20mph zones and limits

20mph sign
20mph zones and limits

Providing detailed information about 20mph zones and limits


This page is an overview of the different types of 20mph zones and limits, the evidence for them, and RoSPA's policy statements.

The majority of pedestrian casualties occur in built-up areas: 19 of the 22 child pedestrians and 338 of the 448 adult pedestrians who were killed in 2016, died on built-up roads. Pedal cyclists are also vulnerable in built-up areas, with more than half of cyclist deaths (62 of 101) and most cyclist casualties (16,886 of 18,321) occurring on these roads.

In 2017, 792 people were killed, 17,125 were seriously injured and 106,580 slightly injured in reported road collisions on built-up roads in Great Britain. A large proportion of these accidents occurred on residential roads, with 102 deaths on B roads in built-up areas and 298 deaths on other minor roads in built-up areas.

The Department for Transport’s current guidance is set out in DfT Circular 01/2013, which encourages traffic authorities to consider the introduction of more 20mph limits and zones, over time, in urban areas and built-up village streets that are primarily residential, to ensure greater safety for cyclists and pedestrians.

There are two distinct types of 20mph areas possible:

20mph zones

20mph zones are designed to be "self-enforcing" due to traffic calming measures which are introduced along with the change in the speed limit. Speed humps, chicanes, road narrowing, planting and other measures are typically used to both physically and visually reinforce the shared nature of the road.

20mph limits

20mph limits consist of just a speed limit change but no physical measures to reduce vehicle speeds within the areas. Drivers are alerted to the speed limit with 20mph speed limit repeater signs.

20mph limits are most appropriate for roads where average speeds are already low — the guidance suggests below 24mph. The layout and use of the road must also give the clear impression that a 20mph speed or below is the most appropriate.

Effectiveness of 20mph speed limits and zones

A large number of evaluation studies have demonstrated a link between the introduction of 20mph zones and a subsequent reduction in casualties. The size of the reductions and the consistency of results over a wide number of areas are further evidence for this link.

There is similarly strong evidence showing the benefits of traffic calming measures, which are used in 20mph zones.

20mph limits without traffic calming also reduces traffic speed, although this effect is smaller than when they are introduced with traffic calming or other measures. Their lower cost means that wider areas can be covered.

As well as road safety benefits, it is important to highlight the contribution that 20mph zones can have in encouraging more physical activity, such as walking and cycling, by contributing towards a safer environment. The money spent on the schemes can also greatly improve the character of a residential area and quality of life of the residents.

RoSPA's policy position on 20mph speed limits

20mph zones are very effective at preventing injuries and RoSPA would like to see their wider use in residential areas.

20mph zones significantly decrease the risk of being injured in a collision and their greater use, especially in residential areas, would help to reduce the number of traffic injuries in the UK.

Local authorities are responsible for determining where 20mph zones and limits should be introduced, but should take advantage of opportunities to introduce them where they are needed.

Consultation and engagement with local communities and other stakeholders is of vital importance, to make sure that safer roads are prioritised where needed and that local communities have input into the schemes' development.

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