Applications and limitations of wrap-around ratio to vehicle speed estimation in pedestrian collision analysis

Road traffic injuries could become the fifth leading cause of death globally by 2030 unless appropriate countermeasures are taken. Reliable reconstruction of collisions is a prerequisite for this, and determination of vehicle impact speed is the critical reconstruction parameter for vehicle?pedestrian collisions. In this paper, a validated Constant Inertial Property pedestrian model is applied in a Monte Carlo simulation environment to assess the feasibility of using pedestrian wrap-around ratio in the estimation of vehicle impact speed for collision scenarios involving a range of pedestrian pre-impact gait positions, anthropometrics, vehicle shapes and braking conditions for wrap type pedestrian impacts. The results show that there is a clearly identifiable increase in wrap-around ratio with vehicle impact speed up to a speed in the region of 40 km/h, after which further increases in impact speed produce very little change in wrap-around ratio. This characteristic is confirmed from fundamental impact and kinematic analysis. Therefore, the results show that for higher-speed cases only minimum speed predictions may generally be reliable. Statistical analyses of the Monte Carlo simulation results are then used to provide Confidence Limits and Odds Tables for accident reconstruction purposes. These provide the first quantitative approach to vehicle speed prediction from pedestrian wrap-around ratio.