Occupant Risk, Partner Risk and Fatality Rate in Frontal Crashes: Estimated Effects of Changing Vehicle Fleet Mass in 15 Years

The effect of vehicle fleet mass on car crash fatalities was estimated, using a new mathematical model to isolate vehicle mass from related factors like size, stiffness and inherent protection. The model was based on fatality risk data, impact speed, fleet mass distribution, and collision probabilities. The fleet mass distribution was changed over 15 years to (a) a homogeneous fleet of 1300 kg cars, (b) a bimodal fleet of 600 and 1600 kg cars, and (c) a 300 kg lighter fleet. Occupant and collision partner fatality risks were estimated for the new fleets. The new fleets were achieved by various strategies, and the average fatality rate was calculated after and during the transition to the new fleet.Occupant fatality risk decreased and partner risk increased as occupants changed to a heavier car. The average fatality rate was 59% higher after the transition to a bimodal fleet mass, and 11 % lower for a homogeneous fleet. A 300 kg lighter fleet had a 8% higher fatality rale, but the strategy influenced the number of fatalities accumulated during the transition. The safest strategy to attain the lighter fleet was to reduce the mass of the heaviest cars first. It was concluded that vehicle fleet mass significantly affects traffic safety. Downsizing consequences can be compensated for by improving inherent vehicle protection or reducing impact speed. The fatalities during downsizing can be limited by choosing an appropriate strategy.