Are 20mph limits safer? New report questions impact of lower limit on road safety

New study finds ‘no significant differences’ between routes with 20mph limits and those with 30mph or 40mph limits

Lowering urban speed limits to 20mph does not significantly improve road safety, a new report suggests.

Analysis of data from before and after the lower limit was introduced on 76 roads in central Belfast in 2016 found “little impact on long-term outcomes” in the city. Comparisons with streets in the surrounding area and elsewhere in Northern Ireland where limits remained 30pmh or 40mph showed there were “no statistically significant differences” in terms of the number of crashes, casualty rates or average traffic speed, according to the report in the Journal of Epidemiology and Community Health.

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However, the report’s authors, including Professor Ruth Hunter of Queen’s University Belfast and Dr Ruth Jepson of the University of Edinburgh, said that lower limits could be combined with other measures to discourage car use and put “people before cars”. They also noted that their study was smaller in scale than other research into the subject.

The report suggested that driver training, CCTV and police communications could combine with 20mph limits to “facilitate an ambitious culture change that shifts populations away from the car-dominant paradigm”. It added that reducing speed limits is “not simply a road-safety intervention” but can be “part of the fundamental reset of the way we choose our life priorities – people before cars”.

There are growing moves around the UK to introduce 20mph limits in urban areas in an effort to reduce casualties and pollution. Some individual councils in England and Scotland have already implemented them and the Welsh Government has committed to lowering speed limits to 20mph on all roads where cars mix with pedestrians and cyclists by September 2023. The Scottish Government also wants to have a 20mph limit on “all appropriate roads in built up areas” by 2025.

Previous studies on 20mph limits have suggested that reducing the limit helped reduce the number and severity of casualties. A 2018 report from Bristol showed that 20mph limits in the city reduced average speeds by 2.7mph and said that casualty figures fell during the period covered by the study. It noted that “it is not possible to state with certainty that the reductions in casualties are due to the introduction of the 20mph limits” but said evidence from other studies meant a “plausible association” between the lower speeds and casualties.

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More recent data from Edinburgh also showed that collisions fell by a third in the two years after speed limits were dropped from 30mph to 20mph in the city centre. And a 2018 report in the Journal of Transport & Health suggested that 20mph zones with traffic calming measures were effective in reducing collisions.

However, a Department for Transport study in 2018 said there “not enough evidence to conclude that that there has been a significant change in collisions and casualties following the introduction of 20mph limits in residential areas”, and suggested speeds had dropped by just 0.7mph in areas where the limit was cut from 30mph o 20mph.

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RAC road safety spokesman Simon Williams said: “The findings of this study are surprising as they appear to suggest that drivers on 20mph roads in Belfast hardly slowed down at all, despite the lower speed limit, which is at odds with other reports. It seems there is a serious problem with compliance as we would expect that even without enforcement average speeds would drop.

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“Consequently, the study may demonstrate a need for councils to find other ways to get drivers to slow down, whether that’s through enforcement or modifying road design with traffic islands, well-designed speed humps or chicanes.”

Mary Williams, chief executive of road safety charity Brake, said 20mph limits were “life-saving” for pedestrians and cyclists. She commented: “It is a matter of physics. At speeds of 20mph or less, drivers have significantly more chance to spot hazards and stop in time. The difference between a 20mph limit and a 30mph limit is a doubled stopping distance.”