Changes to speed limits and crash outcome – Great Western Highway case study

Numerous studies, across many countries, have evaluated the outcomes of changes in prevailing speed limits. Fatalities and injuries have fallen when speed limits have been lowered and have increased when speed limits have been raised. Models of speed changes allow a prediction of the safety benefits of a speed limit reduction. This paper studies the relationship between changes in the posted speed limits and crash history for a section of the Great Western Highway in rural NSW, where the speed limit was reduced from 110 km/h to 100 km/h. This study showed that travel speeds are reduced following a speed limit reduction, with clear safety benefits (26.7% reduction in casualty crashes) consistent with power model. Use of modelling in crash prediction depends, however, on a reasonably accurate estimate of the speed reduction expected.