Exploration of Appropriate Intervals for Locating Speed Limit Signs

The present study was intended to provide data to support guidance on appropriate spacing of speed limit signs. A driving simulator was used to measure driver’s speed in response to speed limit sign spacings of one, two, or four minutes travel at the posted speed in an urban setting, and three, six, or nine minutes travel at the posted speed in a rural setting. The results show that the spacing between signs has negligible effects on drivers’ speed or speed limit compliance. The primary finding of this study was that 20 percent of all speed limit signs were not perceived. This result suggests that measures to ensure that speed limit signs are seen are critical to their effectiveness. Close repetition of signs, speed reduction warning signs, and colored borders on speed limit signs have been suggested as methods to ensure motorists become aware of the posted speed. Research is needed to assess the effectiveness of these measures and to provide guidance on how they should be implemented.