Observing pedestrian reactions when there is a risk of an imminent impact

Science topics April 2015 Road safetyHuman behaviour

Thomas Robert, Researcher TS2 Department, LBMC  Laboratory

Pedestrians account for approximately a quarter of the persons killed in road traffic accidents (ONISR data). In most cases the cause is a collision with a vehicle. To try to reduce the number of fatalities, vehicles are now designed in a way that limits the severity of an impact. Currently, devices that enable vehicles to detect and try to avoid pedestrians are being developed (automatic braking and automatic steering systems).

However, currently these measures are tested and evaluated for extremely simplified situations, which generally ignore the reaction of pedestrians to the accident and the variety of situations which can occur. In most cases, pedestrians have the time to see the vehicle that is likely to hit them and react to the imminent danger. The nature of these reactions is, however, relatively little documented.
IFSTTAR is therefore studying the reactions of pedestrians, both young and elderly, who are crossing the road when a vehicle appears at high speed and threatens to impact them. More precisely, the investigation concerns the effects of this reaction on the level of the risk of impact and the possible consequences of an impact.


An experiment to observe pedestrian reactions

The subjects take turns to move within a virtual environment which simulates a street with a fleet of moving vehicles. The subjects are unaware of the purpose of the study and are simply instructed to cross the street while avoiding vehicles. During one of these crossing manoeuvres, the simulator generates a rapidly moving vehicle, together with the noise of an accident. The reaction of the individuals is measured by a number of sensors. In particular, a movement analysis system1, similar to those used in the video games and cinema animation industries, quantifies subjects’ movements, especially their attempts to avoid the vehicle and their posture at the time of the virtual impact.


The avoidance strategies to be considered

This experiment highlighted the importance and the frequency of pedestrian reactions when faced with the risk of an imminent impact. We can identify three major vehicle avoidance strategies :

  • The attempt to avoid the vehicle by speeding up;
  • The attempt to avoid the vehicle by moving backwards;
  • No attempt to avoid the vehicle, just protection reflexes (for example protecting one’s head with one’s arms).

These reactions have a considerable influence on the pedestrian’s trajectory between the moment when the scenario is initiated or the moment when the pedestrian is detected by an automatic pedestrian avoidance system and the moment of virtual impact.
These reactions have a considerable influence on the pedestrian’s trajectory between the moment when the scenario is initiated or the moment when the pedestrian is detected by an automatic pedestrian avoidance system and the moment of virtual impact.


Influence of the reaction on injury risk

A wide variety of postures as well as some significant avoidance strategies were observed in the course of this study. IFSTTAR’s researchers therefore attempted to find out if the impact conditions affected pedestrian injury risk. Currently, as far as pedestrian impact is concerned, vehicles are only evaluated with regard to an impact with a pedestrian in a standardised pedestrian position. We therefore need to make sure that these standard test conditions are appropriate.
Using a digital model, the injuries resulting from a pedestrian-vehicle impact were evaluated for the various experimentally observed postures and virtual impact speeds as well as for the standard test conditions. It was shown that injury risk is extremely dependent on the impact conditions. However, the estimated risk under standard conditions was higher than that estimated in 95% of the experimental conditions. This therefore tends to show that the current standard test conditions provide a good starting point.



Contacts :
This research was carried out by A. Soni, T. Robert, P. Beillas and F. Rongieras of the LBMC in the TS2 Department, with the participation of D. Ndiaye and F. Vienne of the LEPSIS Laboratory in the COSYS Department.
Anurag Soni’s reasearch was financed by the European Commission as part of the Marie Curie action « Pedestrian pre-crash reactions and their effects on crash outcomes ». Details about the European project on the Cordis website



1 The software used to create the virtual environment was developed by the LEPSIS laboratory in the COSYS Department.

This experiment was carried out in the framework of the legislation concerning the protection of persons in biomedical research and was therefore approved beforehand by the Institute’s Ethics Committee, the Consultative Committee on the Protection of Persons in Biomedical Research and the National Agency for the Safety of Medication and Health-related Products (ANSM).



Find out more...

  • Cavallo, V., Lobjois, R.7 and Vienne, F., (2006) The interest of an interactive road crossing simulation for the study of adaptive road crossing behaviour.Proc. 1st Driving Simulation Conference Asia-Pacific. Tsukuba, Japan.
  • A. Soni, T. Robert, and P. Beillas, Effects of pedestrian pre-crash reactions on crash outcomes during multi-body simulations, in Proceedings of the 2013 International Research Council Of Biomechanics of Injury Conference, 11-13 September 2013 – Gothenburg (Sweden), 2013, pp. 762–776.
  • A. Soni, T. Robert, F. Rongieras, and P. Beillas, Observations on pedestrian pre-crash reactions during simulated accidents. Stapp car crash journal, vol. 57, pp. 157–183, 2013.