Safe speeds

10% of pedestrians would die when struck by a vehicle traveling at 20mph, compared to 50% for vehicles travelling at 30mph, 80% for vehicles travelling at 40mph, and nearly 100% for speeds over 50mph.

United States Department of Transport, 1999
20mph Speed Limits across the UK (thanks to 20’s Plenty for Us)
  • Research from around the world is clear: the faster the vehicle travels, the more likely it will be involved in a collision and the more severe that collision will be.
  • To bring down casualties in large numbers it is vital that 20mph speed limits are applied to both main and residential roads in built-up areas across the UK.
  • But 20mph speed limits cannot be delivered in isolation.
  • Compliance relies on designing streets for lower speeds, reducing road capacity, enhanced programmes of enforcement, and new vehicle technology such as Intelligent Speed Assistance.

Evidence shows that lower vehicle speeds reduce casualties, encourage walking and cycling, and make neighbourhoods quieter, cleaner and more liveable.

  • Reducing the maximum speed of vehicles to 20mph is associated with a 42% reduction in road casualties, London School of Hygiene and Tropical Medicine, 2009
  • People hit by a vehicle travelling at 30mph are four times more likely to die than those hit at 20mph, San Francisco’s Vision Zero Two-year Action Strategy
  • Speed is a factor in around 37% of collisions on London’s roads where a person dies or is seriously injured, Transport for London, Vision Zero Action Plan
  • Even small reductions in speed make a difference. Each 1mph reduction in mean traffic speed is associated with an 6% reduction in collisions, Transport Research Laboratory, 2000.
  • Lower speeds encourage more people to walk and cycle. The proportion of children cycling to school rose from 4 percent to 12 percent in 20mph zones in an Edinburgh trial, City of Edinburgh Council.

Growth of 20mph limits

Across the UK, more than 17 million people now live in local authorities where there are widespread 20mph limits or where the default speed limit has been reduced to 20mph. 20’s Plenty for Us estimate that more than half of the largest 40 urban authorities in the UK have a policy of setting 20mph as the default for their streets.

As of May 2019, more than half of all Londoners (52%) were estimated to live on 20mph streets and roads. In the 13 Inner London boroughs, home to 3.2 million residents, 80% live on 20mph streets.

But most 20mph zones and limits are on still residential roads and not on the main roads where most casualties occur. In London, around three-quarters of casualties of any severity occur on A or B roads. It is vital, therefore, that lower speed limits are applied to these roads if we are going to bring down casualties in large numbers.


Much work must be done to increase compliance with these speed limits, in particular on main roads where the majority of casualties occur. Compliance depends on a number of factors.

TfL’s Vision Zero Action Plan, for example, demonstrates that 20mph speed limits should not be introduced in isolation, but combined with other elements of the Vision Zero approach including:

  • designing for lower speeds (making use of the Lower Speeds Toolkit);
  • introducing protected cycle lanes ;
  • removing centre white lines;
  • reducing road capacity such as gyratories;
  • creating tighter junctions and introducing zebra crossings on all side road entrances;
  • enhanced programmes of enforcement;
  • (and in the longer term) making use of new vehicle technology such as Intelligent Speed Assistance (ISA).


Police enforcement in the UK has traditionally been weak in relation to the harm road traffic offences cause in our society. This has been exacerbated by funding cuts over the past decade which have particuarly affected roads policing.

A number of proposals in the TfL Vision Zero Action Plan seek to redress this including a three-tier approach to enforcement by the Metropolitan Police.

Greater investment in safety cameras is also needed, following the lead of cities in the USA. In New York more than one million speed camera violations fines are issued every year. TfL has stated that it intends to be able to match this level of speed camera enforcement in London

Community Roadwatch in London, funded by TfL, gives residents the opportunity to work with their local police teams using speed detection equipment to identify speeding vehicles in their communities. Outside London, Community Speed Watch is common across the UK.

Community RoadWatch in Hackney, London

In the light of the pressure on police resources, London Councils is currently investigating civil enforcement of speed limits by councils to potentially supplement police enforcement.

Technology to the rescue

Emerging technology may well make a big difference in ensuring vehicles comply with speed limits. Intelligent Speed Assistance (ISA) is now being introduced as standard on all new TfL buses in London (as part of the Bus Safety Standard) and is being considered in relation to working vehicles in London.  

Overridable ISA has also recently been adopted by the EU Parliament as part of a range of measures to improve road safety. From 2022 all new cars, vans, lorries and buses sold in Europe will be fitted with a range of new vehicle safety features such as Automated Emergency Braking which can detect pedestrians and cyclists, as well as overridable Intelligent Speed Assistance (ISA).

Changing behaviour

Examples of effective behaviour change programmes include the 20 Effect in Liverpool and the introduction of Kids Courts in Birmingham. TfL is also planning longer term promotional programmes under the Vision Zero umbrella in London.

Kids Court Birmingham


Organisations that argue that 20mph is the most appropriate speed limit for built-up areas include: World Health Organisation (WHO) (download their Managing Speed document here), British Medical Association (BMA), Faculty of Public Health (FPH), National Institute for Health and Care Excellence (NICE) (more here) Public Health England (PHE) (more here), European Transport Safety Council (ETSC) (more here).

Transport for London (TfL) (the highway authority for nine million people across London), calls on the UK Government to ‘amend the default urban speed limit to 20mph’ in its Vision Zero Action Plan,

Access the 20’s Plenty for Us list of UK towns, cities and villages with 20mph limits here.

%d bloggers like this: