Collision Investigation and Driver Behaviour: An Overview

Driver distraction and inattention are complex, multi-dimensional, problems that collision investigators need to understand if they are to investigate the human factors that contribute to 95% of crashes. Collision Investigators are trained in the forensics of tyres, auto electrics, kinematics, biomechanics and related topics but receive no or very little training on the human factors associated with crashes.

The importance of the behavioural precursors to a crash is illustrated in the findings from the 100 car study, (Virginia Tech University Transportation Institute, 2008). Researchers collected black box data and camera footage from inside 100 vehicles over 2 million miles for 13-months. What is remarkable about their findings is the extremely high level of crashes and near crashes taking place amongst such a small sample. Whilst there were only fifteen police-reported collisions, there were another 82 that went unreported. The study also revealed 761 near crashes (rapid, severe evasive manoeuvre and 8,295 strong evasive manoeuvres.

The study was unique because data analysis showed that 80% of crashes involved driver distraction. The most dangerous contributing factor leading to crashes was fatigue.  Fatigue increases driver distraction vulnerability as the driver withdraws their attention. Fatigue was a factor in 12% of all crashes with fatigued drivers being 4.7 times more likely to be involved in a crash than an alert, attentive driver.

Attention and perception are critical cognitive components for safe driving. Driving is about 90% visual. Inattention to the roadway is due to secondary driving-related tasks and non-specific glances away from the road. There are two main forms of driver distraction. The first form is contingent on the driver’s role in society. For example, an at-work driver may focus on their work demands rather than the road. The second form involves the driver engaged in the wrong aspect of the driving task including internal features of the vehicle (e.g. using a mobile phone) and external features (e.g. street advertisements). The effect of driver distraction cannot be underestimated; using a mobile phone whilst driving increases the risk of crash involvement somewhere between fourfold and ninefold.

With regards to the pereptual component, there are two basic differences in eye movements during visual search – fixations (pause in gaze) and saccades (eyes move to another position). When viewing a traffic scene on the move, fixations typically last 350ms. This is when most visual information is processed. Research has found that there are dramatic differences between novice and experienced drivers in visual search patterns. In hazardous situations, novice eye movements show an increase in fixation durations leading to temporary inattentional blindness to other unfolding hazards. Novices show narrower horizontal visual search strategies, whereas experienced drivers use wider strategies and peripheral vision more. Experienced drivers therefore have a lower visual workload, freeing up capacity for processing relevant cues to hazards.

However, even experienced drivers fail on the basic driving task – especially at night or when visual search is reduced. Poor visual search when driving may occur due to one of many human factors including time pressure, over confidence, risk taking etc. For older drivers, there are other human factors that increase their vulnerability. Visual demands, especially in complex traffic situations overstretch cognitive resources due to declines in attentional capacity with age. This can lead to a failure to respond in time to hazards, misjudge distances when emerging from junctions and failure to accurately perceive the speed of other vehicles.

The academic research underpinning the theories and models of human behaviour in traffic has been developing for several decades and is now a recognized discipline. The MSc in Driver Behaviour at Cranfield University counts Collision Investigators amongst its student base. They have joined the course to acquire knowledge and skills to investigate the human factors in crash causation. The course allows Collision Investigators to draw from a strong academic literature in road user behaviour and help to develop hypotheses about the likely human factors leading up to a crash. This will add a new dimension to the investigation of crashes which, hitherto, has been a neglected science for the profession.

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