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TRANSPORT RESEARCH LABORATORY Department of Transport
Contractor Report 313
HAZARD PERCEPTION IN DRIVERS: A METHODOLOGY FOR TESTING AND TRAINING
by F P McKenna and J L Crick (Department of Psychology, University of Reading)
Copyright Controller HMSO 1994.The views expressed inthis publicationare not necessarily those of the Department of Transport.Extracts from the text may be reproduced, except for commercial purposes. provided the source is acknowledged. The work described in this paper forms part of a Road Safety Division, DOT funded research programme conducted by the Transport Research Laboratory.
Safety Resource Centre Transport Research Laboratory Old Wokingham Road Crowthome, Berkshire RG11 6AU 1994
ISSN 0266-7045
Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1st April 1996. This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.
ABSTRACT The report is concerned with the development of a hazard perception test which aims t o assess the ability of drivers t o anticipate potential hazards as they unfold over time. Following the development of this test three major experiments assess the utility of the test by using a traditional expert-novice contrast and by examining the role of training. The first experiment was concerned with the development and validation of the test. In essence, this involved the testing of groups of expert and novice drivers, groups that would be expected to differ in terms of overall driving skill, and, consequently, also in their ability t o perceive road hazards. The test revealed large, significant differences in the hazard perception abilities of the two groups, with virtually no overlap shown in the distributions of test scores. The Hazard Perception Test was thus able t o correctly categorise every subject as either an expert or a novice. Information derived from this study lead to the production of a more refined form of the test, together with a second, parallel form, to enable before-and-after studies t o be conducted. In experiment two, the new parallel forms of the test were subjected t o validation by investigating the performance of groups of expert and novice drivers. In addition a group of experienced drivers were assessed. By matching the exposure of the experienced group with that of the expert group it was possible to examine the potential role of training (since the training received by the expert group was the major discriminating feature between the expert and experienced groups). The parallel forms of the test were highly correlated with each other and each test was able t o distinguish between the experts and novices. Expert drivers performed more effectively than the experienced drivers, a result suggesting the influence of training on hazard perception.
In experiment three, a direct test of the role of training was carried out by examining a group of drivers undergoing ROSPA's advanced driving course. Relative to the control group the ROSPA group showed a significant improvement in their performance on the hazard perception test following training. The control group showed no significant change. Taken as a whole, the results indicate that the methodology described provides an appropriate and sensitive measure of hazard perception. It has been shown that, based on the performance on this test, there are large differences in the perceptual abilities of novice, experienced and expert drivers. It is also clear that training can exert a positive influence on hazard perception.
CONTENTS
Page
INTRODUCTION
1
EXPERIMENT ONE
4
Method
4
Results and discussion
7
EXPERIMENT TWO
10
Introduction
10
Method
10
Results and Discussion
12
DISCUSSION EXPERIMENTS ONE AND TWO
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EXPERIMENT THREE
16
Introduction
16
Method
17
Results
18
DISCUSSION
19
Implications and Applications
20
REFERENCES
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Appendix 1 Equipment Layout
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Appendix 2 Critical -Incident Questionnaire
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Appendix 3 Details of Videoing Procedures
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Appendix 4 Instructions to Subjects
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Appendix 5 Univariate F-tests
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INTRODUCTION
Hazard perception refers t o the ability t o identify potentially dangerous traffic situations. It will be argued that this ability t o recognise early or anticipate dangerous traffic situations is conceivably one of the key elements in safe driving. Although logically the presence of this ability does not guarantee safe performance the absence of this ability does present a clear threat. By designing a hazard perception test we aim t o assess the effectiveness of the driver's mental model of the traffic network. A mental model is an internal representation of a complex system which is used t o predict and explain interactions with that system. This mental model allows the driver t o accumulate information and then run a simulation thus allowing the driver t o predict future events. t t would be expected that the drivers' mental model would vary not only between individuals but also within individuals across time. For example, in moving from novice t o expert a corresponding shift in the individual's mental model would not only be expected but, theoretically, it would be predicted would be one of the underlying causal mechanisms underlying the shift. Given the well-documented discrepancy in the accident rates of novice and experienced drivers (eg Williams, 1985) it is arguably the case that hazard perception may be one of the significant factors distinguishing experts from novices. There is some empirical evidence to point to the role of higher order perceptual factors. Several in-depth studies of accidents suggest that perceptual errors of one sort or another are a contributory factor in about 50% of accidents that are not the result of driver impairment through alcohol etc.. Two major independent studies, one conducted in the US (Treat, 1980). the other conducted in the UK (Sabey and Taylor, 19801, arrived at the same conclusion: that perceptual or recognition errors as a whole are the predominant causal factor in non-alcohol related road accidents. One implication of these findings is that current driver testing and associated training is failing t o deal adequately with the perceptual shortcomings of drivers. Improvements in tests of static visual acuity or written tests of driving knowledge are unlikely t o make much of an impact on this problem. There is little evidence that poor vision or lack of technical knowledge are responsible for the disproportionate involvement of young drivers in accidents (Burg, 1971; Conley and Smiley, 1976). What is clearly missing is training in those perceptual, or perhaps more accurately, cognitive abilities implicated in road accident aetiology which are currently, it would appear, gained only through long, hardwon and sometimes bitter experience. Unfortunately, there is little evidence that improvements in the quantity and quality of existing training received produces any corresponding improvement in the quality of driving exhibited (Brown, Groeger and Biehl, 1987; Evans, 19911. Unfortunate because evidence for the benefits of "advanced" training would point t o a means of improving road safety in a way that would be much more readily implemented than, for example, attempting merely t o select out problem drivers on the basis of trait characteristics, a moribund approach whose attendant theoretical and practical problems have been explicated at length elsewhere (McKenna, 1983; McKenna, Duncan and Brown, 1986). However, one possible explanation for the apparent lack of success of advanced driver training may lie with the content of those particular training courses that have been evaluated ie. their failure t o focus on hazard perception rather than control skills (Jonah, Dawson and Bragg, 1982). Despite the previous lack of success, the problem remains of
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finding methods of transferring the novice as rapidly and as far as possible from the novice end of the continuum towards the expert end. A major part of the work described here was directed at evaluating the effects of a course of advanced driver training which has not previously been evaluated. First, a methodology had to be developed t o enable the assessment of an individual's hazard perception ability t o be conducted in a reliable, ethically sound and convenient way. Hazard Perception and The Use of Simulators In an attempt t o develop a hazard perception test we have used a visual simulation of the road environment. The provision of a visual simulation then allows an examination of the cognitive abilities required t o detect hazards on the road. As Gopher and Kimchi (1 989) have noted, in the absence of formal principles for the construction of simulators, the dominant design philosophy has been physical fidelity. In general, past work on driving simulation has aimed at providing a simulator which provides fidelity of the perceptualmotor components. Many of these simulators are extremely expensive and provide a very impoverished visual scene. Our approach, by contrast is inexpensive and provides fidelity of the visual scene. Standard driving simulators would simply not be capable of supporting research on higher order perceptual skills.
Efforts t o produce a measure of hazard perception have been recorded in the literature for at least 20 years (McPherson and Kenel, 1968; Currie, 1969; Pelz and Krupat, 1974; Laidlaw, 1975, cited in Brown, 1982; Watts and Quimby, 1979). Their history is characterised by a steady improvement and increasing sophistication in stimulus materials. All employed some kind of simulation in order t o create a measure that could be used in the laboratory, ranging from the slide presentation of McPherson and Kenel, through the model car track of Currie, t o the film presentation and full car-body mock-up of Watts and Quimby. There are t w o lines of evidence that suggest that the use of simulation is a valid strategy in seeking t o measure a higher order perceptual skill such as hazard perception. Quimby and Watts (1981) found that subjects' performance on their hazard perception test conducted in a simulator correlated significantly with their performance on the road. There was a correlation of .78 between the subjects' risk ratings while watching a film of a particular route and their ratings while driving the same route. Hughes and Cole (1 986) examined drivers' distribution of attention when watching a film and when driving on the road. What the drivers reported t o be looking at in each case was much the same; at least there was no significant difference between the two. Other evidence in support of the validity of a simulator-based approach t o the assessment of hazard perception is to be found in previous work which has revealed significant associations between performance in simulators and accident-involvement.
Hazard Perception and Accident Involvement Measures of hazard perception performance in simulators, in fact, are some of the few measures of individual differences appearing in the literature that have shown any correlation with accident involvement. Pelz and Krupat (1974) found that a group of
2
drivers with a low accident rate reacted much more promptly t o the presence of hazards on film than a group of drivers with a high accident rate. Similarly, Quimby and Watts (1981 were able t o show that reaction time t o hazards in their simulator was positively correlated with accident involvement. They also found that, white younger drivers were faster in terms of both simple reaction time and choice reaction time, they were slower than older drivers t o detect hazards. Significant correlations between hazard perception scores and accident involvement were also found with a shortened version of Quimby and Watts' test in a subsequent study conducted by Quimby, Maycock, Carter, Dixon and Wall (1986). Training, Accident Involvement and Hazard Perception In contrast t o the relationship between measures of hazard perception and accidents, the
empirical evidence in support of a relationship between training and accident involvement is slight and inconclusive. Skelly (1968) looked at the relationship between variations in training practices and subsequent accident rates in the UK. Comparing drivers trained by purely professional instruction, those trained purely by friends and relatives and those trained by a combination of the two, it was found that those receiving professional instruction alone actually had the worst accident rate. Similarly, Potvin, Champagne and Laberge-Nadeau (1 988) in a study of the effects of mandatory professional driver training introduced in Canada in 1983, found that the legislation had no appreciable effect on accident rates. There is also little evidence in support of the benefits of post-licensure training. To some extent this lack of evidence may be attributed t o the paucity of work in the area, and t o the inadequacy of experimental design that characterises much of the work that has been undertaken. In a review of 14 evaluative studies of the Defensive Driving Course (an advanced driving course available in the US), Lund and Williams (1985) could only find 5 that were, in their opinion, 'methodologically strong', and of these, none demonstrated any significant gains in subsequent accident avoidance for drivers taking the course, although some were able to demonstrate significant reductions in the number of traffic violations committed by these drivers. In a study of a roughly equivalent course available in the UK, the Better Driving Course run by British Police Forces, Fazakerley (1980) was able t o show improvements in driving performance and knowledge following the course, but its efficacy in reducing accident involvement was not assessed. Accident rates were assessed, however, in Hoinville et at's (1 972) study of drivers who undertook the advanced driving test of the UK's Institute of Advanced Motorists (IAM); it was found that those drivers who had passed the test had 25% fewer accidents than those who failed. In a review of the relevant literature, Brown et al. (1987) could only conclude that "the general verdict on the value of advanced training and testing for road safety must, again, be 'not proven'". Similarly, in Evans' (1991) more recent review, the conclusion remains the same, if not more damning: "post-licensure training programs have not been shown to reduce crash rates".
Exactly why this should be the case is as yet unclear, considering that training has been shown t o be generally successful in other areas of skill acquisition (e.g. Goldstein and Buxton, 1982; Halff, Hollan and Hutchins, 1986; Jensen, 198& It could simply reflect the lack of enough properly controlled studies, or it could be that the best training courses have not yet been evaluated. An equally ptausible explanation, however, is that the
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courses that have been evaluated to date are not addressing those aspects of the driving task that are related t o accident involvement, e.g. hazard perception. If many of the courses evaluated have been those which have focused largely on perceptual-motor skills aspects which in-depth studies of accidents (Sabey and Taylor, 1980) have shown t o be relatively unimportant factors in accident causation it is unlikely that the effects of this kind of training would manifest themselves in reduced accident rates.
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There has been little work on the effects of training on hazard perception per se, an omission that the work reported here was largely designed to redress. Before it was possible t o explore this issue, a reliable laboratory measure of individual differences in hazard perception had t o be developed. This was the primary objective of experiment one.
EXPERIMENT 1 The main aims of Experiment 1 were, firstly, t o develop a reliable and portable test of hazard perception; secondly, t o validate this newly-developed test by examining the performance of drivers that might be expected t o differ widely in terms of hazard perception ability, namely, experts and novices; and finally, t o refine the content of the test for future work.
METHOD Simulator and Paradigm
The simulator was based, in part, on that used by Watts and Quimby (19791, which itself derives from that of Pelz and Krupat (1974). Here the subject sits in a shortened car body and views a film of a driver's-eye view of the road while appropriate sound and car-body vibrations are provided. The subject moves a lever t o give a continuous rating of risk; responses are recorded on a chart recorder. The simulator developed at Reading differed from that of Watts and Quimby in a number of significant respects, apart from exchanging videotape for film. In order t o be portable, the simulator was necessarily simplified. Thus no attempt was made t o simulate the internal environment of the car; there were no pedals or steering wheel, no simulated noise or vibration, nothing that might be considered to contribute redundant realism. Other major developments and departures were made in the interest of greater accuracy. These were: the automation of measurement through the use of computer and associated interface; the recording of discrete responses from a response button rather than recording continuous responses from the manipulation of a lever; incorporating a measure of simple reaction time into the main experimental task, rather than as an adjunct, obviating the need for the extra equipment that would otherwise be required. Details are shown in Appendix 1. In essence, the simulator consisted of a TV monitor and video recorder, interfaced with a computer and response button. The subject views a videotape of a sequence of various road and traffic situations, some of which, either by design or adventitiously, are hazardous. The subject is instructed t o respond with a button press immediately a hazard is detected, rather than make a continuous assessment of risk, as in the case of Watts and Quimby's test. Also on the videotape are signals, of which the subject is unaware, which
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signal the onset of a preselected hazard. The signal from the videotape switches on the computer's millisecond timer which is stopped when the subject, having spotted the hazard, presses the response button. If the subject fails to respond, the computer stops timing after 5 seconds, and a latency of 5 seconds is recorded for that hazard; latencies of 5 seconds thus denote a miss. Video Production Information about commonly-occurring road hazards was gathered by consultation with various expert groups such as Police drivers and driving instructors. Informat interviews and a form of Critical Incident technique (Flanagan, 1 9 5 4 ) were used t o elicit information. The Critical Incident Questionnaire (Appendix 2) was administered via Police driving instructors at the Metropolitan and Thames Valley Potice Driving Schools, and via the magazine of the Driving Instructor's Association. On the basis of this information, a number of hazardous scenarios were generated which were amenable t o subsequent videoing. Some examples of these hazardous scenarios are shown in Table 1. TABLE 1 Example Scenarios
E3 1
Approaching a tight gap, with line of parked cars on the right, faced by opposing vehicle which is obscured by parked cars (non-staged)
E l6
Cyclist suddenly leaves pavement on the left and wanders across path of vehicle (non-staged) ."a
E22
Car approaches at speed from left at roundabout (staged)
E39
Blind right-hand bend, parked cars on left (non-staged)
E46
Lorry parked on right-hand side of suburban back street, obscuring view of oncoming traffic, opposing vehicle competes for gap (staged)
E20
Preceding car stops suddenly on apex of corner, opposing cyclist (staged)
E36
Pedestrian crossing from right at zebra crossing; pedestrian concealed by car reversing from parking space near t o crossing Istaged)
E35
Car reverses obliviously from driveway (staged)
E28
Opposing vehicle pulls out past parked car, moving into path of vehicle (staged)
5
I .
Some of the scenarios were staged for videoing purposes, some occurred fortuitously while videoing. Videoing was carried out in the vicinity of Reading and Bristol. As near as possible a driver's-eye view of the road was obtained by suitable mounting and adjustment of the camera. Neutral sequences, ie sequences without any deliberately contrived hazardous situations, were included at various junctures in both the main video and the practice section. More detailed information concerning video production appears in Appendix 3. Also appearing on the videotape was a sequence designed to provide some measure of reaction time (VIDEORT), in order to take account of individual differences in reaction time and t o later covary out its effects in the hazard perception trials. The sequence devised consisted of a driver's-eye view of a car park in which, at varying intervals, a white volleyball suddenly appeared between a row of parked cars at a distance of 10-15 metres. The subject's task was t o respond with a button press immediately upon seeing the ball. The ball appeared on 10 occasions. The intention was that this reaction-time task should, in most respects, be congruent with the hazard perception task, but involve minimal hazard perception ability. Subjects There were 17 subjects in each group: the novice group was recruited mainly from the University population at Reading. All had passed the British driving test and had been driving for a maximum of three years. The expert group was provided by the Metropolitan Police Driving School at Hendon; they were all instructors at the school, and, by dint of being an instructor, they were all Class One Police drivers. Subjects in the novice group received €3.00 for participating in the experiment.
No attempt was made t o control for age: in this case, age is necessarily confounded with expertise. The mean age of the novice group was 21.4 years; that of the expert group, 34.0 years. The novice group comprised 10 males and 7 females; the expert group were all males. Procedure The novice group were tested in the laboratory at Reading; the expert group, in as near as possible identical conditions at Hendon. Subjects were first shown the reaction time trials of the white volleyball in the car park, followed by a three minute practice session at the main task. The same written instructions were read t o the subject before and after the practice session. A copy of the written instructions appears in Appendix 4. Subjects were then shown the video proper, which was about-30 minutes long. A pool of 35 potentially hazardous incidents were presented for assessment. Subjects were instructed t o respond as quickly as possible as soon as a hazard was identified. At the end of testing, subjects were debriefed and asked t o complete a short questionnaire concerned with general demographic variables and driving experience.
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RESULTS AND DtSCUSSlON
An overall mean score for the hazard perception test was derived by collapsing a subject's reaction times across scenarios. A between groups analysis of covariance with VIDEORT as a covariate indicated that the expert group responded significantly faster than the novice group, F(1,31)= 29.3, p
