20mph Research Study – Summary and PACTS comment

20mph Research Study – Summary and PACTS comment

The Department for Transport has today (22 November 2018) published the 20mph Research Study by Atkins, AECOM and Professor Mike Maher (UCL).

It assesses the outcomes of introducing 20 mph speed limit schemes (ie reducing speed limits from 30mph to 20mph) in residential areas and town centres. These are generally on a wider scale, but “signs only”, ie without the traffic calming measures of earlier 20mph zones. They were introduced for a variety of transport, community and health reasons.

The study finds:

– Public support for 20mph (signed only) limits but concern about non-compliance
– Minor changes in driven speeds: median speed fell 0.7mph in residential areas and 0.9mph in city centre areas
– Faster drivers reduced speed more: 1.1mph and 1.6mph respectively (85th %ile)
– Road characteristics have a much larger impact on driven speeds than whether the road has a 30mph or 20mph limit
– No significant change in short term in collisions and casualties in the majority of case studies
– The majority of people have not noticed a reduction in the speed of vehicles, and do not perceive there to be fewer vehicles driving at excessive speeds
– Small increase in use of active travel modes; mode shift cannot be determined from data.

Commenting on the study, PACTS Executive Director David Davies said,

“PACTS is pleased to see the 20mph Research Study published. It is the largest, most comprehensive and sophisticated study into the effects of 20mph speed limits to be undertaken in the UK, and possibly anywhere in the world. It has taken several years, at a cost of almost £1 million. Most previous studies have been into single sites, with much smaller budgets and, inevitably, less sophisticated data or analysis.

“In an area where there is sometimes more heat than light, the findings of this study deserve to be taken very seriously. Many local authorities have been waiting for this report before deciding whether and how to implement local schemes.”

He added,

“The changes resulting from 20mph limits are disappointing but not surprising. The study finds that signed-only 20mph limits have very small effects on speed and, surprisingly, no statistically significant effect on casualties in the majority of locations. Local people do not perceive changes and behaviour changes are small.”

“An important finding is that “the speed at which people drive is influenced more by the look and feel of the road, than whether a 20mph or 30mph limit is in place. The DfT will need to take account of this and review its guidance to local authorities on setting local speed limits (Circular 01/2013). They must look again for practical, effective measures to reduce speeds and casualties. The burden should not be left with the local authorities.”

“In 2007, on the basis of 20mph zones but before signed only 20mph limits had been introduced, PACTS recommended that “a default speed limit of 20mph in all built up areas is implemented in  ways that achieve high levels of compliance.” (PACTS: Beyond 2010). The emphasis on compliance was important. Broadly speaking, we still support this recommendation. We expanded on this recently in our response to the consultation on default 20mph limits in Scotland.”


[Comment corrected on 26th November]
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