Vehicle-activated signs – a large scale evaluation

  • Published: TRL, 2002
  • Authors: M. A. Winnett and A. H. Wheeler
  • Date Added: 07 Feb 2013
  • Last Update: 25 Oct 2016
  • Format: pdf


To assess the impact of vehicle activated signs on driver speed, RTI numbers and driver understanding of signs (including any regional differences).


Vehicle activated signs were installed at 62 trial sites, mainly on rural single carriageway roads. This includes speed limit roundels, bend warnings, junction warnings and safety camera repeater signs. The effectiveness of these installations was assessed through:

  • Review of before and after collection of speed data
  • Review of before and after RTI data

Nearly 450 drivers took part in opinion surveys at three locations in Norfolk and one in Wiltshire. Opinions were sought about the four sign types.

Key Findings:

  • At the speed limit roundel signs, mean speeds of the traffic as a whole were reduced by between 1 mph and 14 mph.

  • The junction and bend warning signs reduced mean speeds by up to 7 mph, and the safety camera repeater signs yielded a reduction of up to 4 mph.

  • There has been a one-third reduction in RTIs across all of the Norfolk sites combined when compared with the number of RTIs that would have been expected without the signs.

  • Safety camera repeater signs appear to give small additional RTI reductions over safety cameras alone.

  • There was overwhelming approval of the signs. Most drivers had made the connection between their own speed and the signs being triggered.


Safety, speed, signs


Robust government document. Focuses on speed management.