A semi-trailer truck (also known by a wide variety of other terms – see below) is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer attaches to the tractor with a type of hitch called a fifth wheel. Semi-trailer trucks replaced traction engines in commercial and heavy haulage roles. This transition occurred primarily between the 1920s and 1950s, driven by the need for greater efficiency, speed, and reliability.
Other terms There is a wide variety of English-language terms for a semi-trailer truck, including:
American English: Semi-trailer Semi-truck Truck & trailer Trailer truck Semi Big rig Tractor-trailer Eighteen-wheeler
British English: Articulated lorry Artic (short for articulated lorry) Juggernaut Heavy Goods Vehicle/HGV (a more general term encompassing any vehicle over 7.5 tonnes ladenThis meaning is implied by the heading for section 19 of the Road Traffic Act 1988 which refers to "HGVs", although the section itself refers to "heavy commercial vehicles", defined in section 20 as a goods vehicle exceeding 7.5 tonnes operating weight.) Large Goods Vehicle/LGV (synonym of HGV; not to be confused with "Light Goods Vehicle", a term in use before harmonization with EU regulations in 1992)
Canadian English: Transport truck Transfer truck
Regional configurations Europe
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. However, rules limiting the semi-trailers to and 18.75 m are met with trucks carrying a standardized body with one additional 7.82 m body on tow as a trailer. 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. The 1996 EU regulation defines a Europe Module System (EMS) as it was implemented in Sweden. The wording of EMS combinations and EuroCombi are now used interchangeably to point to truck combinations as specified in the EU document; however, apart from Sweden and Finland, the EuroCombi is only allowed to operate on specific roads in other EU member states. Since 1996 Sweden and Finland formally won a final exemption from the European Economic Area rules with 60 tonne and combinations. From 2006, 25.25 m truck trailer combinations are to be allowed on restricted routes within Germany, following a similar (on-going) trial in The Netherlands. Similarly, Denmark has allowed 25.25 m combinations on select routes. These vehicles will run a weight limit. Two types are to be used: 1) a 26-tonne truck pulling a dolly and semi-trailer, or 2) an articulated tractor unit pulling a B-double, member states gained the ability to adopt the same rules. In Italy the maximum permitted weight (unless exceptional transport is authorized) is 44 tonnes for any kind of combination with five axles or more. Czech Republic has allowed 25.25 m combinations with a permission for a selected route.
Nordic countries
Denmark and Norway allow trucks (Denmark from 2008, and Norway from 2008 on selected routes). In Sweden, the allowed length has been since 1967. Before that, the maximum length was unlimited; the only limitations were on axle load. What stopped Sweden from adopting the same rules as the rest of Europe, when securing road safety, was the national importance of a competitive forestry industry. 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.full law text in Finnish language, explanation by Finnish Forest Association in English, 76 tons in the newspaper
, 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