A major contributory factor in road traffic accidents is excessive speed. Automatic speed warning signs, which are triggered when drivers exceed preset threshold speeds, might make drivers more aware of their own excess speed and the speed limit of the road. Such a warning sign became operational in Scole in Norfolk in November 1992, resulting in significant reductions in mean vehicle speeds. This article concerns the installation by Norfolk County Council of a similar interactive sign on one inbound approach at six rural villages in Norfolk in May 1995. Speeds were monitored at the warning signs and in the centre of the villages before, and at one month, six and 12 months after, the signs were installed. The analysis includes the development of a regression model for predicting the likely effects of installing such signs at other similar sites. Overall, the mean speeds for inbound traffic at the signs reduced substantially after installation and these reductions have been largely maintained over the following 12 months. The equivalent 85th percentile speeds have also shown a sustained reduction. There was some evidence that the fastest inbound drivers were affected most. There was a smaller effect on inbound traffic in the centre of the villages. Details of later sign installations at two further villages in Norfolk are also given.
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