Extracts from
SETTING LOCAL SPEED LIMITS
Draft: July 2012
TABLE 2
60 mph - Recommended for most high quality strategic A and B roads with few bends, junctions or accesses
50 mph - 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 50 mph, so lower limit does not interfere with traffic flow.
40 mph - 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
Speed limits should be evidence-led and self-explaining and seek to reinforce people's assessment of what is a safe speed to travel. They should encourage self-compliance. Speed limits should be seen by drivers as the maximum rather than a target speed.
The national limits are not, however, appropriate for all roads. The speed limit regime enables traffic authorities to set local speed limits in situations where local needs and conditions suggest a speed limit which is different from the respective national speed limit.
This guidance introduces, in section 5, the Speed Limit Appraisal Tool, a web-based tool currently (July 2012) under development. It is being designed to help local authorities assess the full costs and benefits, of any proposed schemes and make robust, evidence-based decisions about which limits they put in place.
13. Setting speed limits at the appropriate level for the road, and ensuring compliance with these limits, play a key part in ensuring greater safety for all road users. The relationship between speed and likelihood of collision as well as severity of injury is complex, but there is a strong correlation. As a general rule for every 1 mph reduction in average speed, collision frequency reduces by around 5% (Taylor, Lynam and Baruya, 2000). For typical types of road traffic collisions the risk of death for drivers and pedestrians involved reduces with reduced vehicle speeds and it is particularly important to consider those speeds where the balance tips in favour of survival.
14. Reported road casualty statistics also show the role of exceeding the speed limit and travelling too fast for the conditions as contributory factors in road traffic collisions. In 2010 these two factors were reported to have contributed to nearly 400 road deaths. Other reported contributory factors such as loss of control or careless, reckless or in a hurry can often be related to excess or inappropriate speed, and even where the contributory factors are unrelated to the vehicle speed, higher speeds will often aggravate the outcome of the collision and injuries.
15. This updated guidance provides part of the framework for speed limits, where local authorities can set speed limits on their roads below the national limit, in response to local risk factors and conditions. It will help ensure appropriate and consistent speed limits, which will contribute to reducing the number of road deaths, as well as casualties overall; tackling pedestrian and cyclist casualties in towns and cities; improving the safety on rural roads; and reducing variations in safety from area to area and road to road.
Speed limits are only one element of speed management. Local speed limits should not be set in isolation. They should be part of a package with other speed management measures including engineering and road geometry that respect the needs of all road users and raise the driver's awareness of their environment; education; driver information; training and publicity. Within their overall network management responsibilities, these measures should enable traffic authorities to deliver speed limits and, as importantly, actual vehicle speeds that are safe and appropriate for the road and its surroundings. The measures should also help drivers to be more readily aware of the road environment and to drive at an appropriate speed at all times.
Key points
The Highways Agency is responsible for determining speed limits on the trunk road network. Local traffic authorities are responsible for determining speed limits on the local road network.
It is important that traffic authorities and police forces 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 key factors that should be taken into account in any decisions on local speed limits are:
history of collisions, including frequency, severity, types and causes;
road geometry and engineering (e.g. bends, junctions, barriers);
presence of vulnerable road users;
road function;
existing traffic speeds; and
road environment, including level of road-side development and possible impacts on residents (e.g. severance, noise, or air quality).
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 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, e.g. at a bend.
A study of types of crashes, 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, including the presence or potential presence of vulnerable road users (including pedestrians, cyclists, equestrians or motorcyclists), or whether it needs to be changed. Local residents may also express their concerns or desire for a lower speed limit and these comments should be considered.
The aim of speed management policies should be to achieve a safe distribution of speeds consistent with the speed limit that reflects the function of the road and the road environment. This should imply a mean speed appropriate to the prevailing conditions, and all vehicles moving at speeds below or as close as possible to the posted speed limit, in line with the conditions.
Mean speed and 85th percentile speed (the speed at or below which 85% of vehicles are travelling) are the most commonly used measures of actual traffic speed. Traffic authorities should continue to routinely collect and assess both, but mean speeds should be used as the basis for determining local speed limits.
Occasionally it may be appropriate to use a short length of 40 mph or 50 mph speed limit as a 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 would cause risks or is likely to be less effective.
Speed limits should not be used to attempt to solve the problem of isolated hazards, for example a single road junction or reduced forward visibility such as at a bend, since speed limits are difficult to enforce over such a short length. Other measures, such as warning signs including vehicle activated signs, carriageway markings, junction improvements, superelevation of bends and new or improved street lighting, are likely to be more effective in addressing such hazards. Similarly, the provision of adequate footways can be a more effective means of improving pedestrian safety than lowering a speed limit over a short distance.
SECTION 5: THE SPEED LIMIT APPRAISAL TOOL
This section will contain a description of the speed limit appraisal tool which will be launched later in 2012 and will be available on the DfT website.
The Tool is being designed to help local authorities assess the full costs and benefits of any proposed schemes and make robust, evidence-based decisions about which limits they put in place. It will include effects which cannot be monetised such as quality of life, as well as casualty and other traffic effects.
Local authority representatives and other interested parties are involved in its development and we issued a Call for Evidence, which closed on 30 April, to provide an opportunity for interested parties, including Local Authorities, road safety interest groups and academics, to submit relevant evidence on speed limit changes to assist in developing the tool.
Text on the Tool will be added to this section when its development has progressed further.
In 2010, 68% of road deaths in Britain occurred on rural roads, and 49% of road deaths occurred on single rural carriageway roads subject to the National Speed Limit of 60 mph limit.
The speed limit on single carriageway rural roads should take into account the history of collisions, the road’s function, existing mean traffic speed, use by vulnerable road users, the road's geometry and engineering, and the road environment including level of road-side development.
111. Roads may have primarily either a through traffic function or a local access function. Both need to be provided safely. Mobility benefits will be more important for roads with a through-traffic function, while environmental and community benefits are likely to be of greater importance for the local access roads.
112. There may be many roads below A and B classification that serve a mixed through-traffic and access function. Where that traffic function is currently being achieved without a high collision rate, these roads should be judged as through-traffic roads. If, however, for all or parts of these roads there is a substantial potential risk to vulnerable road users, these sections should be assessed as roads with a local access function.
113. Within routes, separate assessments should be made for each section of road of 600 metres or more for which a separate 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 consistency over the route as a whole.
114. The choice of speed limits should take account of whether there is substantial roadside development and whether the road forms part of a recognised route for vulnerable road users.
115. Table 2 sets out recommended speed limits for roads with a predominant traffic flow function. If walking, cycling, horse riding, community or environmental factors are particularly important on any road section, consideration should be given to using the lower limit.
121. If there are just fewer than 20 houses, traffic authorities should make extra allowance for any other key buildings, such as a church, shop or school.
In some circumstances it might be appropriate to consider an intermediate speed limit of 40 mph prior to the 30 mph terminal speed limit signs at the entrance to a village, in particular where there are outlying houses beyond the village boundary or roads with high approach speeds. For the latter, traffic authorities might also need to consider other speed management measures to support the message of the speed limit and help encourage compliance so that no enforcement difficulties are created for the local police force. Where appropriate, such measures might include a vehicle-activated sign, centre hatching or other measures that would have the effect of narrowing or changing the nature and appearance of the road.
124.
Where the speed limit commences at the village boundary, the village nameplate sign (prescribed in diagram 2402.1 of TSRGD 2002) and speed limit roundel may be mounted together. The combined sign should be located at the point where the speed limit starts, and it may be helpful if drivers can see housing at the same time as the signs, reinforcing the visual message for reduced speed.
125. If there are high approach speeds to a village, or the start of the village is not obvious, village gateway treatments can also be an effective way to slow drivers down. Advice can be found in Traffic Advisory Leaflets 13/93 Gateways (DoT, 1993a), 01/94 VISP – A Summary (DoT, 1994a) and 01/04 Village Speed Limits (DfT, 2004).
127. In situations where the above criteria for a village are not met and there is a lesser degree of development, or where engineering measures are not practicable or cost-effective to achieve a 30 mph limit, but a reduction from the national 60 mph speed limit is considered appropriate, traffic authorities should consider alternative lower limits of 40 or 50 mph.
128. A recommendation to use the framework for the assessment of speed limit options on rural single carriageway roads, in place since the publication of the previous Speed Limit Circular (01/2006), is withdrawn. (what does this mean??)
SETTING LOCAL SPEED LIMITS
Draft: July 2012
TABLE 2
60 mph - Recommended for most high quality strategic A and B roads with few bends, junctions or accesses
50 mph - 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 50 mph, so lower limit does not interfere with traffic flow.
40 mph - 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
Speed limits should be evidence-led and self-explaining and seek to reinforce people's assessment of what is a safe speed to travel. They should encourage self-compliance. Speed limits should be seen by drivers as the maximum rather than a target speed.
The national limits are not, however, appropriate for all roads. The speed limit regime enables traffic authorities to set local speed limits in situations where local needs and conditions suggest a speed limit which is different from the respective national speed limit.
This guidance introduces, in section 5, the Speed Limit Appraisal Tool, a web-based tool currently (July 2012) under development. It is being designed to help local authorities assess the full costs and benefits, of any proposed schemes and make robust, evidence-based decisions about which limits they put in place.
13. Setting speed limits at the appropriate level for the road, and ensuring compliance with these limits, play a key part in ensuring greater safety for all road users. The relationship between speed and likelihood of collision as well as severity of injury is complex, but there is a strong correlation. As a general rule for every 1 mph reduction in average speed, collision frequency reduces by around 5% (Taylor, Lynam and Baruya, 2000). For typical types of road traffic collisions the risk of death for drivers and pedestrians involved reduces with reduced vehicle speeds and it is particularly important to consider those speeds where the balance tips in favour of survival.
14. Reported road casualty statistics also show the role of exceeding the speed limit and travelling too fast for the conditions as contributory factors in road traffic collisions. In 2010 these two factors were reported to have contributed to nearly 400 road deaths. Other reported contributory factors such as loss of control or careless, reckless or in a hurry can often be related to excess or inappropriate speed, and even where the contributory factors are unrelated to the vehicle speed, higher speeds will often aggravate the outcome of the collision and injuries.
15. This updated guidance provides part of the framework for speed limits, where local authorities can set speed limits on their roads below the national limit, in response to local risk factors and conditions. It will help ensure appropriate and consistent speed limits, which will contribute to reducing the number of road deaths, as well as casualties overall; tackling pedestrian and cyclist casualties in towns and cities; improving the safety on rural roads; and reducing variations in safety from area to area and road to road.
Speed limits are only one element of speed management. Local speed limits should not be set in isolation. They should be part of a package with other speed management measures including engineering and road geometry that respect the needs of all road users and raise the driver's awareness of their environment; education; driver information; training and publicity. Within their overall network management responsibilities, these measures should enable traffic authorities to deliver speed limits and, as importantly, actual vehicle speeds that are safe and appropriate for the road and its surroundings. The measures should also help drivers to be more readily aware of the road environment and to drive at an appropriate speed at all times.
Key points
The Highways Agency is responsible for determining speed limits on the trunk road network. Local traffic authorities are responsible for determining speed limits on the local road network.
It is important that traffic authorities and police forces 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 key factors that should be taken into account in any decisions on local speed limits are:
history of collisions, including frequency, severity, types and causes;
road geometry and engineering (e.g. bends, junctions, barriers);
presence of vulnerable road users;
road function;
existing traffic speeds; and
road environment, including level of road-side development and possible impacts on residents (e.g. severance, noise, or air quality).
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 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, e.g. at a bend.
A study of types of crashes, 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, including the presence or potential presence of vulnerable road users (including pedestrians, cyclists, equestrians or motorcyclists), or whether it needs to be changed. Local residents may also express their concerns or desire for a lower speed limit and these comments should be considered.
The aim of speed management policies should be to achieve a safe distribution of speeds consistent with the speed limit that reflects the function of the road and the road environment. This should imply a mean speed appropriate to the prevailing conditions, and all vehicles moving at speeds below or as close as possible to the posted speed limit, in line with the conditions.
Mean speed and 85th percentile speed (the speed at or below which 85% of vehicles are travelling) are the most commonly used measures of actual traffic speed. Traffic authorities should continue to routinely collect and assess both, but mean speeds should be used as the basis for determining local speed limits.
Occasionally it may be appropriate to use a short length of 40 mph or 50 mph speed limit as a 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 would cause risks or is likely to be less effective.
Speed limits should not be used to attempt to solve the problem of isolated hazards, for example a single road junction or reduced forward visibility such as at a bend, since speed limits are difficult to enforce over such a short length. Other measures, such as warning signs including vehicle activated signs, carriageway markings, junction improvements, superelevation of bends and new or improved street lighting, are likely to be more effective in addressing such hazards. Similarly, the provision of adequate footways can be a more effective means of improving pedestrian safety than lowering a speed limit over a short distance.
SECTION 5: THE SPEED LIMIT APPRAISAL TOOL
This section will contain a description of the speed limit appraisal tool which will be launched later in 2012 and will be available on the DfT website.
The Tool is being designed to help local authorities assess the full costs and benefits of any proposed schemes and make robust, evidence-based decisions about which limits they put in place. It will include effects which cannot be monetised such as quality of life, as well as casualty and other traffic effects.
Local authority representatives and other interested parties are involved in its development and we issued a Call for Evidence, which closed on 30 April, to provide an opportunity for interested parties, including Local Authorities, road safety interest groups and academics, to submit relevant evidence on speed limit changes to assist in developing the tool.
Text on the Tool will be added to this section when its development has progressed further.
In 2010, 68% of road deaths in Britain occurred on rural roads, and 49% of road deaths occurred on single rural carriageway roads subject to the National Speed Limit of 60 mph limit.
The speed limit on single carriageway rural roads should take into account the history of collisions, the road’s function, existing mean traffic speed, use by vulnerable road users, the road's geometry and engineering, and the road environment including level of road-side development.
111. Roads may have primarily either a through traffic function or a local access function. Both need to be provided safely. Mobility benefits will be more important for roads with a through-traffic function, while environmental and community benefits are likely to be of greater importance for the local access roads.
112. There may be many roads below A and B classification that serve a mixed through-traffic and access function. Where that traffic function is currently being achieved without a high collision rate, these roads should be judged as through-traffic roads. If, however, for all or parts of these roads there is a substantial potential risk to vulnerable road users, these sections should be assessed as roads with a local access function.
113. Within routes, separate assessments should be made for each section of road of 600 metres or more for which a separate 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 consistency over the route as a whole.
114. The choice of speed limits should take account of whether there is substantial roadside development and whether the road forms part of a recognised route for vulnerable road users.
115. Table 2 sets out recommended speed limits for roads with a predominant traffic flow function. If walking, cycling, horse riding, community or environmental factors are particularly important on any road section, consideration should be given to using the lower limit.
121. If there are just fewer than 20 houses, traffic authorities should make extra allowance for any other key buildings, such as a church, shop or school.
In some circumstances it might be appropriate to consider an intermediate speed limit of 40 mph prior to the 30 mph terminal speed limit signs at the entrance to a village, in particular where there are outlying houses beyond the village boundary or roads with high approach speeds. For the latter, traffic authorities might also need to consider other speed management measures to support the message of the speed limit and help encourage compliance so that no enforcement difficulties are created for the local police force. Where appropriate, such measures might include a vehicle-activated sign, centre hatching or other measures that would have the effect of narrowing or changing the nature and appearance of the road.
124.
Where the speed limit commences at the village boundary, the village nameplate sign (prescribed in diagram 2402.1 of TSRGD 2002) and speed limit roundel may be mounted together. The combined sign should be located at the point where the speed limit starts, and it may be helpful if drivers can see housing at the same time as the signs, reinforcing the visual message for reduced speed.
125. If there are high approach speeds to a village, or the start of the village is not obvious, village gateway treatments can also be an effective way to slow drivers down. Advice can be found in Traffic Advisory Leaflets 13/93 Gateways (DoT, 1993a), 01/94 VISP – A Summary (DoT, 1994a) and 01/04 Village Speed Limits (DfT, 2004).
127. In situations where the above criteria for a village are not met and there is a lesser degree of development, or where engineering measures are not practicable or cost-effective to achieve a 30 mph limit, but a reduction from the national 60 mph speed limit is considered appropriate, traffic authorities should consider alternative lower limits of 40 or 50 mph.
128. A recommendation to use the framework for the assessment of speed limit options on rural single carriageway roads, in place since the publication of the previous Speed Limit Circular (01/2006), is withdrawn. (what does this mean??)
Extracts from “Setting Local Speed Limits” (01/2006)
“Traffic authorities are required to keep their speed limits under review with changing circumstances. It will not be possible to implement and bring about all of the objectives set out in this guidance overnight. Traffic authorities are, however, asked to review the speed limits on all of their A and B roads, and implement any necessary changes, by 2011 in accordance with this guidance. Consistent with their duty in respect of road safety, traffic authorities will wish to focus the use of speed management measures, including more appropriate speed limits, or a combination of these methods, on those roads or routes (not just on A and B roads) with the most pressing problems of collisions and injuries, or where there is a widespread disregard for current speed limits.”
Traffic authorities continue to have the flexibility to set local speed limits that are right for the individual road, reflecting local needs and taking account of all local
considerations.
Local speed limits should not be set in isolation, but as part of a package with other measures to manage vehicle speeds.
The road safety strategy is structured around ten main themes that reflect the needs of both motorised and non-motorised users. At its core is a major focus on three areas –
driver behaviour, enforcement and a safer driving environment. This is often characterised as the ‘three Es’ – education, enforcement and engineering.
Research has in particular proven the correlation between speed and accident frequency and severity, and accident reductions. Much of this evidence has been demonstrated by and around mean vehicle speeds including, for example, how each 1mph reduction in average speed reduces accident frequency by 5%
The key objectives of this guidance are:
•the provision of up-to-date and consistent advice to traffic authorities
•improved clarity which will aid greater consistency of speed limits across the country
•the setting of more appropriate local speed limits, including reduced or increased limits where conditions dictate
•local speed limits that better reflect the needs of all road users, not just motorised vehicles
•improved quality of life for local communities and a better balance between road safety, accessibility and environmental objectives, especially in rural communities
•improved recognition and understanding by road users of the risks involved on different types of road, the speed limits that apply, and the reasons why
•improved respect for speed limits, and in turn improved self compliance
6•continued reductions in the number of road traffic collisions, injuries and deaths in which excessive or inappropriate speed is a contributory factor.
What the road looks like to road users should be a key factor when setting a speed limit.
Mean speeds should be used as the basis for determining local speed limits. These areunderpinned by extensive research demonstrating the well proven relationship between speed and accident frequency and severity, and also reflect 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.
There will be roads, or stretches of road, that suffer from poor compliance with the existing speed limit. Where this happens and the speed limit is considered to be appropriate for the road, there may be a mismatch between the appearance of the road and the driver’s or rider’s perception of the risks of a collision. 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 either 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.
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 traffic authorities should include an assessment of the following factors:
•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.
A key factor when setting a speed 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 what is an appropriate speed, where they can see there are potential hazards, for example outside schools, in residential areas or villages and in shopping streets.
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 be reflective of 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 pedestrian and cycle usage).
Vehicle-activated signs must not be used as an alternative to standard static signing, but as an additional measure to warn drivers of a potential hazard or to remind them of the speed limit in force.
The national speed limit on the rural road network is 60 mph on single carriageway roads and 70 mph on dual carriageways.
The majority of drivers do not reach or exceed the 60 mph limit on many single carriageway roads because it is often difficult to do so because of the characteristics and environment of the road. (but in the real world on the B4077!)
Nonetheless in 2004 some 46% of serious road casualties, and more than half of road deaths, occurred on rural roads.
Speed can be a major factor in the severance of local communities. The speed limit on single carriageway rural roads should take into account traffic and road user mix, the road’s geometry and general characteristics, its surroundings, and the potential safety and environmental impacts.
Building upon the Institution of Highways and Transportation’s rural safety management guidelines (IHT, 1999), traffic authorities are encouraged to adopt a two- tier hierarchical approach that differentiates between single carriageway roads with a strategic or local access function.
Higher speed limits should be restricted to ‘upper tier’ or high quality strategic single carriageway roads where there are few bends, junctions or accesses.
Lower speed limits would be appropriate on ‘lower tier’ single carriageway roads passing through a local community, or having a local access or recreational function. They would also be appropriate where there are significant environmental considerations or where there is a high density of bends, junctions or accesses, or the road is hilly. That's us folks !
It is government policy that, where appropriate, a 30 mph speed limit should be the norm in villages.
Traffic authorities should also consider the use of vehicle-activated signs (VAS), which have proved particularly effective at the approaches to isolated hazards, junctions and bends in rural areas.
In rural areas every effort should be made to achieve an appropriate balance between speeds, speed limits, road function and design, the differing needs of road users, and other characteristics. This balance may be delivered by introducing one or more speed management measures in conjunction with the new speed limits and/or as part of an overall route safety strategy. The aim should be to align the local speed limit so that the original mean speed driven on the road is at or below the new posted speed limit for that road.
Following investigations of the relationship between speed and accidents on rural single carriageway roads, TRL Report 511 (Taylor et al., 2002)successfully classified rural road sections into four groups reflecting their operational characteristics. Drawing upon the accident rate information available for these groups and the minimum total cost at a particular speed, TRL Published Project Report 025 (TRL, 2004) sets the following accident thresholds for upper and lower tier roads, which reflect expected levels associated with a road carrying a given level of traffic and an appropriate balance
between safety and mobility:
•upper tier roads – 35 injury accidents per 100 million vehicle kilometres
•lower tier roads – 60 injury accidents per 100 million vehicle kilometres.
The speed assessment framework operates on the principles that the speed limit choice should be guided by whether the accident rate on a section of road is above or below the respective 35 or 60 injury accident thresholds.
Upper tier A and B roads
•60 mph: high quality strategic roads with few bends, junctions or accesses. When the assessment framework is being used, the accident rate should be below a threshold of 35 injury accidents per 100 million vehicle kilometres.
•50 mph: lower quality strategic roads which may have a relatively high number of bends, junctions or accesses. When the assessment framework is being used, the accident rate should be above a threshold of 35 injury accidents per 100 million vehicle kilometres and/or the mean speed already below 50 mph.
•40 mph: where there is high number of bends, junctions or accesses, substantial development, where there is a strong environmental or landscape reason, or where the road is used by considerable numbers of vulnerable road users.
•30 mph: should be the norm in villages where appropriate.
VILLAGES
111.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, where appropriate, a 30 mph speed limit should be the norm in villages.
112.Traffic Advisory Leaflet 01/04 (DfT, 2004) sets out current policy on achieving lower speed limits in villages, including a broad definition of what constitutes a village. For the purpose of applying a village speed limit of 30 mph, a definition of a village can be based on the following simple criteria relating to frontage development and distance:
•20 or more houses (on one or both sides of the road); and
•a minimum length of 600 metres.
113.If there are just fewer than 20 houses, traffic authorities should make extra allowance for any other key buildings, such as a church, shop or school.
In some circumstances it might be appropriate to consider an intermediate speed limit of 40 mph prior to the 30 mph terminal speed limit signs at the entrance to a village, in particular where there are outlying houses beyond the village boundary or roads with high approach speeds. For the latter, traffic authorities might also need to consider other speed management measures to support the message of the speed limit and help encourage compliance so that no enforcement difficulties are created for the local police force. Where appropriate, such measures might include a vehicle-activated sign, centre hatching or other measures that would have the effect of narrowing or changing the nature and appearance of the road.
116.Where the speed limit commences at the village boundary, the village nameplate sign and speed limit roundel may be mounted together using the format prescribed in diagram 2402.1 of TSRGD. The combined sign should be located as near as practicable to the start of the development, so that drivers see housing at the same time as the signs,reinforcing the visual message for reduced speed.
117.If there are high approach speeds to a village, or the start of the village is not obvious,village gateway treatments can also be an effective way to slow drivers down. Further guidance on the use of gateway and entry treatments is included in Appendix B of this guidance. Advice can also be found in Traffic Advisory Leaflets 13/93 Gateways (DoT,1993a), 01/94 VISP – A Summary (DoT, 1994a) and 01/04 Village Speed Limits (DfT,2004).
118.In situations where the above criteria for a village are not met and there is a lesserdegree of development, or where engineering measures are not practicable or cost-effective to achieve a 30 mph limit, but a reduction from the national 60 mph speed limit is considered appropriate, traffic authorities should consider alternative lower limits of 40 or 50 mph.
SUMMARY
SPEED ASSESSMENT FRAMEWORK – NEW APPROACH TO SPEED LIMIT SETTING FOR SINGLE CARRIAGEWAY ROADS IN RURAL AREAS
1.Speed limits should be considered as only one part of rural safety management. The first priority where accident rates are high should be to seek cost-effective improvements to reduce these rates, targeting the accident types that are over-represented.
2.If high rates persist despite these measures, then lower speed limits may also be considered. But lower speed limits on their own without supporting physical measures, driver information and publicity or other measures will not necessarily change driver behaviour and therefore will result in substantial numbers of drivers continuing to travel at unacceptable speeds. This may lead to significant enforcement cost. So every effort should be made to achieve an appropriate balance between speeds, speed limits, road design and other measures. This balance may be delivered by introducing one or more speed management measures in conjunction with the new speed limits, and/or as part of an overall route safety strategy.
3.An assessment framework has been developed by TRL (Taylor et al., 2002) to help decision-makers weigh up, in a more transparent way, the advantages and disadvantages of each speed limit option and reach a well-founded conclusion for these roads.
4.The basis for the speed assessment framework procedure is:
•a firm theoretical basis for choosing speed limits for road functions, taking account of safety, mobility and environmental factors
•roads classified into two tiers based on road function
•closer integration of speed limit choice, with more general rural road safety management measures
•driver choice of desired speed to be reflected by mean speed
•local flexibility of choice within a consistent overall procedure.
5.The assessment framework combines safety and mobility costs to show how the overall total cost and the balance between the component costs change if different choices of speed limit are made. For a particular road type, total cost is similar over a relatively wide speed range, with mobility benefits being exchanged for safety benefits as speeds decrease.
6.A simple two-tier functional hierarchy should be used, with roads having either primarily a through traffic function (upper tier) or a local access (lower tier) function.
Both need to be provided safely. Mobility benefits will be more important for the upper tier than for the lower tier roads, whilst environmental benefits are likely to be of greater importance for the lower tier roads.
7. There may be many roads below A and B classification which serve a mixed through-traffic and access function. Where that traffic function is currently being achieved without a high accident rate, these roads should be judged against the criteria for upper tier roads.
If, however, for all or parts of these roads there is a substantial potential risk to vulnerable road users, these sections should be assessed against the criteria for lower tier roads.
8.Decisions on speed limits should take account of other accident reduction measures that might be applied. To help in this process, a technical guide has been developed,
Accident Analysis on Rural Roads (TRL, 2004) (downloadable from the TRL web site www.trl.co.uk), which provides information on typical collision rates, and typical proportions of different accident types, on different types of rural road. These can be used to judge whether other site- or route-specific measures might be appropriate that would reduce either speeds or accidents along the route.
9.Mean speed should be used for the assessment. For the majority of roads there is a consistent relationship between mean speed and 85th 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.
10.The aim should be to align the speed limit to the prevailing conditions, and all vehicles moving at speeds as close to the posted speed limit as possible. An important step in the procedure is to gain agreement with local enforcement agencies that the mean speed of drivers on the road with any new speed limits is acceptable.
11.The aim of the framework approach is to achieve a consistent application of speed limit policy throughout the country. But local issues in relation to particular routes can be reflected in the functional tier to which the road is assigned, and also through final decisions on acceptable mean speeds for each limit, on the importance given to local environmental factors, and on the choice of additional measures that could change the appropriate speed limit regime recommended.
Selection procedure
12.Within routes, separate assessments should be made for each section of road of 600 metres or more for which a separate 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 consistency over the route as a whole.
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“Traffic authorities are required to keep their speed limits under review with changing circumstances. It will not be possible to implement and bring about all of the objectives set out in this guidance overnight. Traffic authorities are, however, asked to review the speed limits on all of their A and B roads, and implement any necessary changes, by 2011 in accordance with this guidance. Consistent with their duty in respect of road safety, traffic authorities will wish to focus the use of speed management measures, including more appropriate speed limits, or a combination of these methods, on those roads or routes (not just on A and B roads) with the most pressing problems of collisions and injuries, or where there is a widespread disregard for current speed limits.”
Traffic authorities continue to have the flexibility to set local speed limits that are right for the individual road, reflecting local needs and taking account of all local
considerations.
Local speed limits should not be set in isolation, but as part of a package with other measures to manage vehicle speeds.
The road safety strategy is structured around ten main themes that reflect the needs of both motorised and non-motorised users. At its core is a major focus on three areas –
driver behaviour, enforcement and a safer driving environment. This is often characterised as the ‘three Es’ – education, enforcement and engineering.
Research has in particular proven the correlation between speed and accident frequency and severity, and accident reductions. Much of this evidence has been demonstrated by and around mean vehicle speeds including, for example, how each 1mph reduction in average speed reduces accident frequency by 5%
The key objectives of this guidance are:
•the provision of up-to-date and consistent advice to traffic authorities
•improved clarity which will aid greater consistency of speed limits across the country
•the setting of more appropriate local speed limits, including reduced or increased limits where conditions dictate
•local speed limits that better reflect the needs of all road users, not just motorised vehicles
•improved quality of life for local communities and a better balance between road safety, accessibility and environmental objectives, especially in rural communities
•improved recognition and understanding by road users of the risks involved on different types of road, the speed limits that apply, and the reasons why
•improved respect for speed limits, and in turn improved self compliance
6•continued reductions in the number of road traffic collisions, injuries and deaths in which excessive or inappropriate speed is a contributory factor.
What the road looks like to road users should be a key factor when setting a speed limit.
Mean speeds should be used as the basis for determining local speed limits. These areunderpinned by extensive research demonstrating the well proven relationship between speed and accident frequency and severity, and also reflect 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.
There will be roads, or stretches of road, that suffer from poor compliance with the existing speed limit. Where this happens and the speed limit is considered to be appropriate for the road, there may be a mismatch between the appearance of the road and the driver’s or rider’s perception of the risks of a collision. 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 either 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.
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 traffic authorities should include an assessment of the following factors:
•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.
A key factor when setting a speed 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 what is an appropriate speed, where they can see there are potential hazards, for example outside schools, in residential areas or villages and in shopping streets.
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 be reflective of 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 pedestrian and cycle usage).
Vehicle-activated signs must not be used as an alternative to standard static signing, but as an additional measure to warn drivers of a potential hazard or to remind them of the speed limit in force.
The national speed limit on the rural road network is 60 mph on single carriageway roads and 70 mph on dual carriageways.
The majority of drivers do not reach or exceed the 60 mph limit on many single carriageway roads because it is often difficult to do so because of the characteristics and environment of the road. (but in the real world on the B4077!)
Nonetheless in 2004 some 46% of serious road casualties, and more than half of road deaths, occurred on rural roads.
Speed can be a major factor in the severance of local communities. The speed limit on single carriageway rural roads should take into account traffic and road user mix, the road’s geometry and general characteristics, its surroundings, and the potential safety and environmental impacts.
Building upon the Institution of Highways and Transportation’s rural safety management guidelines (IHT, 1999), traffic authorities are encouraged to adopt a two- tier hierarchical approach that differentiates between single carriageway roads with a strategic or local access function.
Higher speed limits should be restricted to ‘upper tier’ or high quality strategic single carriageway roads where there are few bends, junctions or accesses.
Lower speed limits would be appropriate on ‘lower tier’ single carriageway roads passing through a local community, or having a local access or recreational function. They would also be appropriate where there are significant environmental considerations or where there is a high density of bends, junctions or accesses, or the road is hilly. That's us folks !
It is government policy that, where appropriate, a 30 mph speed limit should be the norm in villages.
Traffic authorities should also consider the use of vehicle-activated signs (VAS), which have proved particularly effective at the approaches to isolated hazards, junctions and bends in rural areas.
In rural areas every effort should be made to achieve an appropriate balance between speeds, speed limits, road function and design, the differing needs of road users, and other characteristics. This balance may be delivered by introducing one or more speed management measures in conjunction with the new speed limits and/or as part of an overall route safety strategy. The aim should be to align the local speed limit so that the original mean speed driven on the road is at or below the new posted speed limit for that road.
Following investigations of the relationship between speed and accidents on rural single carriageway roads, TRL Report 511 (Taylor et al., 2002)successfully classified rural road sections into four groups reflecting their operational characteristics. Drawing upon the accident rate information available for these groups and the minimum total cost at a particular speed, TRL Published Project Report 025 (TRL, 2004) sets the following accident thresholds for upper and lower tier roads, which reflect expected levels associated with a road carrying a given level of traffic and an appropriate balance
between safety and mobility:
•upper tier roads – 35 injury accidents per 100 million vehicle kilometres
•lower tier roads – 60 injury accidents per 100 million vehicle kilometres.
The speed assessment framework operates on the principles that the speed limit choice should be guided by whether the accident rate on a section of road is above or below the respective 35 or 60 injury accident thresholds.
Upper tier A and B roads
•60 mph: high quality strategic roads with few bends, junctions or accesses. When the assessment framework is being used, the accident rate should be below a threshold of 35 injury accidents per 100 million vehicle kilometres.
•50 mph: lower quality strategic roads which may have a relatively high number of bends, junctions or accesses. When the assessment framework is being used, the accident rate should be above a threshold of 35 injury accidents per 100 million vehicle kilometres and/or the mean speed already below 50 mph.
•40 mph: where there is high number of bends, junctions or accesses, substantial development, where there is a strong environmental or landscape reason, or where the road is used by considerable numbers of vulnerable road users.
•30 mph: should be the norm in villages where appropriate.
VILLAGES
111.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, where appropriate, a 30 mph speed limit should be the norm in villages.
112.Traffic Advisory Leaflet 01/04 (DfT, 2004) sets out current policy on achieving lower speed limits in villages, including a broad definition of what constitutes a village. For the purpose of applying a village speed limit of 30 mph, a definition of a village can be based on the following simple criteria relating to frontage development and distance:
•20 or more houses (on one or both sides of the road); and
•a minimum length of 600 metres.
113.If there are just fewer than 20 houses, traffic authorities should make extra allowance for any other key buildings, such as a church, shop or school.
In some circumstances it might be appropriate to consider an intermediate speed limit of 40 mph prior to the 30 mph terminal speed limit signs at the entrance to a village, in particular where there are outlying houses beyond the village boundary or roads with high approach speeds. For the latter, traffic authorities might also need to consider other speed management measures to support the message of the speed limit and help encourage compliance so that no enforcement difficulties are created for the local police force. Where appropriate, such measures might include a vehicle-activated sign, centre hatching or other measures that would have the effect of narrowing or changing the nature and appearance of the road.
116.Where the speed limit commences at the village boundary, the village nameplate sign and speed limit roundel may be mounted together using the format prescribed in diagram 2402.1 of TSRGD. The combined sign should be located as near as practicable to the start of the development, so that drivers see housing at the same time as the signs,reinforcing the visual message for reduced speed.
117.If there are high approach speeds to a village, or the start of the village is not obvious,village gateway treatments can also be an effective way to slow drivers down. Further guidance on the use of gateway and entry treatments is included in Appendix B of this guidance. Advice can also be found in Traffic Advisory Leaflets 13/93 Gateways (DoT,1993a), 01/94 VISP – A Summary (DoT, 1994a) and 01/04 Village Speed Limits (DfT,2004).
118.In situations where the above criteria for a village are not met and there is a lesserdegree of development, or where engineering measures are not practicable or cost-effective to achieve a 30 mph limit, but a reduction from the national 60 mph speed limit is considered appropriate, traffic authorities should consider alternative lower limits of 40 or 50 mph.
SUMMARY
SPEED ASSESSMENT FRAMEWORK – NEW APPROACH TO SPEED LIMIT SETTING FOR SINGLE CARRIAGEWAY ROADS IN RURAL AREAS
1.Speed limits should be considered as only one part of rural safety management. The first priority where accident rates are high should be to seek cost-effective improvements to reduce these rates, targeting the accident types that are over-represented.
2.If high rates persist despite these measures, then lower speed limits may also be considered. But lower speed limits on their own without supporting physical measures, driver information and publicity or other measures will not necessarily change driver behaviour and therefore will result in substantial numbers of drivers continuing to travel at unacceptable speeds. This may lead to significant enforcement cost. So every effort should be made to achieve an appropriate balance between speeds, speed limits, road design and other measures. This balance may be delivered by introducing one or more speed management measures in conjunction with the new speed limits, and/or as part of an overall route safety strategy.
3.An assessment framework has been developed by TRL (Taylor et al., 2002) to help decision-makers weigh up, in a more transparent way, the advantages and disadvantages of each speed limit option and reach a well-founded conclusion for these roads.
4.The basis for the speed assessment framework procedure is:
•a firm theoretical basis for choosing speed limits for road functions, taking account of safety, mobility and environmental factors
•roads classified into two tiers based on road function
•closer integration of speed limit choice, with more general rural road safety management measures
•driver choice of desired speed to be reflected by mean speed
•local flexibility of choice within a consistent overall procedure.
5.The assessment framework combines safety and mobility costs to show how the overall total cost and the balance between the component costs change if different choices of speed limit are made. For a particular road type, total cost is similar over a relatively wide speed range, with mobility benefits being exchanged for safety benefits as speeds decrease.
6.A simple two-tier functional hierarchy should be used, with roads having either primarily a through traffic function (upper tier) or a local access (lower tier) function.
Both need to be provided safely. Mobility benefits will be more important for the upper tier than for the lower tier roads, whilst environmental benefits are likely to be of greater importance for the lower tier roads.
7. There may be many roads below A and B classification which serve a mixed through-traffic and access function. Where that traffic function is currently being achieved without a high accident rate, these roads should be judged against the criteria for upper tier roads.
If, however, for all or parts of these roads there is a substantial potential risk to vulnerable road users, these sections should be assessed against the criteria for lower tier roads.
8.Decisions on speed limits should take account of other accident reduction measures that might be applied. To help in this process, a technical guide has been developed,
Accident Analysis on Rural Roads (TRL, 2004) (downloadable from the TRL web site www.trl.co.uk), which provides information on typical collision rates, and typical proportions of different accident types, on different types of rural road. These can be used to judge whether other site- or route-specific measures might be appropriate that would reduce either speeds or accidents along the route.
9.Mean speed should be used for the assessment. For the majority of roads there is a consistent relationship between mean speed and 85th 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.
10.The aim should be to align the speed limit to the prevailing conditions, and all vehicles moving at speeds as close to the posted speed limit as possible. An important step in the procedure is to gain agreement with local enforcement agencies that the mean speed of drivers on the road with any new speed limits is acceptable.
11.The aim of the framework approach is to achieve a consistent application of speed limit policy throughout the country. But local issues in relation to particular routes can be reflected in the functional tier to which the road is assigned, and also through final decisions on acceptable mean speeds for each limit, on the importance given to local environmental factors, and on the choice of additional measures that could change the appropriate speed limit regime recommended.
Selection procedure
12.Within routes, separate assessments should be made for each section of road of 600 metres or more for which a separate 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 consistency over the route as a whole.
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