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The Simulation of Rural Travel Times to Quantify the Impact of Lower Speed Levels.

Dutschke, J, Woolley, J E (Peer reviewed)

Speed - Travel Speeds

2010

The number and severity of rural road crashes has been shown to decrease with reduced travelling speed. One method of reducing the travelling speed on rural roads is to reduce the speed limit of those roads. Despite the considerable road safety benefits resulting from reduced speed limits, public opposition to the change exists. One of the main concerns of the public is the perceived increase in travel times associated with a reduction in speed limit.

This study quantifies this increase in travel time on a rural road if the sign posted speed limit of 110 km/h was replaced with the default speed limit of 100 km/h. A Markov simulation model of travel time on an undivided rural road was developed. The model includes factors such as vehicle speed distributions, vehicles travelling in the opposite direction and the ability for vehicles to perform an overtaking manoeuvre. Real data collected on rural roads in South Australia that have had a similar reduction in speed limit are used to define the distribution of speeds of vehicles before and after the change in speed limit.

The model shows that the increase in travel time is less than is first predicted by considering only the allowed speed limit. The model also shows that a driver who desires to maintain a constant travel speed must overtake more often when the speed limit is higher than when it is lower.