Objectives: We assessed the effectiveness of speed cameras on Barcelona's beltway in reducing the numbers of road collisions and injuries and the number of vehicles involved in collisions.
Methods: We designed a time-series study with a comparison group to assess the effects of the speed cameras. The "intervention group" was the beltway, and the comparison group consisted of arterial roads on which no fixed speed cameras had been installed. The outcome measures were number of road collisions, number of people injured, and number of vehicles involved in collisions. We fit the data to Poisson regression models that were adjusted according to trends and seasonality.
Results: The relative risk (RR) of a road collision occurring on the beltway after (vs before) installation of speed cameras was 0.73 (95% confidence interval [CI]=0.63, 0.85). This protective effect was greater during weekend periods. No differences were observed for arterial roads (RR=0.99; 95% CI=0.90, 1.10). Attributable fraction estimates for the 2 years of the study intervention showed 364 collisions prevented, 507 fewer people injured, and 789 fewer vehicles involved in collisions.
Conclusions: Speed cameras installed in an urban setting are effective in reducing the numbers of road collisions and, consequently, the numbers of injured people and vehicles involved in collisions.