The relationship between traffic management, speed and safety in neighbourhoods (1986)

Speed reduction is widely recognised as a necessary condition for improving safety in residential areas. However, there is resistance to the concept of reduced local speeds in Australia, and in particular it has been claimed that there is no evidence of a relationship between speed reduction and accident reduction in local streets. This paper reviews recent research literature to see if this is so. It describes the widespread adoption of 30 or 40 km/h neighbourhood speed limits in many parts of Europe, North America and Australia, and the more recent recognition of the need to support lower speed limits with physical changes to the streets. Evidence for a speed/accident relationship is looked at under three headings: the implications of collisions at certain speeds, the accident effects of specific speed control devices, and the accident effects of area-wide speed reduction schemes. It is concluded that there is sufficient evidence that speed reductions are accompanied by accident reductions. Whether or not this amounts to 'proof', and whether speed reduction causes an accident reduction rather than being incidental to it, is still open to debate. However, the paper concludes that arguments over causation are immaterial to the practitioner. The possibility of exploring the speed/accident relationship in local streets by studying the accident process (e.g. using conflict studies) is foreshadowed.