Car Mass and Likelihood of Occupant Fatality

The purpose of this work is to estimate the relationship between car mass and the likelihood that a car will have an occupant fatality. Car occupant fatalities in the 1978 Fatal Accident Reporting System (FARS) data were divided into those killed in two car crashes and those killed in non-two car crashes. The relationship between car mass and the relative likelihood of an occupant fatality in non-two car crashes was determined by examining the number of fatalities in cars of a given mass driven by drivers of a given age divided by an estimate of the number of registered cars of the same mass having owners of the same age. This involves assuming that owners and drivers are the same people -- clearly an approximation. This and other assumptions were necessary because of data limitations.

The relationship between car mass and the relative likelihood of a fatality in a two car crash was determined using the FARS data and the assumption that when cars of the same mass crash, the relative likelihood of an occupant fatality has the same relationship with mass as determined in the non-two car crash analysis. The overall relationship between car mass on likelihood of an occupant fatality was obtained by taking a weighted average of the non-two car and two car cases. Because occupancy rates depend on car mass, the analysis was performed for drivers only as well as all occupants.

This study finds that the likelihood that a car has an occupant or driver fatality is related to the mass of the car. The relationship found may be illustrated by the comparison of fatality likelihoods in 900 kg and 1800 kg cars shown below: