Submission for the Raising of the
Motorway Speed Limit

CONTENTS
 Summary
1.Introduction
2.Background to the 70 mph speed limit
3.Developments in the last 35 years
4.Adverse effects of the 70MPH motorway speed limit
5.Effects of raising the motorway speed limit
  Speed
  Safety
  Environment
  Economy
6.Conclusions
7.Recommendations
 References
 Appendix 1. Value of Time Saved from an Increase in Speed Limit
 Appendix 2. Changes in Vehicle Operating Costs


SUMMARY

The 70 mph speed limit on motorways has been in force since December 1965. It was introduced as an illogical reaction to a series of multiple accidents in poor weather conditions. That such accidents occurred and continue to occur is not surprising, since drivers have never been offered effective training in judging speed and distance within the unique visual environment of a motorway.

A 70 mph speed limit imposed in good conditions could not and has not prevented these accidents. The report on the 70 mph 'experiment' attempted to justify its continuation but provided no valid evidence that accidents had reduced.

In the last 35 years, substantial improvements have been made in vehicle and highway engineering. Drivers have become much more accustomed to motorway driving, even though training is still inadequate. In 1965, 70 mph represented more than 80% of the maximum speed of average cars. Now it represents only 60%. The result is that 56% of car drivers exceed the motorway speed limit.

The widespread lack of compliance with the 70 mph speed limit is an indication of its irrelevance to modern conditions and is detrimental to respect for speed limits in general. Other adverse effects of the outdated speed limit are the creation of traffic bunching, poor lane discipline and lack of driver concentration. It is also preventing the full economic benefits being achieved from the nation's investment in a high-standard motorway network.


This paper assesses the consequences of raising the motorway speed limit to 80 mph or removing it altogether. It looks at the likely effects on actual speeds, safety, the environment and the economy.

The measure of speed generally used when setting speed limits is the 85th percentile speed. This is the speed at or below which 85% of vehicles travel. On motorways in the UK, the 85th percentile speed for cars is approximately 85 mph, i.e. 15 mph above the current limit. An increase in the speed limit to 80 mph would be expected to lead to a rise in the 85th percentile speed of around 2.5 mph, to 87.5 mph. This would mean a greatly reduced percentage of drivers exceeding the speed limit and the majority would be below the Association of Chief Police Officers' guideline level for prosecution. Removal of the speed limit altogether would be expected to lead to an increase in the 85th percentile speed to no more than 95 mph (10 mph more than today), which is the current level on those autobahns in Germany that are unrestricted.

The impact on safety is the most obvious area of concern and there will be those who find it hard to accept that raising the speed limit would not have a detrimental effect. International comparisons, however, show no correlation between motorway speed limits and accident rates. Evidence from the United States indicates that overall accident rates and insurance claims fell when freeway speed limits were raised, contrary to the predictions of many. There is no reason to believe, therefore, that an increase in the motorway speed limit in the UK would result in a higher accident rate and it is possible that it could reduce. The most cautious estimate is that an increased motorway speed limit would be neutral in safety terms.

The impact of a raised motorway speed limit on the environment has been assessed in terms of the emissions of toxic pollutants, carbon dioxide and noise.

Most of the toxic emissions covered by the National Air Quality Strategy (NAQS) are within their target levels or are set to meet them, as emission controls improve. The increases arising from small changes in actual speeds would be insignificant. Levels of only two pollutants, nitrogen dioxide and particulates, are forecast to exceed their NAQS targets under any foreseeable circumstances. In the case of nitrogen dioxide, the target is likely to be exceeded only in the centres of the largest cities. There will not be a problem along sections of motorway where traffic is flowing freely enough to permit a higher speed limit to be exploited.

Transport contributes only a quarter of airborne particulates and most of that comes from the large diesel engines of buses and heavy goods vehicles, which would not be affected by a change in speed limit.

The ABD does not accept that global climate change is caused by human activity and emissions of carbon dioxide (CO2) from the burning of fossil fuels. Nevertheless, even if the gas were accepted to be a 'pollutant', an increase in the motorway speed limit would have a negligible effect on its concentration in the atmosphere. It is calculated that removal of the motorway speed limit altogether would increase man-made emissions in the UK by only 0.4% and all CO2 emissions by just 0.016%.

Higher speeds would have a small effect on the frequency of traffic noise, most of which is generated between a vehicle's tyres and the road surface. The high proportion of heavy goods vehicles on motorways contributes significantly to overall noise levels and will largely mask any change in the component from cars and other light vehicles. Any increases in noise will be much less than the reductions to be achieved from the Government's programme for resurfacing the motorway and trunk road network.

Increasing the motorway speed limit would result in significant economic benefits from time savings and these would greatly outweigh the additional costs of resources consumed, even assuming the high, pre-tax fuel prices which prevailed in 2000. It is estimated that an increase to 80 mph would lead to net savings of around £50 million per year. If the limit were removed altogether, the savings would increase to around £130 million per year. In addition, there would be a significant increase in tax revenue to the Treasury due to increased fuel consumption. This could be as much as £840 million per year if the speed limit were removed altogether.

The ABD recommends, therefore, that there should be an immediate increase in the motorway speed limit to 80 mph. After a suitable period of acclimatisation to a higher speed limit, possibly three years, consideration should be given to a further increase or removal of the limit altogether. Training and testing of drivers must be improved in motorway driving skills, particularly judgment of speed and distance in conditions of restricted visibility. The anomaly under which exceeding the speed limit on motorways is punished more severely than on other roads should be removed.


1.Top of this pageINTRODUCTION
1.1.It is now 35 years since the national speed limit of 70 mph was first imposed, on an experimental basis. The stated reasons for its introduction were controversial at the time and the cynics' view about the 'experiment' was borne out two years later, when the limit was made permanent.
1.2.A great deal has changed in the intervening period. The network of motorways has expanded and drivers have become more experienced with the demands of high-speed roads, both in the UK and in Europe. All aspects of vehicle performance have improved enormously, partly in response to the development of high quality, inter-urban road networks.
1.3.The resulting situation today is that motorways are not only our fastest but also our safest roads. In 1999, 56 per cent of cars exceeded the 70 mph limit, but the accident rate, at 11 accidents per hundred million vehicle kilometres, is around one-eighth the rate on roads in built-up areas1.
1.4.The ABD believes that an increase in the motorway speed limit is long overdue. Our 70 mph limit is one of the lowest on this class of road in Europe and is increasingly held in contempt by drivers. This paper will show that an increase in the speed limit is not only possible without adversely affecting safety or the environment but would have positive benefits.
1.5.Any suggestion that speed limits should be raised is met predictably with horror in some quarters. The debate on this issue needs to rise above the emotive level and focus on the facts. This paper is an attempt to inform that debate.
 
2.Top of this pageBACKGROUND TO THE 70 MPH SPEED LIMIT
2.1The first section of motorway in the UK opened in 1958 (the Preston Bypass, now part of M6), but the M1 between Watford and Crick was the first significant length and was opened the following year. At that time there was no national speed limit on roads outside built-up areas. Few British drivers had experience of motoring on the Continent and those lengths of dual carriageway road that existed in the UK had at-grade junctions and were open to all classes of traffic. Consequently, motorways were a totally new experience for most drivers, for which they were poorly equipped. Advertising campaigns gave basic information on the rules of motorway driving but there was no training for the skills required.
2.2Not only were drivers ill prepared to take advantage of the new roads but so were their vehicles. Many family cars struggled to reach 70 mph, let alone cruise at that speed. Lubricants and tyres were not capable of sustained high-speed use, leading to engine or tyre failures. The roads themselves, whilst excellent in terms of alignment and grade-separated junctions, had no central safety barriers, so it was too easy for an out-of-control vehicle to cross to the other carriageway with disastrous results. There was also no system for warning drivers of hazards ahead.
2.3The result was some spectacular and highly publicised accidents, which led to a belief amongst many people that motorways were inherently dangerous. That perception continues to some extent today, despite the enormous changes that have taken place in the interim. It can be seen in tangible form in the anomaly between the maximum penalties for speeding on motorways (£2,500) and other roads (£1,000), even though all-purpose dual carriageways have the same speed limit, may have at-grade junctions and can be used by cyclists, agricultural vehicles and even pedestrians.
2.4The perception that motorways were dangerous undoubtedly sowed the seed that ultimately led to the introduction of the 70 mph speed limit. The continuation of that view, possibly at a subconscious level, is part of the problem in trying to have a rational debate on the issue today.
2.5One of the most significant differences between driving on a motorway and an all-purpose road is the open aspect of a motorway, with few visual reference points to the sides against which to gauge speed. This is a particular problem in poor visibility, especially fog. The result is that drivers, who have not been trained to beware of this phenomenon and compensate for it, are often unaware that they are travelling at a speed from which they cannot stop within the clear distance ahead of them.
2.6The motorway network expanded during the first half of the 1960s and, by the end of 1965, totalled 629 km in length2. Traffic volumes grew also, leading to increased frequencies of multiple accidents in poor visibility when drivers, with no proper training for motorway driving, fell victim of the trap set by the lack of reference points. Unhelpfully, the media and even the Police dubbed this phenomenon 'motorway madness', implying that it was caused by the wilful recklessness of drivers. In fact, it was the entirely predictable result of the physiological processes by which the brain interprets what the eyes see.
2.7A series of multiple accidents in fog in 1965 led the Government into the all too familiar position, where it felt that it had to be seen to be 'doing something'. The result was a four-month 'experiment', starting on 22nd December 1965, of a mandatory maximum speed limit of 70 mph on all roads previously unrestricted. At the same time, an advisory speed limit of 30 mph was to apply on motorways in poor visibility, when indicated by flashing amber warning lights, controlled by the Police.
2.8The validity of this 'experiment' was highly questionable from the start. A four-month period is inadequate to test any road safety initiative. In this case, the experiment began in mid winter, when weather conditions can vary significantly from one year to the next. Furthermore, a scientific experiment can only be valid if there is a control case against which to test the results. By introducing a maximum speed limit on all roads in the country at once, instead of on a selected sample, it was impossible to differentiate the effects of the speed limit from those of other variables.
2.9The other question that has never been answered is how the introduction of an overall speed limit in good weather conditions was expected to address the problem of accidents in fog. It is totally illogical and an example of the sort of muddled thinking that frequently prevents real improvements in road safety being achieved. One suspects that the dangerous image of motorways that had developed from the early days, referred to above, coupled with a much publicised incident in which a car manufacturer tested a sports-racing car on the M1 at 190 mph, led the Government to look for an excuse to impose a maximum limit. Whatever the real reason, it was clear that there was never any intention to conduct a serious 'experiment' and the 70 mph limit would be made permanent.
2.10The evaluation of the speed limit trial was contained in a report published by the then Road Research Laboratory in 19673. In an article in Autocar magazine4, Lord Chesham, executive vice-chairman of the RAC, said: "Never have so many statistics been compared with so many variable yardsticks. There are enough red herrings in this report to fill the hold of the largest Grimsby trawler afloat."
2.11The report itself acknowledged the difficulties of coming to a definitive view on the effectiveness of the 70 mph speed limit on accident rates, based on the data available. It stated that: "The number of motorway accidents and casualties available for study, even over several years, is relatively small and often inadequate for the detailed studies necessary to reach firm conclusions." Whilst the report claimed that: "In clear weather, on the 73 miles of M1/M10/M45 during the trial period, the accident rate….was significantly lower (by 10 per cent) than the average for the previous five years", it also acknowledged that casualty rates had been falling during the previous six years. It was impossible to claim, therefore, that the reduction in motorway accident rates was attributed to the speed limit and not to the general trend in reduced accident frequency.
 
3.Top of this pageDEVELOPMENTS IN THE LAST 35 YEARS
3.1Since the 70 mph speed limit first came into force at the end of 1965, there have been significant improvements in highway and vehicle engineering. Driver experience in the use of motorways has increased, although there is still no requirement for drivers to undergo training or testing in motorway driving skills. These issues will be explored in more detail in the following paragraphs.
3.2The motorway network has continued to expand since 1965 and, by 1999, totalled 3,358 km in length1. The design standards in terms of horizontal and vertical alignment increased slightly at the end of the 1960s, when the design speed of rural motorways and dual carriageways changed from 70 mph to 120 kph (75 mph).
3.3From the safety point of view, one of the most significant changes in highway engineering has been the almost universal fitment of central reservation barriers. Whilst these are not adequate to prevent vehicles crossing into the opposite carriageway in all circumstances, especially where heavy goods vehicles are involved, they have reduced significantly the opportunities for crossover crashes. Incidents involving vehicles crossing into the opposite carriageway are amongst the most dangerous that can occur on a motorway, as the closing speeds may be high and drivers on the other carriageway have little opportunity to anticipate the danger or react to it. Safety barriers have also been fitted extensively to prevent vehicles hitting bridge abutments and street furniture on the nearside of carriageways and on high embankments.
3.4Another area of significant improvement has been in driver information. The amber flashing lights to warn of poor visibility, introduced with the 70 mph speed limit, were not very successful as they were operated manually at the roadside by the Police, who were unable to ensure that they reflected changing conditions. Since they were often left flashing long after the hazard had disappeared, they quickly lost credibility with drivers. The flashing lights were superseded by matrix signs, which provided more information. These were also under the manual control of the Police, however, albeit from central control rooms, so they still suffered to some extent from out of date information being displayed. The introduction of automatic fog detection systems has improved the quality of information to drivers significantly. The larger matrix information boards that have been installed on some motorways recently enable much more useful warnings to be given.
3.5Improvements in information have not been limited to roadside signs. The network of local radio stations has developed since 1967 and most feature traffic and travel reports at regular intervals. The development of radio receivers with the RDS function has enabled traffic reports to override whatever programme a driver happens to be listening to. In recent years, the Trafficmaster system of roadside beacons to detect congestion has spread to most of the motorway and trunk road network. This allows drivers to receive up to date information about conditions ahead, enabling them to choose an alternative route if desired. As information systems have become more reliable, drivers have gained more confidence in them and are more likely to act on the messages received.
3.6The greatest improvements in the last 35 years by far have been in the areas of vehicle engineering and performance. In 1965, the average top speed of cars listed in Autocar's summary of road test results5 (excluding rare and expensive exotica, few examples of which would be seen on the roads) was 89 mph. Even this figure is on the high side, as the vehicle fleet would contain proportionately more average family cars with performance in the lower part of the range. A more realistic value for the average top speed of cars on the road at that time, therefore, is likely to be around 85 mph. Consequently, the 70 mph speed limit represented about 82% of the maximum speed of cars in 1965.
3.7In 2001, the average top speed of cars listed in Autocar6, excluding exotica, is 122 mph. Again, taking into account the proportion of more mainstream cars in the overall vehicle fleet, a more accurate figure is likely to be around 116 mph. At this figure, the unchanged 70 mph speed limit represents just 60% of the maximum speed of ordinary cars in 2001.
3.8This improvement in vehicle performance has come about from a combination of increased engine efficiency, reduced transmission losses, higher gearing (including five- and even six-speed gearboxes) and vastly improved aerodynamic efficiency. Lubricants and tyres have been developed to cope with sustained driving at speeds well above 70 mph.
3.9The increase in vehicle performance has been more than matched by improvements in both active and passive safety. Active safety covers the features that enable drivers to avoid being involved in accidents. The most obvious area is that of braking performance. In 1965, many cars were still equipped with drum brakes all round, stopping distances were dictated largely by tyre performance and there were no aids to prevent wheel lock-up or to maintain steering control under braking. The braking distance shown in the Highway Code at 70 mph is 75 metres, which was probably a realistic figure in 1965 under good conditions with a reasonably competent driver at the wheel. In 2001, nearly all cars tested by Autocar6 could brake from 60 mph to a standstill in 3 seconds or less. This rate of deceleration is equivalent to a braking distance from 70 mph of 55 metres. When the thinking distance is added, this means that the total stopping distance for a modern car is 76 metres, compared with 96 metres shown in the Highway Code. This represents a 21% improvement in performance since 1965.
3.10These bare figures do not show the whole story. Nearly all cars produced today are fitted with anti-lock braking systems. Not only do these allow relatively unskilled drivers to access a car's full stopping abilities on a consistent basis, they also enable steering control to be maintained whilst doing so. Some more expensive and performance oriented cars are equipped with dynamic stability aids, which will become more widely available in time. These enable vehicles to be kept under control in extreme circumstances, such as when taking avoiding action.
3.11Part of the improvement in braking performance can be attributed to the development of tyre technology. In 1965, radial-ply tyres were only just starting to make significant inroads into the original-equipment market. Today, even quite ordinary cars are fitted with tyres having much greater cornering, braking and wet weather grip than those of the 1960s. The design of suspension systems has become more sophisticated, to take advantage of the abilities of the latest tyres. Even basic modern tyres are capable of being run at sustained speeds above 100 mph without risk of failure.
3.12Another element of active safety is the improved ride comfort, heating and ventilation of modern cars. Couple with reduced interior noise, these improvements enable long distances to be covered without the fatigue induced by the less refined cars of 35 years ago.
3.13Passive safety covers the features that reduce the risk of death or injury to a vehicle's occupants if an accident does occur. In 1965, considerations of passive safety extended to little more than the elimination of sharp edges on the facia, collapsible steering columns and the fitment of static front seat belts, which had to be adjusted to individual wearers. If they were worn at all, therefore, they were often incorrectly adjusted.
3.14Today's cars are fitted with rigid passenger safety cells, with side-impact and rollover protection and deformable structures front and rear. Automatic seat belts all round, often with pre-tensioners, are supplemented by air bags, which may also offer side-impact protection. Improved seat designs with integral head restraints protect against whiplash injuries.
3.15The final element in the equation is the driver. It is deplorable that there is still no legal requirement for drivers to demonstrate a minimum level of competence in motorway driving, either during the basic driving test or in a supplementary test, before a full driving licence is granted. Once a driver has passed the basic test, therefore, motorway driving skills are usually obtained by unsupervised experience, so that faults or bad habits may develop and remain uncorrected.
3.16Notwithstanding this lack of supervised training, most drivers today have much greater experience of driving on motorways than was the case in 1965. Many have gained experience of driving in continental Europe, where motorway speed limits are generally higher than in the UK. As noted in the introduction to this paper, speed surveys show that 56% of car drivers exceed the 70 mph limit on motorways in this country and a significant proportion regard 80-85 mph as a normal cruising speed.
3.17Given all the changes that have occurred in the last 35 years, there is, in the ABD's view, an unanswerable case for an increase in the motorway speed limit.
 
4.Top of this pageADVERSE EFFECTS OF THE 70 MPH SPEED LIMIT
4.1The existence of the 70 mph motorway speed limit has a number of negative effects, many of them on driver behaviour. Poor lane discipline, driving too close to the vehicle in front and bunching of traffic are related problems, leading to danger and inefficient use of the capacity of the road. Since few car drivers travel significantly below 70 mph on motorways in normal conditions, a driver who wants to overtake slower moving traffic without breaking the law can occupy the overtaking lane for several miles. This leads to a queue of potentially faster vehicles building up behind, often at headways which are too short for safety. The inner lanes may be under utilised and impatience may tempt drivers to overtake on the inside.
4.2These effects can be seen quite clearly when a marked police car is in evidence, resulting in traffic in all lanes travelling at virtually the same speed and bunched together. Similar conditions arise where a heavy goods vehicle is attempting to overtake another. Since vehicles of more than 7.5 tonnes gross vehicle weight are restricted to 56 mph by speed limiters, differential speeds are extremely low, leading to the centre lane often being obstructed for long periods. Although not the subject of this paper, experience of the fitment of speed limiters to heavy goods vehicles provides one compelling reason to reject the extension of their use to private cars.
4.3The effects described above are much less in evidence on European motorways, where higher speed limits lead to a greater range of vehicle speeds, quicker overtaking can be achieved legally and there is less bunching of traffic. It is undesirable to create conditions under which speed differentials are so low that traffic in all lanes is travelling at much the same speed, since a relatively minor incident can lead to a multiple accident involving many vehicles.
4.4Another effect of the current speed limit is loss of driver concentration. In particular, where traffic flows are relatively light and weather conditions are good, a driver's attention is likely to wander if forced to drive below the natural cruising speed of car and driver. As shown in the previous section, modern cars are capable of cruising safely at speeds well above 70 mph without causing driver fatigue.
4.5The fact that over half of all car drivers exceed the motorway speed limit must be detrimental to respect for road traffic law in general. The same applies to speed limits elsewhere of course, which is why the ABD favours consistent and realistic speed limits to be applied throughout the country. If speed limits are so badly set that they are ignored by a majority of road users, then the validity of those limits needs to be examined critically.
4.6One of the main reasons for developing the motorway network was to facilitate the fast and efficient movement of people and goods. A speed limit set below the level that can be sustained safely (and below the design speed of the roads) is preventing the full economic returns being achieved on the substantial investment made in the network.
 
5.Top of this pageEFFECTS OF RAISING THE MOTORWAY SPEED LIMIT
5.1The effects of raising the motorway speed limit need to be assessed under four headings: the impact on actual speeds, on safety, on the environment and on the economy. These will each be considered in the paragraphs below.
 
5.2Effects on actual speeds
5.2.1Contained within an annex to a (now superseded) former Department of Transport circular on the setting of speed limits7, is the following statement: "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." Research by the Transport Research Laboratory8 suggests that the effect of changes to speed limits on actual speeds driven is, at most, 25% of the change in the speed limit.
5.2.2An increase in the motorway speed limit by 10 mph would be expected, therefore, to result in no more than a 2.5 mph increase in actual speeds. Speed limits should be set as close as possible to the 85th percentile speed, i.e. the speed at or below which 85% of vehicles travel9. The survey that showed that 56% of cars on motorways exceed 70 mph also showed that 19% exceed 80 mph, i.e. 80 mph is the 81st percentile speed. The 85th percentile speed on motorways must therefore be around 85 mph, so an increase in the speed limit to 80 mph would be expected to increase the 85th percentile speed to no more than 87.5 mph. This would be within 10% of the raised speed limit and within current ACPO guidelines on the threshold for speed limit enforcement.
5.2.3Experience from the United States10 indicates that, in individual States that raised their speed limits following suspension of the 55 mph National Maximum Speed Limit in November 1995, the change in 85th percentile speeds ranged from less than 2 mph to 3.2 mph. In Montana, which abolished daytime speed limits for cars in December 1995, average speeds on rural freeways increased by only 2 mph.
5.2.4On parts of the German autobahn network, where there is a long tradition of having no mandatory maximum speed limit, 85th percentile speeds in 1996 were around 95 mph11. This is just 10 mph higher than the current 85th percentile speed on UK motorways and only 7.5 mph higher than might be expected with an 80 mph limit.
5.2.5The evidence from international experience suggests, therefore, that an increase in the UK motorway speed limit, or even its removal altogether, would have only a modest effect on actual speeds. It would lead, however, to a substantial reduction in the proportion of drivers who habitually break the law.
 
5.3Effects on road safety
5.3.1A comparison of international motorway speed limits and fatality rates is shown on the chart below. It is quite apparent that there is no correlation between the two. The United States, with one of the lowest motorway speed limits, has an almost identical fatality rate to Germany, with no limit. There are clearly far more significant factors than speed that must explain the large differences in fatality rates between countries.

Click to enlarge
Click to view an enlarged version in a new window. Close the window after viewing.

 

5.3.2The greatest experience of raising speed limits on accident rates is from the United States. In 1986/87, the speed limit on interstate roads in some States was raised from 55 mph to 65 mph. The following chart shows the impact on fatality rates between those States that raised the limit and those that did not.

Click to enlarge
Click to view an enlarged version in a new window. Close the window after viewing.

 

5.3.3In 1995, Congress finally repealed the 55 mph federal speed limit altogether and 33 States raised their limits to 65 mph or more. Safety groups and the insurance industry mounted a public relations campaign to protest against higher speed limits, predicting that there would be a massive increase in fatalities and injuries. In fact, there were 66,000 fewer injuries on the roads in 1997 than before the speed limits were raised and the fatality rate between 1995 and 1997 fell from 1.73 to 1.64 per hundred million vehicle-miles travelled12. Another indication of increased road safety is that motor insurance claims fell after speed limits were raised, belying industry concern that insurance costs would increase13.
5.3.4Further evidence that higher speeds do not automatically mean higher accident rates can be seen from the graph below, which shows trends in speeds and death rates on unrestricted German autobahns from 1978 to 1997. It can be seen clearly that the trends are moving in opposite directions.

Click to enlarge in new window
Click to view an enlarged version in a new window. Close the window after viewing.

 

5.3.5There are several possible explanations for an increase in speed limits on major roads (not necessarily just motorways) leading to a reduction in overall accidents. There will be less bunching of traffic, a greater spread of vehicle speeds and driver concentration is more likely to be maintained. Drivers are also able to concentrate on the task in hand, rather than watching for unmarked police cars, radar traps and so on. It is also probable that, in a regime of low speed limits, faster drivers seek alternative routes with less police enforcement but which are inherently more hazardous. An increase in speed limits would attract them back to the roads designed for high speeds.
 
5.4Effects on the Environment
5.4.1The effects of a change to the motorway speed limit on the environment will be assessed under three headings: toxic emissions, 'greenhouse gas' emissions and noise.
Toxic emissions
5.4.2The National Air Quality Strategy (NAQS), published in March 1997, defined air quality standards for eight major air pollutants and set objectives for each one, to be achieved by 2005. The eight pollutants are benzene, 1,3-butadiene, carbon monoxide, lead, nitrogen dioxide, ozone, particles (PM10) and sulphur dioxide. The following paragraphs will look at these in turn.
5.4.3Benzene is a carcinogen. In 1994, road transport contributed 67% of benzene emissions nationally14. The original NAQS air quality objective for benzene was that the annual mean should not exceed 5 parts per billion (ppb) by 2005. An assessment by the Department of the Environment, Transport and the Regions (DETR) on the impact of traffic management on air quality14, predicted that national measures alone (through improved emission controls) would be sufficient to meet this objective. When the NAQS was reviewed in 199915, progress had been such that it was possible to bring forward the achievement of the objective to 2003, with a new indicative level of 1 ppb for 2005.
5.4.4The NAQS objective for 1,3-butadiene, which is also a carcinogen, is for the annual mean not to exceed 1 ppb by 2005. Nationally, road transport contributed 77% of emissions of this pollutant in 199414. The objective will be met through national measures and, at the 1999 review15, it was possible to bring forward the achievement of the objective to 2003.
5.4.5Benzene and 1,3-butadiene are hydrocarbons, emissions of which from modern cars are only one-twentieth of those from pre-catalytic converter vehicles14. Not only are emissions of these substances well within safe levels, they are highest at low speeds, falling rapidly to around 50 kph. The curve of emissions against speed is virtually flat between 70 and 150 kph16. These pollutants are irrelevant, therefore, to a debate on the motorway speed limit.
5.4.6Carbon monoxide is poisonous, reducing the ability of the blood to carry oxygen. In 1995, road transport contributed 75% of carbon monoxide emissions nationally14. The NAQS objective is an eight-hour mean of 10 parts per million (ppm) by 2005. This will also be met by national measures and, at the 1999 review15, it was possible to bring forward the achievement of the objective to 2003. Carbon monoxide emissions are highest at low speeds, falling to their lowest point at around 80 kph, after which they rise slowly again. Even at 140 kph however, carbon monoxide emissions are only a quarter of the level produced at city centre speeds16. Given the very low levels of carbon monoxide emitted by modern cars and progress towards the NAQS objective ahead of schedule, this pollutant is irrelevant to a debate on the motorway speed limit.
5.4.7Lead can affect the nervous system and mental functioning. In 1995, road transport contributed 78% of airborne lead emissions nationally14. This was five years before the withdrawal of leaded petrol from general sale. The original NAQS objective was that by 2005 airborne lead should not exceed 0.5mg/m3 as an annual mean. The switch to unleaded petrol has enabled this objective to be brought forward to 2004 and a new objective to be set of 0.25mg/m3 by 200815. Consequently, this pollutant is irrelevant to a debate on the motorway speed limit.
5.4.8Nitrogen dioxide can affect the way that the lungs and airways function. In 1995, road transport contributed 46% of oxides of nitrogen nationally and total emissions from vehicles are predicted to halve by 2010, despite increased traffic levels14. This will be achieved by improvements in emission controls. The original NAQS objective was that hourly mean levels should not exceed 150 ppb by 2005, with an annual mean of no more than 21 ppb. The review of the NAQS15 proposed a one-hour mean (18 exceedences) of 104.6 ppb (200mg/m3) whilst retaining the annual mean objective of 21 ppb by 2005. The review suggested that this objective would be achieved in most areas, except alongside some major roads in the largest cities. By 2009, only central London and Birmingham would be likely to have roadside exceedences.
5.4.9Emissions of oxides of nitrogen increase almost linearly with speed over a wide speed range16. At the relatively low traffic densities associated with higher motorway speeds, however, overall emissions would be within the NAQS objectives no more than a very short distance from the roadside. These vehicle emissions are diluted and dispersed very quickly with distance from their source and rural motorways do not generally pass close to inhabited dwellings. The few potential problem locations in large cities arise from a combination of traffic density and the canyon effect of adjacent development. Consequently, any increase in nitrogen dioxide emissions as a result of raising the motorway speed limit would be minimal and well within acceptable levels.
5.4.10Ground-level ozone, when it occurs at high concentrations, can cause discomfort to susceptible individuals, inflaming airways and leading to sore eyes and throats. The NAQS objective is that by 2005 the running 8-hour mean should not exceed 50 ppb. Ozone is a secondary pollutant, formed by the action of sunlight on nitrogen dioxide and volatile organic compounds. Some of these are naturally occurring, especially in rural areas, which is one reason why ozone levels are higher there than in towns17. Another reason is that nitric oxide from vehicle exhausts destroys ozone. There is no direct link, therefore, between vehicle flows or speeds and ozone concentrations, so no assessment can be made of what impact, if any, a change in motorway speed limit would make.
5.4.11Particles (PM10) can worsen heart and breathing problems in sensitive individuals. In 1995, road transport contributed 26% of PM10 nationally and total emissions from vehicles are predicted to halve by 2010, despite increased traffic14. Most PM10 emitted by road transport comes from goods vehicles and buses, with less than a third from cars, both petrol and diesel combined. The NAQS objective for 2005 was for running 24-hour means of PM10 not to exceed 50mg/m3. The 1999 review conceded that this objective was effectively impossible to achieve by action at a local level, because of the significant impact of particles blown across the UK from overseas. Even without any contribution from road transport, exceedences of the objective in some urban areas would still occur15.
5.4.12The vehicles that would be affected by a change in the motorway speed limit produce only a small part of the road transport component of PM10. Exceedences of the NAQS objective are most likely to occur in urban areas under certain meteorological conditions. Consequently, emissions of PM10 are irrelevant to a debate on the motorway speed limit.
5.4.13Sulphur dioxide contributes to acid rain. In 1995, the contribution from road transport nationally was 2% of the total14 and most of this was from buses and goods vehicles. The NAQS objective is for a 15-minute mean concentration of no more than 100 ppb by 2005. Given the insignificant contribution of cars to sulphur dioxide emissions, this pollutant is irrelevant to a debate on the motorway speed limit.
5.4.14In summary, the majority of toxic emissions covered by the National Air Quality Strategy are on course to be within the objectives set for them. Only nitrogen dioxide and particles are likely to breach their objectives and then only in particular areas or circumstances. Under the conditions on motorways where higher speeds would be possible, the effects of raising the speed limit on the emissions of these pollutants would be insignificant.
'Greenhouse gas' emissions
5.4.15The ABD does not accept the theory that man-made emissions of carbon dioxide (CO2) are contributing to climate change. There is overwhelming evidence that short-term climate change (from decades to centuries) can be explained almost entirely by variations in output of the sun. The recorded increase in CO2 concentration in the atmosphere in the last 150 years or so is the result of the modest warming that has occurred, not the cause of it.
5.4.16Nevertheless, until the fallacy of man-made global warming theory can be demonstrated conclusively, it is necessary to assess the likely impact on overall CO2 emissions of a change in the motorway speed limit. The rate at which CO2 is emitted is proportional to fuel consumption. This is highest at very low speeds and falls to a minimum at around 70 kph. It increases gradually thereafter16. It has been shown above (paragraph 5.2.2) that the likely effect on actual speeds of an increase in the speed limit to 80 mph would be no more than an increase of 2.5 mph in the 85th percentile speed. Assuming that there would be a similar increase in the average speed (almost certainly an overestimate) and that the current average speed for cars is 72 mph, the overall increase in CO2 emissions from cars using motorways would be about 4%.
5.4.17In 1999, the total volume of motorway traffic by cars, taxis and light vans (which are subject to the same speed limit as cars) amounted to 71.8 billion vehicle-kilometres1. Total traffic on all classes of road by all types of motor vehicle was 467.0 billion vehicle-kilometres. The traffic that would be affected by a change in the motorway speed limit therefore represents 15.4% of the national total. A crude maximum estimate of the increase in CO2 emissions from road transport would thus be 4% of 15.4%, i.e. 0.62%.
5.4.18This figure is unrealistically high, however, for the following reasons. Firstly, not all motorway travel takes place under free-flow conditions, where a higher speed limit could be utilised. Adverse weather conditions will also prevent higher speeds being achieved for part of the time. Whilst difficult to quantify, it is unlikely that more than, say, 60% of total vehicle-kilometres on motorways would be affected by a speed limit change. Secondly, the majority of the 395.2 billion vehicle-kilometres, which would not be affected by the speed limit change, either take place under road conditions where fuel consumption is higher than on motorways, or by larger vehicles with heavier fuel consumption. The average fuel consumption at which these other vehicle-kilometres are travelled is likely to be at least 20% higher than for light vehicles under free-flow motorway conditions.
5.4.19Taking these factors into account, the volume of motorway traffic by cars and light vans that could be affected by a change in the speed limit represents no more than 8% of road transport fuel consumption. An increase of 4% in CO2 emissions from this traffic thus represents an increase of just 0.32% of road transport emissions.
5.4.20Road transport itself contributed 23% of man-made CO2 emissions in the UK in 199818. An increase in the motorway speed limit from 70 mph to 80 mph would thus cause an increase in man-made CO2 emissions of no more than 23% of 0.32%, i.e. 0.074%. It is also very important to remember, however, that man-made emissions represent less than 4% of the total CO2 in the atmosphere. Consequently, the increase in atmospheric CO2 as a result of a 10 mph increase in the motorway speed limit would be no more than 0.003%.
5.4.21If the motorway speed limit were abolished altogether, it has been shown in paragraph 5.2.4 above that the increase in the 85th percentile speed would be no more than 10 mph. It is unlikely that average car speeds would rise by the same amount (as the spread of speeds would tend to increase) but, even if they did, the increase in CO2 would be no more than 22%16. Using the same assumptions as above, this would mean an increase in road transport emissions of 1.76%, an increase in all man-made emissions of 0.4% and an increase in atmospheric CO2 of 0.016%.
5.4.22These increases in atmospheric CO2 concentrations are theoretical, as the amount of CO2 in the atmosphere at a given global temperature is in equilibrium. This means that an increase from one source is counteracted by greater absorption elsewhere. Conversely, a reduction in CO2 emissions is negated by a release of CO2 from other sources19. Attempts to reduce man-made CO2 emissions are futile, therefore, as they will simply be replaced by 'natural' CO2. Nevertheless, even if the additional CO2 resulting from an increased motorway speed limit were to actually affect the atmospheric concentration, it can be seen that the change would be negligible.
Noise
5.4.23At motorway speeds, the dominant component of traffic noise arises from the interaction between vehicle tyres and the road surface. Although speed will have an effect on the frequency of that noise, the most significant factors affecting both the volume and intrusiveness of traffic noise are the type and texture of the road surface.
5.4.24Many of the earlier motorways in the UK were constructed with rigid, concrete carriageways, with brushed surfaces to provide satisfactory levels of grip. These generate noise that is both louder and of a more intrusive frequency than carriageways constructed of flexible, bitumen-based materials. Some concrete motorways have subsequently been overlaid with black-top running surfaces, primarily to restore grip but sometimes to reduce noise in locations where roads pass close to residential areas.
5.4.25In recent years, new surfacing materials have been developed that provide better grip, reduce spray in wet weather and also reduce noise generation. In July 2000, the Government announced a programme to install quieter surfaces on over 60% of the motorway and strategic roads network in England, including all concrete stretches20. The change in surfacing is predicted to reduce the average noise level at the hard shoulder of a typical motorway by three decibels. This reduction is equivalent to halving the volume of traffic. All new roads will be surfaced in quieter materials as a matter of course.
5.4.26The characteristics and levels of noise generated by individual stretches of motorway will depend on the mix of vehicles types and geometric characteristics of the road, as well as the road surface. Motorways carry significant proportions of heavy goods vehicles, which make a substantial contribution to overall noise levels. The change in those levels that would result from modest changes in the speeds of light vehicles, as a result of raising the speed limit, are likely to be much less than three decibels, which is the minimum change that the human ear can detect. Most stretches of motorway where free-flow traffic conditions apply are remote from residential areas in any case. It is considered, therefore, that increased traffic noise is irrelevant to a debate on raising the motorway speed limit.
 
5.5Effects on the Economy
5.5.1The most obvious economic benefit from an increase in the motorway speed limit would be the value of time saved. This can be assessed using the same assumptions made in the section above to estimate increases in CO2 emissions.
5.5.2The detailed calculations are shown in Appendix 1. An increase in the motorway speed limit to 80 mph would save approximately 11 million and 1.5 million vehicle-hours per year respectively for cars and light goods vehicles. Based on the latest values of time21, these represent a saving of £114 million annually, at 1998 prices.
5.5.3Abolishing the speed limit altogether could save approximately 40 million and 5.4 million vehicle-hours per year respectively for cars and light goods vehicles. These would represent a saving of £415 million annually, again at 1998 prices.
5.5.4Against these savings must be offset the increased vehicle operating costs, which are calculated separately for fuel and non-fuel elements21. The detailed calculations are shown in Appendix 2. For an increase in motorway speed limit to 80 mph, the resource cost of the extra fuel consumed (i.e. the cost excluding tax) would be approximately £63.5 million at 2000 prices. There would be a small saving in non-fuel costs, giving an overall increase in vehicle operating costs of about £61 million. Fuel prices in 2000 were 65% higher (before tax) than those in 1998, the year for which the time savings are calculated. If 1998 fuel prices were used, the net increase in vehicle operating costs would be £36 million.
5.5.5Abolishing the speed limit altogether would lead to an increase in the resource cost of fuel of around £287 million (at 2000 fuel prices) which, allowing for the reduction in non-fuel costs, would give an overall increase in vehicle operating costs of £281 million. Using 1998 fuel prices, the net increase in vehicle operating costs would be £165 million.
5.5.6These figures are summarised in the table below.

 All figures in £million/year
80 mph Speed Limit No Speed Limit
1998 Values2000 Prices1998 Prices1998 Values2000 Prices1998 Prices
Time Savings
114
415
Operating Costs
61
36
281
165
Net Benefit
53
78
134
250
 

5.5.7There would be a significant benefit to the economy from an increase in the motorway speed limit, the value of time saved greatly exceeding the increase in operating costs, even when fuel prices are high. Tax is a transfer cost from one part of the economy to another, so it should not be included in a cost-benefit analysis. Nevertheless, at 2000 rates of fuel tax, an increase in the motorway speed limit to 80 mph would yield some £185 million per year extra income to the Treasury. If the speed limit were abolished altogether, the extra tax revenue would be around £840 million.
5.5.8Although a strict economic analysis of the costs and benefits of raising the speed limit must exclude the fuel tax element, it is a very significant part of the costs faced by drivers. The decisions made by individual drivers about whether to take advantage of an increased speed limit would depend on the value they place on their time versus the increased costs they would face. Thus those drivers who value their time the most are more likely to increase their speed than those who value it less. This is one reason why increasing the speed limit would increase the spread of vehicle speeds. It also means that the value of time saved by those who increase their speeds would be greater than the average value assumed in the calculations, but the costs would not. Thus the figures shown above, based on a simple assumption of an increase in average speeds, almost certainly underestimate the benefit to cost ratio that would result.
5.5.9The figures above are also dependent on the assumption made about the proportion of vehicle-kilometres that are travelled in free-flow conditions. The figures should not be seen, therefore, as an accurate quantification in absolute terms of the economic costs and benefits of raising the speed limit. They are, however, indicative of the order of magnitude of those costs and benefits and show quite clearly that the benefits would exceed the costs significantly.
 
6.Top of this pageCONCLUSIONS
6.1From the analysis above it can be seen that an increase in the motorway speed limit by 10 mph to 80 mph would be likely to result in an increase of no more than 2.5 mph in the 85th percentile speed. This is the measure of speed recommended for use in the setting of speed limits. The current 85th percentile speed of cars is well above the existing 70 mph speed limit, so an increase in the limit to 80 mph would greatly reduce the proportion of drivers who regularly break the law. If the motorway speed limit were removed altogether, the 85th percentile speed is unlikely to increase by more than 10 mph.
6.2Increasing the speed limit would result in significant economic benefits from time savings and these would greatly outweigh the additional costs of resources consumed. International comparisons show no correlation between motorway speed limits and accident rates. Evidence from the United States indicates that overall accident rates fell when freeway speed limits were raised there. There is no reason to believe, therefore, that an increase in the motorway speed limit in the UK would result in a higher accident rate and it is possible that it could reduce. The most cautious estimate is that an increased motorway speed limit would be neutral in safety terms.
6.3The impact of a raised motorway speed limit on the environment would be negligible. Most of the toxic emissions covered by the National Air Quality Strategy are within their target levels or are set to meet them. The increases arising from the small changes in actual speeds that would result from an increased speed limit would be insignificant. The increase in CO2 emissions, even if the gas were accepted to be a 'pollutant', would have a negligible effect on its concentration in the atmosphere. Increases in noise levels resulting from higher speeds would be much less than the reductions to be achieved from the Government's programme for resurfacing the motorway and trunk road network.
6.4The ABD believes, therefore, that there is an overwhelming case for an increase in the general speed limit on motorways in the UK. There will be certain locations, however, where retention of the existing speed limit would be appropriate. Such locations could include lengths of motorway where geometric design standards are inadequate or where there are closely spaced interchanges with significant merging and weaving of traffic. By keeping these exceptions to the minimum, it is likely that drivers will respect the need for lower limits where they are retained.
 
7.Top of this pageRECOMMENDATIONS
1. As a first stage, the general motorway speed limit should be raised from 70 mph to 80 mph.
This would bring the UK into line with the majority of countries in the EU. The existing speed limit should be retained in limited circumstances, such as those outlined in paragraph 6.4 above.
2.After a period of time of acclimatisation to a higher speed limit, say three years, the possibility of raising it further or removing it altogether should be reviewed.
3.Training and testing in motorway driving skills should be improved. In particular, drivers must be made aware of the dangers of misjudging their speed in a motorway environment and trained to compensate.
4.The current anomaly between the penalties for exceeding the speed limit on motorways and on other roads should be removed.


 


Top of this pageREFERENCES

1. Data from the Department of the Environment, Transport and the Regions.
2. Transport Statistics Great Britain.
3. RRL Special Report No.6, HMSO, 1967.
4. Autocar, 13th July 1967.
5. Autocar, 12th June 1965.
6. Autocar, 10th January 2001.
7. Circular Roads 1/80 (The setting of local speed limits), Department of Transport, 1980, Annex E.
8. Project Report PR58: Speeds, speed limits and accidents. Transport Research Laboratory, 1994.
9. Circular Roads 1/93 (The setting of local speed limits), Department of Transport, 1993.
10. Effect of speed limits on speed and safety: a review. Chester G Wilmot & Mandar Khanal, Transport Review, October 1999.
11. Data from the Bundesminister Fur Verkehr, Germany.
12. National Highway Traffic Safety Administration, 1998.
13. "Speed Doesn't Kill: The Repeal of the 55 mph Speed Limit." Stephen Moore, Director of Fiscal Policy Studies, Cato Institute. 1999.
14. Air quality and traffic management. DETR, December 1997.
15. DETR Transport Air Quality Seminar, 24th February 1999.
16. Understanding the Impacts of Speed. Richard E Allsop. PACTS Conference — Speed: Whose Business Is It? February 1999.
17. Factbook "Ground-Level Ozone". BMW AG, 1998.
18. National Environmental Technology Centre. Data provided by DETR.
19. The Distribution of CO2 between Atmosphere, Hydrosphere, and Lithosphere; Minimal Influence from Anthropogenic CO2 on the Global Greenhouse Effect. Tom V. Segalstad. University of Oslo. The Global Warming Debate: European Science and Environment Forum. 1996.
20. Transport 2010 — The 10 Year Plan. DETR. July 2000.
21. Transport Economics Note. Values of time and vehicle operating costs. DETR. March 2001.


Top of this page

APPENDIX 1

VALUE OF TIME SAVED FROM AN INCREASE IN SPEED LIMIT

Vehicle-kilometres travelled on motorways in 1999:

Cars63.3 billion
Light vans8.5 billion

Assuming 60% are undertaken in free-flow conditions and 1 km = 0.621 miles, total vehicle-miles per year spent travelling on motorways in free flow:

Cars63.3 x 0.6 x 0.621 = 23.59 billion
Light vans 8.5 x 0.6 x 0.621 = 3.17 billion

Assuming average speed with current speed limit for cars and light vans is 72mph, time spent travelling per year on motorways in free flow:

Cars(23.59 x 109) ÷ 72.0 = 327,638,888.9 hours
Light vans (3.17 x 109) ÷ 72.0 = 44,027,777.8 hours

a) Speed limit raised to 80 mph

If the speed limit were raised to 80 mph, the average speed for cars and light vans is assumed to increase to 74.5 mph. The time spent travelling on motorways per year in free flow would then be:

Cars(23.59 x 109) ÷ 74.5 = 316,644,295.3 hours
Light vans(3.17 x 109) ÷ 74.5 = 42,550,335.6 hours

Thus the time saved per year from an increase in the motorway speed limit to 80mph would be:

Cars10,994,593.6 hours
Light vans1,477,442.2 hours

The all-week average values of time for an average vehicle (1998 prices) are:

Cars£9.23 per hour
Light vans£8.58 per hour

The value of time saved per year would then be:

Cars10,994,593.6 x 9.23 =£101,480,099
Light vans1,477,442.2 x 8.58 =£12,676,454
Total£114,156,553

b) No speed limit

If the speed limit were removed, the average speed for cars and light vans is assumed to increase to 82 mph. The time spent travelling on motorways per year in free flow would then be:

Cars(23.59 x 109) ÷ 82.0 = 287,682,926.8 hours
Light vans(3.17 x 109) ÷ 82.0 = 38,658,536.6 hours

Thus the time saved per year from removal of the motorway speed limit would be:

Cars39,955,962.1 hours
Light vans5,369,241.2 hours

The value of time saved per year would then be:

Cars39,955,962.1 x 9.23 =£368,793,530
Light vans5,369,241.2 x 8.58 =£46,068,090
Total£414,861,620


Top of this page

APPENDIX 2

CHANGES IN VEHICLE OPERATING COSTS

Vehicle-kilometres travelled on motorways in 1999:

Cars63.3 billion
Light vans8.5 billion

Assuming 60% are undertaken in free-flow conditions, total vehicle-kilometres affected by an increase in the motorway speed limit:

Cars63.3 x 0.6 = 37.98 billion
Light vans8.5 x 0.6 = 5.10 billion

Fuel Costs

The relationship between average speed and fuel use is given by the equation:

CarsL = 0.1689 - 0.00282(V) + 0.00001910(V2)
Light vansL = 0.2026 - 0.00328(V) + 0.00002630(V2)

Where: L = fuel consumption (litres per kilometre), V = speed (kilometres per hour)

For the current average speed of 72 mph (115.85 kph), fuel consumption is:

CarsL = 0.1689 - 0.326697 + 0.256345 = 0.098548 l/km
Light vansL = 0.2026 - 0.379988 + 0.352978 = 0.175590 l/km

a) Speed limit raised to 80 mph

If the speed limit were raised to 80 mph, the average speed for cars and light vans is assumed to increase to 74.5 mph (119.87 kph), so fuel consumption would be:

CarsL = 0.1689 - 0.338033 + 0.274444 = 0.105311 l/km
Light vansL = 0.2026 - 0.393174 + 0.377900 = 0.187326 l/km

The increase in annual fuel consumption would be:

Cars(0.105311 - 0.098548) x (37.98 x 109) = 256,858,740 l
Light vans(0.187326 - 0.175590) x (5.1 x 109) =59,853,600 l
Total316,712,340 l

The resource cost of fuel and the total tax on fuel (Excise Duty plus VAT) in 1998 and 2000 were:

19982000
Resource cost12.1 p/litre20.0 p/litre
Tax element55.3 p/litre58.5 p/litre

The increase in resource costs per year would be:

At 1998 Prices316,712,340 x 0.121 = £38,322,193
At 2000 Prices316,712,340 x 0.200 = £63,342,468

The increase in tax revenue per year would be:

At 1998 Prices316,712,340 x 0.553 = £175,141,924
At 2000 Prices316,712,340 x 0.585 = £185,276,189

b) No speed limit

If the speed limit were removed, the average speed for cars and light vans is assumed to increase to 82.0 mph (131.94 kph), so fuel consumption would be:

CarsL = 0.1689 - 0.372071 + 0.332496 = 0.129325 l/km
Light vansL = 0.2026 - 0.432763 + 0.457835 = 0.227672 l/km

The increase in annual fuel consumption would be:

Cars(0.129325 - 0.098548) x (37.98 x 109) =1,168,910,460 l
Light vans(0.227672 - 0.175590) x (5.1 x 109) =265,618,200 l
Total 1,434,528,660 l

The increase in resource costs per year would be:

At 1998 Prices1,434,528,660 x 0.121 = £173,577,968
At 2000 Prices1,434,528,660 x 0.200 = £286,905,732

The increase in tax revenue per year would be:

At 1998 Prices1,434,528,660 x 0.553 = £793,294,349
At 2000 Prices1,434,528,660 x 0.585 = £839,199,266

Non-Fuel Costs

Non-fuel costs are calculated from the formula:   C = a1 + (b1 ÷ V)
Where: C = cost (pence per kilometre), V = speed (kilometres per hour), a1 and b1 are constants for each vehicle type.

CarsC = 3.040 + (15.54 ÷ V)
Light vansC = 4.336 + (38.28 ÷ V)

For the current average speed of 72 mph (115.85 kph), non-fuel costs are:

CarsC = 3.040 + 0.13414 = 3.17414 p/km
Light vansC = 4.336 + 0.33043 = 4.66643 p/km

a) Speed limit raised to 80 mph

If the speed limit were raised to 80 mph, the average speed for cars and light vans is assumed to increase to 74.5 mph (119.87 kph), so non-fuel costs would be:

CarsC = 3.040 + 0.12964 = 3.16964 p/km
Light vansC = 4.336 + 0.31935 = 4.65535 p/km

The decrease in annual non-fuel costs would be:

Cars(0.0317414 - 0.0316964) x (37.98 x 109) =£1,709,100
Light vans(0.0466643 - 0.0465535) x (5.1 x 109) =£565,080
Total £2,274,180

b) No speed limit

If the speed limit were removed, the average speed for cars and light vans is assumed to increase to 82.0 mph (131.94 kph), so non-fuel costs would be:

CarsC = 3.040 + 0.11778 = 3.15778 p/km
Light vansC = 4.336 + 0.29013 = 4.62613 p/km

The decrease in annual non-fuel costs would be:

Cars(0.0317414 - 0.0315778) x (37.98 x 109) =£6,213,528
Light vans(0.0466643 - 0.0462613) x (5.1 x 109) =£2,055,300
Total£8,268,828