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-co ntrol study. ''Cases'' were 45 vehicles involved in severe crashes in the Adelaide metropolitan area; we determined their pre-crash speeds u sing accident reconstruction techniques. For each case, we measured th e speeds of 10 controls using an amphometer; controls were cars not in volved in crashes that passed through the crash location at the same t ime of day, day of week, and season. We found that the risk of involve ment in a severe crash increased as vehicle speed increased. In partic ular, within 60 km per hour zones, compared with vehicles traveling at about the posted limit, vehicles traveling at 75-84 km per hour had a n odds ratio of 7.8 [95% confidence interval (CI) = 1.4-38.8] for a se vere crash, whereas vehicles with speeds in excess of 84 km per hour h ad an odds ratio of 39.0 (95% CI = 9.3-170.5).