Relating severity of pedestrian injury to impact speed in vehicle-pedestrian crashes: Simple threshold model

An ordered, discrete outcome model that relates the severity of injury suffered by a struck pedestrian to the speed of the striking vehicle is derived and then fit to previously published data. Particular care is taken to account for covariate measurement error and for the fact that the data were collected using an outcome-based, or retrospective, sampling plan. The results show similar patterns for children (ages 0-14) and adults (ages 15-59), but for elderly pedestrians (ages 60+) the injuries produced in crashes that involved lower impact speeds tended to be more severe than for the other two groups. Use of the model is illustrated by applying it to two reconstructed vehicle-pedestrian crashes to determine the likely severity of the injury had the driver adhered to a speed limit. Some implications for speed limits on residential streets are also pointed out.