The impact of lowered speed limits in urban areas

The increasing and sometimes conflicting goals of the transport system such as overall
performance and efficiency, mobility, safety and environmental sustainability, have become
increasingly difficult to achieve without major investments in the road infrastructure. New and
affordable ways of reducing levels of road trauma that have a minimal impact on mobility are
keenly sought by the Australian Government, federal and state road authorities and by society at
large. This particular literature study addresses a number of the issues surrounding a lowering of
speed limits in urban areas; a relatively low-cost measure that is likely to have a positive impact on
safety but also a negative impact of some magnitude on mobilty.
The relationship between vehicle speed and accident outcome severity is well established. A major
study conducted by the OECD and the ECMT in 1996 concluded that speeding is the number
one road safety problem in most countries around the world, and that reductions in average
speeds of approximately 5 per cent would yield a reduction in fatalities by as much as 20 per cent
(OECD/ECMT , 2006). Research also indicates that even modest speed reductions can prevent
the occurrence of collisions and significantly reduce the outcomes of those crashes that do occur;
particularly those that involve vulnerable road-users who are more predominant in the urban
environment (e.g. Kloeden, et al. 1997, 2001; Elvik, 2002; G?rder, 2004; Racioppi et al. 2004).
In addition to safety, there are other potential benefits to be gained by speed limit reductions in
urban areas. Those suggested in the literature include an increase in traffic flow and consequent
reduction in congestion and delays, particularly where the roads are functioning at near capacity.
Further, reductions in speed bring about a reduction in vehicle operating costs with less wear and
greater energy (fuel) efficiency, and less pollution and noise (see e.g. Carlsson, 1997; Kallberg and
Toivanen, 1998; Cameron, 2000; Elvik and Vaa, 2004).