Killing kilos in car accidents: Are external costs of car weight internalised?

- Injury and fatality costs of accidents depend on vehicle weight ratio.
- Doubling vehicle weight ratio leads to tenfold increase in fatal accident probability.
- Non-material external costs of car weight are a few Euros per 100 kg in the Netherlands.
- Non-material external costs are more than internalised in Europe via taxes.

Vehicle weight imposes external costs on a car accident collision partner. In the EU, the external costs through material damage are internalised through obligatory insurance, but this does not hold for the external costs related to injuries and fatalities. We estimate these external costs for the Netherlands for two-vehicle crashes. We find that a 500 kg increase in the weight of the other car increases the probability of a fatality by about 70% over the mean fatality rate, in the same order, but somewhat higher than reported for US. For serious injuries, this effect is about 30%, very close to the results for US. However, because the mean fatality/serious injury rate due to two-vehicle crashes is low in the Netherlands, the annual marginal external costs of car weight are small (€50 per 500 kg) and much smaller than the marginal tax of car weight (up to €800 per 500 kg).