The report blamed the increased braking and acceleration that "sleeping policemen" generated as cars negotiated them slowly but then speeded up until reaching the next one. Evidence showed that emissions of carbon dioxide had increased in hump areas by as much as 70 per cent, while other pollutants such as nitrogen oxide, hydrocarbons and carbon monoxide, had similarly risen sharply.

While road humps are often successful in achieving speed reductions of 10mph, they remain deeply unpopular with many drivers. The study, by the Transport Research Laboratory, also found that claims made by traffic engineers for the environmental benefits of road humps "appear to be at odds with the findings of surveys of residents".

It cited schemes in Kent, where residents believed that falls in speed and accidents had been achieved "at some cost" in terms of poorer air quality. The RAC welcomed the report, which would "help to restore the balance" in council planners' thinking about the advantages of humps.