Road user behaviour and the road environment A conceptual and a methodological framework for analysis Farida Saad INRETS-GRETIA Some preliminary remarks Factors contributing to road safety are usually classified in three main groups: Factors related to the design of the road infrastructure, Factors related to vehicles, factors related to road users. In order to define appropriate safety measures, it is necessary to have indepth knowledge on these three factors and the way they interact Farida Saad Some preliminary remarks Road users play a crucial role in the way the road traffic system operates Studying road users' behaviour : fundamental for identifying measures aimed at improving the safety and reliability of the traffic system However, recognising the importance of “road user behaviour” in road safety, does not mean that the preventive measures have to be limited to the areas of education, training or information. Many research studies have shown that road user behaviour is largely dependant on the characteristics of the driving environment Farida Saad Review of research paradigms in road safety Ranney's (1994) “Moving the focus of research away from the driver in isolation and focusing more on the interaction of the driver and driving situations would improve the ecological validity of roadway safety research It would also move theory beyond artificial obstacles created by the idea that human errors contribute to an exceedingly high percentage of accidents and allow work to focus on identifying factors that create incompatibilities among the drivers, the vehicles and roadway systems" (p. 747). Farida Saad Ergonomics To identify and design technical and organizational means for facilitating the driver's interaction with the road environment The road environment The vehicle, The road infrastructure Other road users. The rules of the Highway Code governing the use of the road infrastructure and interactions with other users, sometimes expressed in road markings and road signs Farida Saad Driving Ergonomics To support drivers’ interaction with the road environment : Two main domains The design of the road infrastructure Improving the characteristics of the road network and developing design and planning norms that improve “Road Readability” The design of new driver support systems Providing in-vehicle new sources of information and new devices to help drivers perform the driving task. Psychological research can contribute to the search for solutions by providing a theoretical and methodological framework as well as empirical results likely to support the design and assessment of these measures. Farida Saad Road infrastructure as an interface between Designers and Road Users The road infrastructure conveys a wealth of information that guides drivers’ activity and their interactions with others in situ (explicitly through devices such as road signs and road markings, and implicitly by means of the environmental context and road layout, for example). The design of the infrastructure and the formulation of the rules determining its use: choices made by the designers of the road system (including road and traffic engineers and the legislators of the highway code) Main design issues : compatibility between the choices made by designers and the information drivers need to achieve their objectives and perform their driving task efficiently and safely. Farida Saad Road infrastructure as an interface between Designers and Road users Communication between road designers and road users Compatibility between the formal rules of use underlying the design of the road and the effective rules applied by drivers when using the road (Hale and Stoop, 1988) Formal rules: essentially laid down in the Highway Code. They are taken into account by designers in designing the road infrastructure, together with other technical design principles (Fleury, 1998). Informal rules : rules effectively applied by road users, acquired through practice and experience Farida Saad Design difficulties The multiplicity and diversity of the actors sharing and using the same space, each actor being autonomous, having his/her own objectives, knowledge and strategies. The diversity of the actors involved in a more or less direct way in structuring the road space. Farida Saad Research orientations The malfunctions observed (errors, offences, conflicts, accidents) have led researchers to focus on identifying the factors and mechanisms at the root of these problems. How the road infrastructure could support drivers’ activity “Positive guidance” (Allen and Lunenfeld, 1986) “Road readability” (Mazet, Dubois and Fleury, 1987) “Self-explaining roads” (Theeuwes and Godthelp, 1995) To structure the road network by adopting homogeneous and consistent design principles To identify the relevant infrastructure features likely to provide a clear picture of the functionality of the road space Farida Saad Research Orientations Developing diagnostic methods for spotting critical situations from a safety viewpoint. To identify the information to be conveyed to drivers, to make profound changes in the road infrastructure Developing psychological research: to identify the knowledge and strategies that drivers apply in controlling different driving situations and the tasks to be performed. Improving the design process by bridging the communication gap between road system designers and traffic psychologists Road designers: to spell out the rules of use induced by the design of the road Psychologists: to formulate the results of their research in terms of the drivers’ effective rules of use (Hale and Stoop, 1988) Farida Saad Psychological research in the field of driving ergonomics To describe and categorise driver behaviour in situ (as safe or unsafe, legal or deviant...), To identify the internal factors (relating to the driver himself, such as his experience) and the external factors (the technical and social environment of driving) that account for this behaviour, To reveal the psychological processes (perceptual, cognitive, motivational,) that govern drivers’ activity. Farida Saad Internal and external conditions External conditions Internal conditions Driver behaviour Farida Saad Psychological processes : A simplified model of driver’s categorisation of the road situation and choice of regulating action Information in the road environment Driver’s knowledge Situational Representation Choice of regulating action Farida Saad Psychological research To contribute to increasing knowledge about driver activity And to help develop measures for improving road system operation and safety. Farida Saad Complex situations The questions prompted by the identification of these measures stem from complex situations, whose dimensions must be examined and taken into account when designing research studies, validating the results and formulating recommendations. Applying a systemic approach (see, for example, Hale and Glendon, 1987) entails focusing on interaction phenomena between the driver(s) and the technical and organisational components of the system (vehicle, road infrastructure, legislation, traffic management,...) and hence going beyond a simplified view of causality in analysing system malfunctions. Adopting such an approach implies a joint analysis of the characteristics of the road environment and the characteristics of drivers. Farida Saad Several types of analysis In-depth analysis of road situations To specify the nature of the interactions (with the road infrastructure, with other users, and so on) and the demands (regulatory, structural, dynamic, etc.) drivers have to deal with when driving. Studying driver behaviour To examine how drivers perceive and weigh these different demands, and how they organise, perform and control the different tasks required in situ. To identify the mechanisms that govern their driving and the difficulties they encounter when managing their journeys. Analysing “driving errors” A subject of analysis inasmuch as the mechanisms that induce them must be explained A means of analysis in that they reveal the critical interactions within the system and direct research towards the situations that deserve specific investigation. Farida Saad The prescribed (or formal) task The task to be carried out as conceived by the designer of the system and/or the safety manager. It sets out (more or less explicitly) a number of prescriptions, which are supposed to influence and to some extent guide driver activity. In other words, the prescribed task defines the behaviour expected of the driver, what he should do (in terms of performance and/or procedures to follow). Farida Saad The actual or redefined task What the driver actually does, the demands and constraints that s/he effectively takes into account. Identifying the actual task calls for a detailed analysis of driver behaviour with the aim of determining exactly how drivers organise and perform the driving task: Æ What their goals and intentions are, Æ What information they select from the environment, Æ What motives and criteria underlie their decisionmaking,? Æ What regulating actions they take. Farida Saad Model of analysis (Leplat, 1993) Discrepancy between tasks Prescribed Task Redifined Task Error for the driver Error for the expert Task carried out Farida Saad Critical aspects of the driving task Errors, incidents, conflicts and accidents: limits of drivers' adaptation to their task It is thus important to understand the reasons for such deviations, To identify the conditions in which they are most likely to appear, To analyse the mechanisms that could explain their occurrence. Deviations are particularly common when drivers have to manage changes in road situations and pose serious problems that are known to have a significant impact on the reliability and safety of man-machine systems (Hale and Glendon, op. cit.; Leplat, op.cit.). For the driver, these changes may be more or less predictable and more or less expected, depending on whether or not s/he has the knowledge and the information needed to detect and identify them as s/he drives along. Farida Saad Managing changes in road situations For instance, some research shows that when crossing intersections, drivers may take time to become aware of conflicts with other drivers, or display a certain inertia in the regulating actions they take (Monseur and Malaterre, 1969; Saad et al., 1990). Factors associated with the features of the road environment (disparity between the functional characteristics of an intersection and the regulations governing it, or the visual aspect of the intersection), as well as factors related to driver characteristics (general experience or specific experience of the site), have been identified as the causes of these problems. Farida Saad Critical changes in the road infrastructure Critical variations may occur due to a change in the road infrastructure that the driver could not anticipate in view of the road characteristics upstream of the change: For example, when the driver cannot anticipate the presence of a sharp bend and momentarily loses control of the vehicle, or when the driver does not expect to come across traffic lights and has to make a sudden stop. These critical variations are often related to "coherency" problems in the sequencing of different types of road environment (Fleury, 1988). Farida Saad Critical changes / behaviour of other road users Critical variations may also be related to the behaviour of other road users, when the action they take unexpectedly interferes with the tasks the driver is performing or planning to perform. Different elements could be at the root of these problems, such as the application of contradictory systems of rules by the different participants in a situation, the lack of communication between users, or a failure to understand another driver's behaviour or intentions. Farida Saad The importance of predictive activity In-depth accident studies have highlighted the problems associated with the temporal constraints underlying the occurrence of accidents and have confirmed the importance of predictive activity when driving (Malaterre, 1990; Van Elslande et al., 1998). The disparities between drivers' expectations and predictions and the events that actually occur during their journeys seem to be a result of processing errors and the belated detection of critical situations, reducing the safety margin for resolving them. Farida Saad Main questions How, in the dynamics of driving, do drivers treat changes in road situation ? What in the driver's view constitutes a change in the road situation necessitating an immediate or anticipatory regulating action ? To what extent does the road environment facilitate the detection and anticipation of changes in the road situation ? Farida Saad “Positive Guidance” (Alexander and Lunenfeld, 1986) “Positive Guidance is a procedure that identifies information system deficiencies and provides suitable, expected information when needed, where required and in a form best suited for its intended purpose” The concept of “Positive Guidance” stresses the importance of drivers’ expectations in ensuring their safe and efficient adjustment to the road environment. Expectations are assumed “to influence the speed and accuracy with which drivers process the information and are one of the most important aspects to be taken into account in the design and operation of the system and the provision of information (…). The configuration and the geometry of the road and the traffic control measures that correspond to or strengthen drivers’ expectations help them to react rapidly and safely”. Farida Saad “Self-Explaining Road” ( Theeuwes and Godthelp 1986) The concept of the “Self-Explaining Road” is defined in terms of the processes by which drivers’ expectations are structured. “SER are roads with a design that evokes correct expectations from road users (…). This means that drivers are given direct information about the type of road they are driving along and the type of behaviour required” (, 1995). These concepts advocate a road infrastructure that elicits safe driving behaviour “by design”. This could be achieved by identifying and taking account of drivers’ knowledge and information processing, which plays a critical role in the identification and interpretation of road situations. Farida Saad « Road Readability » To help drivers to detect, identify and interpret current situations Given the dynamic nature of driving and the associated temporal constraints, to facilitate their anticipation of on-coming situations and the events that could occur. Given the collective nature of driving, to facilitate interactions between drivers and to ensure that the rules to be applied for solving potential conflicts are clear and easily understandable. Lastly, and in the longer term, reducing the variability of road infrastructure design should make it easier for drivers to learn its functionality and its use. Farida Saad Expectation Violation Analysis and Review (Alexander and Lunenfeld, 1986) A process designed to identify expectancy violations, pinpoint their sources, and develop information displays to restructure violated expectancies or structure appropriate ones. The analysis and review is initiated by first reviewing the area upstream and downstream of a problem location or assessing a road segment as part of general surveillance. This general review provides an understanding of the land-use, geometric design, traffic operational procedures, and traffic control devices, which serve to structure driver expectancies. Once this understanding is obtained, and /or unidentified problems found through routine surveillance, a detailed analysis is then performed" (). Farida Saad Itinerary approach and global safety approach (Fleury, 1998) These differ from the black spot approach (or analysis of local malfunctions, i.e. at a specifique site) insofar as they take into account broader analytical units (different sections of road, of a town or of a county...). These approaches combine accident analysis and observation of user behaviour. The itinerary approach involves spotting the repetitive aspects of the malfunctions observed and thereby highlighting those that are common to the particular itinerary. The global safety approach draws on different analytical tools, such as the categorisation of roads across a network, accident scenarios and the geographical location of accidents. Farida Saad What is the speed limit ? Farida Saad Farida Saad Questions of method Analysis of driver activity is based on various models and uses very diverse methods and investigative techniques: Interviews or questionnaire surveys of drivers (in or out of traffic situations), Behavioural observation in real traffic (at the site or on board vehicles), Experiments in controlled settings (in the laboratory, on test tracks, or on driving simulators). Farida Saad Type and level of analysis Some observations of behaviour in real situations are made from an essentially descriptive standpoint. They seek to establish some kind of picture of drivers’ behaviour on the road or to establish a quantified relationship between some characteristics of road design and drivers’ behaviour. Observations on the ground can be viewed as exploratory research which seeks to identify the different features of the infrastructure and the traffic conditions linked to the tasks performed and/or to the variables characterising the drivers themselves (age, experience, ...) and which are likely to explain drivers’ behaviour in specific road situations. Other observations are more directly guided by hypotheses about certain psychological processes that could explain the way drivers interact with the road environment. Farida Saad Type and level of analysis Observation of user behaviour in real driving situations : a particularly useful means of investigation in order to acquire greater knowledge of effective driver behaviour and to analyze some of its determining features. Such observation affords a better understanding of how a traffic system operates and also contributes to safety diagnosis. It often represents a vital complement to an analysis of accidents and, where appropriate, may compensate for the shortage of available information on this matter. Farida Saad On-site observation of driver behaviour Day Behaviour at stop sign Type of Vehicle N° BEHAVIOUR AT STOP SIGN Location H Full Stop Near Stop Manoeuvres No Stop Farida Saad Traffic yes no On-site observation of driver behaviour Day: Location Type of overtaking Vehicle N° H Type of overtaken Vehicle OVERTAKING BEHAVIOUR Apparent motives for overtaking Vehicle Vehicle Slower slowing stopped/ Vehicle down pavement Farida Saad Traffic on the opposite lane Yes No An example : Driver’s speed adjustement when crossing intersections Speed (Km/h) 100 95 Intersection 1- N = 10 90 Intersection 3 - N =11 85 Intersection 4 - N = 9 Intersection 5 - N = 9 80 75 400 300 200 100 Intersection 100 Distance (metres) from the centre of the intersection Farida Saad 200 An example : Driver’s speed adjustement when crossing intersections Speed (Km/h) 100 95 90 Experienced drivers. - N= 9 Novice drivers. - N= 10 85 80 75 400 300 200 100 Inter 100 Distance (metres) from the centre of the intersection Farida Saad 200 A critical issue : Behavioural Adaptation Mainly used to signal unexpected or unanticipated behavioural changes that appear in response to the introduction of a change in the traffic system and which may (more or less) jeopardise its expected safety benefits. Behavioural adaptation may be an immediate response to the change introduced in the traffic system or may only appear after a long time period. Although behavioural adaptation is a widely acknowledged phenomenon, the factors likely to explain it and the processes underlying its occurrence (in time and space) and are not clearly established. Farida Saad Behavioural adaptation Several variables have been suggested as factors likely to induce the occurrence of a behavioural response, such as : the drivers’ perception of the change introduced in the traffic system : does the change directly influence the way the driving task is performed, does the change alter the drivers’ subjective safety ? the degree of freedom that the change allows drivers : is there any opportunity for drivers to change their behaviour ? the presence of competitive motives for changing behaviour, and so on (OECD, 1990). Farida Saad
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