20mph speed limits in Bristol save lives, reduce injuries and save the NHS £15 million a year

The 20mph speed limits in residential areas in Bristol have prevented more than four fatal casualties a year, as well as 11 serious and 159 slight injuries, an evaluation by the University of the West of England (UWE Bristol) has found. This is estimated to have saved the NHS £15 million a year, using the Department for Transport’s value for prevention of casualties formula.

The research also showed average speeds have dropped by 2.7mph in the areas with 20mph limits – a larger reduction than other cities have seen. Speeds reduced in 100 of the 106 roads that the researchers looked at. Critics of 20mph limits often cite a lack of compliance as an argument against the schemes. However, this evidence suggests that, overall, while drivers may not be driving below 20mph, they have reduced their speeds by a significant amount.

The study looked at individual speed data from more than 36 million vehicle observations and controlled for other factors that might affect changes in traffic speeds, representing a more sophisticated analysis than previous studies of 20mph limits.

Walking and cycling across Bristol has increased, both among children travelling to school and adults travelling to work. This was one of the key hopes for introducing the limits, as safer neighbourhoods make it easier for people to make active travel choices.

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), welcomed the findings, saying:

“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.

“SHINE – the Health Integration Team focused on healthy urban environments – is pushing for measures that make our neighbourhoods more pedestrian and cyclist friendly. This report demonstrates that 20mph limits do just that.”

YouGov surveys have found a clear majority of the public support 20mph speed limits in Bristol. The latest 2017 survey revealed 62 per cent of Bristolians support the limits on residential roads, and 72 per cent support them on busy streets. These levels are very similar to the rest of the UK. But there is concern about compliance and behaviour of other drivers, as the report authors point out:

“There is cynicism in Bristol (and across Great Britain) about lack of police enforcement of 20mph limits and a lack of compliance from “other drivers”. There is also an apparent “pluralistic ignorance” effect – a widespread belief that there is little support for 20mph limits, whereas the reality is that the opposite is true. These beliefs probably contribute to the claimed lack of compliance from Bristol drivers (40 per cent may not stick to 20mph limits), with levels worse than for Great Britain as a whole (29 per cent). In 2017, Bristol residents adopted both positive and negative extremes compared to Great Britain generally.”

Dr Audrey said:

“Repeated surveys have found that the majority of the public are supportive of 20mph limits. The UWE research shows that people are generally driving more slowly. Now we have reliable local evidence that shows the measures are having the effects that policymakers were hoping for when they first implemented them. Hopefully the message will get out there that 20mph limits are a force for good in our city – and could offer the same benefits to other parts of the UK.”

The report authors agree. They see the Bristol scheme as a model for other cities and towns to follow, to reduce traffic speeds, cut road traffic casualties, and promote community health and wellbeing.