Overall Fatality Risk to the Public at Large to National Weight Mix of Passenger Cars

This report addresses the question of the effect on the fatality risk to the public at large due to shifts in the weight distributions of passenger cars. For example if the weight of the average passenger car were decreased would fatalities increase? If so, by how much? Past studies have stressed the effects on occupants. But even if heavier cars are safer for their occupants the effect on occupants of other vehicles and pedestrians may be affected differently. In this study fatalities are normalized by registrations in 6 passenger car weight classes. On remultiplying by hypothetical numbers of registered vehicles, fatality projections pertaining to hypothetical fleet mixes can be calculated and compared. When fatalities from various base years are used a range of estimates can be formed in an attempt to examine the basic question. When this program is carried out using the Fatality Analysis Reporting System (FARS) fatal accident data for the years from 1978 to 1987 the estimates indicate that the heavier hypothetical fleet (based on a 1978 mix) is probably safer for the public as a whole than the lighter hypothetical fleet (based on 1987). A quantitative estimate is hard to justify, but our results very roughly suggest a 3% advantage in safety for the heavier fleet. When the results are broken down by accident type they are variable: fatalities in single vehicle accidents would probably be considerably less in the heavier fleet while pedestrian deaths may actually be less for the lighter fleet. Because of the difficulty of the question and the inability to control confounding factors all estimates here must be considered tentative and no great accuracy should be ascribed to them.