Transportation Research Part D 10 (2005) 77–95
www.elsevier.com/locate/trd
The economic and environmental benefits of increasing
maximum truck weight: the British experience
Alan C. McKinnon
Logistics Research Centre, Heriot-Watt University, Edinburgh, EH14 4AS, UK
Abstract
This paper assesses the impact of the increase in maximum truck weight in the UK in 2001 on traffic
levels, road haulage costs and emissions. It compares the actual effects of this measure with forecasts made
a year before the weight limit was raised. This forecast took account of three key factors: the migration of
loads to heavier vehicles, a traffic generation effect and the diversion of freight from the rail network. The
net reduction in truck-kms by 2003 was at the upper end of the forecast range, though this is likely to
under-estimate the long term reduction that will be achieved when the road freight sector has fully adjusted
to the new weight limit. The paper includes an historical review of the lorry weight issue in the UK, a comparison with official studies of the issue in the United States and a short discussion of the case for a further
increase in maximum truck weight in Britain.
2004 Elsevier Ltd. All rights reserved.
Keywords: Road freight; Truck weights; Road haulage costs; Emissions; Modal split
1. Introduction
Increasing the legal maximum weight of trucks enables companies to consolidate loads and thus
reduce the amount of vehicle movement required to distribute a given quantity of freight. Under
certain conditions, this can yield both economic and environmental benefits. In 1999, the UK
E-mail address: [email protected]
1361-9209/$ - see front matter 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.trd.2004.09.006
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government commissioned an investigation of the case for increasing the maximum weight of
trucks from 41 tonnes to 44 tonnes. This paper summarises the results of this study, upon which
the government based its decision to raise maximum truck weight to 44 tonnes in February 2001.
It then compares forecasts of the expected economic and environmental benefits with estimates of
the actual benefits that arose over the period 2001–2003. The first three sections of the paper put
the recent analysis of the UK truck weight issue into context, by outlining the recent development
of the British freight transport system, providing some historical background and comparing the
UK situation with that of the US where extensive research has been undertaken on truck size and
weight (TS & W) limits.
2. The British freight transport system
Road is overwhelmingly the dominant mode of freight transport in the UK, accounting for 64%
of tonne-kms in 2001 (Department for Transport, 2003a). Road tonne-kms grew by 69% between
1980 and 2001, mainly as a result of an increase in the average length of haul for road freight from
67 to 95 km. Between 1980 and 1995, railÕs share of the freight market declined from 10% to 6%
(measured in tonne-kms). Since the privatisation of the railfreight sector in 1996, rail has managed
to reverse the earlier decline and by 2001 had slightly increased its share of the freight market to
8%. In its 10 year plan for transport the UK government expressed a desire to increase rail tonnekms by 80% between 2000 and 2010 (Department of the Environment, Transport and the Regions, 2000). This, however, would only expand railÕs share of the freight market from 8% to
10%. Given the current modal imbalance, measures which aim to rationalise road freight operations can potentially yield greater environmental benefit than marginal changes in the modal split.
This was reflected in the governmentÕs strategy document on ÔSustainable DistributionÕ (Department of the Environment, Transport and the Regions, 1999) which was concerned primarily with
methods of reducing the environmental impact of road freight transport. Much of this effort is
being directed at reducing atmospheric emissions. Table 1 indicates the proportion of emissions
of carbon dioxide and other pollutants attributable to heavy goods vehicles (HGVs) (with a gross
weight of 3.5 tonnes or more) in the UK. The UK government is trying to cut these emissions,
partly by promoting greater fuel efficiency and the use of cleaner vehicles, but also by reducing
the rate of truck traffic growth. In a recent review of its 10-year plan, the government stated that
it Ôaims to reduce lorry intensity, that is the extent to which economic growth generates additional
lorry trafficÕ (Department for Transport, 2003b). One of the main ways in which this can be
Table 1
Contribution of HGVs to Atmospheric Emissions in the UK (2000)
Particulates (PM10)
Nitrogen oxides
Carbon dioxide
% of emissions from transport
% of total emissions
38
33
23
17
13
3
Sources: Department of the Environment, Transport and the Regions, 1999; Office of National Statistics, 2004.
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
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achieved is through the consolidation of loads. It is against this background that the government
decided to raise the maximum truck weight in 2001.
3. Historical background
A wide-ranging government enquiry into the UK road freight transport system conducted by
the Armitage Committee in 1979 recommended that maximum truck weight increase from 32.5
to 44 tonnes (Armitage, 1980). The UK government decided not to raise the limit as high as
44 tonnes, but did increase it to 38 tonnes in 1983. Various industry bodies continued to lobby
for a further increase to 44 tonnes. In 1990, the European Commission issued a directive requiring
all member states to permit vehicles registered at 40 tonnes (on 5 axles). The British government
was granted a ÔderogationÕ (or exemption) from this directive for 9 years ostensibly to give it time
to inspect and, where necessary, strengthen around 2000 bridges to support the heavier vehicles.
By 1999, £283 million had been spent on bridge strengthening across the motorway and trunk
road networks, while local authorities had reinforced bridges on strategic routes within their
areas. In 1995, however, the government decided to allow trucks carrying intermodal units to
railheads to operate at gross weights of up to 44 tonnes, partly to offset the weight penalty incurred by unitised loads such as containers and swap-bodies. BritainÕs derogation from the EC
directive ended in January 1999 and since then it has been possible for 5-axle trucks to operate
at gross weights of 40 tonnes. In an effort to encourage companies to spread vehicle weight over
six rather than five axles, and thus reduce road pavement damage per kilometre travelled, the
government introduced a maximum truck weight of 41 tonnes for vehicles with six axles and
assigned them a much lower rate vehicle excise duty (VED). It also asked the new Commission
for Integrated Transport (hereafter called the Commission) in 1999 to examine the case for a
general increase in the weight limit for these 6-axle vehicles to 44 tonnes. The author was
invited by the Commission to assess the likely economic and environmental consequences of this
measure.
4. Comparison with studies of truck size and weight limits in the United States
Over the past 25 years there has been a series of major studies of TS & W limits in the US (US
Department of Transportation, 1981, 2000; Transportation Research Board, 1990, 2002). In the
US the optimisation of TS & W limits has been much more broadly defined than in the UK and
has presented much more formidable analytical problems. Six of the issues that have dominated
discussion of the subject in the US were largely excluded from the CommissionÕs study:
4.1. Inter-relationship between weight and size
The US studies have attempted to integrate the optimisation of vehicle weights and dimensions.
In the UK, on the other hand, the case for altering the weight limit on trucks has traditionally been
assessed in isolation. This is because truck lengths, widths and turning circles are governed by
European Union (EU) regulations and must be agreed at an international level. The weights of
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trucks engaged in cross-border haulage are also subject to EU rules, but decisions on the maximum
gross weights of vehicles operating within countries are devolved to national governments. In public consultations on the truck weight issue, the UK government insisted that vehicles might Ôget
heavier but no biggerÕ (Department of Transport, 1996), recognising that people were more concerned about their size than their weight. This reassurance on vehicle size, however, only related
to vehicle width and length. The UK is unusual in having no legal limit on the maximum height
of trucks, in contrast to most other EU countries where a maximum height limit of 4.2 m is now
the norm. As a result of the high Ôcustom and practiceÕ height limit of 5 m in the UK, there has been
a sharp increase in the number of high-cube, double-deck trucks on BritainÕs roads over the past
decade. This has significance to the truck weight issue, as discussed in Section 13.
4.2. Infrastructural modification
Much of the US research has been concerned with the cost of strengthening road pavements
and bridges to support heavier vehicles. This was not an issue that the Commission was asked
to investigate, for two reasons. First, it had been decided that all vehicles with a maximum gross
weight of 41 tonnes or more should have six axles and that those registered at 44 tonnes would also
have Ôroad-friendlyÕ air suspension. As damage to the road surface is proportional to the fourth
power of the axle weight (rather than the gross weight of the vehicle) (Frith, 1994) and significantly reduced by the use of air suspension, the heavier vehicles would actually cause less damage
to the road surface per kilometre than the previous generation of five axle vehicles plated 1 at 38
or 40 tonnes. Second, the bridge checking and strengthening programme undertaken during the
1990s prepared this infrastructure for vehicles operating at 44 tonnes. As this programme had
been necessitated by an EU requirement to admit trucks with a gross weight of 40 tonnes (on five
axles), it had not been subject to the usual system of transport investment appraisal. In the US,
benefit-cost analyses have examined the economic trade-off between infrastructural investment
and savings in vehicle operating costs discounted over varying time periods. It appears that no
comparable analysis was undertaken in the UK prior to the instigation of the bridge inspection
and strengthening programme in the early 1990s.
4.3. Geographical uniformity
The TS & W issue in the US has been greatly complicated by variations in the regulations
applying at different geographical scales. As Clarke (2000) has observed, ÔUS truck size and weight
limitations are a mishmash of federal, state and local requirements, whose origin and development
evolved and then were subsequently fragmented, jurisdiction by jurisdictionÕ. Efforts to model the
impact of a more standardised set of TS & W limits have had to take account of this spatial variability. In contrast, the UK truck weight limit applies in all parts of the country and to all roads,
with the exception of a few minor rural roads where bridge weight restrictions apply.
1
In the UK, the expression ÔplatingÕ refers to the licensing of a truck in a particular weight class. The certificate
confirming the weight class is contained in a metal ÔplateÕ attached to the vehicle chassis.
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4.4. Road user charges
Economic analyses of TS & W scenarios in the US have included estimates of the level of
road taxes and tolls that would have to be imposed on larger and heavier vehicles to recover additional track and environmental costs. This was also outside the CommissionÕs brief in the UK. An
earlier study for the Department of the Environment, Transport and the Regions (DETR), had
calculated these costs for thirty-three classes of truck, including those plated in the range 41–
44 tonnes (NERA, 1999). This research had not attempted, however, to forecast the use of vehicles
with gross weights in excess of 41 tonnes and any associated rationalisation of road freight movement. Determination of appropriate VED rates for new classes of truck was the responsibility of
the Treasury (i.e. UK finance ministry).
4.5. Emphasis on safety
Much of the discussion on the TS & W issue in the US has been concerned with the safety
of vehicles operating at different size and weight limits. In the UK, it was decided at the outset
that vehicles plated at 44 tonnes would have to meet the same safety standards as 38, 40 and
41 tonne vehicles in terms of braking distances and stability, despite their greater momentum.
The Commission did not need, therefore, to investigate the safety characteristics of 44 tonne vehicles. It was recognised, however, that raising the weight limit could affect the incidence of traffic
accidents by altering the number of vehicle-kms required to move a given quantity of road freight.
The environmental cost calculations therefore included an allowance for variations in the frequency of traffic accidents involving heavy trucks.
4.6. Effects on traffic flow
Modelling work has been undertaken in the US to assess the interaction between larger, heavier
trucks and other categories of vehicle and its overall effect on traffic flow. Much of this research
has focused on the traffic impact of longer combination vehicles (LCVs) with two trailers that are
both very heavy and difficult to overtake (US Department of Transportation, 2000). Such vehicles
are not permitted on BritainÕs roads. It was also assumed in the UK that, given the high power
rating of most vehicles plated at 41 tonnes, an additional 3 tonne payload would have a marginal
effect on average speed. This was confirmed by a standardised road test of similar trucks plated at
41 and 44 tonnes, in which the latter suffered a speed penalty of only 2% (Anon, 2000).
In the US, the Committee for the Study of the Regulation of Weights, Lengths and Widths of
Commercial Motor Vehicles complained that Ôa lack of information about the costs and benefits
of truck transportation and the impacts of size and weight regulations hindered its effort to provide useful policy adviceÕ. It is partly because of this lack of data that Ôfederal size and weight policy has been deadlocked for more than a decade, in spite of a general dissatisfaction with the
regulationsÕ (Transportation Research Board, 2002). The comparable committee in the UK,
which investigated the truck weight issue in 1999–2000, had an easier task to perform, partly because its remit was much more narrowly defined, but also, as discussed below, it had access to
more data on the loading of commercial vehicles.
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5. Review of previous calculations in the UK
Various organisations had tried to estimate the reductions in truck numbers and vehicle kilometres that would result from a maximum weight increase from 38 to 44 tonnes. Their estimates
varied quite widely reflecting differences in methodology and assumptions (Table 2).
All of these studies initially calculated the ratio of the maximum payloads on 38 and 44 tonne
vehicles and multiplied this Ôpayload weight ratioÕ by the average distance travelled annually by
laden 38 tonne vehicles. This yielded a crude initial estimate of the potential saving in vehiclekms. The calculation assumed, however, that all the loads carried on 38 tonne vehicles were
weight-constrained and that, if carried by 44 tonne vehicles, they would continue to be limited
by weight and hence take full advantage of the weight increase. In practice, however, many of
the loads carried on 38 tonne vehicles were limited by other physical or scheduling constraints.
Each of the studies, therefore, scaled down the initial estimate of vehicle-km savings to allow
for these other constraints on vehicle loading. The Freight Transport Association (FTA), for
example, reduced the estimated savings by 20%. This appears to have been a fairly arbitrary figure. Widely differing factors were used to scale down the gross estimates of vehicle-km reductions
and this largely explains the discrepancies between the various estimates in Table 2.
The 1998 calculation made by the DETR was underpinned by the assumption that 38 tonne
vehicles were more than 95% laden on 30% of the distance they travelled loaded. At the time
of this calculation, no data were available on the proportion of loads subject to a weight or volume constraint. It was not possible, therefore, to determine what share of the weight-constrained
loads was also limited by the amount of space in the vehicle. Information on the nature of load
constraints was collected for the first time by the Continuing Survey of Road Goods Transport
(CSRGT) in 1998 in accordance with a statistical directive from the EU. This revealed that
36.8% of the laden-kms travelled by 38 tonne trucks were weight-constrained. On 8.2% of the laden-kms the vehicles were also subject to a volume-constraint, with 28.6% limited solely by maximum weight. The DETRÕs estimate was, therefore, quite accurate. The 1998 DETR model also
incorporated, for the first time, an estimate of the likely diversion of freight from rail.
6. Innovative features of the new analysis
By the time that the Commission began its study in late 1999, the weight limit had already risen
to 40 tonnes for 5 axles trucks and 41 tonnes for vehicles with six axles, as explained above. The
Table 2
Estimated Savings in Vehicle-kms from an Increase in Maximum Truck Weight from 38 tonnes to 44 tonnes
Study
Million Vehicle-kms
Freight Transport Association (1996)
Newton and Frith (1993)
Institute of Highway Engineers,
quoted in House of Lords Select Committee on the European Communities (1994)
Department of Transport (1996)
Department of the Environment, Transport and the Regions (1998a)
770
340–460
880
650
270–500
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CommissionÕs inquiry was therefore concerned with the impact of a further increase from 40/
41 tonnes to 44 tonnes. Its results cannot be directly compared with those of the earlier studies
listed in Table 2. The analysis undertaken for the Commission differed from that undertaken
by the DETR in 1998 in three ways:
1. It incorporated new data collected for the first time in 1998 on the proportions of loads subject to
a weight- and/or volume-constraint. It was assumed that only loads that were weight-constrained (and not volume-constrained) in 38, 40 or 41 tonne vehicles could potentially benefit
from the increase in maximum weight.
2. It allowed for variations in the extent to which weight-constrained loads would ÔmigrateÕ from 38,
40 and 41 tonne vehicles to 44 tonne vehicles. It was not possible to model the degree of load
migration. This would require knowledge of the statistical distribution of load densities. In
the absence of information about the cubic volume of freight moved by road, it is not possible
to analyse load density. Instead, different levels of load migration were postulated and built
into a sensitivity analysis.
3. It allowed for the possibility that the resulting reduction in road transport costs per tonne-km
might increase the total demand for road freight transport. It was recognised that by altering
the trade-off between transport expenditure and other logistical costs, the maximum weight
increase could promote greater centralisation of economic activity and wider sourcing of products, both of which would generate more road freight movement. This had been identified by
environmental pressure groups as a major reason for not raising the weight limit (e.g. Transport, 1997). The issue of Ôinduced trafficÕ has also been addressed in the US (Pickrell and Lee,
1998). It was not possible, on the basis of the available data in the UK, to model the traffic
generation effect. Written and oral evidence submitted to the Commission by major steel,
oil, chemical, power-generating, beer, paper and petfood companies suggested that any generative effect would be very marginal (Commission for Integrated Transport, 2000).
In deriving its 1997 National Road Traffic Forecasts (NRTF), the UK government had to
define the mathematical relationship between road transport costs and average length of haul.
Following a review of previous research, it adopted an elasticity value of 0.1, indicating that
for every 1% reduction in the cost of road transport the average length of haul and hence
amount of freight movement (measured in tonne-kms) would increase by 0.1% (Department
of the Environment, Transport and the Regions, 1998b). This elasticity value was used to predict the amount of new traffic likely to be generated by the increase in the truck weight limit.
7. Assessing the impact on the rail freight sector
An increase in maximum truck weight from 41 tonnes to 44 tonnes (on six axles) would have the
effect of reducing road haulage costs per tonne-km for weight-constrained loads by roughly 11%.
This was in addition to the 7% saving in road haulage costs per tonne-km accruing from the previous increase in the weight limit in January 1999 from 38 tonnes to 40 tonnes for 5-axle and
41 tonnes for 6-axle vehicles. The railfreight companies argued that the full effect of this earlier
maximum weight increase had yet to be felt in full as contractual and operational constraints usually prevent companies from switching mode at short notice.
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One of the initial premises of the CommissionÕs study was that the policy of Ôencouraging freight
consignors to use rail, canal or sea transport should be regarded as a means towards the end of
environmental benefit, not as an end in itself Õ (Commission for Integrated Transport, 2000). Some
erosion of traffic from rail was therefore considered acceptable so long as the increase in maximum truck weight yielded net environmental and economic benefits. The CommissionÕs study
did not attempt to assess the possible diversion of freight from water-borne transport modes.
Written evidence provided to the inquiry by port operators indicated that any traffic diversion
from these modes would be very small. Similarly in the US, the main concern has been over freight
displacement from rail as modelling suggests that relatively small amounts of traffic will divert
from other modes to larger and/or heavier trucks (Pickrell, 2000).
It was generally accepted that an increase in maximum lorry weight to 44 tonnes would cause a
modal shift from rail to road. It could be detrimental to railfreight in three respects:
• Loss of existing traffic to the heavier vehicles.
• Less prospect of winning new traffic.
• Rail freight rates might have to fall to match the lower road haulage costs. This would impair
the profitability of the railfreight companies, dampen their growth prospects and possibly cause
them to scale down investment plans.
The CommissionÕs study did not attempt to quantify any of these effects. Instead, it based its
analysis of modal shift on the results of two previous studies. The first, undertaken by NERA
(1997) estimated that an increase in maximum truck weight from 38 to 44 tonnes would divert
around 5% of freight tonne-kms from rail to road. A later study by OXERA (1999) for the main
railfreight company predicted that the potential traffic loss (measured in tonne-kms) would lie
within the range 7%–19% depending on the level of VED levied on the new 44 tonne vehicles. Neither of these studies based their estimates of the potential displacement of freight from rail to
heavier lorries on empirically-derived cross-modal elasticity values for the UK freight market.
The OXERA analysis was largely based on modal elasticity values for the North American freight
market in the 1980s drawn from a World Bank report by Oum et al. (1990). The NERA figure was
based on the subjective judgement of industry specialists. The estimates of modal diversion were
therefore fairly crude.
Both the NERA and OXERA estimates related to an increase in maximum lorry weight from
38 to 44 tonnes. As maximum lorry weights has already risen to 40/41 tonnes, the CommissionÕs
study was concerned with the incremental effect of a further weight increase to 44 tonnes. For this
purpose, it was assumed that the transfer of freight tonne-kms from rail to road would be a linear
function of the lorry weight limit over the range 38–44 tonnes.
8. Procedure used to forecast the impact of the weight increase
This procedure was divided into eleven stages:
1. Estimates were obtained from the CSRGT of the distances travelled by 38, 40 and 41 tonne
vehicles with weight-constrained loads and the total tonne-kms moved over these distances.
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85
2. Maximum payload weight (MPW) ratios were calculated. These were expressed as the ratios
of the MPWs that could be carried on 38 tonne 5 axle vehicles (24 tonnes), 40 tonne 5 axle
vehicles and 41 tonne 6 axle vehicles (26 tonnes) to the maximum carrying capacity of the
44 tonne 6 axle vehicle (29 tonnes).
3. The vehicle-kms travelled with weight-constrained loads were multiplied by the MPW ratios
to estimate the potential gross saving in laden vehicle-kms.
4. The gross saving in laden vehicle-kms was converted into a gross saving in total vehicle-kms
by allowing for empty running. It was assumed that the average empty running figure for 38,
40 and 41 tonne vehicles (28%) would also apply to the new 44 tonne vehicles.
5. High, medium and low Ômigration factorsÕ were applied to the gross savings in vehicle-kms in
recognition of the fact that some loads would reach volume, scheduling or other constraints
at a MPW of less than 29 tonnes. Separate migration factors were used for 38 and 40/41 tonne
vehicles. These factors were chosen subjectively though in consultation with a group of industry specialists and road freight operators.
6. Allowance was made for traffic generation by applying the NRTF elasticity value of 0.1 to the
estimated saving in road haulage costs per tonne-km from increasing MPWs from 24 to
29 tonnes (for 38 tonne vehicles) and 26 to 29 tonnes (for 40/41 tonne vehicles). The traffic generation factors were applied to road freight tonne-kms carried by vehicles carrying weightconstrained loads.
7. Allowance was made for three levels of modal diversion: high—19% of tonne-kms transfer to
road (based on OXERAÕs worst case scenario), medium—10% transfer (mid range estimate)
and low 5% shift (based on the NERA study).
8. The average load factor for new 44 tonne vehicles (on laden trips) was estimated with reference to the current load factors of the 38, 40 and 41 tonne vehicles derived from CSRGT data.
These were, respectively, 63%, 72% and 82%. On this basis, it was assumed that the 44 tonne
truck would have an average load factor of 70%.
9. The net savings in vehicle-kms were calculated for each of the levels of load migration and
modal diversion.
10. The net savings in vehicle-kms were translated into transport cost savings. This was done
using an average vehicle operation cost value of £0.65 per vehicle-km obtained from the
Motor Transport cost tables (Anon, 1999).
11. Environmental cost savings were derived using monetary valuations of air pollution, climate change, noise disturbance and traffic accidents provided by AEA Technology. At
an early stage in its deliberations, the Commission had decided that only road vehicles
meeting the Euro II emission standard or above would be allowed to travel at 44 tonnes.
(This standard was introduced by the European Commission for new heavy trucks in
October 1996 and set the maximum level of emissions for carbon monoxide, hydrocarbons, nitrogen oxide and particulates at, respectively, 18, 78, 650 and 185 gm/km.)
The 44 tonne weight limit would therefore be used to accelerate the adoption of cleaner vehicle technology. The environmental calculations therefore assumed that all 44 tonne
trucks would achieve the Euro II emission level. The environmental estimates for railfreight were based on the use of the new, cleaner Class 66 locomotives. Average environmental externalities were valued at 0.87 pence per tonne-km for road and 0.28 pence per tonne-km
for rail.
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A series of Excel spreadsheets was constructed to perform the analysis.
It was recognised that the accuracy of the calculation rested on several factors, particularly:
• Subjective estimates of the likely degree of load migration to 44 tonne trucks.
• Assumptions about the future load factor and level of empty running for these vehicles.
• Estimates of modal shifts and the price elasticity of demand for road freight transport derived
by previous studies.
• CSRGT statistics on vehicle loading constraints.
Given the available data, expert judgements had to be made, partly on the basis of an extensive
consultation exercise. The Commission received many written and oral submissions from a broad
range of organisations with an interest in the truck weight issue. The list of organisations can be
found in an appendix of the CommissionÕs interim report (Commission for Integrated Transport,
2000). Uncertainty about some of the key parameters was also addressed by the use of sensitivity
analyses.
9. Results of the forecasting exercise
Table 3 shows the forecast reductions in truck-kms resulting from the maximum weight increase at different levels of load migration and modal diversion. According to the mid-range estimate, based on ÔmediumÕ levels of load migration and modal diversion, the annual volume of
truck traffic would be reduced by around 100 million vehicle-kms, equivalent to approximately
230 return journeys each day between London and Edinburgh. This would translate into annual
road haulage cost savings of £60–80 million (in 2000 prices excluding VED) and a reduction of 80–
100 000 tonnes in annual emissions of carbon dioxide. The mitigation of environmental effects (air
pollution, climate change, noise and traffic accidents) was be valued, on a annual basis, at approximately £35 million. Even within the worst case scenario, combining a low degree of load consolidation in 44 tonne vehicles with a high diversion of freight from rail, the proposed maximum
weight increase would still yield both economic and environmental benefits and not require policy-makers to trade-off economic gains against environmental costs. This assumed that the traffic
Table 3
Forecast Reductions in Vehicle-kms Resulting from Maximum Truck Weight Increase (millions of vehicle-kms per
annum)
Modal diversion
High (19%)
Medium (10%)
Low (5%)
Load migration level
High
from 38t truck 70%
from 40/41t truck 90%
Medium
from 38t truck 50%
from 40/41t truck 80%
Low
from 38t truck 30%
from 40/41t truck 70%
114
146
188
62
94
137
10
42
85
Adapted from the Commission for Integrated Transport (2000).
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
87
generating effect was adequately captured by the use of a price elasticity of demand value for road
freight of 0.1. Further sensitivity analysis revealed, however, that this elasticity value would have
to be increased to 0.94 to eliminate the saving in vehicle-kms under central case assumptions. As it
was extremely unlikely that the traffic generative effect would be so pronounced, the conclusion
that increasing maximum truck weight to 44 tonnes would produce net economic and environmental benefits appeared fairly robust. On this basis, the Commission concluded that this measure
would yield Ôsmall, but significantÕ economic and environmental benefits. As this was in keeping
with the UK governmentÕs Ôsustainable distributionÕ strategy (Department of the Environment,
Transport and the Regions, 1999), the government decided to raise the maximum truck weight
to 44 tonnes in February 2001. To be registered at this weight limit, trucks had to run on six axles,
meet Euro II emission standards and be equipped with air suspension.
10. Industry response to the increase in maximum truck weight
It has been argued that, Ôresponsible regulation is a process: the regulatory authority should do
the best prior analysis possible, but once regulations have been changed, the consequences must
be systematically observed and adjustments made where necessaryÕ (Transportation Research
Board, 2002). In the remainder of this paper we will report the results of the first analysis of
the effects of the increase in maximum truck weight in the UK to 44 tonnes. It uses data collected
over the first three years of the new weight limit to show how the road freight sector has responded and the resulting impact on traffic levels, transport costs and emissions.
Since February 2001, there has been a pronounced shift to vehicles licensed to operate with a
gross weight of 44 tonnes. By the end of 2003, approximately 52% of HGVs with gross weights of
38 tonnes or above were licensed to operate at 44 tonnes (Fig. 1). Almost two-thirds of the tonnekms handled by vehicles in the Ô38 tonnes and aboveÕ category were moved in 44 tonne vehicles. It
is important to emphasise, however, that not all of this freight movement took full advantage of
the additional payload capacity on 44 tonne trucks. In 2003, these vehicles were only fully laden
(by weight alone) on approximately 22% of the distance that they travelled loaded. Their average
No of Vehicles Licensed
60000
50000
40000
30000
20000
10000
0
38 tonnes
2001
40 tonnes
41 tonnes
2002
44 tonnes
2003
Fig. 1. Numbers of trucks licensed in heavier weight classes: 2001–2003. Source: Department for Transport,
unpublished data.
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payload was only 17.9 tonnes, well below the maximum of 29 tonnes and an average load that
could comfortably be carried on a vehicle plated at 38 tonnes. Why then are so many vehicles
now licensed at 44 tonnes when most of the loads that they carry do not require operation at this
weight limit?
The reason is that licensing the truck at the highest legal weight gives operators maximum flexibility at little extra cost. Many road hauliers, for example, like to have the opportunity to carry
the occasional heavy load, even although most of the traffic they handle does not require the
44 tonne weight limit. As vehicle tax (VED) on 44 tonne vehicles (with the obligatory six axles)
is identical to that on six-axle 41 and 40 tonne vehicles and around 50% lower than on five-axle
40 tonne vehicles, companies do not have to pay any extra tax for the additional carrying capacity.
In analysing the impact of the 44 tonne weight limit, it is important to distinguish the popularity
of this vehicle weight class from the economic and environmental benefits that have accrued from
its introduction. To assess these benefits, it is necessary to focus on loads transported by 44 tonne
trucks which could not have been carried (legally) on vehicles plated at lower weights prior to 2001.
In the next section, we assess the magnitude of these benefits using unpublished CSRGT data on
weight- and volume-constrained loading of trucks at the upper end of the vehicle weight range. The
actual benefits will then be compared with the forecasts made by the CommissionÕs study in 2000.
11. Procedure for assessing the impact of the 44 tonne weight limit
The analytical procedure used to estimate the actual benefits closely resembles stages one to
four in the forecasting procedure outlined earlier (Fig. 2). Using CSRGT data on the proportions
of road freight movements subject to a weight and/or volume constraint, it was possible to estimate the total distance travelled annually by 44 tonne trucks with a weight-constrained load
(Dc). It was assumed that if the weight limit had not been raised to 44 tonnes, weight-constrained
freight movement in 44 tonne vehicles would have been handled by fully-laden 41 tonne trucks. 2
To calculate how much extra truck traffic this would have generated, Dc was multiplied by the
ratio of the maximum payload weights (MPW) of 44 tonne to 41 tonne vehicles (i.e. 29 tonnes/
26 tonnes = 1.12).
Allowance had then to be made for the amount of empty running likely to be associated with
the extra distance run loaded by 41 tonnes. For this purpose, empty running data were obtained
from the CSRGT for this class of vehicle. In 2003, 26.3% of the distance travelled by 41 tonne
vehicles was run empty. Adding laden- and empty-kms yielded an estimate of the total number
of additional kilometres that 41 tonne vehicles would have had to run in the absence of 44 tonne
vehicles. This was adopted as a measure of the reduction in truck-kms resulting from the weight
increase and used to derive estimates of operating cost and emissions savings. Vehicle operating
cost data were obtained from the Freight Transport Association (2004a). Similar environmental
ratios were used to those obtained from AEA Technology for the CommissionÕs study. The anal-
2
The 41 tonne 6-axle vehicle can carry a very similar weight to a 40 tonne 5-axle vehicle, as the extra axle weighs
approximately one tonne. Some of the weight-constrained freight movement at 44 tonnes might have been carried in
40 tonne 5-axle vehicles. Given the parity in carrying capacity, this does not affect the results.
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
Estimate of distance run by 44 tonne trucks with
weight-constrained loads (from CSRGT)
Allow for empty running associated with the
laden-kms saved
Estimate of the reduction in total truck-kms
89
Multiply this distance by the ratio of the maximum
payload weight of 44 tonne trucks to the maximum
payload weight of 41 tonne trucks (1.12)
Estimate of the potential reduction in laden-kms from the
use of 44 tonne trucks
Translate savings in total truck-kms into reductions in
haulage costs and environmental effects
Fig. 2. Analytical procedure used to estimate the benefits of the truck weight increase.
ysis was conducted on CSRGT data for each of the years since the weight increase took effect to
observe trends in the uptake of the higher weight limit and the associated benefits.
12. Results of the impact assessment
Table 4 summarises the results of the analysis. It shows how the annual reduction in vehiclekms and corresponding economic and environmental savings have increased as the road freight
sector has adjusted to the 44 tonne weight limit. In 2003, the most recent year for which data
are available, approximately 134 million truck-kms were saved as a result of the weight increase.
This is roughly a third higher than the CommissionÕs mid-range forecast of the reduction in vehicle-kms. In comparing the CommissionÕs forecast with what has actually happened, however, one
must consider four other factors: the length of time it will take for road freight operations to fully
adjust to the new weight limit, any traffic generation effect, diversion of freight from rail to road
and changes in the vehicle tax levels in recent years.
12.1. Time-scale
The load migration factors used in the CommissionÕs forecasting model related to an unspecified future date at which the full impact of the 44 tonne vehicle had been felt. The CSRGT data
Table 4
Estimated Savings from the Increase in Maximum Truck Weight to 44 tonnes
2001
2002
2003
Reduction in annual truck-kms (million)
Saving in vehicle operating costs (£million) 2004 prices
Fuel saving (million litres) (average 0.377 litres/km or 7.5 mpg)
53
44
20.1
104
85
39.1
134
110
50.6
Reduction in emissions (tonnes)
• Carbon dioxide
• Nitrogen oxide
• Particulates (PM10)
53 800
351
12.5
104 800
684
24.4
135 700
884
31.5
90
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
suggest that the migration of weight-constrained loads to the heavier weight limit was still continuing in 2003, though at a diminishing rate. It is difficult to judge how long this process will continue. If one projects the ÔtaperingÕ of the annual vehicle-km savings over the past three years, they
would level off at around 170 million vehicle-kms by 2006–7.
12.2. Traffic generation
The CommissionÕs forecast allowed for the possibility that transport cost reductions resulting
from the maximum weight increase might generate additional road freight demand. Between
2001 and 2003, road tonne-kms did increase slightly from 149 to 152 million (Department for
Transport, 2004), but this 0.7% per annum growth was well below the historic average growth rate
of 2.7% experienced between 1980 and 2001. Tonnes-km carried by the heaviest vehicles (38 tonnes
and above) increased by 2%, but this too was below the historic average rate of 3.2%. Between 2001
and 2003, annual tonne-kms handled by these vehicles increased by 2 billion per annum. The CommissionÕs mid-range estimate was that, by reducing the cost of road haulage, the uplift in maximum
weight to 44 tonnes would generate around 168 million tonne-kms per annum. This would have
represented only 8% of the actual growth. There is little evidence, however, that the truck weight
increase has, as yet, generated much additional demand for road freight movement.
12.3. Modal diversion
The main railfreight company, EWS, reported in 2002 that Ôit was too early to determine the impact of 44 tonne HGVs. No instant loss of business was ever expected, but in the longer term, EWS
has identified up to 20% of business which could be at riskÕ (Commission for Integrated Transport,
2002a). The negative effect of the increase in the truck weight limit was, however, mitigated by the
decision of the Rail Regulator 3 in October 2001 to halve the infrastructure charges paid by railfreight operators. This concession, worth £500 million per annum, took Ôaccount of increased competitive pressures from other transport modes and recent decisions on 44 tonne lorries and vehicle/
fuel duty which have given road haulage a competitive edge over railÕ (Office of the Rail Regulator,
2001). In addition, the governmentÕs 10 year transport plan included investment of £4 billion to
support railfreight (Department of the Environment, Transport and the Regions, 2000). The Commission has argued that these measures Ôshould be sufficient to protect rail freight from the impact
of 44 tonne lorriesÕ (Commission for Integrated Transport, 2002b). Between 2000 and 2003 total
rail tonne-kms fluctuated around 18–19 billion and its share of the road-rail freight market remained fairly stable at 11% (Fig. 3) (Strategic Rail Authority, 2004; Department for Transport,
2004). There is no evidence, therefore, of the mid-range reduction of 10% in railfreight tonnekms which the Commission factored into its cost-benefit analysis of the lorry weight increase. It
is, nevertheless, very difficult to isolate the effect of this measure from all the other influences on
railÕs competitive position and even harder to determine the counterfactual.
3
Within the privatised UK rail industry the rail regulator is Ôresponsible for the regulation of access to the railways
and promotion of competition in the provision of rail services. He is also responsible for promoting efficiency and
economy of those providing railway services and protecting the interests of railway service users.Õ
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
91
25
20
15
10
5
0
1995 1996 1997 1998 1999 2000 2001 2002 2003
Tonne-kms(bn)
% road/rail market share
Fig. 3. Trends in rail tonne-kms and market share, 1995–2003. Source: strategic rail authority, 2004; Department for
Transport, 2004.
12.4. Changes in vehicle taxes
In 2001, the government substantially reduced VED on trucks and narrowed tax differentials
between vehicle weight classes (Table 5). The VED rate introduced for the new category of vehicles with gross weights of over 41 tonnes was well below that assumed by the CommissionÕs study.
Nor had it been anticipated that the same tax rate would apply to 44 tonne, 41 tonne and 40 tonne
vehicle operating with six axles. No effort was therefore made by the government to capture in
higher taxes any of the additional economic benefit from operating at the higher weight limit. This
partly explains why the load migration to 44 tonne vehicles was greater than forecast.
Overall, therefore, the CommissionÕs mid-range forecast significantly under-estimated the
reduction in truck-kms observed in 2003. It is likely too that the benefits of the increase in maximum weight have not yet peaked. Full adjustment of the national truck fleet to the higher weight
limit will probably take several more years. The reduction in vehicle-kms may stabilise around
25% above its 2003 level within the next 2–3 years. This reduction of around 170 million truckkms would be significantly above the upper boundary of the CommissionÕs forecast (137 million
truck-kms). The CommissionÕs forecast appears to have under-estimated the degree of load consolidation in 44 tonne trucks partly as a result of a contemporaneous change in the tax regime, and
over-estimated the extent of the modal shift from rail to road. The degree of modal shift would
probably have been significantly higher had the Rail Regulator not compensated the railfreight
sector for the lorry weight increase by reducing track access charges. As the actual reduction in
Table 5
Changes in Vehicle Excise Duty on the Heaviest Categories of Truck (£per annum)
Gross Vehicle Weight
38 tonne
40 tonne
41 tonne
44 tonne
2 axle tractor/3 axle trailer
3 axle tractor/3 axle trailer
2000
2003
2000
2003
2710
3950
1200
1850
1280
2500
2500
650
1200
1200
1200
Sources: Treasury (2000); Driver and Vehicle Licensing Agency (2003).
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A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
truck-kms is greater than predicted and the erosion of freight from rail less than expected, the estimated economic and environmental benefits quoted in the CommissionÕs study have to be revised
upwards.
13. The case for a further increase in truck weight
It has recently been suggested that Ôwe need a new, high level and informed debate on the issue
of lorry weights and dimensions with a view to ensuring that we are not penalising industry by
unnecessarily constraining new design opportunitiesÕ (Freight Transport Association, 2004b).
Some other EU countries have truck weight limits in excess of 44 tonnes. In the Netherlands
and Finland, for example, six axle trucks can have a maximum gross weight of, respectively,
50 tonnes and 53 tonnes. In Sweden the limit for certain categories of long combination vehicle
is 60 tonnes.
Load consolidation opportunities are likely to diminish as maximum truck weight increases,
given the statistical distribution of load densities. As the weight limit rises, an increasing proportion of loads will be constrained by volume (i.e. they will Ôcube outÕ before they Ôweigh outÕ). This
can be seen by comparing the proportions of laden-kms subject to different types of load constraint in years when different maximum weight limits applied (Table 6). A comparison of the situation in 1999 with that in 2003 shows that the increase in the weight limit reduced the proportion
of laden-kms subject to a constraint while significantly tilting the balance from weight to volume
constraints. In 2003, a much larger proportion of loads was volume-constrained than weight-constrained. Greater economic and environmental benefit would therefore be gained from an increase
in vehicle dimensions than from a further increase in the weight limit. The case for enlarging vehicles also appears to be strengthening as a result of a long term decline in the average density of
road freight. It has also been observed in the US that Ôaverage operating weights of tractor
semi-trailers have actually gone down slightly in recent yearsÕ partly as a result of Ôdecreases in
cargo densityÕ (US Department of Transportation, 2000). While there are no proposals at present
to increase the maximum length or width of trucks, it is possible to expand cubic capacity vertically by raising their height and/or lowering their floors. This generally allows companies to insert
a second deck and carry two layers of pallets (McKinnon and Campbell, 1997). In recent years
there has been a sharp increase in the number of double-deck vehicles on BritainÕs roads, as oper-
Table 6
Nature of load constraints at the truck weight limits in 1999 and 2003
1999a
1999a
2003
Truck Weight Limit
% of laden-kms
load-constrained
Nature of load constraint
(% of load-constrained laden-kms)
Weight
Volume
Weight and Volume
40 tonne (5-axles)
41 tonne (6-axles)
44 tonne
70
77
59
69
47
37
21
42
49
10
12
14
Source: Department for Transport, unpublished data.
a
Figures relate to the 3rd quarter.
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
93
Table 7
Industrial sectors making the greatest use of 44 tonne trucks
% of road tonne-kms carried in 44 tonne trucks
Coal and coke
Beverages
Petrol and petroleum products
Wood and timber
Fertiliser
Agricultural products
Iron and steel products
78
73
61
61
56
54
52
Source: Department for Transport, unpublished data.
ators take advantage of the relatively generous height clearances under bridges and tunnels. This
growth in the use of double-deck vehicles has probably been reinforced by the increase in maximum truck weight in 2001, though this has yet to be empirically investigated.
In 2003, 44 tonne trucks travelled 22% of their laden-kms with loads constrained only by
weight. This suggests that there remains some potential for consolidating loads in even heavier
vehicles, particularly in those industrial sectors producing and distributing dense products, such
as coal, drinks, petroleum products and timber (Table 7). The analytical procedure employed
by the Commission could be applied again to quantify this potential.
It is likely that any new proposal to increase maximum truck would be very controversial and
fiercely resisted, particularly by environmental pressure groups and the rail freight industry. It
would make it more difficult for the government to achieve the 80% growth target it set for rail
tonne-kms in its 10 year transport plan, especially as the industrial sectors deriving greatest benefit
from truck weight increases produce many of the dense, primary products that have traditionally
constituted railfreightÕs core market.
14. Conclusion
The UK governmentÕs decision to increase maximum truck weight to 44 tonnes in 2001 was
very contentious. While there was general agreement that economic benefits would flow from
the greater consolidation of loads, many suspected that the environment would suffer as a result
of the reduction in haulage costs generating more road freight movement and freight traffic being
diverted from rail to road. The CommissionÕs investigation of the issue suggested that, even after
allowing for these effects, raising the weight limit could yield net environmental as well as economic benefits.
The research reported in this paper has used unpublished data from the UK governmentÕs main
road freight survey to determine what has actually happened over the first three years of the new
weight limit. It indicates that the Commission under-estimated the degree of load consolidation in
44 tonne vehicles and over-estimated the degree of modal diversion from rail. Little statistical evidence has so far emerged to show that the weight increase has accelerated the rate of road freight
traffic growth. This study therefore confirms that the increase in maximum truck weight has
94
A.C. McKinnon / Transportation Research Part D 10 (2005) 77–95
yielded significant economic and environmental benefits. Indeed these benefits appear to be greater than expected.
As 44 tonners run just under a quarter of their mileage fully-laden, a case could be made for a
further increase in the weight limit. The methodology employed by the Commission in its earlier
study could be used to evaluate this case, though some revision of key parameters on load migration, traffic generation and modal diversion would be required in the light of recent experience
with the 44 tonne weight limit.
Forecasting the impact of the truck weight increase was much easier in the UK than in the US
where arguably more research has been done on this issue than in any other country. The issue
was simplified in the UK by decoupling weight limits from size limits, assuming that road infrastructure could accommodate the heavier vehicles, standardising the weight limit across the whole
country and maintaining existing truck safety requirements. Analysis was also facilitated by the
availability, since 1998, of official data on the nature of the physical constraints on vehicle loading. The CommissionÕs forecasts, nevertheless, had still to rely on a significant amount of expert
judgement on the degree of load migration to heavier vehicles, the diversion of freight from rail
and the elasticity of demand for road freight movement. There was also uncertainty about the future vehicle tax regime and about the nature and scale of compensatory financial support to the
railfreight sector. When these factors are taken into account, the CommissionÕs forecasts of the
economic and environmental benefits of increasing maximum truck weight appear to have been
reasonably accurate.
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