Our approach is based on the Department for Transport’s (DfT) guidance which seeks a common national approach to setting speed limits.

Underlying principles

National Highways (NH) is responsible for determining speed limits on the strategic road network (SRN).

Dorset Council is responsible for determining speed limits on the local road network.

It is important that the council and Dorset Police work closely together in determining, or considering, any changes to speed limits.

The full range of speed management measures should always be considered before a new speed limit is introduced.

The underlying aim should be to achieve a ‘safe’ distribution of speeds. The factors that should be taken into account in any decisions on local speed limits are:

  • history of collisions
  • road geometry and engineering
  • road function
  • composition of road users (including existing and potential levels of vulnerable road users)
  • existing traffic speeds
  • road environment

While these factors need to be considered for all road types, they may be weighted differently in urban or rural areas. The impact on community and environmental outcomes should also be considered.

The minimum length of a speed limit should generally be no less than 600m to avoid too many changes of speed limit along the route.

Speed limits should not be used to attempt to solve the problem of isolated hazards such as a single road junction or reduced forward visibility, for example, at a bend.

Urban speed management

A summary of the criteria for various urban speed limits.
Speed limit (mph)  Where a speed limit should apply
20 (including 20mph zone)

These should not be introduced as a blanket measure, but 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. There could be consideration of the safety case and local support to ensure their use is appropriate.

For more information, please see our 20mph limits and zones page


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, wherever possible, cater for the needs of non-motorised 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.

Street lit areas in towns - 30mph

Unless signed otherwise, street lit roads have a speed limit of 30mph. Signing is only required to indicate the beginning of a 30mph limit in a street lit area. Strict signing regulations do not allow repeater signs to be installed for 30mph limits by virtue of street lighting. The street lighting serves as the reminder of the speed limit.

Rural speed management

The criteria for various rural speed limits.
Speed limit (mph) Where speed limit should apply

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


Fear of traffic can affect people’s quality of life in villages and it is self-evident that villages should have comparable speed limits to similar roads in urban areas. It is, therefore, government policy that a 30mph speed limit should be the norm through villages.

It may also be appropriate to consider 20mph limits or zones in built-up village streets that are primarily residential in nature, or where pedestrian and cyclist movements are high, where there is a safety case and local support. Such limits should not, however, be considered on roads with a strategic function or where the movement of motor vehicles is the primary function.

Traffic Advisory Leaflet 01/04 (DfT, 2004) sets out the policy on achieving lower speed limits in villages.

Requesting a speed limit reduction

For a speed limit reduction request to be formally considered by Dorset Highways, it should be submitted and fully supported by the relevant Dorset Councillor and / or town / parish council.