Response to Department for Transport Consultation: Examining the Speed Limit for HGVs over 7.5 tonnes on Single Carriageway Roads

January 2013


The Alliance of British Drivers (ABD) was formed in 2012 by the merger of the Association of British Drivers (founded 1992) and the Drivers’ Alliance. It campaigns for a better deal for Britain’s motorists. It is a voluntary organisation funded by subscriptions and donations from members and supporters. It currently has around 4,500 members and a further 3,000 supporters on social media sites. The ABD receives no funds from public bodies or private-sector businesses, so is truly independent. It is a member of the Parliamentary Advisory Council for Transport Safety and the National Council of Voluntary Organisations.

The ABD`s national committee has agreed the response to this consultation. The response is in line with the policies outlined on the ABD’s website. Individuals who join or support the ABD are assumed to support its policies in general, so it is not necessary (nor would it be practicable) to seek the views of the entire membership in preparing responses to consultations of this type.

The ABD’s responses to the questions asked in the consultation document are set out below.

Q.1 Policy Option 1: Raise the national speed limit for HGVs over 7.5t from 40 to 50 mph on single carriageway roads. Is this your preferred policy option?
The ABD strongly supports this option. The current 40 mph speed limit, when complied with, causes significant delays to cars and light goods vehicles, creating frustration that can lead to impatience and dangerous overtaking. These problems are particularly acute on busy, single-carriageway trunk and A-roads, where the alignment may allow light vehicles to easily maintain speeds at the 60 mph limit, but where the volume of oncoming traffic means that overtaking opportunities are rare.

Historically, compliance with the 40 mph HGV limit has been low on these roads, but in recent years there has been a noticeable increase in compliance, especially among certain national fleet operators such as supermarkets. A single vehicle maintaining a steady 40 mph becomes, in effect, a rolling road block, creating very long tailbacks. These can persist for many miles, especially in parts of the country where dual carriageways and motorways are few and far between. The result is not only increased journey times for the drivers trapped in such queues, but also very poor journey time reliability. In effect, drivers must assume they will spend long periods behind slow HGVs and allow extra time accordingly.

Raising the HGV speed limit to 50 mph would greatly alleviate these problems, leading to faster, more reliable journey times, less need for overtaking and consequently less danger. It is a long-overdue move that the ABD supports wholeheartedly.

Q.2 Policy Option 2: Raise the national speed limit for HGVs over 7.5t from 40 to 45 mph on single carriageway roads. Is this your preferred policy option?
This is not the ABD’s preferred policy option as it would not go far enough to alleviate the problems caused by the current HGV speed limit.

Q.3 Do you consider there to be any additional policy options, or variants of policy options 1 and 2?
As noted in the answer to question 1, the main benefits of raising the HGV speed limit to 50 mph would be felt on faster, long-distance routes such as trunk and A-roads. If the DfT felt that safety concerns might not allow a blanket increase to 50 mph on all single carriageway roads, a compromise could be to retain the current limit on roads below B-road status. These roads are mainly used by HGVs only for local access and the speed differential between HGVs and cars is much lower than on higher classification routes.

The ABD is not advocating such a two-tier speed limit system, as a straightforward increase on all single carriageway roads is simpler to understand and HGV drivers are professionals, who are quite capable of varying their speed safely according to the conditions within an overall 50 mph limit. The benefits of raising the limit on the higher classification roads are so important, however, that they should not be lost because of concerns about possible higher speeds on local roads.

Q.4 In your opinion does the current 40 mph speed limit cause any of the following: unnecessary costs to vehicle operators; congestion; avoidable overtaking collisions; an uneven playing field for businesses; or anything not mentioned in this list?
Clearly, HGV operators who require their drivers to adhere rigidly to the 40 mph limit are increasing their journey times compared with their competitors. This obviously has a direct cost and may also limit their vehicles daily range due to driver hours restrictions. On the other hand, they may benefit from a slight reduction in fuel consumption. These operators are also imposing costs on the drivers of other vehicles that are delayed by them, which must be taken into account.

Overtaking on single-carriageway roads is the most potentially hazardous manoeuvre that drivers undertake. Consequently, minimising the need to overtake by reducing the spread of vehicle speeds would have a beneficial effect on road safety. Evidence to this effect is given in answer to question 6.

Q.5 We welcome views from HGV operators and trade associations about whether they feel the balance of savings and costs of extra speed detailed in the Impact Assessment reflects their own experience or expectations?
In addition to the general comments set out at the beginning of this response, the ABD has the following points to make on specific paragraphs in the revised circular:

The ABD does not intend to comment on behalf of HGV operators, but is concerned that the Impact Assessment does not attempt to quantify the time savings to car and van drivers and their passengers, who would no longer be held up behind HGVs currently travelling at 40 mph. Most of those savings would be accrued during the working day, when a significant proportion of car and van drivers using major roads would be travelling for business purposes. While the National Transport Model may be unable to calculate these time savings, the likelihood is that they could easily exceed the savings to HGV operators themselves. In the ABD’s view, therefore, the monetised benefits shown in the Impact Assessment are much lower than would be achieved in reality. It is essential that this is borne in mind in deciding whether to proceed with the speed limit increase.

Q.6 Do you have any opinion or evidence on the effect of ‘platooning’ on road safety, or on the frequency or severity of collisions involving HGVs on single carriageway roads and what effect an increase in their maximum speed limit on these roads would have on safety?
Where HGVs are travelling well below the speed of lighter vehicles, which is often the case on major single-carriageway roads where an HGV driver is complying with the 40 mph limit, it is self-evident that those faster vehicles will be delayed by the HGV. The road safety implications of this situation are complex.

A car driver who catches a slow-moving HGV has to decide whether to seek an opportunity to overtake or follow behind the HGV. If the former course of action is taken, a misjudged overtaking manoeuvre could lead to a head-on collision with an oncoming vehicle, which might or might not also involve the HGV, or the oncoming driver might be involved in a loss-of-control accident in avoiding the overtaking car.

Where drivers decide to remain behind a slow-moving HGV, all too often they follow at a headway that is inadequate to allow a more determined driver to overtake the queue safely in stages. Consequently, the overtaking driver must either pass the entire queue in one attempt or force his way into the queue when an oncoming vehicle appears. This may cause the overtaken driver to brake, causing following drivers to do likewise, possibly leading to a rear-end shunt further back in the queue. Another hazard is that a driver might pull out to overtake without checking the mirrors, into the path of a driver who is already overtaking.

Platoons of vehicles also restrict the ability of drivers to join, leave or cross the major road. In particular, a driver wishing to turn right from the opposite direction might be stationary for a significant period while waiting for the platoon to pass. This leaves the turning driver vulnerable to being hit from the rear, especially if there is no dedicated right-turn facility. Also, if the driver of the right-turning vehicle has turned its steering to the right, in anticipation of making the turn, and is hit from behind, the vehicle will be shunted into the path of the oncoming traffic. This could result in a secondary accident.

It is clear, therefore, that platoons headed by slow-moving HGVs create conditions that can lead to several types of accident, some of which will not involve the HGV at all. The HGV driver may be quite unaware of accidents occurring in the queue behind. It is likely that many of these accidents will not be recorded by the police as being related to the presence of slow-moving HGVs, so the full extent of the accidents arising from the 40 mph speed limit is impossible to determine from official figures. It is almost certainly greater than realised.

Research in the USA1 by Charles C Lave into the relationship between fatality rates, average speed and speed variance on a variety of road types found that there is no statistically discernible relationship between the fatality rate and average speed, but there is a strong relationship with speed variance. His paper refers to earlier research by David Solomon2 on the relationship between accident rates and speed variance, from which the graph below is reproduced, confirming Lave’s findings.


It can be seen that vehicles travelling slightly faster than the mean speed have the least accident involvement. Note that the accident involvement rate (vertical scale) is logarithmic, so risk rises exponentially as deviations from the optimum speed increase. For vehicles travelling 20 mph below the mean speed, the risk is seven or eight times greater than that of a driver travelling at the safest speed.

Lave’s paper also refers to theoretical work undertaken by Ezra Hauer3, in which he calculated the number of overtakes at various speeds and thus the frequency of opportunities for collisions to occur. The theoretical distribution that resulted was near identical to Solomon’s curve in Figure 1.

Raising the HGV speed limit to 50 mph would significantly reduce the speed variance between light and heavy vehicles, especially on faster roads, and would thus improve road safety by reducing the opportunities for collisions to occur.

Q.7 Do you have any opinion or evidence on what effect an increase in the maximum speed limit for HGVs over 7.5t on these roads would have on non-HGV vehicle speeds such as cars?
Clearly, on roads where the current 40 mph HGV speed limit is inhibiting the ability of drivers of other vehicles to maintain higher speeds, raising the HGV speed limit would allow those drivers to travel at a speed closer to the level they would choose. This would reduce the need for overtaking and the formation of platoons of slow-moving vehicles.

Q.8 The Department invites information on where there are single carriageway roads which are subject to the national speed limit, or are signed at 50 mph, in areas where there are air quality problems.
The ABD is not in a position to answer this question but suspects that there will be few such roads, as air quality problems are mainly found in urban areas with lower speed limits.
Q.9 What impacts, if any, do you think there will be to the following if an increased speed limit for HGVs over 7.5t on single carriageway roads is introduced?
  a) Air Quality Management Areas (AQMAs);
  b) EU air quality standards;
  c) Noise levels;
  d) Areas currently identified as noise hotspots.
Since the majority of roads likely to be affected by a change in the HGV speed limit are rural or semi-rural, impacts under these headings are likely to be insignificant and probably within normal day-to-day variation due to fluctuating traffic levels.
Q.10 If as a result of either of the policy options being implemented there was a reduction in ‘platooning’ do you think there would be a significant impact on:
  a) Noise;
  b) Air quality.
Again, any impact is likely to be small and could be beneficial, as reduced platooning would mean traffic is more evenly spread out.
Q.11 Do you think either of the policy options goes against the underlying principles of the EU Environmental Noise Directive or of the Noise Policy Statement for England?
Q.12 Do you think that all of the potential health and social costs of the policy options have been considered in the Impact Assessment?
Yes, although, as explained above, the potential benefits to road safety have not been fully understood or appreciated.
Q.13 Do you believe an increase in speed for this class of vehicle on these roads will cause more HGVs over 7.5t to use single carriageway roads, which do not currently?
This is unlikely. HGV drivers will use the roads most suitable for reaching their destinations. In the more rural parts of the country, dual carriageway or motorway routes do not exist, so drivers have no alternative but to use single carriageways. It is unlikely that HGV drivers would use low-classification roads more than they do at present, as the geometry of these roads would often make it impossible to exploit a higher speed limit.
Q.14 Do you think some freight may switch from rail or water to HGVs, if the speed limit is increased on these roads for these vehicles?
This is very unlikely. Rail and water transport are most suitable for specific types of freight that make those modes the most economic. Most freight already using the roads cannot economically be moved by other means. Rail, water and road serve different markets for freight transport.
Q.15 Do you think that there may be added wear and tear on these roads if the speed limit is increased for these vehicles?
Roads that are maintained in good condition should not suffer any significant extra wear and tear as a result of a speed limit increase. Once a carriageway has become damaged through structural failure, or surface damage such as potholing, the impact of HGVs can exacerbate the problem quite quickly, even with the current speed limit. It is not unreasonable to expect that the higher classification roads, used by most of the HGV traffic that would be able to take advantage of a higher limit, should be maintained in a condition suitable for such use.
Q.16 Do you think that the increase in the national speed limit for HGVs over 7.5t on single carriageways would make it more likely that local authorities would introduce more local speed restrictions, and if so on which roads?
There is a risk that some local authorities might see the increase in the HGV speed limit as an excuse to lower some limits, especially on roads below B-road status. This would be unjustifiable, as actual speeds are unlikely to change significantly on these lower classification roads. If significant numbers of local authorities indicate that they would reduce speed limits if the HGV limit were increased, then the option of raising the limit only on higher classification routes should be considered. The ABD does not favour differential HGV speed limits according to road class (see question 3), but also does not want to see another round of speed limit reductions by local authorities.
Q.17 If you are an organisation that provides information and you believe that an increased speed for this class of vehicle on single carriageways would incur costs for your organisation in the form of publicity or conversion costs please indicate what these may be.
This question is not applicable to the ABD.


1 Lave, Charles A, “Speeding, Coordination and the 55 MPH Limit,” The American Economic Review, Vol. 75, No. 5 (Dec, 1985), pp 1159-1164.
2 Solomon, David, “Accidents on Main Rural Highways Related to Speed, Driver, and Vehicle,” Federal Highway Administration, U.S. Department of Transportation, July 1964.
3 Hauer, Ezra, “Accidents, Overtaking and Speed Control,” Accident Analysis and Prevention, January 1971, 3, 1-12.