Numerical Validation of the Pedestrian Crossing Speed Calculator (PCSC) using Finite Element Simulations

In fatal pedestrian to vehicle collisions, accident investigators must attempt to reconstruct events that led up to the collision to determine liability in a court of law. In the absence of suitable video footage, the vehicle speed is calculated using particle based throw distance calculators such as the Searle method. Until recently, no methods concentrated on the velocity of the crossing pedestrian, vital for determining responsibility. A new approach, the Pedestrian Crossing Speed Calculator (PCSC), which uses evidence left on the bonnet and windscreen along with pedestrian anthropometry to calculate a pedestrian crossing speed, has been proposed in a previous research, and validated against three real accidents where the pedestrian approach was orthogonal to the vehicle. The range of application of the PCSC theory is investigated in this paper. This study has considered 48 Finite Element simulations to further validate the PCSC against a saloon type and SUV vehicles. In the case of the saloon type, the PCSC theory for a pedestrian crossing approach angle <10°, i.e. a pedestrian crossing trajectory no longer perpendicular to the vehicle trajectory, has been fully vindicated. The study has also confirmed the PCSC hypothesis stating that for saloon vehicles the relationship between and increase in bonnet dent width was caused by an increase in pedestrian gait angle. The study also concluded that the PCSC theory was less conclusive in the case of SUV collisions.This paper confirms that PCSC is unique and can have an important role in the field of accident reconstruction and for law enforcement; with the potential to determine vehicle speeds from a known pedestrian crossing speed, which will allow the calculation of the vehicle velocity in the absence of physical evidence left on the road surface.