Review of traffic calming schemes in 20 mph zones

  • Published: TRL, 1996
  • Authors: D.C. Webster and A.M. Mackie
  • Date Added: 05 Feb 2013
  • Last Update: 04 Jul 2014
  • Format: html

Objectives:

To review the effect of traffic calming using 20 mph zones.

Methodology:

A literature review was undertaken to assess the impact of six 20 mph zones around the UK.

Key Findings:

  • The most quoted reason for applying for an authorisation of a 20 mph zone was RTI reduction indicating that safety is the main justification for implementing the schemes.

  • Most zones were in predominantly residential areas, with about 10 per cent being in town or city centres.

  • The average size of the zones was 0.28 sq.km.

  • The most common traffic calming measures used in 20 mph zones were round topped and flat topped humps and speed tables. Speed cushions were used in some more recent schemes.

  • The 20 mph zones have been successful in substantially reducing speeds and RTIs in the areas where they have been applied.

  • Child pedestrian and child cyclist RTIs fell by 70 and 48 per cent respectively after scheme installation giving an overall reduction of 67 per cent for all child RTIs.

  • The reduction in RTIs for all cyclists was 29 per cent.

  • Speed results show that the average speed at a calming measure was 13.2 mph while between measures it rose to 17.8 mph.

  • This indicates that the calming measures are effective at enforcing the 20 mph limit.

  • There was a 6.2 per cent reduction in RTIs for every 1 mph reduction in vehicle speed.

  • RTI migration into surrounding areas was not found to be a problem but care should still be taken in design of schemes to prevent traffic transferring to unsuitable routes.

Themes:

Speed reduction, RTI reduction, 20 mph zones, traffic calming

Comments:

Good example of reductions in RTIs numbers resulting from speed reductions.

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