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Dorset Council speed limit policy

This policy has been prepared to reflect the Department for Transport’s (DfT) guidance which seeks a common national approach to setting speed limits.

Priority will be in areas where there are recorded collisions. Speed limits should be evidence led, self-explanatory and encourage self-compliance. Indeed, if a speed limit is set in isolation, or is unrealistically low, it is likely to be ineffective and lead to disrespect for the speed limit. Alternative speed management options should always be considered before a new speed limit is introduced; all decisions taken will be evidence based.

In this article

Urban speed management

Summary of speed limit criteria in urban areas

The table shows a summary of the criteria for various urban speed limits.

Speed limit (mph) Where speed limit should be considered
20 (including 20mph zone)

In streets that are primarily residential and in other town or city streets where pedestrian and cyclist movements are high, such as around schools, shops, markets, playgrounds and other areas, where motor vehicle movement is not the primary function.


In other built-up areas (where motor vehicle movement is deemed more important), with development on both sides of the road.


On higher quality suburban roads or those on the outskirts of urban areas where there is little development, with few cyclists, pedestrians or equestrians. On roads with good width and layout, parking and waiting restrictions in operation and buildings set back from the road. On roads that, where possible, cater for the needs of nonmotorised users through segregation of road space and have adequate footways and crossing places.


On dual carriageway ring or radial routes or bypasses that have become partially built up, with little or no roadside development.

20mph speed limits

  • 20mph limits should not be implemented on roads with a strategic function or on a main road. The advice from the Police is that the limits must be self-enforcing.

  • The speed of traffic should be naturally at or around 20mph and have mean speeds no greater than 24mph. Where vehicle speeds are substantially higher than this then traffic calming will be required

20mph zones

  • 20mph zones have similar criteria to 20mph limits but repeater signs are not required. The purpose of a 20mph zone is to create conditions in which drivers naturally drive at 20mph, this usually means substantial traffic calming would be required

  • 20mph zones usually have entrance or “gateway” features to mark the start of the zone

30mph - street lit areas in towns

  • 30mph limits are considered the normal in street lit areas (where there are 3 or more lighting columns not more than 183m apart)

  • these areas will demonstrate a high degree of frontage development with pedestrian activity, driveways, junctions, traffic signals and crossings. Generally residential areas and town centres

  • terminal signs will be positioned as close as practicable to the start of visual development. Where forward visibility is restricted, signs may be extended outwards to meet standard forward visibility requirements

  • apart from the terminal 30mph signs no other repeater 30mph signs or road markings are permitted


Generally higher quality suburban roads away from town centres with less frontage development but with side roads, some bends and traffic signals / crossings.


In exceptional circumstances where the road environment permits such as ring or radial routes.

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Rural speed management

Summary of speed limit criteria single carriageway roads with a predominant motor traffic flow function

The table shows the criteria for various rural speed limits.

Speed limit (mph)Where speed limit should be considered

Recommended for most high quality strategic A and B roads with few bends, junctions or accesses.


Should be considered for lower quality A and B roads that may have a relatively high number of bends, junctions or accesses. Can also be considered where mean speeds are below 50mph, so lower limit does not interfere with traffic flow.


 Should be considered where there are bends, junctions or accesses, substantial development, a strong environmental or landscape reason, or where there are considerable numbers of vulnerable road users

Village 30mph speed limit

Where appropriate 30mph is considered the normal in villages.

  • the DfT defines a village relating to simple criteria based on the density of frontage development and distance: The density of frontage development should be 20 or more houses with extra allowance for key buildings such as schools and churches, with a minimum of 3 houses per 100m section within the proposed 30mph limit. A preferred minimum length of 600m to avoid too many changes of speed limit along a route
  • 30mph limits are not permitted on country lanes or for covering potential hazards such as bends or “T” junctions outside villages and towns
  • terminal signs will be positioned as close as practicable to the start of visual development. Where forward visibility is restricted, signs may be extended outwards to meet standard forward visibility requirements
  • carriageway roundels (a painted “30” marking on the road) can be used in conjunction with “entrance” signs. Repeater roundels will only be considered in exceptional circumstances where signs are obscured and must be accompanied with a sign

30mph village speed limits are appropriate where the mean speed of vehicles is not greater than 34mph. Where speeds are higher, or if the village criteria are not met, a reduction to 40mph may be more appropriate particularly on the approach to villages where properties may be situated beyond the main core of the village. These should be limited in use and consideration should first be given to speed reduction measures such as warning signs or carriageway narrowing with lines. Roads, where reduction to 40mph from the national speed limit may be appropriate, should have some frontage development with driveways or have other key building such as schools or churches. Sporadic development or isolated groups of houses should only be considered if the criteria are met.

40, 50 or 60mph speed limit?

The national speed limit on the rural road network is 60mph on single carriageway roads and 70mph on dual carriageways. Rural single carriageway roads are split into two categories in relation to their function:

  • upper tier roads roads catering for primary through traffic typically, but not necessarily, “A” and “B” class roads. Here the speed limit can be 60 or 50mph
  • lower tier roads – roads with a local access function where quality of life issues are important - typically C and Unclassified roads. Here the speed limit can be 50 or 40mph.

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Traffic Signs Regulations and General Directions (TSRGD) 2016

The latest version of the TSRGD saw a relaxation in the regulations that surround the signing of speed limits. TSRGD 2016 gives local highway authorities greater flexibility regarding the signing of speed limits.

Previous regulations were very prescribed and strict. The regulations now do not prescribe how many speed limit terminal or repeater signs are required.

Standard practice for the council will be to install two (one on either side of the road) speed limit terminal signs for the entry into a reduced speed limit with consideration being available for only using one terminal sign if the road layout does not allow for two.

The relaxations allow the council to consider only having one terminal sign when entering a higher speed limit. The relaxations also allow the council to be more flexible on how many repeaters signs are required.

Previous regulations prescribed a set minimum number of repeater signs based upon the length of a speed limit. TSRGD 2016 does not provide a number for required repeater signs. Technically this means that no repeaters are required however the council recognises that to have no (zero) speed limit repeater signs would not be reasonable in all cases but it does allow us to be more flexible and pragmatic about where repeaters signs would be most appropriate.

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