Section 3: Responsibility and Underlying Principles
This section identifies which Traffic Authority is responsible for determining local speed limits on what roads, and the underlying principles to be used to determine appropriate speed limits.
The Scottish Executive is responsible for determining local speed limits on the trunk road and motorway network. Local Traffic Authorities are responsible for determining local speed limits on the local road network
Important that Traffic Authorities and police forces work closely together in determining, or considering, any changes to speed limits
Alternative speed management options should always be considered before a new speed limit is introduced
The underlying aim should be to achieve a 'safe' distribution of speeds which reflects the function of the road and the impacts on the local community. The needs of vulnerable road users must be fully taken into account
What the road looks like to road users should be a key factor when setting a speed limit
Mean speeds should be used to determine local speed limits. This reflects what the majority of drivers perceive as an appropriate speed to be driven for the road
The minimum length of a speed limit should generally be not less than 600 metres 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 such as a bend.
Responsibility for local speed limits
22. The Scottish Executive is responsible for determining local speed limits on the trunk road and motorway network, and Local Traffic Authorities for determining local speed limits on the local road network. In this Circular, the term Traffic Authority will be used to denote both the Scottish Executive and Local Traffic Authorities.
23. Reflecting wider road safety partnership working arrangements, it is important that Traffic Authorities and police forces work closely together in determining or considering any changes to local speed limits. It is equally important that neighbouring Traffic Authorities work closely together, especially where roads cross boundaries, to ensure speed limits remain consistent.
24. All mandatory speed limits other than the national limits are made by speed limit order. Further details are set out in Section 4, The Legislative Framework. Traffic Authorities must follow the full consultation procedure set out in the Local Authorities' Traffic Orders (Procedure) (Scotland) Regulations 1999, before any new mandatory speed limit is introduced. Guidance on the procedure is provided in SODD Circular 7/1999. Traffic authorities should, as part of this process, consult any local community likely to be affected by the proposals and, where appropriate, local community groups representing those likely to be affected, before making the speed limit order.
Considerations in setting local speed limits
25. A study of types of accidents, their severity, causes and frequency, together with a survey of traffic speeds, should indicate whether an existing speed limit is appropriate for the type of road and mix of use by different groups of road users, or whether it needs to be changed. Concerns may also have been expressed by the local community. It may well be that a speed limit need not be changed if the accident rate can be improved, or wider quality of life objectives achieved, by other speed management measures. Alternative options should always be considered before proceeding with a new speed limit.
26. Where poor compliance with the speed limit is a problem but the speed limit is considered to be appropriate for the road or stretch of road, there may be a mismatch between the appearance of the road and the driver's or rider's perception of the risks of an accident. Or a lower speed limit may have been applied to reduce severance of a local community produced by fast moving traffic. If local engineering and/or education solutions have been tried and the road is unsuitable or inappropriate for major engineering changes, some form of enforcement may be necessary. However, it is again important that Traffic Authorities and police forces work closely together before any remedial action is taken.
27. Before introducing or changing a local speed limit, Traffic Authorities will wish to satisfy themselves that the benefits exceed the disbenefits. Many of the costs and benefits do not have monetary values associated with them but should include an assessment of :
- accident and casualty savings
- traffic flow and emissions
- journey times for motorised traffic
- journey time reliability
- the environmental impact
- the level of public anxiety
- the level of severance by fast moving traffic
- conditions and facilities for vulnerable road users
- the cost of associated engineering or other physical measures and their maintenance
- the cost and visual impact of signing and possible environmental impact of engineering or other physical measures
- the cost of enforcement
The underlying principles
28. The underlying aim of speed management policies should be to achieve a 'safe' distribution of speeds which reflects the function of the road and the impacts on the local community. This should imply a mean speed appropriate to the prevailing conditions, and all vehicles moving at speeds as close to the posted speed limit as possible.
29. As well as being a key indicator of whether a local speed limit is appropriate, the estimated accident and injury savings should also be an important factor when considering changes to a local speed limit.
30. A key factor when setting a limit is what the road looks like to the road users, such as its geometry and adjacent land use. Drivers are likely to expect and respect lower limits, and be influenced when deciding on an appropriate speed, where they can see there are potential hazards, for example outside schools, in residential areas or villages, and in shopping streets.
31. A principal aim in determining appropriate speed limits should therefore be to provide a consistent message between the road geometry and environment, and for changes in speed limit to reflect changes in the road layout and characteristics. The following will be important factors when considering what is an appropriate speed limit:
- road function (strategic, through traffic, local access etc)
- road geometry (width, sightlines, bends, junctions and accesses etc)
- road environment (rural, residential, shop frontages, schools etc)
- level of adjacent development, and
- traffic composition (including existing and potential levels of pedestrians and cycle usage).
32. Different road users perceive risks and appropriate speeds differently. Drivers and riders of motor vehicles often do not have the same perception of the hazards of speed as do pedestrians, cyclists and horse riders. The needs of vulnerable road users must be fully taken into account in order to encourage these modes of travel and improve their safety. Setting appropriate speed limits is a particularly important element in urban safety management, with significant benefits for pedestrians and cyclists. Similarly, as vehicle speeds are generally higher on rural roads, accident severity and the risk to vulnerable road users are also greater. In both situations, speed limits should seek to encourage walking and cycling and to protect local community life.
33. In order to influence driven speeds to below a new lower local limit it is important that the limit is signed correctly and consistently. Any new limit should also be accompanied by education and, where appropriate, effective engineering changes to the road itself. Without these measures the actual driven speeds are unlikely to be reduced to below the new limit.
34. On rural roads there is often a difference of opinion as to what constitutes a reasonable balance between risk of an accident, travel efficiency and environmental impact. Higher speed is often perceived to bring benefits in terms of shorter travel times for people and goods. However, evidence suggests that when traffic is travelling at constant speeds, even at a lower level, it may result in shorter and more reliable overall journey times. With inappropriate speed for the conditions also come costs, the greatest of which is death and injury to people, increased community severance and environmental impacts. The objective should be to seek an acceptable balance between costs and benefits so that speed management policies take account of environmental, economic and social effects as well as the reduction in casualties they may achieve.
35. Mean speeds should be used to determine local speed limits as this reflects what the majority of drivers perceive as an appropriate speed to be driven on the road. It is also felt to be easier for road users themselves to understand. This is a change from the use of 85 th percentile speed advised in Circular 1/93, which refers to the speed at, or below which 85 per cent of the traffic is travelling.
36. For the majority of roads there is a consistent relation between mean speed and 85 th percentile speed. Where this is not the case, it will usually indicate that drivers have difficulty in deciding the appropriate speed for the road, suggesting that a better match between road design and speed limit is required. The aim should be to align the speed limit so that the original mean speed driven on the road is at or below the new posted speed limit for that road.
37. The minimum length of a speed limit should generally be not less than 600 metres to avoid too many changes of speed limit along a route. In exceptional circumstances this can be reduced to 400 metres, or even 300 metres on roads with a purely local access function. Anything shorter is not recommended. The length adopted for a limit will depend on the limit applied and also on the conditions at or beyond the end points. The terminal points of speed limits need to take account of the particular local circumstances, such as steep gradients, sharp bends, hump-backed bridges or other hazards, and also good visibility of the signs. Similarly, an extension may be required to provide good visibility of the speed limit signs. A limit may also need to be extended so as to cover any new access to an industrial or residential estate.
38. For consistency it is important that within routes, separate assessments should be made for each length of road of 600 metres or more for which a different speed limit might be considered appropriate. When this is completed, the final choice of appropriate speed limit for individual sections might need to be adjusted to provide reasonable consistency over the route as a whole.
39. Occasionally, it may be appropriate to use a short length of 40 mph or 50 mph speed limit as an intermediate transition between a length of road subject to a national limit and another length on which a lower limit is in force, for example on the outskirts of villages or urban areas with adjoining intermittent development. However, the use of such transitional limits should be restricted to sections of road where immediate speed reduction causes real difficulty or is likely to be less effective.
40. 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 such as a bend, as they would be difficult to enforce over such a short length. Other measures such as warning signs, carriageway markings, junction improvements, superelevation of bends and new or improved street lighting are likely to be more effective. Similarly, the provision of adequate footways can be an effective means of improving pedestrian safety as an alternative to lowering a speed limit over a short distance.
41. Where several roads with different limits enter a roundabout, the roundabout should be restricted at the same level as the majority of the approach roads. If there is an equal division, for example where a 30 mph road crosses one with a limit of 40 mph, the roundabout itself should take the lower limit. If all the approach roads have the same limit, the roundabout itself should have that same limit.
42. As set out in paragraph 4, the main purpose of local speed limits is to provide for situations where it is considered appropriate for drivers to adopt a speed that is different from the national speed limit. However, that limit does not imply that it is a safe speed under all conditions and drivers should be encouraged to adopt still lower speeds if conditions warrant.