Ergonomics Of THE Driver`s Interface With The Road Environment

Road user behaviour and the road environment
A conceptual and a methodological framework for
Farida Saad
Some preliminary remarks
Factors contributing to road safety are usually classified in three main
ƒ Factors related to the design of the road infrastructure,
ƒ Factors related to vehicles,
ƒ 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
ƒ Road users play a crucial role in the way the road traffic system operates
ƒ Studying road users' behaviour : fundamental for identifying measures aimed at
improving the safety and reliability of the traffic system
ƒ 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.
ƒ Many research studies have shown that road user behaviour is largely dependant on
the characteristics of the driving environment
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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).
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To identify and design technical and organizational means for facilitating the
driver's interaction with the road environment
The road environment
ƒ The vehicle,
ƒ The road infrastructure
ƒ Other road users.
ƒ 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
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Driving Ergonomics
To support drivers’ interaction with the road environment : Two main domains
ƒ The design of the road infrastructure
Improving the characteristics of the road network and developing design and planning
norms that improve “Road Readability”
ƒ 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.
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Road infrastructure as an interface between Designers
and Road Users
ƒ 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).
ƒ 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.
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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
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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.
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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
ƒ “Positive guidance” (Allen and Lunenfeld, 1986)
ƒ “Road readability” (Mazet, Dubois and Fleury, 1987)
ƒ “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
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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)
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Psychological research in the field of driving ergonomics
ƒ To describe and categorise driver behaviour in situ (as safe or unsafe,
legal or deviant...),
ƒ 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,
ƒ To reveal the psychological processes (perceptual, cognitive,
motivational,) that govern drivers’ activity.
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Internal and external conditions
External conditions
Internal conditions
Driver behaviour
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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
Choice of
regulating action
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Psychological research
To contribute to increasing knowledge about driver activity
And to help develop measures for improving road system operation
and safety.
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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
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.
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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
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.
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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).
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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.
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Model of analysis (Leplat, 1993)
Discrepancy between tasks
Prescribed Task
Redifined Task
the driver
the expert
Task carried out
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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.
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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
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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).
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Critical changes / behaviour of other road
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
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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.
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Main questions
ƒ How, in the dynamics of driving, do drivers treat changes in road
situation ?
ƒ What in the driver's view constitutes a change in the road situation
necessitating an immediate or anticipatory regulating action ?
ƒ To what extent does the road environment facilitate the detection and
anticipation of changes in the road situation ?
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“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
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”.
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“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.
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« 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.
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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"
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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
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.
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What is the speed limit ?
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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
Behavioural observation in real traffic (at the site or on board
Experiments in controlled settings (in the laboratory, on test tracks,
or on driving simulators).
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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.
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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
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On-site observation of driver behaviour
Behaviour at
stop sign
Type of
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On-site observation of driver behaviour
Type of
Type of
Apparent motives for
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Traffic on the
opposite lane
An example : Driver’s speed adjustement when crossing
Speed (Km/h)
Intersection 1- N = 10
Intersection 3 - N =11
Intersection 4 - N = 9
Intersection 5 - N = 9
Distance (metres) from the centre of the intersection
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An example : Driver’s speed adjustement when crossing
Speed (Km/h)
drivers. - N= 9
drivers. - N= 10
Distance (metres) from the centre of the intersection
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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
Behavioural adaptation may be an immediate response to the change
introduced in the traffic system or may only appear after a long time
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.
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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).
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