Europe in London, England The main difference between tractor units in
Europe and
North America is that European models are
cab over engine (COE, called "forward control" in the
United Kingdom), while the majority of North American trucks are "conventional" (called "normal control" or "bonneted" in the UK). European trucks, whether
straight trucks or fully
articulated, have a sheer face on the front. This allows shorter trucks with longer trailers (with larger freight capacity) within the legal maximum total length. Furthermore, it offers greater maneuverability in confined areas, a more balanced weight-distribution, and better overall view for the driver. The major disadvantage is that for repairs on COE trucks, the entire cab has to hinge forward to allow maintenance access. In Europe, usually only the driven tractor axle has dual wheels, while single wheels are used for every other axle on the tractor and the trailer. The most common combination used in Europe is a semi tractor with two axles and a cargo trailer with three axles, one of which is sometimes a
lift axle, giving 5 axles and 12 wheels in total. This format is now common across Europe as it is able to meet the EU maximum weight limit of without overloading any axle. Individual countries have raised their own weight limit. The U.K., for example, has a limit, an increase achieved by adding an extra axle to the tractor, usually in the form of a middle unpowered lifting axle (midlift) with a total of 14 wheels. The lift axles used on both tractors and trailers allow the trucks to remain legal when fully loaded (as weight per axle remains within the legal limits); on the other hand, these axle set(s) can be raised off the roadway for increased maneuverability or for reduced fuel consumption and tire wear when carrying lighter loads. Although lift axles usually operate automatically, they can be lowered manually even while carrying light loads, in order to remain within legal (safe) limits when, for example, navigating back-road bridges with severely restricted axle loads.
For greater detail, see the United Kingdom section, below. When using a
dolly, which generally has to be equipped with lights and a
license plate,
rigid trucks can be used to pull semi-trailers. The dolly is equipped with a
fifth wheel to which the trailer is coupled. Because the dolly attaches to a
pintle hitch on the truck, maneuvering a trailer hooked to a dolly is different from maneuvering a fifth wheel trailer.
Backing the vehicle requires the same technique as backing an ordinary truck/full trailer combination, though the dolly/semi setup is probably longer, thus requiring more space for maneuvering. The tractor/semi-trailer configuration is rarely used on
timber trucks since they use the two major advantages of having the weight of the load on the drive wheels, and the
loader crane used to lift the logs from the ground can be mounted on the rear of the truck behind the load, allowing a short (lightweight) crane to reach both ends of the vehicle without uncoupling. Also, construction trucks are more often seen in a rigid + midaxle trailer configuration instead of the tractor/semi-trailer setup.
Continental Europe The maximum overall length in the
EU and
EEA member states was with a maximum weight of if carrying an
ISO container. truck combinations were developed under the branding of
EcoCombi which influenced the name of
EuroCombi for an ongoing standardization effort where such truck combinations shall be legal to operate in all jurisdictions of the European Economic Area. With the 50% increase in cargo weight, the fuel efficiency increases an average of 20% with a corresponding relative decrease in carbon emissions and with the added benefit of one third fewer trucks on the road. Finland, with the same road safety issues and equally important forestry industry, followed suit. The change made trucks able to carry three stacks of
cut-to-length logs instead of two, as it would be in a short combination. They have one stack together with a crane on the 6×4 truck, and two additional stacks on a four axle trailer. The allowed gross weight in both countries is up to depending on the distance between the first and last axle. In the negotiations starting in the late 1980s preceding Sweden and Finland's entries to the European Economic Area and later the European Union, they insisted on exemptions from the EU rules citing environmental concerns and the transportation needs of the logging industry. In 1995, after their entry to the union, the rules changed again, this time to allow trucks carrying a standard
CEN unit of to draw a standard semi-trailer on a dolly, a total overall length of 25.25 m. Later,
B-double combinations came into use, often with one container on the B-link and a container (or two containers) on a semi-trailer bed. In allowing the longer truck combinations, what would take two semi-trailer trucks and one truck and trailer to haul on the continent now could be handled by just two 25.25 m trucks – greatly reducing overall costs and emissions. Prepared since late 2012 and effective in January 2013, Finland has changed its regulations to allow total maximum legal weight of a combination to be . At the same time the maximum allowed height would be increased by ; from current maximum of to . The effect this major maximum weight increase would cause to the roads and bridges in Finland over time is strongly debated. However, longer and heavier combinations are regularly seen on public roads; special permits are issued for special cargo. The mining company
Boliden AB have a standing special permit for combinations on select routes between mines in the inland and the processing plant in
Boliden, taking a load of ore.
Volvo has a special permit for a , steering B-trailer-trailer combination carrying two containers to and from
Gothenburg harbour and the
Volvo Trucks factory, all on the island of
Hisingen. Another example is the ongoing project
En Trave Till () started in December 2008. It will allow even longer vehicles to further rationalize the logging transports. As the name of the project points out, it will be able to carry four stacks of timber, instead of the usual three. The test is limited to
Norrbotten county and the
European route E4 between the timber terminal in
Överkalix and the sawmill in Munksund (outside
Piteå). The vehicle is a long truck trailer combination with a gross weight exceeding . It is estimated that this will give a 20% lower cost and 20–25% emissions reduction compared to the regular truck combinations. As the combination spreads its weight over more axles, braking distance, road wear and traffic safety is believed to be either the same or improved with the truck-trailer. In the same program two types of combinations will be tested in
Dalsland and
Bohuslän counties in western Sweden: an enhanced truck and trailer combination for use in the forest and a b-double for plain highway transportation to the mill in
Skoghall. In 2012, the Northland Mining company received permission for combinations with normal axle load (an extra dolly) for use on the
Kaunisvaara-
Svappavaara route, carrying iron ore. , the longest and heaviest truck in everyday use in Finland is operated by transport company Ketosen Kuljetus as part of a
pilot project studying transport efficiency in the timber industry. The combined vehicle is long, has 13 axles, and weighs a total of . Starting from 21 January 2019 the Government of Finland changed the maximum allowed length of truck from . New types of vehicle combinations that differ from the current standards may also be used on the road. The requirements for combinations also include camera systems for side visibility, an advanced emergency braking and lane detector system, electronic driving stability system and electronically controlled brakes. Maximum length of a vehicle combination 34.5 metres Maximum length of a vehicle combination 34.5 metres
United Kingdom , representing
Renault at
Silverstone In the
United Kingdom, a semi-trailer truck is known as an 'articulated lorry' (or colloquially as an 'artic'). The maximum permitted
gross weight of a semi-trailer truck without the use of a Special Type General Order (STGO) is . In order for a 44,000 kg semi-trailer truck to be permitted on UK roads the tractor and semi-trailer must have three or more axles each. Lower weight semi-trailer trucks can mean some tractors and trailer having fewer axles. In practice, as with double decker buses and coaches in the UK, there is no legal height limit for semi-trailer trucks; however, bridges over do not have the height marked on them. Semi-trailer trucks in continental Europe have a height limit of . Vehicles heavier than 44,000 kg are permitted on UK roads but are indivisible loads, which would be classed as abnormal (or oversize). Such vehicles are required to display an STGO (Special Types General Order) plate on the front of the tractor unit and, under certain circumstances, are required to travel by an authorized route and have an escort. Most UK trailers are long and, dependent on the position of the fifth wheel and
kingpin, a coupled tractor unit and trailer will have a combined length of between . Although the Construction and Use Regulations allow a maximum rigid length of , this, combined with a shallow kingpin and fifth wheel set close to the rear of the tractor unit, can give an overall length of around . In January 2012, the
Department for Transport began conducting a trial of longer semi-trailers. The trial involves 900 semi-trailers of in length (i.e. longer than the current maximum), and a further 900 semi-trailers of in length (i.e. longer). This will result in the total maximum length of the semi-trailer truck being for trailers in length, and for trailers long. The increase in length will not result in the weight limit being exceeded and will allow some operators to approach the weight limit which may not have been previously possible due to the previous length of trailers. The trial will run for a maximum of 10 years. Providing certain requirements are fulfilled, a Special Types General Order (STGO) allows for vehicles of any size or weight to travel on UK roads. However, in practice, any such vehicle has to travel by a route authorized by the Department of Transport and move under escort. The escort of abnormal loads in the UK is now predominantly carried out by private companies, but extremely large or heavy loads that require road closures must still be escorted by the police. In the UK, some semi-trailer trucks have eight tyres on three axles on the tractor; these are known as six-wheelers or "six leggers," with either the centre or rear axle having single wheels which normally steer as well as the front axle and can be raised when not needed (i.e. when unloaded or only a light load is being carried; an arrangement known as a TAG axle when it is the rear axle, or mid-lift when it is the center axle). Some trailers have two axles which have twin tyres on each axle; other trailers have three axles, of which one axle can be a lift axle which has super-single wheels. In the UK, two wheels bolted to the same hub are classed as a single wheel, therefore a standard six-axle articulated truck is considered to have twelve wheels, even though it has twenty tyres. The UK also allows semi-trailer truck which have six tyres on two axles; these are known as four-wheelers. In 2009, the operator Denby Transport designed and built a
B-Train (or B-Double) semi-trailer truck called the
Denby Eco-Link to show the benefits of such a vehicle, which were a reduction in road accidents and result in fewer road deaths, a reduction in emissions due to the one tractor unit still being used and no further highway investment being required. Furthermore, Denby Transport asserted that two Eco-Links would replace three standard semi-trailer trucks while, if limited to the current UK weight limit of , it was claimed the Eco-Link would reduce carbon emissions by 16% and could still halve the number of trips needed for the same amount of cargo carried in conventional semi-trailer trucks. This is based on the fact that for light but bulky goods such as toilet paper, plastic bottles, cereals and aluminum cans, conventional semi-trailer trucks run out of cargo space before they reach the weight limit. At , as opposed to usually associated with B-Trains, the Eco-Link also exerts less weight per axle on the road compared to the standard six-axle semi-trailer truck. The vehicle was built after Denby Transport believed they had found a legal-loophole in the present UK law to allow the Eco-Link to be used on the public roads. The relevant legislation concerned the 1986 Road Vehicles Construction and Use Regulations. The 1986 regulations state that "certain vehicles" may be permitted to draw more than one trailer and can be up to . The point of law reportedly hinged on the definition of a "towing implement", with Denby prepared to argue that the second trailer on the Eco-Link was one. The Department for Transport were of the opinion that this refers to recovering a vehicle after an accident or breakdown, but the regulation does not explicitly state this. During BTAC performance testing the Eco-Link was given an "excellent" rating for its performance in maneuverability, productivity, safety and emissions tests, exceeding ordinary semi-trailer trucks in many respects. Reportedly, private trials had also shown the Denby vehicle had a 20% shorter stopping distance than conventional semi-trailer trucks of the same weight, due to having extra axles. The active steer system meant that the Eco-Link had a turning circle of , the same as a conventional semi-trailer truck. Although the Department for Transport advised that the Eco-Link was not permissible on public roads, Denby Transport gave the Police prior warning of the timing and route of the test drive on the public highway, as well as outlining their position in writing to the Eastern Traffic Area Office. On 1 December 2009 Denby Transport were preparing to drive the Eco-Link on public roads, but this was cut short because the Police pulled the semi-trailer truck over as it left the gates in order to test it for its legality "to investigate any... offenses which may be found". The Police said the vehicle was unlawful due to its length and Denby Transport was served with a notice by the
Vehicle and Operator Services Agency (VOSA) inspector to remove the vehicle from the road for inspection. Having returned to the yard, Denby Transport was formally notified by Police and VOSA that the semi-trailer truck could not be used. Neither the Eco-Link, nor any other B-Train, have since been permitted on UK roads. However, this prompted the
Department for Transport to undertake a desk study into semi-trailer trucks, which has resulted in the longer semi-trailer trial which commenced in 2012.
North America In
North America, the combination vehicles made up of a powered truck tractor and one or more semitrailers are known as "semis", "semitrailers", "tractor-trailers", "big rigs", "semi-trucks", "eighteen-wheelers", or "semi-tractor-trailers". The
tractor unit typically has two or three
axles; those built for hauling heavy-duty commercial-construction machinery may have as many as five, some often being
lift axles. The most common tractor-cab layout has a forward engine, one steering axle, and two
drive axles. The fifth-wheel trailer coupling on most tractor trucks is movable fore and aft, to allow adjustment in the weight distribution over its rear axle(s). Ubiquitous in Europe but less common in North America since the 1990s, is the
cabover engine configuration, where the driver sits next to or over the engine. With changes in the US to the maximum length of the combined vehicle, the cabover was largely phased out of North American over-the-road (long-haul) service by 2007. Cabovers were difficult to service; for a long time, the cab could not be lifted on its hinges to a full 90-degree forward tilt, severely limiting access to the front of the engine. , a truck could cost , while the diesel fuel cost could be $70,000 per year. Trucks average from , with fuel economy standards requiring better than efficiency by 2014. Power requirements in standard conditions are at or at , and somewhat different power usage in other conditions. The
cargo trailer usually has
tandem axles at the rear, each of which has
dual wheels, or eight tires on the trailer, four per axle. In the US it is common to refer to the number of wheel hubs, rather than the number of tires; an axle can have either single or dual tires with no legal difference. The combination of eight tires on the trailer and ten tires on the tractor is what led to the
moniker eighteen wheeler, although this term is considered by some truckers to be a
misnomer (the term "eighteen-wheeler" is a nickname for a five-axle over-the-road combination). Many trailers are equipped with movable
tandem axles to allow adjusting the weight distribution. To connect the second of a set of doubles to the first trailer, and to support the front half of the second trailer, a converter gear known as a "dolly" is used. This has one or two axles, a fifth-wheel coupling for the rear trailer, and a tongue with a ring-hitch coupling for the forward trailer. Individual states may further allow longer vehicles, known as "longer combination vehicles" (
LCVs), and may allow them to operate on roads other than Interstates.
Long combination vehicle types include: pup trailers • Doubles (officially "
STAA doubles", known colloquially as "a set of joints"): Two trailers. • B-Doubles: Twin trailers in B-double configuration (very common in Canada but rarely used in the United States). • Triples: Three trailers. • Turnpike Doubles: Two – trailers. • Rocky Mountain Doubles: One trailer (though usually no more than ) and one trailer (known as a "
pup"). • In Canada, a Turnpike Double is two trailers, and a Rocky Mountain Double is a trailer with a "pup". The US federal government, which only regulates the
Interstate Highway System, does not set maximum length requirements (except on auto and boat transporters), only minimums. Tractors can pull two or three trailers if the combination is legal in that state. Weight maximums are on a single axle, on a tandem, and total for any vehicle or combination. There is a maximum width of and no maximum height. Roads other than Interstates are regulated by individual states, and laws vary widely. Maximum weight varies between to , depending on the combination. Most states restrict operation of larger tandem trailer setups such as triple units, turnpike doubles, and Rocky Mountain doubles. Reasons for limiting the legal trailer configurations include safety concerns and the impracticality of designing and constructing roads that can accommodate the larger
wheelbase of these vehicles and the larger minimum turning radii associated with them. In general, these configurations are restricted to the Interstates. Except for these units, double setups are not restricted to certain roads any more than a single setup. They are also not restricted by weather conditions or "difficulty of operation". The Canadian province of Ontario, however, does have weather-related operating restrictions for larger tandem trailer setups.
Oceania Australia Australian road transport has a reputation for using very large trucks and
road trains. This is reflected in the most popular configurations of trucks generally having dual drive axles and three axles on the trailers, with four tyres on each axle. This means that Australian single semi-trailer trucks will usually have 22 tyres, which is generally more than their counterparts in other countries. Super single tyres are sometimes used on tri-axle trailers. The suspension is designed with travel limiting, which will hold the rim off the road for one blown or deflated tyre for each side of the trailer, so a trailer can be driven at reduced speed to a safe place for repair. Super singles are also often used on the steer axle in Australia to allow greater loading over the steer axle. The increase in loading of steer tyres requires a permit. Long haul transport usually operates as B-doubles with two trailers (each with three axles), for a total of nine axles (including steering). In some lighter duty applications, only one of the rear axles of the truck is driven, and the trailer may have only two axles. From July 2007, the Australian Federal and State Governments allowed the introduction of B-triple trucks on a specified network of roads. B-Triples are set up differently from conventional road trains. The front of their first trailer is supported by the
turntable on the prime mover. The second and third trailers are supported by turntables on the trailers in front of them. As a result, B-Triples are much more stable than road trains and handle exceptionally well. True road trains only operate in remote areas, regulated by each state or territory government. In total, the maximum length that any articulated vehicle may be (without a special permit and escort) is , its maximum load may be up to 164 tonnes gross, and may have up to four trailers. However, heavy restrictions apply to the areas where such a vehicle may travel in most states. In remote areas such as the
Northern Territory great care must be taken when sharing the road with longer articulated vehicles that often travel during the daytime, especially four-trailer road trains. Articulated trucks towing a single trailer or two trailers (commonly known as "short doubles") with a maximum overall length of are referred to as "General access heavy vehicles" and are permitted in all areas, including metropolitan. B-doubles are limited to a maximum total weight of 62.5 tonnes and overall length of , or if they are fitted with approved FUPS (Front Underrun Protection System) devices. B-doubles may only operate on designated roads, which includes most highways and some major metropolitan roads. B-doubles are very common in all parts of Australia including state capitals and on major routes they outnumber single trailer configurations. Maximum width of any vehicle is and a height of . In the past few years, allowance has been made by several states to allow certain designs of heavy vehicles up to high but they are also restricted to designated routes. In effect, a 4.6 meter high B-double will have to follow two sets of rules: they may access only those roads that are permitted for B-doubles
and for 4.6 meter high vehicles. In Australia, both conventional prime movers and
cabovers are common, however, cabovers are most often seen on B-doubles on the eastern seaboard where the reduction in total length allows the vehicle to pull longer trailers and thus more cargo than it would otherwise. File:B double logging truck in Australia.jpg|An Australian
prime mover Kenworth and B double trailer combination File:Road Train2.jpg|
Volvo road train in Australia File:Red B-double truck.jpg|B-double truck on the
Sturt Highway New Zealand New Zealand legislation governing truck dimensions falls under the Vehicle Dimensions and Mass Rules, published by
NZ Transport Agency. New rules were introduced effective 1 February 2017, which increased the maximum height, width and weight of loads and vehicles, to simplify regulations, increase the amount of freight carried by road, and to improve the range of vehicles and trailers available to transport operators. Common combinations in New Zealand are a standard semi-trailer, a
B-train, or a rigid towing vehicle pulling a trailer with a drawbar, with a maximum of nine axles. Standard maximum vehicle lengths for trailers with one axle set are: • Semi-trailer: • Simple: • Pole: Trailers with two axle sets can be long, including heavy rigid vehicles towing two trailers. Oversized loads require, at minimum, a permit, and may require one or more pilot vehicles.
High-productivity motor vehicle (HPMV) permits are issued for vehicles exceeding 44 tonnes, or the above dimensions. Trucks up to 62 tonnes were allowed, with an initial bridge strengthening program costing $12.5m. ==Construction ==