Bristol’s 20mph zones have prevented more than four fatalities a year, reduced injuries and saved the NHS an estimated annual £15m, according to a recent report.

The in-depth study by UWE Bristol finds restrictions on traffic speed in residential areas across the city have led to a drop in the number of motor-related casualties and also helped boost walking or cycling.

Public health experts say the evaluation provides “vital evidence” that 20mph zones save lives, make roads safer and argue they should be held up as an example to be followed in other towns and cities.

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Research conducted over two and a half years looked at speed data from more than 36 million vehicle observations and found that the measures saved 4.53 lives, prevented 11.3 serious injuries and 159.3 slight injuries per year and led to an average speed reduction of 2.7mph.

The data was released on Tuesday, February 13, the day Bristol City Council announced it will be carrying out a review of the zones this spring to look at the effectiveness of lower speed limits in certain areas.

Speaking at a full council meeting in January, Steve Jones, Conservative councillor for Stockwood, raised questions about the effectiveness of the 20mph zones. Calls were also made by both Labour and Tory councillors in 2014 to halt the roll-out of the speed restrictions.

The council says it will be consulting with residents and councillors to determine how well 20mph zones are working in individual neighbourhoods and assessing if anything can be done better.

Commenting on the findings of UWE’s study, Dr Suzanne Audrey, senior research fellow in public health at the University of Bristol and co-director of the Supporting Healthy Inclusive Neighbourhood Environments Health Integration Team (SHINE) said: “This is vital evidence that 20mph limits are effective – both in preventing casualties and encouraging healthy behaviour in the neighbourhoods where they’re brought in.

“If more people feel they can walk and cycle around residential areas rather than get in their cars, this brings enormous benefits to health, community cohesion and air quality.”

The report’s authors accept that there is a degree of cynicism around 20mph zones and, in particular, lack of police enforcement and non-compliance of motorists – but the study saw a reduction in speed on 100 of the 106 roads surveyed in Bristol.

Even if drivers do not slow to 20mph, their average speed drops by a “significant amount”.

Rod King MBE, founder and campaign director of 20’s Plenty for Us group welcomed the findings, saying: “Default 20mph limits are an important foundation for making our places better places to be.

“They are affordable, reduce speeds, reduce casualties and make our places friendlier for walking and cycling. This study shows that the public health benefits are significant.

“It is now time to standardise on a 20mph default at national level to increase benefits, reduce implementation costs and maximise the excellent return on public funds.”

The research took a holistic, public health approach to evaluation and figures for the reduction in casualties are based on the Department of Transport’s formula.

The report’s lead author Dr Paul Pilkington, a senior lecturer in public health at UWE, said: “It offers a model for other towns and cities across the world, who are seeking to reduce traffic speeds, cut road traffic casualties, and promote community health and wellbeing through road danger reduction.”

Leader of the Green group of councillors, Eleanor Combley welcomed the report, saying: “With these amazing impacts, it’s no wonder a clear majority of people in Bristol support 20mph, as demonstrated repeatedly in surveys conducted by the council and UWE.”

She voiced concerns about the possibility that the council could roll back the 20mph zones and called on mayor Marvin Rees to commit to keeping them.

Combley added: “Having large, unbroken, safe areas is what has made Bristol’s 20mph more successful than other cities. Breaking those areas up by increasing the speed on some roads cutting through them will put all these benefits at risk.”

The findings of UWE’s report will feed into the council’s review process.

Mhairi Threlfall, the cabinet member for transport, said: “What we need to establish is where 20mph appears to be working and where it may not be as effective. The statistics from this report give us a good indication of that.

“However, it is important that we have a clear idea of how 20mph is affecting individual areas.”

The review will begin in spring 2018 and is expected to take place over an eight week consultation period. No decisions have yet been made on which roads will be included within the review.

Read more: Council calls for halt to 20mph speed limits