Western Australia introduced a default 50 km/h general urban speed limit on built-up roads state-wide in December 2001. The model chosen for 50km/h speed limit in Western Australia was to change the default general urban speed limit of 60km/h for built-up areas to 50 km/h by regulation in the Road Traffic Code. This model resulted in the erection of very few actual 50 km/h speed signs.

This study is restricted to the Perth Metropolitan Area where initially 135 sites were surveyed as a baseline study prior to the introduction of the 50 km/h speed limit. 115 of these speed surveys were on roads that were blanketed to the speed limit of 50km/h, and the remainder on roads that preserved to old speed limit of 60 km/h.

This paper provides a quantitative analysis on the results of three speed surveys conducted to measure driver speeds on local roads, one in November 2000 before the introduction of the blanket 50 km/h speed limit in December 2001, and 6 month and 12 month subsequent surveys in June 2002 and November 2002.

Reductions in speed behaviour were assessed in terms of 85th speed percentile, mean speed, and proportion of drivers travelling below 60 km/h on both roads that became 50km/h and roads that remained at 60 km/h.

For roads that became 50 km/h, six months and twelve months after implementation the 85th speed percentile was reduced by 2.6 km/h and 2.0 km/h, respectively. Similarly, for roads that became 50 km/h the mean speed was reduced by 1.87 km/h six months after implementation, and by 1.33 km/h twelve months after implementation.

For roads that remained and were signed at 60 km/h some but not as high reductions in the 85th speed percentile and mean speed were recorded.

The most significant finding resulting from the reduction in speed limit from 50 to 60 km/h on local roads is associated with the change in driving behaviour. There was a decrease of 6.91% of drivers travelling above 60 km/h, 29.30% to 22.38 %, equating to a 24% reduction in percentage of drivers travelling in speeds in excess of 60 km/h.