Road Speed Limits: Economic Effects of Allowing more Flexibility

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On rural roads, the speed that a driver chooses will affect their travel time, vehicle operating costs and crash costs. Recent Austroads valuations of these costs are used in this paper to estimate the total economic cost to society of travelling at different speeds on roads with different crash rates. Critical in this analysis is estimating the change in crash cost that would result from a change in vehicle speeds. This report assumes a 10 km/h change in average speeds produces a 30% change in crash costs based on international evidence. For a hypothetical mix of cars and trucks on a rural road with an average crash cost, the speed that produces the lowest total of travel time cost, vehicle operating cost and crash cost is between 90 and 100 km/h. On a hypothetical road with a low crash rate (and a crash cost one quarter of the average), the optimum speed is between 110 and 120 km/h. Achieving different speed regimes is not just a matter of changing the posted speed limit. The paper concludes by suggesting that ITS technology could be used to vary and manage speeds.

  • Road Speed Limits: Economic Effects of Allowing more Flexibility