Recently Ms. White examined the econometrics of traffic accidents in an attempt to measure the benefits and costs of changing the number of light trucks on the road. Professor White's paper can be downloaded from http://econ.ucsd.edu/miwhite/suv-revision.pdf.
Ms. White notes that changing average vehicle size could, in principle, increase or decrease the cost of accidents.
Suppose the cost of a small vehicle-large vehicle collision is $50, the cost of a small vehicle/small vehicle collision is $45, and the cost of a large vehicle-large vehicle collision is $40.
If all vehicles are small, and there are 10 accidents a year, the total cost of the accidents is $450. But if 10 percent of the small vehicles are replaced by large ones, the average cost of collisions becomes $458.50, since more collisions will be between large and small vehicles. On the other hand, if 60 percent of the vehicles on the road are large, the average cost of a collision is only $456, since more collisions are between large vehicles.
Think about a safety-conscious soccer mom choosing a vehicle. If there are mostly small cars in her town, she can reduce the risk to her and her family in the event of a collision by buying an S.U.V.
The unfortunate side effect is that the large S.U.V. would cause significant damage to smaller cars if she was involved in an accident.
The laudable private incentive to choose a safe vehicle could, perversely, reduce overall safety.
In addition, Ms. White finds that people involved in single-vehicle crashes are more likely to be killed or seriously injured if they are in S.U.V.'s or light trucks rather than cars. This may be a result of the increased likelihood of rollovers.
