Interim evaluation of the implementation of 20 mph speed limits in Portsmouth

This document summarises the findings of an interim evaluation of the impact of a 20 mph speed limit scheme which used signing alone to cover 94 per cent of Portsmouth's residential roads. It reports on monitored changes in traffic speeds and road casualties comparing data for 'before' and 'after' scheme implementation. The background to the scheme and the involvement of a wide range of stakeholders are described. The area was divided into 6 sectors. The average speed across the sectors was found to be 0.9 mph lower than before the speed limit was imposed. Where speeds had been higher than 24 mph the average reduction was 7 mph although some average speeds were still above 24 mph. Total accident reduction was 13 per cent but there were wide variations between sectors. The results of the project were compared with the effect of 20 mph zones implemented in a similar scheme in Hull. It is concluded that the speed reduction achieved is less than in a 20 mph zone as speeds are already low, roads with higher average speeds did benefit and that on the limited evidence available casualty reductions were not demonstrated.

  • Corporate Authors:


  • Publication Date: 2009


  • English

Media Info

  • Pagination: 4p

Subject/Index Terms

Filing Info

  • Accession Number: 01151439
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Mar 1 2010 8:27AM