The majority of all traffic accidents occur in the urban environment, where there is a more complex traffic environment and a higher predominance of road users that are more susceptible to injury and fatality in the event of an accident. A relatively straightforward and cost-effective speed management measure, involves reducing speed limits. The relationship between vehicle speed, accident risk and accident outcome severity is well established in traffic safety literature. Research shows that reduced speed is likely to bring about a reduction in average travel speed and have a positive impact on both the number of accidents and accident outcome severity. Other secondary benefits are also derived including: reduced fuel and vehicle operating costs, and significant reductions in vehicle emissions and noise. A key issue surrounding the effects of lowering speed limits in urban and metropolitan areas concerns the impact on mobility and the environment. A hypothesis that is investigated in this literature review is that a reduction in average travel speed brought about by reducing urban speed limits, is only likely to have a marginal impact on travel time. Research tends to support this notion given that average speeds are influenced by many other factors including driver attitudes and preferences; roadway design; forms of traffic regulation at intersections; and prevailing traffic conditions (levels of congestion; weather; etc). Research studies in Australia in relation to the then proposed reduction of the default urban speed limit from 60 to 50 km/h, indicated only minimal impact on individual travel times and large benefits to society as a result of the reduction in crash trauma. Findings following the introduction of the default urban speed limit indicate the overall success of this measure and high level of community support. Recent research suggests that there are still large benefits to be gained by introducing an “across the board” reduction of speed limits to 50 km/h on all types of urban and metropolitan roads that presently have a 60 km/h speed limit. National traffic safety philosophies such as the Swedish 'Vision Zero' recognise the importance of restricting speed to appropriate levels to ensure that there are no serious or fatal injuries. Safety and energy efficiency must be prioritised in order to achieve sustainability in the transport system. As a first step in this direction, the default urban speed limit on residential streets in Stockholm, Sweden has been reduced to 30 km/h. Other European towns are now following this example, and a growing interest can be noticed in Australia for similar speed limits to be introduced in order to meet the designated targets of the national Safe System approach and State and Territorial road safety strategies and action plans. (Author/publisher)
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