Vehicle speed and risk of a severe crash.

We examined the relation between the speed of passenger cars and risk of involvement in a severe crash, in an urban setting, using a case-control study. "Cases" were 45 vehicles involved in severe crashes in the Adelaide metropolitan area; we determined their pre-crash speeds using accident reconstruction techniques. For each case, we measured the speeds of 10 controls using an amphometer; controls were cars not involved in crashes that passed through the crash location at the same time of day, day of week, and season. We found that the risk of involvement in a severe crash increased as vehicle speed increased. In particular, within 60 km per hour zones, compared with vehicles traveling at about the posted limit, vehicles traveling at 75-84 km per hour had an odds ratio of 7.8 [95% confidence interval (CI) = 1.4-38.8] for a severe crash, whereas vehicles with speeds in excess of 84 km per hour had an odds ratio of 39.0 (95% CI = 9.3-170.5).