Restricting a city’s speed limit to 20mph reduced road deaths by almost a quarter and serious injuries by a third, according to new research involving the University of East Anglia.

Accident rates fell even without extra traffic-calming measures and police patrols – making the scheme cost-effective, the study found.
 
The relatively modest cost of replacing speed limit signs not only improved road safety but also enhanced quality of life for residents, researchers say.

Dr Karen Milton, from UEA’s Norwich Medical School, said: “20mph speed limits have been rolled out in many areas of the UK to reduce urban road collisions and casualties.

“We wanted to see how successful these schemes are in terms of reducing road deaths and serious injuries.

The team investigated the impact of 20mph speed limits in Edinburgh and the study is the UK’s most extensive evaluation of 20mph speed limits to date.

Dr Milton said: “We found that prior to the new restrictions, 45 out of 100 cars in the city travelled above 25 mph. One year later, the figure had dropped to 31. 
 
“Average speeds also fell, as did the number of collisions, which fell by 40 per cent. And there were 409 fewer casualties – a drop of 39 per cent.
 
“A breakdown of the casualty figures reveals that fatalities dropped by 23 per cent and serious injuries fell by 33 per cent,” she added.

The research was led by the University of Edinburgh, in collaboration with UEA and the Universities of Cambridge, St Andrews and Bristol, Queen’s University Belfast and walking and cycling charity Sustrans.

The team worked with local and national traffic authorities to gauge the effectiveness of 20mph restrictions introduced by the City of Edinburgh Council in 2016.
 
The new limits were applied in 80 per cent of Edinburgh’s streets in a bid to cut accidents, encourage more walking and cycling and create more pleasant neighbourhoods.
 
The research, which also assessed a smaller scheme in Belfast, found that reducing traffic speed also helps to create better quality environments. 
 
Researchers measured liveability – safety, health, sustainability, education, transport, amenities and living standards – and found it improved in both cities after the introduction of speed restrictions.

Project leader Prof Ruth Jepson, of the University of Edinburgh, said: “The study shows that city-wide speed reductions can reduce collisions and casualties and that they were increasingly accepted by the local community.”
 
The study was funded by the National Institute for Health Research, which has also published the findings.

A separate study involving UEA also shows that most people are supportive of 20mph speed limits. 

Dr Milton said: “Public opinion plays a crucial role in the success or failure of schemes like these that are aimed at improving public health. So we also wanted to see how people reacted to new 20mph speed limit schemes by analysing public opinion on Twitter.”

In collaboration with researchers at the University of Edinburgh and the University of Cambridge, the team analysed more than 24,000 tweets about the new 20mph speed limit policies implemented in Edinburgh and Belfast.

They looked at Tweets from before and after the speed restriction policies were put in place – including whether they were positive, negative or neutral towards the slower speed limit policy.

They expected to find evidence of public backlash against the policies. 

But they found that most people were supportive – with commonly used hashtags focusing on road safety and other potential benefits including a reduction in air pollution.

Dr Milton said: “Overall, the tone of the tweets was positive or neutral towards the implementation of the speed limit policies.

“We found that the majority of the public, or at least those who express views on Twitter, are supportive of 20mph speed limits and think that these schemes should be implemented at scale. 

“This was surprising, as there is a perception among policymakers that there would have been public backlash against the lower speed limits. 

“This is really important because we know that policymakers can feel anxious about public reaction to the implementation of policy changes like lowering speed limits to 20mph. 

“Our research suggests that policymakers should be less concerned about public backlash in response to lower speed limits,” she added.
  
‘Tweeting about Twenty: An analysis of interest, public sentiments and opinion about 20mph speed restrictions in two UK cities’ is published in the journal BMC Public Health.