Traffic calming using 20 mph zones was introduced in the UK in January 1991. The paper reviews the design and effectiveness of the schemes which Local Highway Authorities have installed. By the end of 1992, thirty-six zones had been given approval for temporary status, and four of the authorisations had been made permanent. The most quoted reason for applying for a 20 mph zone was accident reduction, but high traffic speeds and "rat-runs" causing unsuitable use by through-traffic were also seen as problems. The Department of Transport encourages local authorities to make the 20 mph zones part of area-wide safety management schemes to try to avoid accident migration, but generally schemes were quite small, comprising only a very limited network of roads or occasionally only one road. There was an average of about 25 measures per scheme, usually flat-topped road humps. There is a requirement that such physical engineering measures be used to ensure compliance with the 20 mph limit. Early indications of effects on accidents are encouraging. The overall reduction is 65 per cent with no evidence of increase in the surrounding untreated areas. (A)
Abstract