Do traffic signals at roundabouts save lives?

  • Published: Transport for London, 2005
  • Authors: Transport for London
  • Date Added: 07 Feb 2013
  • Last Update: 16 May 2014
  • Format: pdf


A study to measure the effect of traffic signals at roundabouts on safety.


The study analysed the casualty data at selected roundabouts ‘before’ and ‘after’ signal control was implemented. A total of twenty sites were selected, equally divided between at grade (standard) and grade separated junctions. For each of the twenty sites the casualty data was obtained for the 36 month period ‘before’ and for the same length of time ‘after’ the date of signal implementation. When signals were implemented as part time operation, the ‘before’ and ‘after’ data were re-examined and casualty data analysed for the specific times of operation.

Key Findings:

  • Signal control is usually installed at a roundabout to improve traffic capacity and to balance a junction at high flows. Supporting reasons may include reducing RTIs or provide surface level crossings for pedestrians. With the increasing vehicle demand, signal control at roundabouts is becoming a common measure in traffic management.

  • At standard roundabouts there was a good decrease in total RTIs after the installation of signals of 107 (28 per cent), which is an average reduction of 10.7 RTIs at each site for a 36 month period. This is a saving of just over 3.5 RTIs per site each year.

  • There were significant casualty reductions in most categories. The largest was in RTIs involving a pedal cycle which reduced by 56 RTIs (80 per cent).


Signals, safety, RTIs, roundabouts


Robust government document. However, the focus is on signals, rather than signs and markings.