Understanding accident processes

Science topics April 2015 Road safetyHuman behaviour

Thierry Brenac, Researcher - TS2 Department, LMA Laboratory

     To develop accident prevention measures it is helpful to understand the processes involved in the sequence of events and situations which lead to collisions.

    A very wide range of processes are involved in pedestrian accidents1. A few recurring problems, which are frequently factors during an accident can nevertheless be identified.


The main dangers facing pedestrians

    Firstly, obstacles to visibility play a decisive role in many accidents. In particular, when a pedestrian steps out from between two stationary or parked vehicles, an oncoming driver has very little time to react, even when travelling at moderate speed.
    Suddenly crossing the road when excessively focused on a goal (catching a bus, meeting an acquaintance on the other side of the road, etc.) is another frequent characteristic of pedestrian accidents, particularly in the case of children and adolescents2. However, other attentional or information seeking deficiencies may also be involved. For example, at an intersection motorists need to give way to other vehicles which may use a great deal of their attention, meaning that pedestrians go unnoticed. Less often, unusual design characteristics (for example some contraflow lanes) may cause pedestrians to wrongly identify the direction of traffic and look the wrong way when crossing.
    In addition, motorists often fail to notice pedestrians at night-time, even when there is street lighting. This is even more common when it rains at night. Under these conditions a pedestrian crossing the road may not be seen by a motorist and knocked down. Furthermore, both the pedestrians and drivers involved in night-time accidents are more likely to have consumed alcohol. Outside built-up areas, the few pedestrians walking along the carriageway are at very high risk as drivers may not see them and impact them at high speed because their vision is disturbed by the headlamps of oncoming vehicles. Such accidents are particularly serious. Another category of severe accident involves pedestrians who are occupied around broken down vehicles on high speed roads (motorways, dual carriageways, etc.), who are noticed too late by a driver.


Understanding accident processes - Ifsttar - A stationary bus on a pedestrian crossing (Photo credit: IFSTTAR)

Specific problems with some types of vehicles

    Goods vehicles, buses and powered two-wheelers sometimes play a specific role in pedestrian accidents. Goods vehicles often impact pedestrians when reversing because their drivers usually have restricted rear visibility. Because of their size, HGVs and buses are more likely than cars to knock pedestrians down when making turning manoeuvres. Also, due to their size, buses and trucks often impede visibility causing pedestrian accidents3.
    Powered two-wheelers are more likely than cars to impact a pedestrian4. In particular, when they drive fast next to long queues of stationary vehicles, there is a high risk of an impact with pedestrians crossing the road, as the queues of vehicles obstruct visibility.

    Overall, the in-depth analysis of pedestrian accidents suggests many possible ways of making improvements, in particular through road design, the organisation of transport systems, vehicle design and road user education and training.




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1 Scénarios types d’accidents impliquant des piétons et éléments pour leur prévention, par T. Brenac, C. Nachtergaële et H. Reigner. Les Collections de l’INRETS. Arcueil : INRETS (2003). Download from the IFSTTAR bookshop.

2 « Insécurité routière des jeunes piétons : processus d'accidents et stratégies de prévention », par T. Brenac. Territoire en mouvement, t. 2008, no 1, p. 14-24 (2010). Available on Territoire en mouvement

3 « The indirect involvement of buses in traffic accident processes », par T. Brenac et N. Clabaux. Safety science, vol. 43, no 10, p. 835-843 (2005). Accessible through ScienceDirect

4 « Powered two-wheeler drivers’ risk of hitting a pedestrian in towns », par N. Clabaux, J.-Y. Fournier et J.-E. Michel. Journal of Safety Research, vol. 51, p. 1-5 (2014). Accessible through ScienceDirect