Does Reducing Traffic Speed Using Speed Cameras Reduce the Number of Collisions?

Speed management is a policy based on the theory that the number of road traffic collisions is directly related to the speed of traffic. It is claimed that the number of collisions can be reduced simply by reducing vehicle speeds, but does the evidence support this claim where slower speeds have been achieved using speed cameras?

At all camera sites nationally, there were 22% fewer collisions1 in the first three years of camera operations (compared to the three years before), but this figure included the effect of regression to the mean.

Official speed camera reports have either ignored the RTM effect or made complicated estimates of its influence.

Rather than make an estimate, this report takes a new approach of simply excluding RTM. This should obtain the most accurate evaluation of speed cameras to date and should also be far easier to understand.

Key Conclusions

• Speed cameras have not made any impact in preventing road traffic collisions.

• There was no reduction in the number of collisions at fixed (Gatso) camera sites after they were installed and there was no reduction in the number of collisions at mobile camera sites after they started operating.

• Even after compensating for other influences, such as rising traffic volumes and safer vehicle design, the cameras are still not demonstrated to have resulted in any reduction in collision rates. In fact, collision rates increased at mobile speed camera sites following deployment relative to all roads in the Thames Valley area.

• There was found to be no relationship between vehicle speeds and the number of collisions. Reductions in speeds at camera sites (both average and above the speed limit) did not result in any reduction in the number of collisions.