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Slowing city traffic cuts road deaths by a quarter, study shows

Published: 04 October 2022

Restricting a city's speed limits to 20mph can reduce road deaths by almost a quarter, NIHR-funded research finds.

Accident rates across Edinburgh fell without extra traffic-calming measures and police patrols. Serious injuries fell by a third too, the study showed.

Replacing speed limit signs improved road safety and enhanced residents’ quality of life. The speed limit scheme was cost-effective, researchers say.

Before 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.

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.

Fatalities dropped by 23 per cent and serious injuries fell by 33 per cent.

Experts at Edinburgh University led the study. It is the UK’s most extensive evaluation of 20mph speed limits so far.

They worked with local and national traffic authorities to gauge the effectiveness of 20mph restrictions. The City of Edinburgh Council introduced the speed limits scheme in 2016.

The scheme applied to 80 per cent of Edinburgh’s streets aiming to cut accidents. It aimed to encourage more walking and cycling and create more pleasant neighbourhoods.

Researchers also assessed a smaller scheme in Belfast. This found reducing traffic speed also helps 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 supportive of the speed limits increased. Their willingness to obey the limits did too.

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 proposed the scheme. He 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 Belfast scheme was restricted to city centre street. It led to a two 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.

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

The NIHR’s Public Health Research (PHR) Programme funded the study.

Read the full report in the journal Public Health Research

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