Proceedings of the International Conference on Heavy Vehicles, HVTT10: 10th International Symposium on Heavy Vehicle Transportation Technologies

By Alan O'Connor

This reference collects the latest information from the International Conference on Heavy Vehicles, specifically as it relates to Heavy Vehicle Transport Technology.  Among the topics detailed are: interactions between heavy vehicles or trains and the infrastructure, environment and other system users; heavy vehicle and road management information-measurements, data quality, data management; freight mobility and safety; vehicle classification, size and weight evaluation, regulations, and enforcement; and traffic and road safety.

• Language: English
• Publisher: Wiley
• Release date: Mar 4, 2013
• ISBN: 9781118557488

Book preview

The EU’s rules on weights and dimensions and the realities of sustainable mobility

Principal administrator with the ‘Logistics and Co-Modality’ Unit and responsible for all DG TREN’s ongoing logistics research and current 7FP projects. Responsible for combined transport legislation and, most relevantly, the ‘weights and dimensions’ Directive 96/53 on which a study was launched to recommend whether or not to adapt the directive and if so, where.

John Berry

European Commission, DG/TREN Brussels, Belgium

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ABSTRACT: This paper describes the position of Heavy Goods Vehicles within the EU Commission’s evolving transport policy. The paper commences by establishing the continued upwards trend in freight growth, made more so by the accession into the European Union of the ten central European States. It discusses Co-Modality, the maximisation of the efficiency and effectiveness of each transport mode, acting individually and collectively, from the backdrop to the Commission’s recently launched ‘Logistics action Plan’, which included the highly controversial topic of truck ‘weights and dimensions’ limits, as dictated by Directive 96/53. The paper presents the study that was launched in December 2007 that aims to give answers to this issue.

KEYWORDS: Freight transport growth, Co-Modality, Sustainable mobility, Action plan on logistics, Truck weights and dimensions legislation, Modular concept.

RESUME : Cet article décrit le rôle des poids lourds dans l’évolution de la politique des transports de la Commission Européenne. Il commence par rappeler la tendance haussière continue de la croissance du fret, due à l’entrée dans l’Union européenne des dix états de l’Europe centrale. La co-modalité, l’optimisation de l’efficacité et de la capacité de chaque mode de transport, considéré individuellement et collectivement, sont présentés dans le contexte du plan d’action sur la logistique lancé récemment par la Commission, qui intègre le sujet hautement controversé des limites de poids et dimensions des camions fixées par la directive 96/53. L’étude lancée en décembre 2007 qui vise à apporter des réponses à cette question est présentée.

MOTS-CLES: Croissante du transport de fret, co-modalité, mobilité durable, plan d’action sur la logistique, réglementation des poids et dimensions des camions, concept modulaire.

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1. Transport growth

The following background to freight transport in the EU is extracted from the Commission’s Common Transport Policy White Paper review—Keep Europe Moving and the recent public consultation by the Commission concerning ‘Internalisation of Transport Cost externalities’.

Transport services play a central role in modern society and economy. They account for 4.3% of EU’s value added and employ about 8.5 million persons.

Over the past decades, transport has increased in line with economic growth. Thus, freight transport growth has been 2.8% per year on the period 1995-2005 while the real GDP grew by 2.3% per year on the same period, at the same time passenger transport has grown 1.9% per year. Freight transport demand has increased more strongly for modes offering greater flexibility, in particular road transport.

The EU enlargement has had an important impact on all the drivers of transport demand; the size of the Union has expanded by almost a quarter with enlargement. Up to 2006, i.e. before the Accession of Bulgaria and Romania, enlargement had similar effects to the previous enlargement to Spain and Portugal, with rates in cross-border traffic with the new Member States growing at 10% per year.

Table 1. Freight total growth (in %)

EU-15 are those 15 Member States who were the members of the European Union up to 2004; EU-10 are the 10 Member States that acceded to the EU in 2004; EU-25 are all member States bar Romania and Bulgaria who acceded to the EU in 2007.

2. Objectives for future

The future EU transport policy needs to provide the mobility for economic growth and social welfare while, in parallel, tackling the negative effects that the increasing transport causes.

These wide objectives may be addressed via four complementary directions: (1) developing and improving economic and resource efficiency of transport modes and systems; (2) ensuring high level services and protection to users and their environment, while integrating the social dimension of the transport industry; (3) increasing the deployment of new technologies; (4) and strengthening the role of EU at the international level.

Developing and improving economic and resource efficiency is the key objective of the Lisbon strategy. A higher economic efficiency will enable a reduction of transport costs and the resources used. Freed resources, e.g. in work time and energy savings, may thus be put to better use in other sectors of the economy or in improved transport services. More and/or better mobility will foster the productivity of the European economy and the Union’s global competitiveness.

The use of the existing infrastructures has to be reconsidered. Better network management and the intensive use of the new technologies are required in order to improve the quality of the services rendered, and to reduce, if necessary, the needs for new infrastructures.

Also, a comprehensive and pragmatic transport policy introducing a variety of organisational and technology using measures, ranging from logistics to ITS deployment, will contribute to reducing the costs of freight and passenger transport in terms of time, money and environmental impacts.

3. Transport’s ‘externalities’

Although the benefits of transport services are widely acknowledged, transport activities generate nuisances/costs to other transport users, but also to society in general, including the local population and future generations. More specifically, transport growth may lead to the need to increase infrastructure capacity of several modes and is continuing to exert pressure on air quality, the climate and land use. Furthermore, noise is still a nuisance for many people, and fatal and serious accidents (in road transport) remain at an unacceptable level.

Transport produces external effects that have an impact on most of the population notably in urban areas. The total social cost of road provision and use (excluding vehicle operating cost) amounts on average to some 4% of GDP in Western Europe. The social costs are divided as follows: infrastructure costs 1.5%, congestion around 1%, external costs of accidents 0.5%, air pollution 0.6%, noise 0.3% and global warming 0.2% (UNITE study 2004).

Although efforts have been made to reduce pollution (Figure 1), gas emissions and noise, some environmental damages continue to increase, affecting a large number of citizens (health) and the ecosystem (biosphere, soil, water…).

Figure 1. Evolution of emission of air pollutants from road and other modes of transport

Noise emitted by transport has detrimental effects on health with the WHO recently showing that the magnitude of health effects from exposure to traffic noise is very significant. Although several Community measures have been taken to reduce noise pollution, there is no evidence that the exposure to transport noise has been substantially reduced. Air pollution still remains a challenge in dense and high traffic areas.

More worrying are the trends of greenhouse gases emissions. Global warming imposes costs to future generations and should be tackled from now as transport is a large and soon to be the largest contributor to greenhouse gases emissions. Currently, 26% of CO2 come from transport of which 85% are from road transport. CO2 emissions from transport have increased by 29% from 1990 to 2004 while CO2 emissions in other sectors of the economy (industry, households etc.) have been reduced or stabilised. However, the evolution is not homogeneous across modes of transport and inland navigation and rail have reduced emissions of CO2 over the past decade (Figure 2).

Figure 2. EU25 CO2 from road transport (1990-2003)

Road fatalities are unacceptably high although they have decreased by 21.4% between 2000 and 2004 in the EU as a whole (Figure 3). In 2005, there were still 41 274 persons killed in EU25. Besides high private costs due to loss of relatives or friends, accidents impose costs to society (medical costs, police costs, material damages…), which are only partially covered by existing insurance systems. Furthermore, accidents may also imply non recurrent congestion problems when traffic is dense, increasing travel time spent for other users.

Heavy goods vehicles (HGV) account for around 1/3 of the external costs of road transport and the road transport level of internalisation is between 0.5 and 0.6. However, a more disaggregated perspective highlights the disparities of the situation. More specifically, passenger cars are already paying for the social costs of their use which is not the case for heavy goods vehicles.

Figure 3. Road fatalities in the EU (1991-2010)

Figure 4. Index of level of internalisation — road transport (2000-2005)

The level of internalisation also differs between countries (Figure 4). For example, in countries such as Luxembourg or Austria, the index might be negative for trucks. Rapid growth of freight transport by road with consequential congestion, road accidents and pollution caused by heavy road transport are amongst the economic, social and environmental problems that need to be tackled by increasing the share of intermodal transport operations. European competitiveness needs to be maintained and transport is an essential part of this process. Advanced and integrated logistics solutions would allow freight transport operations to be carried out optimally in all circumstances thereby giving Europe a competitive edge.

4. Co-Modality

The 2006 revision of the Transport White Paper Keep Europe Moving (COM2006a) concluded that the EU needs to establish a framework that encourages improvements to the individual modes of transport as well as their combinations in multi-modal transport chains for a sustainable transport system. Better utilisation of transport infrastructures, protection against fossil fuel-induced price increases and a reduction of the negative environmental and social effects should be the principal objectives of such a policy. For the more remote regions of the European Union, competitively priced access to the major markets remains an important concern. The key to achieving these objectives lies in the notion of co-modality: the efficient use of transport modes operating on their own or in multi-modal integration in the European transport system to reach an optimal and sustainable utilisation of resources.

The European Commission issued a Communication on Freight Transport Logistics in Europe (COM2006a) in June 2006. The document highlighted the economic importance of the European logistics sector and identified a number of areas for possible action at European level, suggesting that these should be further developed in a logistics action plan.

5. A review on the size and weight of heavy goods vehicles

The Commission’s Action Plan on Logistics, launched on 17the October 2007 included, as one of some thirty action areas, the need to examine whether an update of Directive 96/53/EC is warranted, in particular in relation to the modular concept’s use in international traffic and subject to any necessary qualifications, to review the conditions under which current vehicle weight and size limitations should be maintained.

5.1. Background

The 2006 revision of the Transport White Paper Keep Europe Moving (COM2006b) in introducing the concept of Co-Modality concluded that the EU needs to establish a framework that encourages improvements to the individual modes of transport as well as their combinations in multi-modal transport chains for a sustainable transport system. Better utilisation of the transport infrastructure and a reduction of the negative environmental and social effects are the principal objectives of such a policy.

5.2. Freight vehicle weights and dimensions legislation

The Commission considers that the rules on the dimensions of vehicles and loading units should match the needs of advanced logistics and sustainable mobility (COM2006a).

Directive 96/53/EC sets out the maximum allowable vehicle and loading dimensions in national and international road transport in the EU. However, while the Directive harmonises across the EU the maximum dimensions of road vehicles and sets agreed levels for weights that would permit free circulation throughout the EU, it permits different national rules on the maximum weights. Member States may deviate from the maximum dimension limitations in national transport in certain pre authorised circumstances, the ‘modular concept’ or as it has been called, the ‘gigaliner’ or the ‘Euro-combi’ being the most relevant example. Also, various industrial sectors have argued for an easement in the weights and dimension restrictions to accommodate more efficient loading (i.e. more pallets or passenger cars) or to carry a heavier payload.

The Commission is examining the option of adapting Directive 96/53 to take account of technological developments and changed transport requirements, in particular as regards:

– The potential for heavier two vehicle combinations, perhaps allowing 44 tonnes on six axles for general cargo or for carrying all types of Intermodal Loading Units (ILUs) in combined transport operations. Currently, the possibility of using the 44 tonne two vehicle combination in international transport is limited to a three axle motor vehicle with a two or three axle semi-trailer carrying a 40-foot ISO container as a combined transport operation (Directive 96/53/EC Annex 1, point 2.2.2);

– Operation of the modular concept or a variation thereof in international transport (by the adaptation of Directive 96/53/EC-art. 4(4(b)), subject possibly to strict criteria on the vehicles and their equipment, on drivers, on the roads permitted and subject to weight limitations. The modular concept is a vehicle combination composed from vehicle units that are themselves within the statutory dimension limits but in combination could be longer than the maximum authorised length of the usual two-vehicle combination of a tractor/semi-trailer (16.5 m) and the truck/trailer combination (18.75 m). In its 25.25 m version currently used the modular concept’s load space is therefore around 50% greater. The feasibility of non-modular combinations within the overall limitations shall also be examined;

– The use of 45 foot (13.72m) long containers in cross-border transport operations;

– Introduction of harmonised loading dimensions such as the overhang for car transportation.

Directive 85/3 (the first to set standards for international transport) and the consolidated Directive 96/53 have served Europe well. By establishing rules in international transport the Directives have been vital for the EU’s transportation policy: this fact is recognised by both the logistics and the vehicle manufacturing industry (both motor and trailer/semi-trailer). However, the Directive was not capable of harmonising the maximum weight limits within national transport or the maximum dimensions of a fully loaded vehicle. Both impede free circulation.

Today, as against twelve and more years ago when the freight vehicle aspects of the Directive were last adapted, there is an array of road safety and axle/tyre/suspension improvements that can mitigate the negative effects of bigger and/or heavier vehicles and vehicle combinations.

Trials have been done, are ongoing or are planned that aim to assess and quantify the effects of the modular concept’s use in both international as well as national transport. These trials, together with the experiences of Sweden and Finland who already operate the modular concept, have assessed the modular concept’s effect on: the likely reduction in the number of freight journeys, congestion, fuel efficiency, business efficiency, CO2 emissions, road safety, road damage, modal shift, impact on bridges and roads, adaptation and classification of the infrastructure, traffic flow etc.

Allowing the modular concept into international transport is a key objective for a number of freight shippers and commercial businesses. It is also the most prominent concern of the combined transport operators who fear the modular concept will adversely affect their industry and hence the potential for shifting road freight to rail through combined transport operations. Several Member States are showing enthusiasm for the concept while some others are hostile but most are, like DG TREN awaiting the results of the trials and their evaluations. The request for change comes from equipment suppliers and logistics operators that are concerned about the capacity of the transport system.

5.3. Purpose of the study

DG TREN has sought external expertise to assess the trials that have been done or are ongoing and provide technical assistance to gather key stakeholders opinions and to present recommendations as to whether the Commission should support the adaptation of Directive 96/53. If so, then recommendations are needed on whether any adaptation regarding larger or heavier vehicle configurations should be supported by imposed restrictions on their use (e.g. restricted to designated routes), the driver’s qualifications and aptitude and the vehicle’s particular technical standards and maximum weight and which matters can be left to bilateral agreement between adjacent Member States who wish to operate these vehicles.

The study will gather and synthesise the data on various studies and experiments on bigger and heavier vehicle and vehicle combination limits, including the use of the modular concept in Europe as well as the use of similar, longer and/or heavier vehicle combinations by third countries, e.g. USA, Australia. The project should in addition gather a sufficiently broad collection of experience (national administrations, police and traffic enforcement departments, commercial vehicle manufacturers, freight forwarders, shippers, combined and Intermodal transport operators, road safety organisations, environmental groups, other road users, infrastructure specialists, transport economists, scientific institutes as well as potential users) and should assess and provide technical documents for discussion of the various scenarios. It shall also provide quantitative and qualitative data to help the Commission carry out its impact assessment on any proposed adaptation.

The Study will focus on the effects, both positive and negative, of the use of bigger and/or heavier vehicles, including the modular concept in its various forms and at various maxima weight levels in and between adjacent and consenting Member States. The effects will be on:

– Road safety — the effect of bigger vehicle combinations in traffic, albeit on designated routes in isolation and as a comparison with equivalent conventional two-vehicle combination movements;

– Energy efficiency and CO2 emissions per tonne-km and per vehicle-km and then overall for the Member States involved with likely projections for the EU as a whole;

– Noxious emissions (effect on PM and NOx levels) and the contribution the concept has towards meeting or transgressing the statutory emission levels;

– Effect on road infrastructure, bridges, parking, loading, transportation;

– Effect on Combined Transport and other Intermodal transport operations;

– Effect on meeting current and future freight transport demand.

The task of the contractor will be to:

– Review available, relevant literature

– The study shall assess the economic, environmental and social effects of any policy change and produce relevant transport and market scenarios for a short to medium (2015/2020) timeframe preferably by modelling or by adapting existing transport demand models.

– Organise a set of targeted interviews with experts from industry, combined and Intermodal transport operators and users and member State representatives;

5.4. Policy options

Assessment will be on the impact of increasing conventional vehicle and vehicle combination weights and dimensions limits. The policy options that are to be considered are:

– Option A: business as usual-no adaptation of the Directive with the modular concept only permitted in National transport, restrictions of 40 tonnes on the maximum weight limit of two vehicle combinations in international transport, 44 tonnes allowed only on combined transport when carrying the 40ft ISO container, the standard 45ft container overhanging the rear of the semi-trailer by around 12 cm and only permitted in national transport, no harmonised requirements on the size of a fully loaded vehicle

– Option B: adapt the Directive to: permit the modular concept to circulate between Member States with harmonised restrictions and maximum limits defined in the Directive. Those restrictions could include some or all of the following: the combination’s use, i.e. on designated routes only, the level of road pricing, the vehicle combination’s technical standards, standards for the driver and limitations regarding the concept’s maximum load. The contractor shall stipulate what those requirements may be and what is reasonable and assess the impact of different scenarios; permit the 44tonne two vehicle combination in international transport when using a six-axle combination or for carrying all types of Intermodal Loading Units (ILUs) in combined transport operations; permit the maximum dimensions of a loaded vehicle or vehicle combination to increase albeit provided certain technical characteristics and/or vehicle safety equipments are utilised

– Option C: as option B but with some or all specification limits and/or restrictions defined by Member States individually or by adjacent Member States together. The Directive would therefore allow Member States room for manoeuvre as to what restrictions they place on the use of the modular concept and any bigger or heavier vehicle or vehicle combination.

– Option D: as option B but including certain non-modular vehicle combinations.

The study shall assess the cost implications and the benefits and consequences of these options. In particular assessment shall be made of the effect of adjustments to the Directive on modal shift from other transport modes. The consortium will critically assess and evaluate all the factors that must be taken into account. The range of factors to be considered is not limited to those described above but can include others that the consortium thinks are relevant. However at least the factors described must be fully evaluated.

The consortium will generate likely options for the development and application of the modular concept and the other features described above. The study will be completed before August 2008.

6. References

COM(2006a), Keep Europe Moving — Sustainable mobility for our continent; Midterm review of the European Commission’s 2001 Transport White Paper, 314 final.

COM(2006b), Freight Transport Logistics in Europe — the key to sustainable mobility, Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions, 336 final.

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A history of freight transport prior to the modern truck

Director of Connecteast (an Australian toll road company), director & past-president of the Royal Automobile Club of Victoria, past-president of the Australian Automobile Association, past Principal of Sinclair Knight Merz, past Director of Major Projects and Director of Quality and Technical Resources at VicRoads, past Executive Director of the Australian Road Research Board and Principal Research Scientist at BHP. Recipient of the Order of Australia and of the Australian Centenary Medal.

Maxwell Lay

Connecteast

Mont Waverley, Australia

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ABSTRACT: The paper provides a short world history of trucks from the earliest times to the present. It describes how people and animals provided the first sources of power. The paper then traces the development of load-carrying vehicles, from dragged branches, through to sledges, to wheeled vehicles. It describes and defines the load-carrying capacity of the various transport modes. It emphasises both the importance and uniqueness of the invention of the wheel, and then of the axle which led to the development of carts and wagons and then of steerable wagons. Despite these inventions, the paper notes that for most the history of civilisation, transport of freight by land was slow and inefficient. The factors which caused this to change arose as a consequence of the Industrial Revolution — better roads, the power of steam and then of internal combustion and the effectiveness of pneumatic tyres and well-designed suspension systems. The paper also describes the often futile attempts to regulate and control the damage caused by trucks.

KEYWORDS: Truck (lorry), Animal, Power. sled, Wheel, Axle, Cart, Wagon, Industrial revolution, Roads, Steam power, Internal combustion, Pneumatic, Suspension, Regulation.

RESUME : Cet article retrace l’histoire des camions dans le monde depuis les débuts jusqu’à aujourd’hui. Il montre comment les personnes et animaux ont fourni les premières sources d’énergie. Il trace ensuite le développement des véhicules de transport de marchandises, des branches traînées et traîneaux aux véhicules à roues. Il décrit et définit la capacité de transport des divers modes. L’importance et l’originalité de l’invention de la roué est mise en exergue, puis de l’essieu qui a permis de développer des charrettes puis des chariots et ensuite des chariots dirigeables. Malgré ces inventions, pendant la majeure partie de l’histoire de la civilisation, le transport terrestre de marchandises est resté lent et inefficace. Les facteurs de progrès sont nés de la révolution industrielle — de meilleures routes, l’énergie de la vapeur puis de la combustion interne, puis l’efficacité des pneumatiques et des mécanismes de suspensions. L’article cite aussi les tentatives nombreuses et infructueuses pour réguler et contrôler les dommages induits par les camions.

MOTS-CLES: Camion, poids lourd, animal, énergie, traîneau, roue, essieu, charrette, chariot, révolution industrielle, routes, énergie de la vapeur, combustion interne, pneumatique, suspension, réglementation.

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1. Animal power

After the creation and widespread application of footpaths, which are extensively discussed in Ways of the World (Lay 1992), the world’s second major transport development was the use of animals, initially as beasts of burden and subsequently for pulling ploughs and sleds. The invention of the wheel was a much later development.

When freight first had to be moved, human hands, shoulders, hips, and heads were all gainfully employed. When the capacity of the unaided human was exceeded, the solid stick was the obvious tool to use, first to transfer the load to the shoulders and then to allow it to be shared as a yoke between two people. For less coherent loads, the technology expanded to include wicker baskets hung from the shoulders by rope or carried on the head. Such people-powered freight techniques are still in quite effective use today in parts of Asia and Africa. Experienced porters can carry 25 kg whilst travelling at 25 km/day. For shorter distances, loads of about half body-weight are common, and peak loads over very short distances can exceed 175 kg. The Chinese have used labourers carrying slings and bamboo poles to move loads of up to a tonne distributed at about 25 kg per bearer.

When the loads to be carried demanded greater strength or power than could by supplied by humans, the humans innovated by using their domesticated feed animals as beasts of burden, transferring the wicker baskets from human shoulders to the backs of cattle to produce the first pack animals. The domestication of large animals probably occurred about 7000 B.C., initially to provide humans with a secure source of food. Their use to provide transport power was a convenient secondary development. For most of its history the world’s roadway system has operated with domesticated animals as its sole source of motive power. Humans, cattle, onagers, donkeys, asses, dogs, goats, horses, mules, camels, elephants, buffaloes, llamas, reindeer and yaks are some of the species that have found useful transport employment

Pack transport took a step forward in about 3500 B.C. when the domesticated donkey came out of Africa. From that time forward the pack animal has been an unobtrusive but vital part of our transport operations. For example, from 2000 B.C. organized pack animal convoys operated in the Middle East. The early packhorse could carry up to 50 kg in two baskets but, by the end of the Middle Ages, breeding and loading improvements meant that a packhorse could carry about 120 kg, or a third of its body-weight, for up to 25 km. Similarly, donkeys could carry about 75 kg, mules 100 kg, and camels 175 kg. Despite these improvements, the role of the pack-animal was clearly limited by its load capacity. To overcome this restriction, long strings, or drifts, of up to fifty packhorses tied tail to nose worked many scheduled freight routes, with regular packhorse services operating in Europe from the fifteenth to the nineteenth century, often on their own separate packways. They were a major means of land transport.

As agrarian societies expanded, there was a growing need to move produce from fields to storehouses and processing areas and, later, to market. This demand could not be met by simply carrying the load on an animal’s back. A breakthrough in freight technology was required. The potential for this breakthrough had arisen in about 5000 B.C. when the castration of domesticated cattle was found to produce an excellent power source in the ox, which could haul horizontal forces that were between four and ten times greater than the vertical forces that it could carry on its back. This development was probably driven more by the needs of agriculture than of transport and the first hauled device was probably the plough, beginning as a hooked branch or log that was dragged across the ground, creating useful furrows. For both power and ease of harnessing, oxen worked in pairs, connected to either side of the plough log by a wooden crossbar yoke. Oxen were relatively easy to harness in this manner, as they pull from their prominent shoulders and humped backs.

It would not have been long before the cattle-harnessing technology developed for ploughing led to the thought that the same harness and crossbar yoke coupled to two dragged logs, rather than to one, would provide a platform for load-carrying, sometimes called a travois. In the simplest form the front of the load platform is carried on the animal’s back and the rear slides along the ground. The next development was the sled, which was a flat platform that was dragged along the ground. This required a more elaborate construction and a new type of harness. However, if it operated over smooth surfaces with a friction coefficient of under 0.10, it could carry a greater load than could either the travois or pack horse. The sled is still used for freight transport in parts of the world. There is evidence of sleighs in use in 6000 B.C. As ice has a low friction coefficient, sleighs require little haulage force and therefore need a simpler technology and less power, as reflected in the common use of dog teams. By about 5000 B.C. castrated cattle had become the first work-horses of the road.

2. Invention of wheeled transport

The next stage of transport development was probably associated with the enhancement of the sled and travois. Small rollers between the pole ends of the travois or under a sled would have usefully reduced the dragging friction. A number of societies used such devices which were commonly called truck or truckle carts. Whether these transport issues were the demands that led to the invention of the first wheel remains a matter of conjecture. Early wheels were also used for pottery, and perhaps the original motivation for the invention was production rather than motion. Nevertheless, it does appear that the wheel was invented in Middle East in about 5000 B.C. The oldest known vehicle wheel comes from the southern Russian steppes and dates from about 3000 B.C. The uniqueness of the invention is evident in that, until Columbus reached the Americas in 1492, none of the relatively advanced civilizations there had developed practical wheeled vehicles. Nor was the wheel developed indigenously in Southeast Asia, southern Africa, or Australia.

An important next stage was the use of an axle to join two wheels together and thus give vehicles increased stability and load capacity. By about 3000 B.C. a variety of vehicles in the Middle East had begun to make practical use of the wheel. The first were two-wheeled carts based on an A-frame with the draught animals at the apex and the axle forming the cross bar of the A. A major break-through was to carry the forward vertical component of the load being hauled on the ox’s back rather than on its shoulders. This change increases haulage capacity by about 50 percent, but eluded many civilizations. Cumbersome four-wheeled wagons followed in about 2500 B.C. Their weight meant that only oxen were able to provide the necessary haulage power. The initial wagons had a single hauling shaft as they were based on precedents established for yoked oxen.

Wagons without a steerable front axle were relatively simple and cheap, but created major problems, particularly when faced with sharp curves or when their wheels became caught in deep ruts. The development of generally useful wagons and carriages therefore required steerability to be developed as the next stage in the invention sequence. This was achieved in about 500 B.C. (although some commentators put the date as early as 1500 B.C.) with the production of an axle capable of swiveling about a vertical axis. Such vehicles can be readily detected in accurate drawings because the front wheels had to be small enough in diameter to pass under the floor of the vehicle. The technology did not spread rapidly. There were only a few steerable wagons in fourteenth-century England, and they were not widespread until the seventeenth century.

Harnessing animals in line was common by about 100 B.C. and dramatically increased the size of the payloads that could be hauled. However, it was not widely used by the Romans, thus restricting them to two effective animals per heavy vehicle and severely limiting their haulage capacity. Roman harnesses also tended to choke animals during a hard haul and did not permit the animal to slow the vehicle on a downhill slope. During this period, horses were also being used for haulage. However, hauling requires a much more sophisticated technology for the horse than for the ox, because the horse pulls from forward of the shoulder. Under load, the breast band and neck strap of a yoke tend to press on the horse’s windpipe, causing choking and suffocation. An effective horse harness therefore needs a carefully structured, padded collar resting on the horse’s shoulder in order to prevent harness pressure on the windpipe. It also works best with a pair of shafts, rather than a single shaft. The introduction of such a harnessing arrangement increased the haulage capacity of the horse fourfold. Nevertheless, its application was not widespread, preventing many communities from using the horse to its fullest. It did not arrive in Europe from central Asia until 750 A.D., well after the Romans. All this had major transport implications. A pair of horses that should have hauled three tonne could only manage 0.5 t with Roman carts and harnesses.

Horses became more commonplace in the eleventh century and gradually began to supplant the ox. Many factors influenced the decision as to whether horses or oxen were to be used for haulage. Both had about the same haulage capacity, but horses could make 30 km cart trips each eight-hour day, whereas oxen could only travel half that distance. The ox produces about the same tractive pull as the horse but at only about half the speed (2 km/h rather than 4 km/h), so its power output is halved. Oxen were more difficult to organize but could keep going over more days, required less water, were easier to feed and harness, were more able to manage difficult terrain, and were less likely to be bogged. Their hooves were more durable than those of an unshod horse, however this last advantage began to disappear with the development of the horse shoe in 700 A.D.

Thus the major land-based movement of freight in the last millennium has been by cartage, due mainly to the pack animal’s low 50 kg load capacity. This meant that about twelve packhorses were needed to carry the same load as a single horse and cart. In the eleventh and twelfth centuries carts rather than wagons still predominated in Europe. By the thirteenth century, as the improved harnessing technology spread, both carts and wagons were in common service. Thus, during the fourteenth century transport had a profound effect on the countryside, changing farming from a subsistence life style to a market-oriented industry. Professional carriers also became commonplace, providing a remarkably economical service which only added about ten percent to the cost of a typical commodity for hauls of 80 km.

Most citizens of the fifteenth century still regarded wheeled vehicles as external interlopers. However, when Queen Elizabeth travelled to Warwick in England in 1572, her baggage was conveyed in six hundred carts. By 1599 regular cart-based freight services were operating between London and the Ipswich cloth industry. Similar scheduled services expanded rapidly over the next forty years, although the technology was only selectively available. Carts were not introduced into the more remote parts of Devon, Wales, and Scotland until the nineteenth century. In such areas, freight movement by dragged sleds remained common as long as roads remained poor. Within urban communities much freight was moved by wheelbarrow, a device which also found some application in intercity transport. The growing use of cart and wagon was not met with universal acclaim. In 1669 Courtney Poole urged his colleagues in the English Parliament to ban all carts and wagons, because they discouraged navigation. The vehicles also severely damaged many roads, provoking strong administrative reactions and ingenious technical rejoinders.

The large four-wheeled wagon was primarily a German development. In the mid eighteenth century, German settlers on the Conestoga Creek in Pennsylvania produced the famous Conestoga wagons with their distinctive bright blue bodies, red trim, and white canopies. Weighing a little over 1 t, the wagons were hauled by four to six horses travelling at about 3 km/h and had a capacity of between 3 & 6 t, depending on the road surface. A useful feature was a boat-shaped floor, which prevented cargo from being displaced during a rough ride. By the 1850s the loads that could be carried on conventional vehicles ranged from 2 t on a two-wheeled cart to 8 t on a four-wheeled wagon. For up to eight hours of travel at 5 km/h, a properly harnessed horse produced a pulling force of one-tenth of its weight when travelling over good foothold. Thus a half-tonne horse produced a pulling force of 0.5/10 = 0.05 t, which was equivalent to the output of five men. A poor surface has a coefficient of friction of about 0.05 so a typical load capacity for a range of highway conditions was (0.05 t)/0.05 = 1 t/horse. For long distances the load capacity was closer to 0.5 t/horse, and this was also the value used for battlefield conditions. Roman vehicles and horses had had a load capacity of only a 0.3 t/horse, even over relatively good surfaces.

Over a day, a horse produced a constant energy output, no matter how it was worked. The well-known horsepower unit was first calculated by James Watt and was based on the assumption that a strong 0.75 t horse travelling for a short time at 3.7 km/h could pull a cart with a tractive force of one tenth of its weight, i.e. of 0.75 x 0.1 x 9.8 = 735 N, which gives a power output of 735 x 3.7/3.6 = 746 W, or one horsepower. Over a full day, the same horse can only produce about 500 W.

Its low load capacity made freight transport by wagon inordinately expensive for long-distance hauls and so, for much of history, the boat and barge have been by far the more effective means of moving freight. Even when Rome was at its peak and at the hub of its enormous road system, it preferentially received its food supplies by water. In the twelfth century, Frederick I of the Holy Roman Empire declared the Rhine to be the king’s highway. An estimate from 1818 was that it cost as much to haul 1 t of payload 50 km by road as it did to move it across the Atlantic by ship. Relative costs to move 1 t through 1 km in the nineteenth century were downriver barges, 1; canal barges, 5; rail, 10; and road, 30.

3. Wheel Loads

The load that a vehicle can carry is of vital interest to the vehicle operator. However, for the road manager the key question is the load and the pressure that each individual wheel applies to the pavement. In addition, to reduce both its weight and its rolling resistance over good surfaces, the hauler needs a narrow wheel with a narrow tyre, whereas the road manager requires a large tyre-pavement contact area to protect the pavement. Thus, the joint questions of the maximum load to be carried by wheels and the required width of tyres have long been key points of debate in road management, both to prevent road damage and to provide a basis for charging users based on the wear and tear that they cause. Nevertheless, over time and at all levels, there are numerous and continuing examples of high-level debate and decision-making hopelessly confusing issues separately related to total load and axle load.

The earliest recorded load limits date from 50 B.C., when the Romans restricted vehicle loads to about 250 kg. The situation slowly evolved and in 438 A.D. their Theodosian Code set the limits at 750 kg for an ox-drawn wagon, 500 kg for a horse-drawn wagon, and 100 kg for a cart. The pace of change did not quicken, for in 1622 England prohibited loads greater than 1 t being carried on any vehicle operating during the winter. A significant improvement in road conditions then led in 1765 to the maximum permissible load carried on English roads being raised to 6 t. This remained a practical upper limit for many years. The wheel load limits in use in 1809 are given in Table 1. The illogic of these load limits giving a decrease in contact pressure as the width increased was recognized but ignored.

Table 1. 1809 United Kingdom wheel load limits for four-wheeled vehicles

Traditionally, when load limits have been widely promulgated, they have been just as widely flouted. The Theodosian Code restricted the number of animals that could be used to haul a vehicle because a horsepower approach was far easier to police and measure than was a load limit. In 1508 the method was adopted by the city council of Paris, banning wagons drawn by more than two horses. In 1629 an English Act prohibited more than five horses from drawing any vehicle; after forty years the horsepower limit was relaxed from five to seven. A similar alternative was to limit the number of wheels. For instance, from 1622 to 1661 an English law decreed that only two-wheeled vehicles could be used on English roads. The main consequence of the two-wheel law was to produce grossly overloaded carts.

Another technique was to limit tyre width. An English Act of 1662 required tyres to be at least 100 mm wide. This act was soon suspended and then repealed in 1670 when it was found that the new wide wheels would not fit into many of the country’s well-established ruts. The rut problem must have diminished, for the width limit was raised to 225 mm in the 1753 Broad Wheels Act, which additionally required 450 mm wide tyres to be used when very heavy loads were being carried. Protests led to an amendment two years later that permitted the use of 150 mm wide tyres for wagons pulled by fewer than seven horses. A subtle variation introduced in 1765 imposed lower penalties on wagons whose fore and aft wheels were staggered laterally so that they ran in different but adjacent wheel-paths. In 1767 vehicles with tyres at least 225 mm wide were permitted to be drawn by up to seven horses and those with 400 mm tyres to be drawn by any number of horses. The toll roads of the eighteenth and nineteenth century imposed higher tolls on narrow-tyred vehicles in an attempt to discourage their use.

A major effect of these regulations was to favour the use of broad-wheeled freight wagons using 400 mm wide tyres. These inefficient vehicles required teams of a dozen or so horses, effectively pulling loads of only 700 kg each. In England they were first used on turnpike roads, where they were granted five years of toll-free operation. Such vehicles were commonplace for over sixty years until the final abolition of many of the tyre-oriented regulations in the Highway Act of 1835.

A closely related, and equally ineffective, eighteenth-century attempt to circumvent the wheel width regulations was the use of very large conical wheels that rolled and slid on the roadway. They were little more than narrow wheels legalistically disguised as broad ones to gain the broad-wheel concessions. The result merely demonstrated the distorting effect of wheel-control legislation, as the tapering meant that much of the contact surface had to be dragged rather than rolled along the road. A sometimes more constructive adaptation was the use of dished wheels to provide lateral strength and obviate the need for heavy spokes… sometimes, because the adaptation was also used to evade the wheel-width laws by keeping the actual contact width small.

On poor surfaces wide tyres were used to permit easier passage of the vehicle, provided that enough motive power was available. Indeed, a few late eighteenth-century heavy wagons used great rollers rather than conventional wheels but it was rarely possible to make the rolling surfaces wide enough and the power sources large enough for the devices to be practical. Haulers thus had to find other ways to overcome poor pavement surfaces. One such alternative was the use of very large diameter wheels; 1.6 m diameters were common in 1800, although wheels of this size made it difficult to provide a steerable front axle. The basic principle followed over most of transport history has been to make the vehicle suit the road, with little attempt at adapting the road or the system to the vehicle. Sidney and Beatrice Webb in their comprehensive review in 1913 referred to events in the eighteenth and nineteenth century as an: "interminable series of enactments, amendments and repeals--successive knots of amateur legislators laying down stringent rules. Direct policing of load regulations was not easy as quantitative load levels were not obvious to the eye and their direct control required some means by which they could be ascertained. The initial method involved winching the vehicle to be weighed off the ground and determining its weight by a system of steelyard levers and scales. Public weighing facilities were introduced into Dublin in 1555, to eschew the loss to excessive and untrue tolls". In 1602 a toll on carts weighing over a tonne was introduced in Kent. In 1741, British turnpikes were permitted by law to charge extra tolls on loads over 3 t. The tax was strongly but fruitlessly opposed, with opponents pointing out that it would merely encourage more small carts. In 1744 John Wyatt invented the modern weighbridge platform and hence made weighing vehicles far more feasible. Not coincidentally, at the same time weighing devices were legalized and the rights to operate them were let annually, usually by public auction. The moves were clearly successful as in 1751 a further law made such facilities compulsory on turnpikes within 50 km of London.

In addition to overload due to the load on a single wheel, a further problem is that of pavement wear and tear due to frequent usage, even by traffic within legal load limits. Iron tyres were favoured by haulers because they not only permitted tyres and wheels to be narrowed but also lasted far longer than the timber alternative. However, road maintainers viewed them much less favourably because they abraded the road surface and produced high contact stresses. The problem was often worsened by the practice of driving iron nails with prominent heads into the tyre’s running surface in order to provide better surface traction. In medieval times iron tyres were sufficiently common and damaging for a number of towns to prohibit their use. Subsequently, many cities had occasion to ban the entry of iron-wheeled vehicles.

At the beginning of the 20th century, many laws still existed requiring a millimetre of tyre width for each 10 to 18 kg carried. A typical formula was:

where the values of C = 15 for earth, 10 for macadam and 2 for paved roads approximated the strength of those pavements. However, at this time internal combustion (IC) trucks with solid rubber tyres were launching a new, destructive attack on road pavements. The problem was most severe in the United States where surplus trucks from World War I caused particular havoc. A major Bureau of Public Roads research program showed the great advantage of using pneumatic rather than solid tyres and recommended a higher maximum wheel load of about 4.5 t if pneumatic tyres were used, due to their greater area of contact with the pavement. Although European practice was to adopt a somewhat larger value, wheel loads themselves have remained relatively constant since those decisions in the early 1920s. This type of reaction is an almost inevitable result of having a road infrastructure that changes far more slowly--perhaps at fifty-year intervals--than the associated vehicle technology. The major increases in gross truck loads to around 100 t have been the result of adding more wheels and more axles to trucks, rather than of raising wheel loads. The number of passages of legally loaded wheels thus depends only on the total freight task.

The pneumatic tyre was introduced to make the bicycle a usable and useful tool. This in itself was important, but the key long-term effect was to overcome the millennia-old narrow wheel/high-contact-pressure problem. The pneumatic tyre allowed high loads to be applied to wheels in the knowledge that the tyre would spread the load over an area such that the contact pressure would approximate the tyre inflation pressure. A small calculation will demonstrate this. Wheels with solid tyres could carry loads of up to 2 t. Such loads are large enough to damage pavements, and the use of narrow tyres exacerbates the problem. For a 2 t load and a typical steel tyre width of 100 mm, the contact pressure between tyre and pavement is about 2 MPa. On the other hand, the modern truck wheel can carry double the load with contact pressures of only 0.7 MPa, and with far less impact than the solid wheel, thus significantly reducing the actual stresses caused in both pavement and vehicle.

In practice, the favourable load distributing effect of the pneumatic tyre was far more dramatic. Pavement engineering uses the concept of equivalent standard axles or ESA, to compare the damaging effects of various vehicles. The ESA value of a particular wheel configuration is the number of passes of the standard axle that would do equally as much pavement damage. Table 2 gives some damage equivalents for the beginning of the 20th century, when two dramatically different transport technologies were overlapping. The advantage of the rubber pneumatic tyre is very obvious. The early trucks were too heavy for the first generation of rubber tyres, which could only carry