Relative risk of driver death in a two-car crash is estimated as a function of the mass of each car using driver and pedestrian fatalities coded in the Fatal Accident Reporting System (FARS). This study uses model-year 1980 and later cars. A three parameter analytical function fitted to the estimated risks generated the following findings. When a driver transfers to a lighter car that driver's risk increases, while the other involved driver's risk declines. When cars of the same mass crash into each other, fatality risk is lower when both cars are heavier. If one of the equal-mass cars is replaced by another lighter by any amount, the increase in fatality risk to the driver in the car of reduced mass exceeds the reduction in fatality risk for the driver in the unchanged car (that is, net risk increases). Net driver fatality risk or net fatalities in a car population increases, provided that: (1) any car in the population is replaced by a lighter one, or (2) one population of identical cars is replaced by another population of lighter identical cars. Making all cars in a population of uniform mass while keeping the average mass constant increases net fatality risk.
Samenvatting