Time and Distance Halo Effects of an Overtly Deployed Mobile Speed Camera

This study investigated time and distance halo effects of mobile overt speed cameras. It was hypothesised that there would be a substantial reduction in vehicle speeds at an operational camera site and that this effect would gradually dissipate over distance from the camera vehicle. It was tentatively predicted that vehicles’ speeds may remain below baseline levels for some time after removal of the speed camera. Electronic data loggers were used to accurately record each vehicle’s speed as it crossed a set of induction loops buried in the road. Loops were spaced every 500 metres for 3.5 kilometres of a 100 kph high quality and high volume road section. Speeds were compared with baseline measures for each data collection point and across points. The first hypothesis was supported. There was a significant 6 kph reduction in mean and a 7 kph reduction in 85th percentile vehicle speeds, and the number of vehicles exceeding the speed limit fell from 53 % to 16 % immediately adjacent to the operational camera. However, these effects had completely disappeared by 1,500 metres downstream. Upstream halos were negligible. There was no time halo effect. In conclusion, this research found that mobile overt speed cameras are effective in reducing vehicle speeds. However, the reduction in speed is only for a relatively short distance and in a one-off trial only occurs while the camera is in operation.