The costs and benefits of speeding
Various commentators (notably including Tom Nankivell) have raised the issue of the costs and benefits of current speed limits and of more or less rigorous enforcement of those limits, and have asked that I consider costs as well as benefits of enforcing speed limits. I’m going to give some back-of-the-envelope numbers in an effort to inform the debate. The total economic cost of road crashes in Australia is at least $20 billion per year (This BTRE study gives direct costs of $15 billion for 1996, but an analysis based on economic welfare theory would include substantial costs (for example, in the BTRE analysis, there is zero cost in the case when a retired person is killed instantly in a crash).
The main cost of speeding restrictions is that of additional travel time. Assuming that complete abolition of speed limits would reduce average travel time by 20 per cent (very generous, since a lot of travel is on congested roads where the speed limit isn’t a constraint), and taking the BTRE estimate that value of reduced travel time is $10/hour, the total travel time cost of speed limits is around $5 billion per year.
It’s pretty obvious that abolishing speed limits altogether would raise road death rates by more than 25 per cent (the NT is the only jurisdiction in Australia without speed limits and its death rates are several times higher than in the rest of the country, though there are other factors as well as speed in play). The same argument applies, essentially pro-rata to more limited relaxation of limits. It gets harder to justify further reductions as the limit gets lower, but I’d say there’s a pretty good case for more general application of 50k limits in suburban areas to cover everything except main roads.
Turning to other costs and benefits, the survey evidence I’ve seen suggests that the disutility imposed by speeders on other drivers (particularly through tailgating, forcing their way back into traffic etc) is at least as large as any psychic benefits gained by the speeders.
Finally, on the enforcement issue, one point that has secured a lot of agreement is that variance in speed is as much of a problem as speed itself. On the assumption that there are a large number of law-abiding drivers travelling at or near the legal limit, and vehicles such as trucks that cannot safely exceed the limit, this provides a strong argument for both rigorous enforcement and tight tolerances. It also implies that excessively slow driving should be penalised.