Objective To assess the effectiveness of speed cameras in reducing the numbers of crashes and people injured on the arterial roads of Barcelona, and to assess their long-term effectiveness on the beltway. Methods Time series analyses were performed separately for the arterial roads and the beltway. The stretches of arterial roads encompassing 500 m before and after the location of a speed camera were considered the enforced stretches, the remaining stretches of arterial roads being considered the comparison group. The outcome measures were the numbers of crashes and of people injured. Quasi-Poisson regression models were fitted, controlling for time trend, seasonality and implementation of other road safety measures. Results Both on the enforced and non-enforced arterial road stretches, the risks of crashes and people injured were similar in the two periods. On the beltway, reductions of 30% (95% CI 38% to 20%) and 26% (95% CI 36% to 14%) were observed, respectively. Conclusions Speed cameras do not reduce the numbers of crashes or people injured on the arterial roads of Barcelona. However, they are effective in the short and in the long-term on the beltway. Speed enforcement through fixed speed cameras is thus effective in medium–high-speed roads, although effectiveness could not be generalised to roads with lower speed limits and traffic lights.