'Secret' vehicle activated speed limit reminder signs have been used as a means of warning drivers that they are travelling too fast by the activation of a sign triggered when the speed of the vehicle is above a preset level. This report reviews the published results from 13 of these 'secret' sign sites which have been used in the UK, other European countries and the USA. Single 'secret' signs were used at ten sites and a pair of 'secret' signs were used at three of the sites. The main conclusions are that 'secret' vehicle activated speed limit reminder signs can lead to reduced vehicle speeds of about 2 mph at the sign and some of this reduction is maintained some distance downstream. There was an encouraging 40% reduction in accidents but the accident numbers were small. Vandalism was reported as a problem at some non-UK sites. (A)

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