Impact of lower speed limits for road safety on network operations

The project consolidated the available research on the impacts of lower speed limits on network operations. It extended this knowledge to bridge an identified knowledge gap regarding urban arterial roads by modelling the impacts of a substantial speed limit reduction on various network performance indicators, including travel time, mean speeds, air pollutant emissions, fuel use and casualty crashes during peak traffic periods. Total social cost impacts of speed limit reductions were also estimated. On the basis of the literature review, it can be concluded that speed limit reductions would have the strongest impact on network operations (increased travel time, lower speeds, reduced casualty crashes) on roads with low levels of congestion and with few intersections. On the basis of the modelling, it can be concluded that speed limit reductions would have no appreciable effect on urban arterials during times of congestion. These findings should be taken into account when considering application of lower speed limits for road safety reasons. The methodology developed under this project may be applied by road authorities to provide evidence-based evaluation of speed limit changes.