travellers, personnel and third persons together. This is a risk perspective that might be held by a citizen looking at the different transportation systems objectively. It is also a perfectly possible ground for personal decision-making by a traveller. It is reminiscent of the risk perspective held by ecologically ori-
A
1977-93;
281 persons 57 x lo9 km 1 fatality in 200 x lo6 km
Domestic air traffic in scheduled operations Number of fatal accidents: Number of take offs/landings: (Resulting risk: Estimated risk: (Western Europe; Oster et al. 1992)
dispute in favour transportation.
risk (SCB 1994; Luftfartsverket
Minimizing
inter city transportation
With car traffic the risk level increases drastically. It is about 15 times greater than with the former risk perspective. With rail traffic the risk level increase is even more drastic-about 35 times (see Table 2). With this interpretation of risk (and safety), air travel is the safest mode of transportation for all distances of practical interest to regular flights. That is, by changing our measure of what we mean by risk, we have come to a completely different result with regard to transportation safety. TOTAL
FATALITY
RISK
It is also possible for the private car to become a minimum risk alternative. If we subtract the seriously injured from the case above we will have a meaning of risk that is favourable for car travel. This meaning of risk is similar to the meaning above. Only here, considerations are restricted to fatalities. It is an equally possible (although probably not as common) ground for personal decision-making as the two risk perspectives considered earlier. The risk per km of train travel in this case will still fall below the risk of car driving. However, this difference is offset by the fact that the road system is more fine-meshed than the railroad system, which means that a trip by car generally saves travel distance as compared to a trip by train. The private car will on average be quite competitive in relation to train travel over all distances. The car will also have an advantage over nonstop flying up to about 150 km and up to double that distance for flights with an intermediate stop at Arlanda/ Table 2. Statistical
background
411
Stockholm. A middle-aged driver-with only two thirds of the average driver’s risk (SCB, 1989)--may compete with flying risks up to 50% longer distances. RISK CONTRIBUTION TRIPS
OF ACCESS
Points of departure and destination are seldom located at airports or railway stations. Normally you have to go by car or bus to gain access to an airport or a railway station and similarly to reach your point of destination. These access trips at both ends of a main trip will tend to increase the risk for the air and rail alternatives. The length of the access trips is normally only a fraction of the city to city distances considered in the main analysis; typically 20% or less (10% or less for rail). Access trips by car can therefore lead to a risk increase in air and rail travel by up to 20% of the car risk level. If the access trips are undertaken by bus, the risk increase will be even less than that because of the better safety record of buses as compared to cars. Normally you will also have to walk some distance at both ends of a trip to get to your point of destination. Jorgensen (1993) has presented a detailed analysis of access trips for an urban transport situation. He concludes that pedestrian access trips are the dominant risks of “low-risk” travel alternatives like bus and local train. That is, getting to and from a bus or train is by far the riskiest part of such trips. Inter city travel has different characteristics. First, inter city trip distances are about one order of magnitude greater (or more) than distances in the
for total risk of serious injury or fatality (SCB 1994; Luftfartsverket 1977-93; SJ 1986-94)
Private car All serious and fatal injuries: Total driver and passenger distance: Resulting risk: Air trafic in scheduled operations Serious and fatal injuries (including international traffic): Estimated
risk
risk:
Passenger train (State railways) (1) All serious and fatal injuries or fatalities in train accidents, at level crossings and other occasions: Total traffic: Resulting risk: (2) All serious and fatal injuries; embarkation, disembarkation, fall or jump from train in movement: Number of trips: Resulting risk:
4031 persons 91 x lo9 person-km 1 in 14x106km
(1993) (1993)
43 (38 fatal, 5 serious)
(1975-92)
(no “third person” victims) 1.0 per lo6 departures (25% above case l/table 1)
566 persons
(1985-93)
54 x lo9 passenger-km 1 in 95 x lo6 person-km 17 passengers
(1985-93)
524 x lo6 1 per 30x lo6 trips
(1985-91)
(1985-91)
412
P. WULFF
Table 3. Statistical Private car All fatalities: Total driver and passenger Resulting risk:
background
for total fatality
distance:
Air trajic in scheduled operations Estimated risk:
Passenger train (State railways) (1) All fatalities in train accidents, at level crossings and other occasions: Total traffic: Resulting risk: (2) All fatalities; embarkation, disembarkation, fall or jump from train in movement: Number of trips: Resulting risk:
Jorgensen study (5-15 km), but pedestrian access trips are likely to be of about the same length. The relative importance of access trips on foot will therefore be about one order of magnitude smaller (at least) than in the Jorgensen study. Also, Swedish pedestrian risk rates seem to be low in comparison with international rates. The fatality rate is less than half the rate reported for Great Britain (Collings 1994) and close to the lower of two values reported for Denmark (by Jorgensen, assuming a daily walking distance of around 1 km per person). Further, Jorgensen is analyzing routine trips to and from work. Car riders can be expected to have found fairly optimal parking solutions for these kinds of trips. This will generally mean that walking distances are minimized. According to Jorgensen the average walking distance for car riders is only about 10% of the average walking distance for local train passengers. Parking solutions can be expected to be less optimal for car drivers on inter city trips. Therefore, walking distances to end-points in a city visited will tend to be longer than walking distances from car to workplace. That is, access trip lengths-and riskswill be less unevenly distributed between travel modes than in the Jorgensen study. This will lessen the importance of access trip risks with regard to risk ranking. With trip end-points in suburban areas, private car travel will generally leave you with less distance to walk and less pedestrian risks to take than an aeroplane plus bus, or a train plus bus alternative. But with trip end-points in central city areas it may be the other way round because of central area parking problems. Also, if an aeroplane or train trip is complemented with a ride in a taxi, the pedestrian
risk (SCB 1994; SJ 1986-94)
533 91 x lo9 person-km 1 in 170 x lo6 km
(1993) (1993)
0.9 per lo6 departures (10% above case 1)
27 1 persons
(1985-93)
54 x lo9 passenger-km 1 in 200 x lo6 person-km 11 persons
(1985593)
524 x lo6 1 per 50 x lo6 trips
(1985-91)
(1985591)
phase of the total trip and its associated risks will tend to be smaller than for the car driving alternative. Before leaving the access trip problem let us indicate a possibility of quantitative analysis. The critical part of pedestrian movement is the crossing of streets with car traffic. Assuming an average of at least two crossings per person per day, there are more than 6000 million street crossings annually in Sweden. This activity results in less than 100 pedestrian fatalities (94 in 1993; SCB 1994). The fatality risk per crossing would then be below one in 60 million. This is a fairly low figure. A door to door trip with up to 10 pedestrian crossings, which would probably include the majority of all car, air and rail trips undertaken, would entail a pedestrian fatality risk of only a fraction of one in a million. This would only marginally influence the safety ranking between transportation modes. A similar line of reasoning could be employed for the risk perspective where serious injuries are included (580 pedestrian fatalities + serious injuries in 1993; SCB 1994). CONCLUSIONS In the above-mentioned study by Jorgensen (1993) the transportation alternatives were seen to have a risk ranking which is not much influenced by the choice of risk perspective (individual fatality risk, individual risk of injury, total fatality risk, total risk of injury). According to Jorgensen, for trips confined to the central part of a city, risk ranking is independent of the choice of risk perspective (1. bus, 2. car, 3. bicycle). For trips between suburb and centre there are, in the Jorgensen study, some shifts in ranking between train and bus. Either may be the minimum risk alternative
Minimizing
inter city transportation
depending on risk perspective. Car is consistently the last alternative and bicycle the last but one, out of the four alternatives considered. We have arrived at a rather different conclusion regarding inter city travel. When analysing which among car, air and train travel is a risk minimizing alternative, we have found all three to be. Which alternative comes out as the safest depends on the risk perspective chosen and to some extent on distances considered. The three perspectives on the meaning of risk that have been used are similar to those used in the Jerrgensen study. All relate to physical harm, but they differ with respect to who comes to harm and the extent of harm considered. The results are summarized in Fig. 2. For the air and train travel alternatives there has been a more or less complete shift of preference between risk perspectives 1 and 2. For the private car there is a partial shift of preference as we move to the third risk perspective. The only general conclusion to be drawn from these observations is that the private car is not a risk minimizing alternative for long distance travel. A risk comparison between the car and air travel alternatives was made by Sivak et al. (1991). Their conclusion was that flying is always safer than driving for an average driver “for any reasonable combinations of the trip distance and number of flight segments”. The results obtained here do not agree with that conclusion. With the higher Swedish (West European) risk level for flying we find a safety niche for the private car up to 150-300 km with risk perspectives 1 and 3 (although the train is a safer alternative with perspective 1).
IRisk perspective
I Safest mode of transportation I
O-Distance
-
1500 km
Fig. 2. The safest mode of inter city travel changes with risk perspective and distance. (Access trips are assumed to have little impact or cancel out between alternatives.)
risk
413
The influence of access trips on the risk ranking of alternatives seems generally to be limited. This is partly due to the fact that the proportion of access to total trip length is (at least) about an order of magnitude less than for trips within a city. It is also due to the fact that the burden of access trip risk seems to fall less unevenly on the inter city travel alternatives than on the urban ones. Also, Swedish pedestrian risks tend to be low. All this works toward lessening the risk impact of access trips and not upsetting the minimum risk rankings made. The point that can be made with respect to access trips is that they may to some extent be chosen. Debarking from a train at a railway station, for instance, leaves you with a choice of continuing on foot, by bus or by taxi to the point of destination. Taxi would seem to be the preference as that would minimize the relatively high-risk activity of walking (across streets). Therefore, it is not quite fair to add statistical averages of access trip risks when summing up total inter city trip risks. To sum up the main conclusion of this paper; if we as individuals want to minimize transportation risk, we should first decide on what we would mean by risk. Am I as a traveller concerned solely with my own chances of survival or do I want also to avoid being part of situations where others die violently or get seriously injured? Until we have a clear idea of our preferences, the safety race between car, aeroplane and train remains undecided.
REFERENCES Collings, H. Transport Statistics Great Britain. London: HMSO; 1994. Evans, L.; Frick, M. C.; Schwing, R. C. Is it safer to fly or drive? Risk Analysis 10: 239-245; 1990. Jorgensen, N. The safety of different means of transport in urban traffic. Paper given at ISATA Conference; Aachen, September 1993. Luftfartsverket 19xx. (The Civil Aviation Administration 19~~). Official Statistics of Sweden; 1977-1993. (Annual publication) Oster, C. V.; Strong, J. S.; Zorn, C. K. Why airplanes crash: Aviation safety in a changing world. Oxford University Press; 1992. SCB. Risker pi vlg-vlgda risker. (Road risks-weighed risks). Statistics Sweden; 1989. SCB. Trafikskador ‘93. (Traffic injuries ‘93). Statistics Sweden; 1994. Sivak, M.; Weintraub, D. J.; Flannagan, M. Nonstop flying is safer than driving. Risk Analysis 11: 145-148; 1991. SJ. Trafiksgkerheten. (Traffic safety). Swedish State Railways; 1986-94. (Annual publication)