20mph Zones and Limits (2012)
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Overview
This factsheet explains the different types of 20mph zones and limits, the evidence for them, their purpose and contains RoSPA's policy statements on 20mph zones and limits.
There are still a high number of casualties on urban roads in the UK. In 2010, there were 739 fatalities and a total of 147,323 casualties reported on built up (1) roads in Great Britain. A large proportion of these accidents occurred on residential roads, with 107 fatalities on B roads and 263 fatalities on other minor C and unclassified roads
Speed management including the use and enforcement of speed limits is a practical and established way of reducing injuries, and therefore urban 20mph zones and limits present a way of significantly reducing the likelihood of a serious injury.
The Department for Transport's current guidance is set out in DfT Circular 01/2006 which encourages and supports Local Authorities to implement 20 mph limits and zones in situations where there is a particular risk to vulnerable road users.
The guidance sets out that the purpose of 20 mph areas is to create conditions in which drivers naturally drive at around 20 mph as a result of traffic calming measures or the general nature of the location.
There are two distinct types of 20mph areas possible:
20mph zone
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, which 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, and 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.
There is less evidence that a change in speed limit alone has such a large effect although there are also fewer research studies.
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.
It is important that casualty data is used when deciding where 20mph zones and limits should be introduced.
Early evidence indicates that 20mph limits are much less effective than 20mph zones and do rely on visual and environmental cues to encourage drivers to adopt lower speeds.
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.
References
- From Reported Road Casualties Great Britain: 2010 Annual Report. Built up roads are defined in Reported Road Casualties GB as "roads with speed limits (ignoring temporary limits) of 40 mph or less
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