Researchers from Queen’s University Belfast, the Universities of Edinburgh, Cambridge, East Anglia, St Andrews and Bristol collaborated with walking and cycling charity Sustrans in the study.

The Belfast scheme, which was restricted to city centre streets, led to a 2 per cent drop in casualties and collisions, and minor reductions. 

Researchers say results reflect the scheme’s narrower reach and its implementation in an area where traffic speeds were already low prior to the trial – on average less than 20mph.

Professor Ruth Hunter, from Queen’s University, said: “City-wide expansion of 20mph limits in Belfast would likely lead to further reductions in casualties, collisions and other important public health outcomes.”

Accident rates across Edinburgh 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.

Prior to the new restrictions, 45 out of 100 cars in Edinburgh travelled above 25 mph – one year later, the figure had dropped to 31.

Average speeds on affected roads also fell, according to the study – the UK’s most extensive evaluation of 20mph speed limits so far.

Researchers say the number of collisions in one year fell by 40 per cent to 367, 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. 

Researchers 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 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. 

One year after implementation, the number of people who were supportive of the speed limits increased, as did their willingness to obey the limits. 

Researchers interviewed residents to assess the overall impact. They also examined official records and data, and studied how decisions were reached and regulations were enforced.

Project leader Professor 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.”

Edinburgh City Council’s former transport and environment convener, Lesley Hinds – who proposed the scheme – said: “It is encouraging to see the reduction in deaths, accidents and speeds. 

“It is also good there is an increase in support from the public in residential streets as well as in the city centre.”

The study was funded by the National Institute for Health Research, which has also published the findings.

Link to NIHR Report. https://www.journalslibrary.nihr.ac.uk/phr/XAZI9445/#/abstract

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