Review of 20 mph zones in London Boroughs

Traffic calming measures are used to reduce vehicle speeds and consequently accidents. A national study by TRL of two hundred 20 mph zones in 1996 showed that 20 mph zones were very successful. TRL was commissioned by the London Accident Analysis Unit (LAAU) in October 2002 to review the performance of 20 mph zones in London. Detailed information was received for 115 zones and the main measures used were road humps, raised junctions and speed cushions. On average the measures were spaced between 50 and 95 metres apart. Most of the zones were residential areas with over half containing schools or colleges. Seventy-eight of the zones which had a sufficiently long ‘after’ period, of at least a year, were used in the accident analysis. The results of the study are very encouraging suggesting large accident and casualty savings.