Road Safety

This study investigated the efficacy of Speed Limiting Locally Operating Warning Signs (SLLOWS) at a number of sites in the Perth metropolitan area. It was found that SLLOWS were successful in reducing vehicle speed at all locations (3-4 km/h on average), although the magnitude of the effect varied across locations. While there was generally a residual (halo) effect after the signs were removed, the magnitude of this effect was small (of the order of 1 km/h). It was also found that the effectiveness of SLLOWS was quite local; speeds reverted to pre-SLLOWS levels by 460 metres downstream of the sign. Finally, there was evidence that deployment of SLLOWS across successive days of the week resulted in a gradual decrease in efficacy (habituation effect). It was concluded that SLLOWS are most useful when they are employed as temporary and local speed moderating tools.