FYI – regarding 20 mph Speed Limits and Zones

FYI – regarding 20 mph Speed Limits and Zones
October 10, 2019 Comments Off on FYI – regarding 20 mph Speed Limits and Zones Infrastructure Nomad

Source document: Department for Transport – circular-01-2013

Worth reading for those who want to lobby for a change once the VF roads are adopted.


79.20 mph zones and limits are now relatively wide-spread, with more than 2,000 schemes in operation in England, the majority of which are 20 mph zones.

80.20 mph zones require traffic calming measures (e.g. speed humps, chicanes) or repeater speed limit signing and/or roundel road markings at regular intervals, so that no point within a zone is more than 50 m from such a feature. In addition, the beginning and end of a zone is indicated by a terminal sign. Zones usually cover a number of roads.

81. 20 mph limits are signed with terminal and at least one repeater sign, and do not require traffic calming. 20 mph limits are similar to other local speed limits and normally apply to individual or small numbers of roads but are increasingly being applied to larger areas.

82.There is clear evidence of the effect of reducing traffic speeds on the reduction of collisions and casualties, as collision frequency is lower at lower speeds; and where collisions do occur, there is a lower risk of fatal injury at lower speeds. Research shows that on urban roads with low average traffic speeds any 1 mph reduction in average speed can reduce the collision frequency by around 6% (Taylor, Lynam and Baruya, 2000). There is also clear evidence confirming the greater chance of survival of pedestrians in collisions at lower speeds.

83.Important benefits of 20 mph schemes include quality of life and community benefits, and encouragement of healthier and more sustainable transport modes such as walking and cycling (Kirkby, 2002). There may also be environmental benefits as, generally, driving more slowly at a steady pace will save fuel and reduce pollution, unless an unnecessarily low gear is used. Walking and cycling can make a very positive contribution to improving health and tackling obesity, improving accessibility and tackling congestion, and reducing carbon emissions and improving the local environment.

84.Based on this positive effect on road safety, and a generally favourable reception from local residents, traffic authorities are able to use their power to introduce 20mph speed limits or zones on:

  •  Major streets where there are – or could be – significant numbers of journeys on foot, and/or where pedal cycle movements are an important consideration, and this outweighs the disadvantage of longer journey times for motorised traffic.

This is in addition to

  • Residential streets in cities, towns and villages, particularly where the streets are being used by people on foot and on bicycles, there is community support and the characteristics of the street are suitable.

85.Successful 20 mph zones and 20 mph speed limits are generally self- enforcing, i.e. the existing conditions of the road together with measures such as traffic calming or signing, publicity and information as part of the scheme, lead to a mean traffic speed compliant with the speed limit. To achieve compliance there should be no expectation on the police to

provide additional enforcement beyond their routine activity, unless this has been explicitly agreed.

86.Evidence from successful 20 mph schemes shows that the introduction of 20 mph zones generally reduces mean traffic speed by more than is the case when a signed-only 20 mph limit is introduced. Historically, more zones than limits have been introduced.

87.A comprehensive and early consultation of all those who may be affected by the introduction of a 20 mph scheme is an essential part of the implementation process. This needs to include local residents, all tiers of local government, the police and emergency services, public transport providers and any other relevant local groups (including for example, groups representing pedestrians, cyclists, drivers, or equestrians). Further details about consultations are set out in Appendix A.

88.It is important to consider the full range of options and their benefits, both road safety and wider community and environmental benefits and costs, before making a decision as to the most appropriate method of introducing a 20 mph scheme to meet the local objectives and the road conditions.

20 mph zones

89.20 mph zones are very effective at reducing collisions and injuries. Research in 1996 showed that overall average annual collision frequency could fall by around 60%, and the number of collisions involving injury to children could be reduced by up to two-thirds. Zones may also bring further benefits, such as a modal shift towards more walking and cycling and overall reductions in traffic flow, where research has shown a reduction by over a quarter (Webster and Mackie, 1996). There is no evidence of migration of collisions and casualties to streets outside the zone. (Grundy et al, 2008; Grundy et al, 2009).

90.20 mph zones are predominantly used in urban areas, both town centres and residential areas, and in the vicinity of schools. They should also be used around shops, markets, playgrounds and other areas with high pedestrian or cyclist traffic, though they should not include roads where motor vehicle movement is the primary function. It is generally recommended that they are imposed over an area consisting of several roads.

91. A 20 mph zone is indicated by 20 mph zone entry and exit signs (TSRGD, diagrams 674 and 675). The statutory provisions (direction 16(1) TSRGD) require that no point within the zone must be further than 50 metres from a traffic calming feature (unless in a cul-de-sac less than 80 metres long).

92.The Department has recently made significant changes to facilitate and reduce the cost for providing 20 mph zones in England. Traffic authorities can now place any of the following:

a) repeater speed sign (TSRGD diagram 670)
b) a speed roundel road marking (TSRGD diagram 1065) c) oracombinationofbothofthesesigns
d) traffic calming features

93.At least one traffic calming feature as defined in direction 16(2) TSRGD must be placed in a 20 mph zone and the features and signing must still be placed at intervals not greater than 100 metres: it is not the intention to remove physical features, but to ensure that the most appropriate measure is used to ensure the continuity of the zone. Only where speeds are already constrained to near the limit should local authorities consider placing the speed limit sign or a roundel marking, in addition to physical features within a zone.

94.These new arrangements should significantly reduce the requirement for signing and traffic calming features. Traffic authorities can now incorporate wider areas within a 20 mph zone, by effectively signing 20mph speed limits on distributor roads where traffic calming features are not suitable, or for small individual roads or stretches of road, where mean speeds are already at or below 24 mph. Where a 20 mph zone leads into a 20 mph limit, it is important to use the correct signing to indicate this. It is not appropriate to use the sign that indicates the end of a 20 mph zone and the start of a different, higher speed limit. Instead, a standard 20 mph terminal sign (TSRGD 2002, diagram 670) must be used.

20 mph speed limits

95.Research into signed-only 20 mph speed limits shows that they generally lead to only small reductions in traffic speeds. Signed-only 20 mph speed limits are therefore most appropriate for areas where vehicle speeds are already low. This may, for example, be on roads that are very narrow, through engineering or on-road car parking. If the mean speed is already at or below 24 mph on a road, introducing a 20 mph speed limit through signing alone is likely to lead to general compliance with the new speed limit.

96.20 mph limits covering most streets in Portsmouth have demonstrated that it is possible to introduce large-scale 20 mph limits in some built-up environments. Traffic speeds in most of the streets treated were relatively low (less than 20 mph) to start with. The early evidence suggests that it is likely that some speed and casualty reductions have taken place and this is consistent with previous research that has indicated that 20 mph limits without traffic calming reduce mean speeds by about 1 mph on average. A minority of streets in Portsmouth had average speeds of 25 mph or higher before the 20 mph speed limits were introduced and here the reductions in average speed tended to be greater, but insufficient to make the resulting speeds generally compliant with the new 20 mph limits. City-wide schemes may also contribute to changing travel and driving behaviour

positively in the longer run, and the objectives of the Portsmouth speed limits spread well beyond improving road safety. Schemes need to aim for compliance with the new speed limit.

97.The implementation of 20 mph limits over a larger number of roads, which the previous Speed Limit Circular (01/2006) advised against, should be considered where mean speeds at or below 24 mph are already achieved over a number of roads. Traffic authorities are already free to use additional measures in 20 mph limits to achieve compliance, such as some traffic calming measures and vehicle activated signs, or safety cameras. Average speed cameras may provide a useful tool for enforcing compliance with urban speed limits.

98.A 20 mph speed limit is indicated by terminal speed limit signs, and amendments to TSRGD (January 2012) require at least one speed limit repeater sign to be placed. Traffic authorities should ensure sufficient repeater signs are placed to inform road users of the speed limit in force. Chapter 3 of the Traffic Signs Manual provides guidance on the placing of repeater signs.

99.Every English authority has a traffic sign authorisation which permits them to place a 20mph speed roundel road marking as a repeater sign, without the requirement for an upright sign, to reduce unnecessary signing.

100. The amendments regulations to TSRGD (January 2012) have also provided thresholds below which speed repeater signs are no longer required by Direction 11 of TSRGD, but may still be placed if considered necessary. These thresholds are determined by carriageway length and the applicable speed limit.

101. Where traffic calming measures are placed, they should be signed in line with regulations (TSRGD 2002, diagram 557.1–4 and 883).

Variable 20 mph limits

102. Traffic authorities have powers to introduce 20 mph speed limits that apply only at certain times of day. These variable limits may be particularly relevant where for example a school is located on a road that is not suitable for a full-time 20 mph zone or limit, such as a major through road. To indicate these limits, variable message signs are available (TSRGD, Regulation 58). To reduce costs and sign clutter, the Department will consider authorising the placing of a single variable message sign on the approaching traffic lane (rather than signs on both sides of the road) on a case by case basis.

103. The Secretary of State has provided a special authorisation for every English traffic authority to place an advisory part-time 20mph limit sign, with flashing school warning lights. This can be a more cost-effective solution, where appropriate, and reduces the requirement for signing.


104. Traffic calming involves the installation of specific physical measures to encourage lower traffic speeds. There are many measures available to traffic authorities to help reduce vehicle speeds and ensure compliance with the speed limit in force. These are required at regular intervals in 20 mph zones and may be used in 20 mph limits. As set out above, speed limit traffic signs and/or speed roundel markings can now also be used by traffic authorities in England.

105. The Highways (Road Humps) Regulations 1999, The Highways (Traffic Calming) Regulations 1999, and Direction 16 of TSRGD 2002 (as amended) give details of the traffic calming measures that meet the requirements for a 20 mph zone.

106. These calming measures range from more substantive engineering measures to lighter touch road surface treatments and include, for example:

  • road humps;
  • road narrowing measures, including e.g. chicanes, pinch-points or overrun areas;
  • gateway
  • road markings; and
  • rumble devices.

107. A recent review of 20 mph zone and limit implementation (Atkins, 2009) shows that the vast majority of traffic calming measures in use are speed humps, tables, cushions or rumble devices, so called vertical deflections, but traffic authorities will want to consider the full set of available measures.

Digiprove sealCopyright secured by Digiprove © 2019
About The Author
All original content on these pages is fingerprinted and certified by Digiprove
%d bloggers like this: