Top of this page1. Introduction

Since the 1960s, local highway authorities have had the power to set local speed limits on roads where they believe that the national speed limit is not appropriate. They have been assisted in doing this by Government guidance on speed limit setting. While this guidance has been amended from time to time, prior to 2006 it was always based on research showing that drivers respect speed limits only if they are close to the speed at which they would choose to travel if there was no limit.
The method of setting speed limits based on this research is often referred to as the "85th percentile" principle, i.e. a speed limit is set as close as possible to the speed that 85 per cent of drivers would not exceed anyway. This method produces the best compliance and means that the majority of drivers will be travelling at a legal speed. (For a fuller explanation, see the ABD's briefing paper, "Speed Limits: their correct use, setting and enforcement," which can be found on the ABD's website at
Increasingly in recent years, many local authorities have been reducing speed limits contrary to Department for Transport (DfT) guidance incorporating the 85th percentile principle. There are various reasons for this, including: a misguided belief that lower speed limits lead to lower speeds and fewer accidents; pressure from local residents or environmental groups; a desire to improve conditions for 'vulnerable' road users; or a political philosophy that car use should be discouraged by making driving unpleasant. The result has been a proliferation of new speed limits, many of which are illogical, unrealistically low and unnecessary, with wide variations between different areas. Respect for speed limits has been undermined and, quite often, the effect on accidents has been the opposite of that expected.
Against this background, in August 2006 the DfT issued a new circular on the setting of local speed limits, superseding the previous one issued in 1993. The new version has made fundamental changes to the way speed limits are set, notably the use of mean (average) speeds rather than the 85th percentile speed, and the adoption of a 'hierarchy' for rural single carriageway roads. These changes have, in effect, rewarded the actions of those authorities that ignored the previous advice.
The new guidance will encourage many highway authorities to reduce speed limits still further. The Government requires all highway authorities to review speed limits on their A and B roads by 2011. One aim of the new guidance is claimed to be a more uniform application of speed limits across the country. This could in theory lead to some limits being raised, but there is likely to be opposition to raising speed limits from the misinformed and from anti-car groups.
We can expect, therefore, a wave of new speed limit proposals, most of which will be for lower limits. The requirement to review all existing speed limits does, however, give ABD members an opportunity to be proactive, by demanding a voice in the review process. In this way we can try to counter the views of those who will be pressing for further lowering of speed limits - views that are rarely challenged.
Consequently, the scope of this document has been extended to cover more than just objecting to specific proposals as they are published - it now provides advice on how to approach your local highway authority before its proposals are finalised. In order to do this effectively, members will need a working knowledge of the contents of the DfT's latest guidance. This is the subject of the following section.

Top of this page2. Government guidance on speed limit setting

The latest government guidance is contained in Circular Roads 1/2006: Setting Local Speed Limits. The document runs to 48 pages, including appendices. Set out below are the underlying principles and key points of the guidance, and how they may be used in objecting to a proposed speed limit reduction or recommending that an existing limit is raised. Copies of the circular may be downloaded free of charge from the DfT website ( or obtained, for £9 per copy, from The Stationery Office (0870 600 5522).
Top of this page2.1 Underlying principles of the guidance
The key points set out in the circular are reproduced below, together with comments:
It is important that traffic authorities and police forces work closely together in determining, or considering, any change to speed limits.
Highway authorities have a statutory duty to consult the police about any proposed changes to speed limits. Of those police forces that responded to the DfT consultation before publication of the new guidance, two-thirds opposed the use of mean speeds instead of the 85th percentile as the basis of speed limit setting. Their concern was that this change would lead to lower speed limits being set, with reduced self-compliance and the need for greater enforcement. The remainder supported the move because it would be easier for the public to understand, not necessarily because it would result in more appropriate speed limits being set.
It is worth bearing in mind, therefore, when opposing a speed limit reduction, that the police may not be entirely supportive of it, either. Some police forces take a more robust line than others in opposing absurdly low speed limits, but the highway authority should always be asked for a copy of the police view on the proposal. When seeking a role in the speed limit review process, building a relationship with the police may be worthwhile - the police might even welcome an ally in the battle with those organisations promoting lower speed limits.
Alternative speed management options should always be considered before a new speed limit is introduced.
Some highway authorities regard the introduction of a speed limit as the automatic response to any accident problem or concern about traffic speeds. While the circular is based on a false presumption that lower speeds are inherently desirable, it does at least state that a reduced speed limit is not the only way of controlling speeds. For example, measures that change the way a road looks to a driver may lead to lower speeds without any change to the speed limit.
When a lower speed limit is proposed, therefore, the highway authority should be asked to explain what alternatives have been considered and why they have been rejected.
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.
This statement partly reflects the adoption of a hierarchy of rural roads for speed limit setting purposes, based on their function (e.g. strategic or local route; residential; recreational; use by walkers/cyclists, etc). While some aspects of a road's function will be obvious to drivers, the need for a low speed limit because a road has been categorised within a particular level of a bureaucratic hierarchy will not.
Drivers obviously need to reduce their speed when there are cyclists, pedestrians or equestrians around, but the numbers of such vulnerable road users are not constant throughout the day or week. A low speed limit that applies around the clock will not be respected, therefore, when those potential hazards are not present. This point needs to be made when speed limit reductions are proposed, especially in the case of 'lower tier' roads within the hierarchy.
Traffic authorities will wish to satisfy themselves that the benefits exceed the disbenefits before introducing or changing a local speed limit.
At least the guidance acknowledges that there are costs as well as 'benefits' from the introduction of new speed limits (many of the benefits being perceived rather than real). As well as (predicted) accident savings, other factors that highway authorities are told to take into account are: journey times for motorised traffic; environmental impact (including additional signs and engineering measures); community severance and public anxiety; conditions and facilities for vulnerable road users; the cost of any engineering measures; and the cost of enforcement.
The cost-benefit analysis in support of a speed limit proposal should be scrutinised for any false assumptions, and it might be suggested to the highway authority that there may be additional impacts that should be assessed in appropriate cases. For example, the imposition of a low speed limit on a significant length of a major route could lead to some drivers diverting to less suitable and possibly less safe roads.
What the road looks like to road users should be a key factor when setting a speed limit.
This is fundamental to realising how drivers respond to speed limits. Drivers adjust their speed according to the visual information they are receiving about the road ahead. They reduce their speed when they see potentially hazardous features - road narrowings, sharp bends, junctions, restricted visibility, roadside development, pedestrians, cyclists, etc - and increase it when those hazards are absent. It is vital, therefore, if a speed limit is to achieve self-compliance, that the limit matches the visual clues that drivers receive. In circumstances where the visual clues do not convey the true extent of hazards ahead, simply reducing the speed limit will not be effective - the driver's view needs to be changed.
It is also vital that speed limits change at the points where the character of the road changes, not a long way in advance. Many urban speed limits have been extended along rural approach roads in a mistaken belief that drivers will slow to the speed limit by the time they reach the built-up area. This often has the opposite effect - drivers ignore the speed limit because it does not match the visual environment at the point where it starts, and they may slow down less when they reach the point where the lower limit may be appropriate.
The adoption of mean speeds as the basis of speed limit setting is likely to lead to more instances where the speed limit is seen as too low for the hazard density, resulting in less compliance.
Mean speeds should be used as the basis for determining local speed limits. These are underpinned 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.
This claimed justification for moving to mean speeds for speed limit setting, which is at the heart of the new guidance, does not stand up to scrutiny. The 'extensive research' that has supposedly demonstrated a 'well proven' relationship between speed and accident frequency consists of a couple of desk-top studies from the 1990s and early 2000s, which were clearly commissioned by the government in order to justify the decision that had already been made - to make speed reduction and speed limit enforcement the core of road 'safety' policy.
The first of these reports was published in 1994 by the Transport Research Laboratory (TRL) and includes the now infamous claim that a 1mph reduction in average speeds leads to a 5 per cent reduction in accidents. A detailed exposure of the false assumptions and dubious statistical techniques used to produced this claimed relationship can be found on the ABD's website at
Later reports sought to refine this overall claim to develop separate relationships for different types of road. They all suffer from the same basic flaw: they compare accident rates on roads of similar type that have different average speeds. When similar roads have different average speeds, however, this is because they have different traffic flows, and accident rates vary with traffic flow. Thus both accident rate and average speed are a function of traffic flow, and not of each other. For this reason, the Transport Research Laboratory recommended that "...roads with very different flow rates should NOT be studied together." The emphasis is that of TRL itself and the quote comes from a technical guide on accident analysis for rural roads, published in 2004 (Published Project Report 026).
The second part of the justification for switching to mean speeds - that they reflect what the majority of drivers perceive as an appropriate speed - is patently absurd. It was true when speed limits were set to the 85th percentile level, but the mean speed is that exceeded by around half of all drivers. (It is not exactly half because the mean speed is not the same as the 50th percentile, unless the distribution of speeds is perfectly symmetrical about the mean. In most real-life situations, however, the difference between the mean and the 50th percentile will be small.) If only half of drivers regard a speed limit as appropriate for a particular road, that does not constitute a 'majority'.
In objecting to proposed speed limit reductions, especially for blanket speed limits along whole routes, these flaws in the guidance need to be emphasised. It should also be pointed out that safe driving requires speed to be varied to suit the changing circumstances along a road - slowing down where there are more hazards and speeding up where there are fewer. A blanket speed limit imposes an unnecessary speed reduction where higher speeds are safe, but may be too high where the hazards are greatest.
The overuse of speed limits encourages drivers to divest themselves of responsibility for judging a safe speed, relying instead on the signs beside the road. This can lead to drivers failing to slow down sufficiently for hazards. Instead of assuming that a lower speed limit will lead to lower speeds and fewer accidents, regardless of the causes of those accidents, highway authorities should be analysing the factors leading to individual accidents and addressing them directly.
The TRL report published in 1994 that first produced a claimed average speed/accident relationship also looked at the effect of changes in speed limit on the actual speeds driven. It found that average speeds changed by a maximum 25 per cent of the change in speed limit, whether up or down, e.g. a change in speed limit of 10mph would be expected to have an effect on average speeds of no more than 2.5mph. This conclusion can be used to disabuse those who believe that reducing a speed limit by 10 or 20mph will have an equivalent effect on actual speeds. It will not - indeed, the further that a speed limit departs from the 85th percentile, the less effect it is likely to have.
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.
Frequent changes of speed limit are undesirable because they can cause confusion. The longer a speed limit, however, the greater the likelihood that it will cover sections of road with significant changes in character, making the chosen speed limit a compromise that is poorly matched to any part of the road. The speed limit is then of little value to drivers as an indication of a safe speed.
This is a good argument for a general presumption against the use of local speed limits on a whole-route or blanket basis. Speed limits should be used sparingly, to highlight locations where the character of the road is markedly different from the rest of the route or area.
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.
This is one of the few pieces of sound advice carried over from the previous guidance. Isolated hazards should be dealt with on an individual basis, by engineering out the problem or providing extra warnings to drivers. Vehicle-activated signs that flash a warning if a driver is approaching at a speed above a certain threshold are especially effective, and have been shown to reduce speeds to safe levels without the legal sanction of a speed limit.
Top of this page2.2 Urban speed limits
Speed limits in built-up areas are least affected by the new guidance. The general urban speed limit of 30mph remains unchanged. The guidance states that the introduction of 20mph speed limits and zones is supported "where there is a particular risk to vulnerable road users."
The use of 20mph zones is controlled by a legal requirement to install traffic calming measures to make the zone self-enforcing, so that speed limit repeater signs are not required. A 20mph speed limit may be introduced without traffic calming, with mandatory use of repeater signs, but the guidance recognises that a 20mph speed limit, on its own, is unlikely to lead to a reduction in speeds of more than 2mph. For this reason, the guidance suggests that a 20mph speed limit should not be introduced if mean speeds are more than 24mph, unless traffic calming measures are also proposed.
Highway authorities may also set 40mph or 50mph speed limits on urban roads where appropriate. Appendix C to the guidance tabulates the characteristics of speed limits for roads in urban areas. It is reproduced in the appendices at the end of this document.
Top of this page2.3 Rural speed limits
This section of the guidance relates almost entirely to the setting of speed limits on single carriageways - the national speed limit of 70mph for dual carriageways should only be reduced if there are specific factors that make it unsafe to travel at that speed. The assessment framework set out in the circular does not apply to dual carriageways.
The assessment framework for rural single carriageway roads divides them into upper and lower tiers, depending on their strategic or local access function. Within each tier, there are accident rate thresholds to help highway authorities decide between different speed limits. The characteristics of upper and lower tier roads, and the accident rate thresholds, are summarised in Appendix D to the circular, which is reproduced in the appendices at the end of this document.
Significant points in the circular that could be of value when opposing a speed limit reduction (or proposing an increase) are as follows:
Speed limits should be considered as only one part of rural safety management, and what the road looks like to the road users, the road function, traffic mix, and road and rural characteristics should be taken into account.
This should be self-evident, but too many local authorities fail to look beyond speed limit reductions when dealing with an accident problem.
Where accident rates are high, traffic authorities should seek cost-effective improvements to reduce these rates by targeting the particular types of accidents taking place.
Again, this should be self-evident, and highway authorities should be asked about the analyses they have carried out into accident causes before they proposed a lower speed limit. The circular also commends the use of vehicle-activated signs (as mentioned in section 2.1 above) for dealing with problems at isolated hazards.
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.
This is very important - the guidance requires that the speed limit should never be lower than the actual mean speed. Under the previous guidance, a speed limit could be set that was below the 85th percentile speed by up to 20 per cent. Where this has been the case, it is unlikely that any further reduction in speed limit would be justified using the mean speed. However, highway authorities have flouted the previous guidance with impunity, so they may feel able to do the same with the new version. Any attempt to set speed limits below the mean speed should be resisted strenuously.
Widespread implementation of speed management over the whole minor rural road network could require a costly and environmentally sensitive increase in the level of signing. Traffic authorities should seek to ensure that a sensible balance is achieved.
There are no proposals to relax the signing requirements for speed limits, so that any reductions below the national speed limit of 60mph will require terminal and repeater signs in the normal way. It would certainly be costly and intrusive to sign low speed limits on all country lanes, and is quite unnecessary as most road users are capable of adjusting their speed to a safe level, below the national speed limit where required, without constant instruction and regulation. This issue should be used as a major deterrent to highway authorities seeking to impose blanket low limits.
It is important to note that [the outcome of the assessment] does not imply that speed limits should automatically be reduced. Indeed, in some cases the assessment may suggest that the existing speed limit may already be inappropriately set or too low, and an increased limit should be considered.
This is another important point and means that, in some cases, a local speed limit has been set that is not required - rather than just raising it, it should be scrapped altogether and be replaced by the national speed limit. Again, a presumption against the use of local speed limits, except where really needed, should be stressed.
Annex E of the 1980 circular on speed limit setting shows evidence of the beneficial effects of raising unrealistic speed limits, including little change in actual speeds and, in some cases, reductions in accidents. While the circular itself is obsolete, the evidence in this annex is still relevant, since it reflects the way drivers respond to speed limits - which is a function of human nature. The annex is reproduced in the appendices at the end of this document and is useful ammunition for dealing with those people who believe that raising speed limits would inevitably lead to an increase in accidents.
It is government policy that, where appropriate, a 30mph speed limit should be the norm in villages.
No one would argue that a 30mph speed limit should not apply in settlements that meet the normal perception of a village, but the official definition is 20 or more houses (on one or both sides of the road) and a minimum length of 600 metres. Some settlements meeting these criteria could be visually very different from the everyday idea of a 'village', especially if the road is wide and the properties set well back. The words 'where appropriate' may be significant and should be pointed out to those seeking 30mph limits unreasonably.
Top of this page2.4 Quiet Lanes and Home Zones
The concepts of Quiet Lanes and Home Zones have developed in recent years and are included in the guidance on speed limit setting for the first time. Quiet Lanes are minor rural roads with little through traffic and may be used by walkers, cyclists or equestrians. Home Zones are local residential roads where non-motorised users have priority over vehicles. Both designations require the involvement of residents. Legal speed limits are set in the same way as for other roads, but low speeds should generally be assured by a scheme's design. By their nature, Quiet Lanes and Home Zones will generally affect only those people who live in or very near to them.

Top of this page3. How speed limits are set

Local highway authorities are able to set speed limits by making an order under the provisions of the Road Traffic Regulation Act 1984. The point is, anyone can make an objection to a proposed speed limit and the highway authority must give proper consideration to any objections received. This means that, if an objector raises issues which were not considered by the authority when it resolved in principle to set the speed limit, then those issues must be put before the elected members of the authority. A decision is then made on whether to proceed with, modify or abandon the proposal.

Highway authorities have to take objections seriously and give a reasoned justification for rejecting them, otherwise they could lay themselves open to challenge in a judicial review. This would obviously be a very expensive course of action and one which few individuals would be able to contemplate, but authorities are unlikely to take the chance, especially if an objection is submitted by someone who seems to know what they are talking about. A number of similar objections making the same points also carry more weight than just one. It is not a good idea, however, to send several copies of the same letter signed by different individuals. Local authorities are suspicious of such orchestrated campaigns. It is much better if each individual composes their own letter.

Top of this page4. Other Traffic Regulations

The advertisement and objection process applies not just to the setting of speed limits but to the imposition of any form of traffic regulation, such as banned turns, weight limits and waiting restrictions. The skill from the traffic engineer's point of view is to anticipate the likely grounds of objection and to address them in the initial report to the authority's members, seeking their approval in principle. Any objections can then be dealt with fairly easily. Few highway authorities will ever have received a serious objection to a speed limit order, so a carefully worded letter could give them a nasty shock!

Top of this page5. So what can you do?

So what does this mean for those of us who are trying to preserve some sanity in our traffic laws? First, it means keeping our eyes open to what our local highway authorities are proposing. The official notices pages of local papers may not be the most exciting read, but it is worth spending a few minutes a week scanning them for notifications of proposed traffic regulation orders. If you spot a proposal with which you disagree, you must submit your objection in writing, to the address given in the notice and by the published closing date.
In order to make an effective objection, you will need to know the grounds on which the authority is proposing to make the order. Local papers will often report the proceedings of Council committees in their editorial pages. These may give you advance warning of what is proposed, often weeks or even months before the official notice is published. Take note of any controversial proposals and go along to the local library, where the agendas and minutes of all Council committees are available for inspection. You should be able to take copies of any reports you need. If the official notice was the first you heard of the proposal, phone the relevant Council department and ask which committee made the decision and on what date. That will save you a lot of time at the library.
Whether or not you have seen the committee report which led to the proposal, go along to the Council office cited in the official notice and inspect the documents on deposit there relating to it. These will include, as a minimum, a map and schedule specifying the exact length of road involved and a 'statement of reasons'. The latter is important, as you will see later, so you should make a copy of it, word for word. Also make a note of any other information which may be available: for instance, if there is an existing speed limit, which the new order seeks to reduce, there may be a copy of the current order showing the date when it came into effect. This could also be used in support of an objection.
Top of this page5.1 Summary of Information Collection Tasks

Top of this page6. How to compose a letter of objection

To ensure that there can be no doubt about the proposal to which you are objecting, the subject heading of your letter should reproduce exactly the official title of the proposed order. An example might be:

Right at the start, make it clear that you are submitting a formal objection and the basic reasons for doing so. You can then go on to elaborate them.
At this point it is suggested that you quote the statement of reasons given by the Council for proposing the order, so that you can then show why you think the proposed speed limit will not fulfil the Council's wishes. Although they will vary slightly, the following example is typical of the reasons given for most speed limit proposals:
"The Council propose to make the above-named Order to restrict vehicle speeds to speeds appropriate to the environment in the interests of safety of all road users."
The phrase "to restrict vehicle speeds" implies a belief that speeds can be reduced simply by lowering the speed limit. As already shown, research proves that this is not the case and even the Government's latest advice on the setting of speed limits acknowledges the fact.
You should then make any relevant points or ask relevant questions concerning the council's proposal and how it was developed, if they are not dealt with adequately by the documents that you have managed to acquire. These questions should relate especially to the guidance set out in Circular Roads 1/2006, described in section 2 above. To summarise, these points could include any or all of the following: In the case of a speed limit proposal in an urban area, the following points may be relevant: For proposed rural speed limits, the following points may be relevant: At the end of the letter you need to make it quite clear that your objection will not be withdrawn unless the council can satisfy you about the concerns you have raised. You should also request that your objection is acknowledged and information provided about the way in which it will be considered. This will be done in one of two ways: either by a report to the committee, to be considered at a meeting open to the public (your letter will be attached to the report and will thus become a public document) or, if powers have been delegated to a cabinet member, by a formal consultation between that member and the relevant chief officer. In the latter case, the report will still be available for public scrutiny, but it will not be considered at a full meeting of the committee.
It is advisable to be selective about submitting objections: check the road concerned carefully, noting its characteristics in relation to the descriptions given in the appendices to the DfT's guidance. Take photographs at relevant points to show the road environment as seen by a driver. Be sure that the proposed speed limit really is excessively low, so that you cannot be accused of objecting just for the sake of it.
As a final point, highway authorities are not acting illegally if they impose speed limits that do not meet the criteria in the DfT's advice. In most cases, they will have done so in the absence of any objections, because few people will have been aware of their intentions until the speed limit signs appear, by when it is too late. If you object on the basis that the DfT criteria have not been followed, however, they will be on very weak ground if they cannot demonstrate either that the criteria have been met or they can produce a convincing argument as to why the criteria should not be applied in the case in question. A bland statement such as "it is council policy" is not adequate and should be challenged.
If you think your objection has been dismissed lightly, make a formal complaint to the council that it has not properly considered your views. If you are still unsatisfied, you can seek intervention by the Local Government Ombudsman. Note, however, that the Ombudsman can only concern himself with whether a council has followed correct procedures, not with the council's decision itself. The Ombudsman is only likely to consider your case, therefore, if the council failed to make an adequate response to your objection. If it did so, but you disagree with the decision, the Ombudsman is powerless.
Top of this page6.1 Summary of main points when Objecting

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Top of this page8. Appendices

Top of this page8.1 Appendix C to Circular Roads 1/2006 : Speed Limits in Urban Areas

Speed Limit
In town centres, residential areas and in the vicinity of schools where there is a high presence of vulnerable road users.
The standard limit in built-up areas with development on both sides of the road.
Higher quality suburban roads or those on the outskirts of urban areas where there is little development. Should be few vulnerable road users.
Should have good width and layout, parking and waiting restrictions in operation, and buildings set back from the road.
Should wherever possible cater for the needs of non-motorised users through segregation of road space, and have adequate footways and crossing places.
Usually most suited to special roads, dual carriageway ring or radial routes or bypasses which have become partially built up.
Should be little or no roadside development.

Top of this page8.2 Appendix D to Circular Roads 1/2006 : Speed Limits for Single Carriageway Roads in Rural Areas*

Speed Limit
Upper tier - roads with predominant traffic flow function Lower tier - roads with important access and recreational function
Recommended for most high quality strategic A and B 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 with this speed limit.
Recommended only for the best quality C and Unclassified roads with a mixed (i.e. partial traffic flow) function with few bends, junctions or accesses.
In the longer term, these roads should be assessed against upper tier criteria.
Should be considered for lower quality A and B roads which may have a relatively high number of bends, junctions or accesses.
When the assessment framework is being used, the accident rates should be above a threshold of 35 injury accidents per 100 million vehicle kilometres at higher speeds.
Can also be considered where mean speeds are below 50 mph, so lower limit does not interfere with traffic flow.
Should be considered for lower quality C and Unclassified roads with a mixed function where there are a relatively high number of bends, junctions or accesses.
When the assessment framework is being used, the accident rate should be below a threshold of 60 injury accidents per 100 million vehicle kilometres.
Should be considered where there is a high number of bends, junctions or accesses, substantial development, where there is a strong environmental or landscape reason, or where there are considerable numbers of vulnerable road users. Should be considered for roads with a predominantly local, access or recreational function, or if it forms part of a recommended route for vulnerable road users.
When the assessment framework is being used, the accident rate should be above a threshold of 60 injury accidents per 100 million vehicle kilometres.
Should be the norm in villages

* Recommended speed limits to which traffic authorities are encouraged to move over a period of time, subject to their meeting local needs and considerations.
Top of this page8.3 Appendix E to Department of Transport Circular Roads 1/1980
The Effect of Altering Levels of Speed Limits: Summary of Experience
  1. It is a common but mistaken belief that drivers allow themselves a set margin over the prevailing speed limit, and that if a limit is raised by 10 mph, they will travel 10 mph faster. In fact, an increase in an unrealistic speed limit rarely brings an increase in traffic speeds. ("Unrealistic" is here used to mean "substantially below the 85 percentile speed"). It is much more likely that there will be no change, or even a fall. It seems that drivers relieved of the frustrations of too low a limit rarely abuse the higher one. Indeed it is not unusual for the accident rate to fall when a poorly-observed limit is raised. This may mean that reduced frustration leads to changes in driving behaviour conducive to accident reduction.

  2. The evidence for asserting that speeds and accidents do not increase in proportion to an increase in speed limit comes from studies made before and after unrealistic local limits have been raised. Some of the main evidence is summarised in paragraphs 3-9 below.

  3. In 1960, a Departmental Road Safety Committee reporting on the results of the experimental introduction of 40 mph speed limits in the London area concluded that the raising of the limit had resulted in no appreciable change in speeds, while the accident rate remained substantially the same. The committee considered that the higher limit had achieved its purpose of removing unjustifiably low speed limits, and encouraging a proper standard of enforcement.
  4. A before and after study carried out at 20 locations through Kent, where the limit had been raised from 30 mph to 40 mph, showed a fall in speed, or no change, in 80% of the measurements taken, and a small increase in the others. The total number of accidents fell by almost 20%.

  5. In 1973 the Metropolitan Police produced the results of a study on six sections of trunk road where — in accordance with the Department's criteria — speed limits had been raised from 40 to 50 mph, or from 30 mph to 40 mph. At four locations the 85 percentile went up by less than 2 mph and at two locations it went down. Allowing for a general decrease in accidents, the reduction in the number of accidents at these places was 15%.

  6. When the speed limit in Park Lane, London W1, was increased from 30 mph to 40 mph in 1970, the 85 percentile speed fell from 43.6 mph (measured in 1970) to 39.2 mph (measured in 1974).

  7. In 1974, the Midland Road Safety Unit reported the results of a study of a large number of speed limit changes from 30 mph to 40 mph. Their conclusion that there had been no significant increase in either speeds or accidents was in line with the conclusions from a similar exercise for cases in other parts of the country carried out within the Department.

  8. The Department has recently conducted a survey of the effects of changing the levels of speed limits in various parts of the country. The results indicate that raising speed limits has little effect either on the speeds of vehicles or the rates of accidents.

  9. The following examples of local speed limit changes from 30 mph to 40 mph illustrate this point.

      85th Percentile Speed Accident Rate
    County Road Before After Before After
    Cheshire A41 44 43 1.06 0.6
    Lancashire B5253 43 37 0.78 0.85
    West Yorkshire A58 40/43 47/52 1.45 0.65
    Warwickshire A34 42/42 43/43 0.5 0.65
    Warwickshire B4453 42/44 43/43 3.2 1

    The table above shows that, in the one instance in which speeds rose, the accident rate went down.

  10. With the removal of the energy conservation speed limits in June 1977, the national speed limit went up from 50 to 60 mph on single carriageway roads and from 60 to 70 mph on dual carriageway roads. This afforded an ideal opportunity to judge if traffic responds to national speed limit changes in the same way as it does to local changes. A survey of speeds at 49 points throughout the country made in July 1977, compared with a similar survey in July 1976, showed that for cars and motorcycles with a headway of at least 5 seconds there was no change in the mean speed on single carriageway roads and a 1 mph on single carriageway roads and 2 mph on dual carriageway roads (sic). An analysis of national accident rates in the months following the changes shows no evidence that raising the limits caused any increase in the number of accidents.

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