We are responsible for speed limits on all public roads in Somerset, except the M5 and trunk roads (A36 and A303). The reason for providing speed limits is to improve safety for all road users.
We set local speed limits where drivers should adopt a speed which is different from the national speed limit because of local needs and considerations. Local speed limits can be reduced or increased, depending on the conditions and evidence.
The Department for Transport has issued guidance to be used for setting all local speed limits on single and dual carriageway roads in urban and rural areas.
Our criteria for setting the right limit for any road takes into account existing traffic speed, accident history, the amount of traffic, frequency of junctions, and building development and amenities. Unrealistic speed limits are frequently abused and can prove very expensive and difficult for the police to enforce.
Any changes to, or the implementation of, speed limits should be in accordance with the latest Department for Transport guidance.
These are governed by Department for Transport (DfT) guidance on the Setting of Local Speed Limits (Circular Roads 01/2006).
Speed limits should be evidence-led, self-explaining and seek to reinforce people’s assessment of what is a safe speed to travel. They should encourage self-compliance and not be seen by drivers as being a target speed at which to drive in all circumstances. In deciding an appropriate speed limit for a road, one of the key issues to be studied is the existing speed of traffic – setting speed limits too far below measured traffic speeds is very unlikely to be effective.
Successful 20mph zones and speed limits should generally be self enforcing. Such speed limits are unlikely to be complied with on roads where vehicle speeds are substantially higher than this unless accompanied by traffic calming measures.
Research by the Transport Research Laboratory (TRL) showed that where speed limits alone were introduced, speed reductions of only about 2mph were achieved. 20mph speed limits are therefore only recommended in areas where vehicle speeds are already low (24mph or below is recommended) or additional traffic calming measures are implemented.
The standard speed limit in urban areas in 30mph, representing a balance between the mobility and safety of road users, especially more vulnerable groups. These are generally built-up areas where frontage development with individual accesses on both sides of the road exist, such as city streets, towns and residential areas.
Hazards, such as junctions, inadequate visibility, pedestrian crossings, schools, recreation grounds and public amenities support the need for a 30mph limit and make it appear sensible to the motorist.
The 40mph limit is used in similar built-up areas to the 30mph limit, but where the traffic hazards cause less risk of accidents. For example, the buildings may be set back from the road and be in an area of lower density, perhaps sometimes with service roads, or grass verges between the road and pavement.
Main traffic routes (for example, ring and radial routes) with good width and layout, but with a high proportion of two-wheeled vehicles and pedestrians may be restricted to the 40mph limit. By-passes and other important traffic routes which have become partially developed, or main roads through villages, may also be included in a 40mph limit.
50 and 60
A speed limit of 50mph can be made on high standard roads where the area has become lightly built up with some frontage development. The traffic composition is likely to be light in terms of pedestrian and cycle activity, and crossings are provided by means of subways and bridges.
High standard roads with restricted visibility or junctions may be considered for the 50mph limit and rural roads, not necessarily developed, but with features that attract traffic manoeuvres such as cafés, sports grounds and filling stations. Dual carriageways may be restricted to a 60mph limit where some of the above features exist.
We do not have a specific speed limit fund. Some communities and parish councils can apply where the change does not qualify for Local Transport Plan (LTP) funding.
Providing speed limits comply with the DfT guidelines, do not conflict with LTP objectives and the parish councils meet the full costs, there is no reason why new limits should not be introduced.
Traffic calming is a way of controlling the speed of vehicles. As the highway authority, we make physical alterations or implement traffic management measures.
The aim of traffic calming is to improve safety, reduce speed disturbance and anxiety, and enhance the environment.
You can contact us to request information about new or existing traffic calming measures.
There is a series of advisory leaflets to assist and inform about improvement scheme submissions on our Small Improvement Schemes page.
Speed humps and platforms
These are probably the most effective form of traffic calming available for controlling vehicle speeds. Their effectiveness relies on creating a vertical deflection to vehicles as they pass over them which in turn transmits discomfort to the drivers and other vehicle occupants. On traffic sensitive routes, such as bus routes, speed cushions are used in preference to speed humps. The cushions allow larger vehicles, such as buses, emergency vehicles and HGVs, across them with minimal deflection so giving a smooth ride to the occupants, but still reducing the average speeds of private and small vehicles. Here are descriptions of the various types:
- Round Top: This type of hump has a rounded profile, typically 3.7 metres long.
- Flat Top: This type of hump consists of an upward slope followed by a flat section, minimum length of 2.5 meters, and a downward slope. It can be made flush with the footway to provide a convenient crossing place for pedestrians. Another version of this type of hump, often used within housing estates, is the ‘speed table’ or ‘platform’ that consists of a flat top hump over an entire road junction.
- Speed Cushion: This type of road hump occupies part of the traffic lane and usually 2 are installed across the road. The spacing is such that cars will be slowed, but larger vehicles such as buses and emergency vehicles will suffer little inconvenience. Size and shape can differ but 1.6m x 3.1m is typical although larger sizes can be used without any adverse effects on buses and emergency services. However, measures may need to be considered to deter random parking in the area of the cushions, which could otherwise create problems for buses attempting to drive over the cushion, or prevent cyclists and motorcyclists from using the nearside gap between the kerb and the cushion. This type of hump will have little effect on the speed of heavy vehicles or motorcycles.
- Raised table junctions: These are normally installed as part of a road hump scheme and the vertical deflection includes the whole junction.
- Chicanes: These can be effective in reducing vehicle speeds on wider roads. Although chicane designs vary considerably they generally consist of 2 types:
(a) single lane working made up of kerb buildouts, staggered on alternate sides of the road, narrowing the road so that traffic from one direction has to give way to opposing traffic;
(b) two-way working, using kerb buildouts to provide deflection, but with lanes separated by road markings, or a central island. The single lane working chicane relies heavily on opposing traffic flows to influence speeds. However, the need to accommodate long/large vehicles generally ensures that smaller vehicles, such as cars and motorcycles, can often negotiate the chicane at higher speed. Chicanes are often very difficult to accommodate where there are regular private drives and accesses.
Where a small central island is used, this can influence speeds. The roundabout geometry should make sure there is adequate deflection to slow vehicles down on approaching the roundabout and prevent them accelerating away too quickly as they exit.
Mini-roundabouts should only be considered where they create a 3 arm mini-roundabout and the central island should be raised for better visibility. Double mini-roundabouts can be used at offset 4 arm junctions if there is sufficient offset of the minor roads.
Coloured surfacing – this can be used to heighten driver awareness. Anti-skid surfacing can be used to heighten driver awareness or give particularly good resistance to skidding.
Gateways – these are features at the entry to villages and towns, generally where the speed limit begins, to increase driver awareness.