Published: 1st JANUARY 2019

Our position on 20 mph speed limits in built-up areas

We strongly support a 20 mph default speed limit in all built-up areas across the UK to make everyone’s journey safer.

20pmh sign on an urban street

This policy position was published by Sustrans in January 2019.


  • The majority of pedestrian and cycling injuries occur in built-up areas as a result of collisions with motor vehicles. Increased vehicle speed also increases the chance of being injured and the severity of injuries resulting from a collision.

  • Many local authorities in the UK have implemented 20 mph speed limits to improve road safety. However, the situation is still a postcode lottery and most people live in built-up areas where 30 mph is still normal.

  • Sustrans believes speed limits should be set with a presumption in favour of safety rather than speed. We strongly support a UK-wide 20 mph default speed limit in built-up areas to make everyone’s journey safer. 20 mph can also help to reduce the perceived dominance of motor vehicles on our streets helping to create streets and places that are more attractive for people to walk, cycle and enjoy.


Speed limits are designed with the intention of keeping people safe, especially more vulnerable road users. In 1934 the UK introduced a 30 mph speed limit in built-up areas, however since this time the amount of motor traffic on our streets has risen dramatically.

Today the majority of pedestrian casualties occur in built-up areas, and people cycling are also vulnerable with over half of cyclist deaths and most injuries occurring on urban roads1,2.

Higher speeds significantly increase the chance of being injured in a collision. Research consistently demonstrates the risk of pedestrians being struck by cars increases at higher speeds, as does the severity of the impact3. A review of studies suggests the risk of pedestrian fatality is approximately 1.5% at 20mph when hit by a vehicle in comparison to 8% at 30mph4. In other words, the chance of being killed is five times higher if hit at 30mph in comparison to 20mph.

Public Health Wales believes that lowering the default speed limit to 20mph could have substantial Public Health benefits5. Public Health Wales suggested that a default 20mph speed limit could save around six lives per year, prevent 1,000 casualties and save the Welsh economy £50 million6.

This evidence has led to many local authorities choosing to reduce speed limits for many roads in built-up areas to 20 mph. Whilst no government data exists, some estimates suggest around 25% of the UK population is now said to have a 20 mph limit on the streets where they live, learn, shop or work7.

Where studies have taken place there is strong evidence that 20 mph speed limits are effective in making the roads safer for children and young people, and increasing walking and cycling. In Bristol, a report by the University of the West of England, found area-wide 20 mph pilots saw increases of 12% in walking and cycling levels and 35% of people felt safer. In the city, 20 mph streets have 40% fewer road casualties with the greatest reduction found in the numbers of young children killed and injured8.

In addition to 20 mph speed limits, 20mph zones may be used. 20mph zones are designed to be "self-enforcing" due to traffic calming measures which are introduced along with the change in the speed limit, such as road narrowing, planting and other measures to both physically and visually reinforce the need to drive more slowly. A London study published in the BMJ found the introduction of the 20 mph zones was associated with a reduction in casualties and collisions of around 40% and the numbers of killed or seriously injured children were reduced by half9.

Globally, 20 mph or 30 kph limits are seen as best practice and are strongly recommended by the World Health Organization (WHO), the Organisation for Economic Co-operation and Development (OECD) and the EU Transport and Tourism Committee.

What we think

We strongly support a 20 mph default speed limit in all built-up areas across the UK to make everyone’s journey safer.

Slower traffic speeds where we go about our daily lives are a key element in improving actual and perceived road safety – and to signal a shift in government priorities and its approach to road safety. 

This would be especially beneficial for the most vulnerable people in society, including children and people with disabilities. Slower speeds emphasise the dual function of our streets - to improve both place and movement, and incorporating the movement of vehicles in a safer, more inclusive manner.

Studies suggest that 20mph streets can encourage more people to walk and cycle. Evidence from 20mph pilots in Scotland indicates that when people feel safer, they are more likely to walk and cycle. Monitoring before and after the rollout of 20mph across the South Edinburgh showed an increase of 7% for journeys on foot, an increase of 5% for journeys by bike and a decrease of 3% for journeys by car10.

Slowing traffic speeds also improves public health by allowing people to be more active, significantly reducing the burden on our health system. A reduction in the national default speed limit in built-up areas from 30 mph to 20 mph would ensure that the majority of journeys walked or cycled could be made along streets with slower speeds. Furthermore, in some cases we would support 10 or 15 mph speed limits where appropriate, for example people prioritised streets in areas of high footfall and where cars are seen as guests11.

Whilst studies suggest people do drive more slowly on 20 mph streets than corresponding 30 mph streets, motorists do not always observe the present official speed limits. Making 20 mph universal for all areas should go a long way to changing UK driving habits in urban areas, however for some streets we advocate the use of 20 mph in parallel with other measures including the redesign of streets, and enforcement where necessary, to reinforce reduced driving speeds. This approach is commonly known as 20 mph zones.


1. Sustrans defines a built-up area as any area where people live and work – from villages to city centres and where streets/roads/lanes are typically lined with buildings and public spaces. Roads here will almost always serve both movement and place functions.

2. Reported Road Casualties GB, 2016, ‘Table RAS30016’

3. ROSPA, 2017. Road Safety Factsheet - 20mph Zones and Speed Limits Factsheet

4. Rosén, E. et al. (2011) ‘Literature review of pedestrian fatality risk as a function of car impact speed’, Accident Analysis and Prevention, 43: 25-33.

5. Public health Wales, 2018. Position statement on 20mph speed limits.

6. Public Health Wales, 2018. Background Paper – Public Health Wales believes that lowering the default speed limit to 20mph in Wales could have substantial public health benefits.

7. 20s Plenty, 2018. Global Consensus that 20mph is best practice.

8. Pilkington, P., Bornioli, A., Bray, I. and Bird, E. (2018) The Bristol Twenty Miles Per Hour Limit Evaluation BRITE) Study. University of the West of England.

9. Grundy, C et al. 2009. Effect of 20 mph traffic speed zones on road injuries in London, 1986-2006: controlled interrupted time series analysis. BMJ, 339. b4469.

10. Edinburgh City Council, 2013. South Central Edinburgh 20mph limit pilot evaluation.

11. For example the City of London’s draft Transport Strategy seeks permission from the Department for Transport to adopt a City-wide 15mph speed limit by 2022.

Share this page