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The need for regular monitoring of the exposure of pedestrians and cyclists to traffic
Accid. Anal. & Prey., Vol. 14, No. 5, pp 341-344. 1982 Printed in Great Britain.
0001.-4575182i05f~341-414503.0010 !~ 1982 Pergamon Press Ltd
THE NEED FOR REGULAR MONITORING OF THE EXPOSURE OF PEDESTRIANS AND CYCLISTS TO TRAFFIC C. I. HOWARTH Department of Psychology,Universityof Nottingham,Nottingham,England Abstract--Regular monitoring of the exposure of pedestrians and cyclists to traffic would enable one to calculate the risk per km or per road crossing of those forms of travel. This informationwould allow us to estimate the effect on accident rates of changes in modes of travel. It would also enable us to estimatethe possible effectsof safety measuresaimed at pedestrians and cyclists. After a discussion of the costs and the advantages and disadvantages of various methods of monitoring the exposure of pedestrians, it is recommendedthat a combinationof questionnaire techniques and observationsat random sites will provide all the informationrequired at the lowest possible cost.
Most countries monitor the amount of vehicular traffic on their roads. Many different methods are used, from questioning random samples of drivers about their current journey, to estimating mileage from petrol sales. Moreover, motor vehicles are usually licensed, so that we know, very accurately, how many are in use during a particular period. These different exposure measures enable us to calculate risk figures such as accidents per motor vehicle, or accidents per 100,000km travelled. From these figures we can make comparisons of the risks to different types of road users, such as, motor cyclists, car users, and passengers in public service vehicles. They also enable us to assess the possible effects of various suggestions for reducing accidents, or of projected changes in transport patterns. We know, from such studies, that if more people could be persuaded to commute to work, by bus rather than by car, the number of people killed or injured while travelling in vehicles would be very much reduced. But an increase in bus usage would also produce an increase in pedestrian travel at the beginning and end of a journey. We cannot, as yet, predict what effect this would have on the total risk involved in the journey to work, because there have been very few studies of the relationship between pedestrian travel and accidents, and there are no regular studies of the exposure of pedestrians to traffic, from which the effect of increased pedestrian travel can be calculated. To make such a calculation one would need estimates of the mileage covered by different classes of pedestrian, the number of roads they cross, and the vehicular traffic flow on the roads they cross. Vehicular flow would fall if there were a major switch to public transport. This would reduce the risk of each pedestrian journey, and predictions of the overall effect of a switch from cars to buses must take that into account. There are, at present, few reliable estimates of accidents per pedestrian mile or of accidents per road crossing as a function of traffic density. To a lesser extent the same is true of travel by bicycle. There is no regular monitoring of distances travelled by bicycle, although there are a few isolated studies from which estimates of risk per kilometre of travel have been calculated. As a result we cannot estimate at all accurately the effects on accidents of persuading more people to commute on bicycles. There is no doubt that commuting by bicycle would result in a considerable saving of oil, and little doubt that it would improve the health of the people doing it. But it would be irresponsible to encourage people to use bicycles while we are unable to tell them much that is useful about the increased risk of accidents which they would incur. This absence of reliable measures of risks to pedestrians and cyclists makes it difficult to estimate the likely effects on accidents of changes in commuter behaviour, or of changes in transport policy. For these purposes the following types of information are essential: For pedestrians (1) an estimate of the mileage travelled by different classes of pedestrian (e.g. age, occupational group and other transport used); (2) an estimate of the number and type of roads they crossed; (3) an estimate of the traffic density on the roads they cross. For cyclists similar information is required, plus estimates of traffic density at sites other than road crossings. In addition to providing information about the effects of switching from one mode of transport to another, exposure studies can help improve safety within a particular mode of 341
342
C.I. HOWARTr~
travel. For example, we know that, despite spectacular accidents in which many deaths result, travel on motorways is actually safer than travel on ordinary roads. We know this because, in proportion to mileage travelled, accidents are less probable on motorways. This sort of information is not available for pedestrians. For example, pedestrians (particularly children) are often urged to cross roads away from junctions, and in some places barriers are erected which physically force the pedestrian to move away from the junction before crossing the road. The justification for these measures is the high proportion of pedestrian accidents which occur at junctions. But a number of studies have shown that an even greater proportion of road crossings occur at junctions, so that the accident rate per road crossing may actually be less at junctions. That is, it may be safer to cross at junctions, and attempts to prevent pedestrians doing so may actually increase the risk of accidents. Some pedestrian safety programmes have been evaluated by estimating the risk per road crossing both before and after the installation of the safety measure. The most thorough of these are the evaluations of the zebra and pelican crossings. But these have been based on special purpose studies at the sites where the crossings are installed. It is possible that these crossings, while reducing risk at the particular sites, may actually increase risks elsewhere. More extensive and regular exposure studies are needed to check this possibility and simultaneously to provide better information on which to base future safety programmes. For these purposes the following additional information would be required: For pedestrians (4) a classification of the sites of road crossings by type of road layout and pedestrian safety measures used; (5) an estimate of temporary features of the road crossing such as the presence of parked cars, pedestrian density and nearness of moving vehicles. For cyclists similar information could also be gathered. There is no point in gathering exposure data in greater detail than is available fro'm the accident statistics. In some cases there is an obvious need to change the detail recorded on accident statistics in order to take full advantage of the monitoring of exposure. I hope these comments are sufficient to establish the need for regular monitoring of travel on foot and by bicycle, and also to indicate just what information the monitoring system should aim to provide. The rest of this paper will be devoted to a discussion of the relative merits of different methods of monitoring pedestrian travel. It will be based on the experience of the Accident Research Unit at Nottingham University in estimating the exposure of child pedestrians to traffic. The principal techniques available are: (a) Self report from a sample of people, either marking their journeys on a map or keeping a diary. This is usually done from memory. (b) Following a sample of people to record their movements objectively and in detail. (c) Monitoring a sample of road sites and recording pedestrian movements objectively. Methods (a) and (c) are variants of the two methods most frequently used to monitor vehicular travel. Method (b) is easier to use for pedestrians than for faster travel on wheels. In the Nottingham studies of exposure of children to traffic we have used all three and, in addition, have asked parents to estimate the movements of their child on a particular day. Thus we have been able to compare the types of information available from the different techniques and to estimate their relative costs.
INFORMATION AVAILABLE FROM THEDrFFERENTTECHNIQUES It is not possible to get all five types of information from any one of the three methods. Hence decisions about the method to be used must depend upon the type of information required. The following discussion of their various merits is based on Routledge, RepettoWright and Howarth (1976). (i) Mileage travelled. Information about mileage travelled on foot can be obtained from methods Ca) and (b). Self report, even by children, is reasonably accurate but even better estimates were obtained by observers following children home from school and recording a commentary on a small sound recorder. The great advantage of self report is that it gives 24-hr data very easily. The use of outside observers is more appropriate to peak travel times, and it would be prohibitively expensive to try to get 24 hr data by observation.
Regular monitoringof the exposureof pedestrians and cycliststo traffic
343
(2) Number and type of roads crossed. All three methods provide this information although, as already mentioned, the self report method is the only one from which we can get 24-hr data. Routledge et al. found that method (b), the "following study", produced the highest estimate of roads crossed, the children produced a slightly lower estimate, and the parents a still lower estimate. There is every reason to believe that the following study produced the best estimates. When one looks at fine detail, the following studies and the random site studies produce slightly different results. For example, the following studies produced a greater proportion of road crossings masked by parked cars than did the random site studies. The reasons for this are still unresolved. (3) Tra1~ic density at site of road crossing. Only the random site study enables this to be estimated at the same time as road crossings are counted. However, it is a simple matter to count traffic densities separately, once road crossing sites have been identified, so this is not a serious shortcoming of the other two methods. (4) Classification of road layout at place of crossing. All three techniques provide this information, although the self report and following techniques depend heavily on consulting maps afterwards to get the details. (5) Temporary features of road crossing situations such as the presence of parked cars or the nearness of moving vehicles are only obtainable from the two methods of objective observation, and of these two, the random site technique provides this information most easily, and in greatest detail. There are also differences in detail between the following studies and the random site studies. We have now done, for slightly different purposes, three replications of the following study and five replications of the random site technique. The differences between them could be due to different points of observation, or to differences in sampling. A hybrid study, which used fixed site observations at sites selected from a previous following study, produced results closer to those of the other random site studies. This suggests that the problem is not one of sampling, but that the difference is due to the greater accuracy of observation possible for a well positioned stationary observer. We find that the random site observer can gather much more detailed information than the moving observers in the following studies. All three methods use sampling techniques. For the self report and the following studies a sample of pedestrians is taken. For the random site studies one observes a sample of road sites. Fortunately for our peace of mind, when raised by their different raising factors, the two sampling methods give very similar whole population estimates. THE RELATIVE COST OF THE DIFFERENT TECHNIQUES One can only compare costs for particular types of information. Since all three methods provide estimates of the number of roads crossed, the easiest comparison is the cost per recorded road crossing. In our studies the figures were: Self report £0.40, Random site £0.73 (or £0.37 if adult crossings are included); Following studies £1.53. The costs are zt approx. 1976 prices. Two values are given for the random site studies, since, although we were only interested in children, adult road crossings were counted at no extra cost. The best value for money would seem to be a combination of self report and random site studies. Together, these two techniques seem to give all the information required. SOME SELECTED RESULTS Although we are still attempting to improve these techniques, some very useful results have already been obtained. They illustrate the sort of information which could become routinely available if regular monitoring of pedestrian travel could be done. (a) From self report and the following studies we can compare, for the first time, the risk per kilometre of travel for children walking to school, with the risk they would run using other forms of transport. Table 1 shows some of our results. It can be seen that the risk per kilometre is comparable to the risk taken by motor cyclists, and that is approx. 20 times more dangerous for a child to walk to school than go by school bus. The weakness of the comparison is that school buses are probably safer than the average bus, while the risk of pedestrian accidents around buses has not been included. These two sources of error will, at least partially, cancel each other [Howarth and Repetto-Wright, 1978].
344
C. [. HOWARTH Table 1. Death and injuries per 100 million km Type of Travel
Deaths
Fatal and Serious Accidents
Vehicles
0.06 (represents iO years average)
Rail
Public Service Vehicles
(Passengers)
Cars and Taxis (Drivers) Pedal Cycles
(Cyclists)
Motor Cycles
(Drivers)
0.2
3.8
0.7
9.7
7.3
120.3
14.9
311.9
Pedestrians 8 - IO years 5 - 7 years
(travelling from school) (travelling from school)
8.0
97.0
19.0
201.0
The vehicular figures are taken from the DOT publication 'Road Accidents in Great Britain 1975' The Pedestrian figures are based o'~ our e,~n studies of children's travel to and from school.
(b) We can also compare the risk for children of different ages and for the two sexes. It is well known that, at the most vulnerable ages, between 5 and 8, boys have twice as many accidents as girls. It used to be thought that this is because boys are allowed greater freedom and are therefore more exposed to traffic. This is not so, since all our studies show that, at the vulnerable ages, and at peak travel times, boys are no more exposed to traffic than are girls. This remains the case even when one makes allowance for the fact that girls are more likely to be accompanied by an adult. It can also be shown that the risk per road crossing falls steadily between the ages of 5 and 15. The peak in accidents at age 6 is due to the rather sudden increase in the exposure of children to traffic when they go to school [Howarth et al., 1974). (c) From estimates of traffic densities we can give limited answers to such questions as "Is the greater risk of crossing major roads, proportional to the increased probability of encounter with a car?" This enables one to predict the effect of changes in traffic density on pedestrian risk. Like a number of other studies our data show accidents to be roughly proportional to traffic density. (d) We measure traffic density in a slightly unusual way by calculating the proportion of the road "taken up" by vehicles. This includes the length of the vehicle, plus the space in front of the vehicle (its shadow) which no pedestrian could cross without being hit if the vehicle failed to brake. This method of measuring traffic density allows one to calculate the number of accidents which would occur if no one made any attempt to avoid them. By comparing this figure with the actual number of accidents, one can calculate the percentage of potential accidents which are avoided. Even for 5-7 yr olds this figure turns out to be 99.99%, i.e. only one in ten thousand potential accidents is not avoided [Howarth et al., 1974]. (e) In the random site technique our observers are able to record both pedestrian and driver behaviour in some detail. This enables us to discover who is responsible for avoiding all but 0.01% of potential accidents. Results to date suggest that most of the avoiding is done by children, and that drivers fail to take adequate precautionary action in the presence of children [Howarth and Lightburn, 1980]. REFERENCES Howarth C. I. and Lightburn A., How drivers respond to pedestrians and vice versa. In Human Factors in Transport Research, Vol. 2 User Factors: Corn[err, the Environment and Behaviour (Edited by Oborne D. J. and Levis J. A.). Academic Press, London, 1980. Howarth C. I. and Repetto-Wfight R., The measurement of risk and the attribution of responsibility for child pedestrian accidents. Sa[ety Education 144, 10-13, 1978. Howarth C. l., Routledge D. A: and Repetto-Wright R., An analysis of road accidents involving child pedestrians. Ergonomics 17, 319-330, 1974. Routledge D. A., Repetto-Wright R. and Howarth C. I., Four techniques for measuring the exposure of young children to accident risk as pedestrians. Prec. Int. Con[. Pedestrian Sa[ety, Vol. I, 7BI-7B7, Haifa, Israel, 1976.
0001.-4575182i05f~341-414503.0010 !~ 1982 Pergamon Press Ltd
THE NEED FOR REGULAR MONITORING OF THE EXPOSURE OF PEDESTRIANS AND CYCLISTS TO TRAFFIC C. I. HOWARTH Department of Psychology,Universityof Nottingham,Nottingham,England Abstract--Regular monitoring of the exposure of pedestrians and cyclists to traffic would enable one to calculate the risk per km or per road crossing of those forms of travel. This informationwould allow us to estimate the effect on accident rates of changes in modes of travel. It would also enable us to estimatethe possible effectsof safety measuresaimed at pedestrians and cyclists. After a discussion of the costs and the advantages and disadvantages of various methods of monitoring the exposure of pedestrians, it is recommendedthat a combinationof questionnaire techniques and observationsat random sites will provide all the informationrequired at the lowest possible cost.
Most countries monitor the amount of vehicular traffic on their roads. Many different methods are used, from questioning random samples of drivers about their current journey, to estimating mileage from petrol sales. Moreover, motor vehicles are usually licensed, so that we know, very accurately, how many are in use during a particular period. These different exposure measures enable us to calculate risk figures such as accidents per motor vehicle, or accidents per 100,000km travelled. From these figures we can make comparisons of the risks to different types of road users, such as, motor cyclists, car users, and passengers in public service vehicles. They also enable us to assess the possible effects of various suggestions for reducing accidents, or of projected changes in transport patterns. We know, from such studies, that if more people could be persuaded to commute to work, by bus rather than by car, the number of people killed or injured while travelling in vehicles would be very much reduced. But an increase in bus usage would also produce an increase in pedestrian travel at the beginning and end of a journey. We cannot, as yet, predict what effect this would have on the total risk involved in the journey to work, because there have been very few studies of the relationship between pedestrian travel and accidents, and there are no regular studies of the exposure of pedestrians to traffic, from which the effect of increased pedestrian travel can be calculated. To make such a calculation one would need estimates of the mileage covered by different classes of pedestrian, the number of roads they cross, and the vehicular traffic flow on the roads they cross. Vehicular flow would fall if there were a major switch to public transport. This would reduce the risk of each pedestrian journey, and predictions of the overall effect of a switch from cars to buses must take that into account. There are, at present, few reliable estimates of accidents per pedestrian mile or of accidents per road crossing as a function of traffic density. To a lesser extent the same is true of travel by bicycle. There is no regular monitoring of distances travelled by bicycle, although there are a few isolated studies from which estimates of risk per kilometre of travel have been calculated. As a result we cannot estimate at all accurately the effects on accidents of persuading more people to commute on bicycles. There is no doubt that commuting by bicycle would result in a considerable saving of oil, and little doubt that it would improve the health of the people doing it. But it would be irresponsible to encourage people to use bicycles while we are unable to tell them much that is useful about the increased risk of accidents which they would incur. This absence of reliable measures of risks to pedestrians and cyclists makes it difficult to estimate the likely effects on accidents of changes in commuter behaviour, or of changes in transport policy. For these purposes the following types of information are essential: For pedestrians (1) an estimate of the mileage travelled by different classes of pedestrian (e.g. age, occupational group and other transport used); (2) an estimate of the number and type of roads they crossed; (3) an estimate of the traffic density on the roads they cross. For cyclists similar information is required, plus estimates of traffic density at sites other than road crossings. In addition to providing information about the effects of switching from one mode of transport to another, exposure studies can help improve safety within a particular mode of 341
342
C.I. HOWARTr~
travel. For example, we know that, despite spectacular accidents in which many deaths result, travel on motorways is actually safer than travel on ordinary roads. We know this because, in proportion to mileage travelled, accidents are less probable on motorways. This sort of information is not available for pedestrians. For example, pedestrians (particularly children) are often urged to cross roads away from junctions, and in some places barriers are erected which physically force the pedestrian to move away from the junction before crossing the road. The justification for these measures is the high proportion of pedestrian accidents which occur at junctions. But a number of studies have shown that an even greater proportion of road crossings occur at junctions, so that the accident rate per road crossing may actually be less at junctions. That is, it may be safer to cross at junctions, and attempts to prevent pedestrians doing so may actually increase the risk of accidents. Some pedestrian safety programmes have been evaluated by estimating the risk per road crossing both before and after the installation of the safety measure. The most thorough of these are the evaluations of the zebra and pelican crossings. But these have been based on special purpose studies at the sites where the crossings are installed. It is possible that these crossings, while reducing risk at the particular sites, may actually increase risks elsewhere. More extensive and regular exposure studies are needed to check this possibility and simultaneously to provide better information on which to base future safety programmes. For these purposes the following additional information would be required: For pedestrians (4) a classification of the sites of road crossings by type of road layout and pedestrian safety measures used; (5) an estimate of temporary features of the road crossing such as the presence of parked cars, pedestrian density and nearness of moving vehicles. For cyclists similar information could also be gathered. There is no point in gathering exposure data in greater detail than is available fro'm the accident statistics. In some cases there is an obvious need to change the detail recorded on accident statistics in order to take full advantage of the monitoring of exposure. I hope these comments are sufficient to establish the need for regular monitoring of travel on foot and by bicycle, and also to indicate just what information the monitoring system should aim to provide. The rest of this paper will be devoted to a discussion of the relative merits of different methods of monitoring pedestrian travel. It will be based on the experience of the Accident Research Unit at Nottingham University in estimating the exposure of child pedestrians to traffic. The principal techniques available are: (a) Self report from a sample of people, either marking their journeys on a map or keeping a diary. This is usually done from memory. (b) Following a sample of people to record their movements objectively and in detail. (c) Monitoring a sample of road sites and recording pedestrian movements objectively. Methods (a) and (c) are variants of the two methods most frequently used to monitor vehicular travel. Method (b) is easier to use for pedestrians than for faster travel on wheels. In the Nottingham studies of exposure of children to traffic we have used all three and, in addition, have asked parents to estimate the movements of their child on a particular day. Thus we have been able to compare the types of information available from the different techniques and to estimate their relative costs.
INFORMATION AVAILABLE FROM THEDrFFERENTTECHNIQUES It is not possible to get all five types of information from any one of the three methods. Hence decisions about the method to be used must depend upon the type of information required. The following discussion of their various merits is based on Routledge, RepettoWright and Howarth (1976). (i) Mileage travelled. Information about mileage travelled on foot can be obtained from methods Ca) and (b). Self report, even by children, is reasonably accurate but even better estimates were obtained by observers following children home from school and recording a commentary on a small sound recorder. The great advantage of self report is that it gives 24-hr data very easily. The use of outside observers is more appropriate to peak travel times, and it would be prohibitively expensive to try to get 24 hr data by observation.
Regular monitoringof the exposureof pedestrians and cycliststo traffic
343
(2) Number and type of roads crossed. All three methods provide this information although, as already mentioned, the self report method is the only one from which we can get 24-hr data. Routledge et al. found that method (b), the "following study", produced the highest estimate of roads crossed, the children produced a slightly lower estimate, and the parents a still lower estimate. There is every reason to believe that the following study produced the best estimates. When one looks at fine detail, the following studies and the random site studies produce slightly different results. For example, the following studies produced a greater proportion of road crossings masked by parked cars than did the random site studies. The reasons for this are still unresolved. (3) Tra1~ic density at site of road crossing. Only the random site study enables this to be estimated at the same time as road crossings are counted. However, it is a simple matter to count traffic densities separately, once road crossing sites have been identified, so this is not a serious shortcoming of the other two methods. (4) Classification of road layout at place of crossing. All three techniques provide this information, although the self report and following techniques depend heavily on consulting maps afterwards to get the details. (5) Temporary features of road crossing situations such as the presence of parked cars or the nearness of moving vehicles are only obtainable from the two methods of objective observation, and of these two, the random site technique provides this information most easily, and in greatest detail. There are also differences in detail between the following studies and the random site studies. We have now done, for slightly different purposes, three replications of the following study and five replications of the random site technique. The differences between them could be due to different points of observation, or to differences in sampling. A hybrid study, which used fixed site observations at sites selected from a previous following study, produced results closer to those of the other random site studies. This suggests that the problem is not one of sampling, but that the difference is due to the greater accuracy of observation possible for a well positioned stationary observer. We find that the random site observer can gather much more detailed information than the moving observers in the following studies. All three methods use sampling techniques. For the self report and the following studies a sample of pedestrians is taken. For the random site studies one observes a sample of road sites. Fortunately for our peace of mind, when raised by their different raising factors, the two sampling methods give very similar whole population estimates. THE RELATIVE COST OF THE DIFFERENT TECHNIQUES One can only compare costs for particular types of information. Since all three methods provide estimates of the number of roads crossed, the easiest comparison is the cost per recorded road crossing. In our studies the figures were: Self report £0.40, Random site £0.73 (or £0.37 if adult crossings are included); Following studies £1.53. The costs are zt approx. 1976 prices. Two values are given for the random site studies, since, although we were only interested in children, adult road crossings were counted at no extra cost. The best value for money would seem to be a combination of self report and random site studies. Together, these two techniques seem to give all the information required. SOME SELECTED RESULTS Although we are still attempting to improve these techniques, some very useful results have already been obtained. They illustrate the sort of information which could become routinely available if regular monitoring of pedestrian travel could be done. (a) From self report and the following studies we can compare, for the first time, the risk per kilometre of travel for children walking to school, with the risk they would run using other forms of transport. Table 1 shows some of our results. It can be seen that the risk per kilometre is comparable to the risk taken by motor cyclists, and that is approx. 20 times more dangerous for a child to walk to school than go by school bus. The weakness of the comparison is that school buses are probably safer than the average bus, while the risk of pedestrian accidents around buses has not been included. These two sources of error will, at least partially, cancel each other [Howarth and Repetto-Wright, 1978].
344
C. [. HOWARTH Table 1. Death and injuries per 100 million km Type of Travel
Deaths
Fatal and Serious Accidents
Vehicles
0.06 (represents iO years average)
Rail
Public Service Vehicles
(Passengers)
Cars and Taxis (Drivers) Pedal Cycles
(Cyclists)
Motor Cycles
(Drivers)
0.2
3.8
0.7
9.7
7.3
120.3
14.9
311.9
Pedestrians 8 - IO years 5 - 7 years
(travelling from school) (travelling from school)
8.0
97.0
19.0
201.0
The vehicular figures are taken from the DOT publication 'Road Accidents in Great Britain 1975' The Pedestrian figures are based o'~ our e,~n studies of children's travel to and from school.
(b) We can also compare the risk for children of different ages and for the two sexes. It is well known that, at the most vulnerable ages, between 5 and 8, boys have twice as many accidents as girls. It used to be thought that this is because boys are allowed greater freedom and are therefore more exposed to traffic. This is not so, since all our studies show that, at the vulnerable ages, and at peak travel times, boys are no more exposed to traffic than are girls. This remains the case even when one makes allowance for the fact that girls are more likely to be accompanied by an adult. It can also be shown that the risk per road crossing falls steadily between the ages of 5 and 15. The peak in accidents at age 6 is due to the rather sudden increase in the exposure of children to traffic when they go to school [Howarth et al., 1974). (c) From estimates of traffic densities we can give limited answers to such questions as "Is the greater risk of crossing major roads, proportional to the increased probability of encounter with a car?" This enables one to predict the effect of changes in traffic density on pedestrian risk. Like a number of other studies our data show accidents to be roughly proportional to traffic density. (d) We measure traffic density in a slightly unusual way by calculating the proportion of the road "taken up" by vehicles. This includes the length of the vehicle, plus the space in front of the vehicle (its shadow) which no pedestrian could cross without being hit if the vehicle failed to brake. This method of measuring traffic density allows one to calculate the number of accidents which would occur if no one made any attempt to avoid them. By comparing this figure with the actual number of accidents, one can calculate the percentage of potential accidents which are avoided. Even for 5-7 yr olds this figure turns out to be 99.99%, i.e. only one in ten thousand potential accidents is not avoided [Howarth et al., 1974]. (e) In the random site technique our observers are able to record both pedestrian and driver behaviour in some detail. This enables us to discover who is responsible for avoiding all but 0.01% of potential accidents. Results to date suggest that most of the avoiding is done by children, and that drivers fail to take adequate precautionary action in the presence of children [Howarth and Lightburn, 1980]. REFERENCES Howarth C. I. and Lightburn A., How drivers respond to pedestrians and vice versa. In Human Factors in Transport Research, Vol. 2 User Factors: Corn[err, the Environment and Behaviour (Edited by Oborne D. J. and Levis J. A.). Academic Press, London, 1980. Howarth C. I. and Repetto-Wfight R., The measurement of risk and the attribution of responsibility for child pedestrian accidents. Sa[ety Education 144, 10-13, 1978. Howarth C. l., Routledge D. A: and Repetto-Wright R., An analysis of road accidents involving child pedestrians. Ergonomics 17, 319-330, 1974. Routledge D. A., Repetto-Wright R. and Howarth C. I., Four techniques for measuring the exposure of young children to accident risk as pedestrians. Prec. Int. Con[. Pedestrian Sa[ety, Vol. I, 7BI-7B7, Haifa, Israel, 1976.