The evaluation of a South Australian 40 km/h speed limit

Abstract

At present, Lower Urban Speed Limits (LUSL) have been applied to residential areas most jurisdictions in Australia including parts of Adelaide, South Australia; Tasmania, South East Queensland; areas of New South Wales; Western Australia and the whole of Victoria and the Australian Capital Territory. Given the current high amount of community support that the anticipation and implementation of such schemes enjoy, what is the emerging evidence to indicate if they are effective in terms of various measures? The purpose of LUSL is to reduce speeds, thereby enhancing road safety and improving the amenity value of local streets for residents. What is the magnitude of any benefits the implementations are achieving - do we yet have enough of the pieces of the jigsaw to see what the picture is? What do we mean if we say that the 40km/h limit is working? Do we mean something materially different if we say that the 50km/h limit is working? Although commonly justified on the grounds of road safety, which is readily measurable for a large scheme, the application of LUSL reaches well beyond the call for improved road safety statistics, and an assembly of less well defined factors is involved. Indeed, the support for such schemes could be seen as a cry from the community for some concept of improved amenity for which obtaining a reduction in traffic speed is just a proxy. This consideration is reflected in other approaches in Europe (for example, the MASTER project and Intelligent Speed Adaptation Trials in Sweden and The Netherlands) where a framework for speed limits is evaluated in a more holistic light. This paper seeks to present evidence quantifying the impacts of LUSL in terms of measured speeds and volumes, community attitudes, environmental impacts, travel times and road safety out-comes based on published and emerging evidence. Much of the evidence is based on research into the city-wide Unley 40km/h scheme in Adelaide and computer simulation modelling of the mobility and environmental effects of LUSL.