In rural areas, higher speed limits will generally result in people travelling faster and a reduction in travel time. However, time savings are only significant over long distances. For example, raising the speed limit from 100 km/h to 110 km/h will save 5.5 minutes if you are travelling 100 km (assuming there are no delays). In built up areas, time savings from higher speed limits are hard to achieve due to the stop start nature of the journey and tend to be negligible for short journeys. In some circumstances, lower travel speeds may reduce travel times by minimising flow breakdown. Flow breakdown is disruption to the steady flow of vehicles at uniform speed. It occurs when traffic volumes are close to the capacity of the road and any erratic or unexpected driving manoeuvres, such as lane changing or sudden breaking, leads to stop start driving conditions. Austroads’ report titled, “Impact of lower speed limits for road safety on network operations” (AP-T143/10) presents a review of literature on the effect of reduced speed limits on network operations. It concluded that reduced speed limits would have greatest effect on travel time along roads with minimal congestion and number of intersections. It also concluded that, for arterial roads within urban environments, reduced speed limits would have no appreciable effect during times of congestion. So, broadly speaking, higher speed limits can reduce travel time, but only over long distances.
