An Evidence Based Method to Calculate Pedestrian Crossing Speeds in Vehicle Collisions

Pedestrian accident reconstruction is necessary to establish cause of death, i.e. establishing vehicle collision speed as well as circumstances leading to the pedestrian being impacted and determining culpability of those involved for subsequent court enquiry. Epidemiological reviews have suggested that 77% of pedestrian accidents involve a vehicle frontal impact and that 89% of pedestrians are struck laterally, 65% in a walking and 20% in a running stance. Understanding the complexity of the pedestrian attitude during an accident investigation is necessary to ascertain the causes leading to the tragedy. Current methods only focus on vehicle impact speed calculation, like the Searle pedestrian throw method, however no method currently focuses on the pedestrian crossing element. A generic new method, named Pedestrian Crossing Speed Calculator (PCSC), based on vector algebra, is proposed to compute the pedestrian crossing speed at the moment of impact. PCSC uses vehicle damage and pedestrian anthropometric dimensions to establish a combination of head projection angles against the windscreen; this angle is then compared against the combined velocities angle created from the vehicle and the pedestrian crossing speed at the time of impact. This method has been verified using one accident fatality case in which the exact vehicle and pedestrian crossing speeds were known from Police forensic video analysis. PCSC was then applied on 2 other accident scenarios and correctly corroborated with the witness statements regarding the pedestrians crossing behaviours.
The implications of PCSC could be significant once fully validated against further future accident data, as this method is reversible, allowing the computation of vehicle impact velocity from pedestrian crossing speed when the Searle limitations are encountered as well as verifying witness statements.