Editing Semi-trailer truck (section)

== Regional configurations ==
=== Europe ===
[[File:artic.lorry.arp.750pix.jpg|thumb|left|A [[Renault Magnum]] 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]]),<ref name="Kilcarr2017">{{cite web |last=Kilcarr |first=Sean |date=10 August 2017 |title=Getting cabover crazy |url=http://www.trucker.com/galleries/getting-cabover-crazy |access-date=20 May 2018 |work=American Trucker}}</ref> while the majority of North American trucks are "conventional" (called "normal control" or "bonneted" in the UK).<ref name="Sutcliffe2013">{{cite journal |last=Sutcliffe |first=Mike A. |date=Summer 2013 |title=The Sales & Service Literature of Leyland Motors Ltd |url=http://www.leylandsociety.co.uk/publications/torque/pdf/Torque060.pdf |journal=Leyland Torque |publisher=The Leyland Society |issue=60}}</ref><ref name="Hjelm2009">{{cite book |chapter=European Truck Aerodynamics – A Comparison Between Conventional and CoE Truck Aerodynamics and a Look into Future Trends and Possibilities |title=The Aerodynamics of Heavy Vehicles II: Trucks, Buses, and Trains |publisher=Springer |series=Lecture Notes in Applied and Computational Mechanics |first1=Linus |last1=Hjelm |first2=Björn |last2=Bergqvist |volume=41 |pages=469–477 |date=2009 |doi=10.1007/978-3-540-85070-0_45 |isbn=978-3-540-85069-4}}</ref>  European trucks, whether [[rigid truck|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.{{CN|date=October 2024}}

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 [[axle#Lift axle|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 {{convert|40,000|kg|lb|abbr=in}} without overloading any axle. Individual countries have raised their own weight limit. The U.K., for example, has a {{convert|44,000|kg|lb|abbr=in}} 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|United Kingdom section]], below.''{{CN|date=October 2024}}

When using a [[dolly (trailer)|dolly]], which generally has to be equipped with lights and a [[Vehicle registration plate|license plate]], [[rigid truck]]s can be used to pull semi-trailers. The dolly is equipped with a [[Fifth-wheel coupling|fifth wheel]] to which the trailer is coupled. Because the dolly attaches to a [[pintle|pintle hitch]] on the truck, maneuvering a trailer hooked to a dolly is different from maneuvering a fifth wheel trailer. [[Backing up|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 truck]]s 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.{{CN|date=October 2024}}

====Continental Europe====
[[File:Alle Varianten LZV.jpg|thumb|left|All EuroCombi variants being considered for Europe-wide adoption]]
The maximum overall length in the [[European Union|EU]] and [[European Economic Area|EEA]] member states was {{convert|18.75|m|ft|abbr=on}} with a maximum weight of {{convert|40 or 44|t|1}} if carrying an [[ISO container]].<ref name="sn" /> However, rules limiting the semi-trailers to {{convert|16.5|m|ft|0|abbr=on}} and 18.75&nbsp;m are met with trucks carrying a standardized {{convert|7.82|m|ft|0|abbr=on}} body with one additional 7.82&nbsp;m body on tow as a trailer.<ref>{{cite journal |url=http://www.mne.psu.edu/ifrtt/ConferenceProceedings/ISHVWD_9_2006/docs/pdfs/session%206/s6-2%2090.pdf |title=Study Of Stability Measures And Legislation Of Heavy Articulated Vehicles In Different OECD Countries |publisher=[[University of Seville]], [[KTH Royal Institute of Technology|KTH]] and [[Scania AB]] |first=J. |last=Wideberg |display-authors=etal |date=May 2006 |access-date=30 October 2012 |archive-date=24 November 2020 |archive-url=https://web.archive.org/web/20201124021452/https://www.mne.psu.edu/ifrtt/ConferenceProceedings/ISHVWD_9_2006/docs/pdfs/session%206/s6-2%2090.pdf |url-status=dead }}</ref> {{convert|25.25|m|ft|0|adj=on}} 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.<ref name="sn" /> 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. <!-- see de:EuroCombi and nl:EuroCombi --> Since 1996 Sweden and Finland formally won a final exemption from the European Economic Area rules with 60&nbsp;tonne and {{convert|25.25|m|ft|0|adj=on}} combinations. From 2006, 25.25&nbsp;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&nbsp;m combinations on select routes. These vehicles will run a {{convert|60|t|1|adj=on}} 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&nbsp;m combinations with a permission for a selected route.{{CN|date=October 2024}}

====Nordic countries====
[[File:Scania (4-series) with EU-trailer. 25.25 meters.jpg|thumb|A truck with a [[swap body]] pulling a trailer using a [[dolly (trailer)|dolly]]; the overall length is {{convert|25.25|m|ft|0|abbr=on}}]]

Denmark and Norway allow {{convert|25.25|m|ft|0|abbr=on}} trucks (Denmark from 2008, and Norway from 2008 on selected routes). In [[Sweden]], the allowed length has been {{convert|24|m|ft|abbr=on}} 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.<ref name="sn">{{cite journal |url=http://www.modularsystem.eu/download/facts_and_figures/confederation_of_swedish_enterprise_pub2004100041.pdf |title=Fewer Trucks Improve the Environment |publisher=[[Svenskt Näringsliv]] |first=K. |last=Ramberg |date=October 2004 |access-date=30 March 2009 |archive-date=20 July 2011 |archive-url=https://web.archive.org/web/20110720164911/http://www.modularsystem.eu/download/facts_and_figures/confederation_of_swedish_enterprise_pub2004100041.pdf |url-status=dead }}</ref><ref>{{cite web |url=http://www.regeringen.se/pressmeddelanden/2015/04/tva-regeringsbeslut-for-langre-och-tyngre-fordon/ |title=Två regeringsbeslut för längre och tyngre fordon |publisher=Regeringskansliet |date=16 April 2015 |access-date=27 September 2015}}</ref> 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 logging|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 {{cvt|60|t}} depending on the distance between the first and last axle.{{CN|date=October 2024}}

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 [[Swap body|CEN unit]] of {{convert|7.82|m|ft|0|abbr=on}} to draw a {{convert|13.6|m|ft|0|abbr=on}} standard semi-trailer on a dolly, a total overall length of 25.25&nbsp;m. Later, [[B-double]] combinations came into use, often with one {{convert|20|ft|m|0|abbr=on|order=flip}} container on the B-link and a {{convert|40|ft|m|0|abbr=on|order=flip}} container (or two {{convert|20|ft|m|0||abbr=on|disp=out}} containers) on a semi-trailer bed. In allowing the longer truck combinations, what would take two {{convert|16.5|m|ft|0|abbr=on}} semi-trailer trucks and one {{convert|18.75|m|ft|0|abbr=on}} truck and trailer to haul on the continent now could be handled by just two 25.25&nbsp;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 {{cvt|76|t}}. At the same time the maximum allowed height would be increased by {{convert|20|cm|in|0|abbr=on}}; from current maximum of {{convert|4.2|m|ft|1|abbr=on}} to {{convert|4.4|m|ft|1|abbr=on}}. The effect this major maximum weight increase would cause to the roads and bridges in Finland over time is strongly debated.{{CN|date=October 2024}}

[[File:40 foot container turnpike double 2.jpg|thumb|{{cvt|40|ft|disp=flip}} container turnpike doubles have been tested in Sweden<ref>[https://www.combine-project.com/sites/default/files/content/resource/files/combine_output_wp3.4.pdf HCT as an enabler for Combined Transports – A Study on potentials of implementing HCT-vehicles in Sweden]</ref>]]
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 {{convert|76|t|adj=on}} combinations on select routes between mines in the inland and the processing plant in [[Boliden]], taking a  {{convert|50|t|adj=on}} load of ore. [[Volvo Group|Volvo]] has a special permit for a {{convert|32|m|ft|abbr=on}}, steering B-trailer-trailer combination carrying two {{convert|40|ft|m|0|abbr=on|order=flip}} containers to and from [[Gothenburg|Gothenburg harbour]] and the [[Volvo Trucks]] factory, all on the island of [[Hisingen]].<ref>{{cite journal |url=http://magazine.volvotrucks.com/global/Articles/International/2008/10/The-next-environmental-improvement--long-truck-rigs/The-next-environmental-improvement--long-truck-rigs/ |title=The next environmental improvement: Long truck rigs |journal=Volvo Trucks |date=3 October 2008}}</ref> Another example is the ongoing project ''En Trave Till'' ({{lit|One more pile|One more stack}}) 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 {{convert|30|m|ft|0|abbr=on}} long truck trailer combination with a gross weight exceeding  {{convert|90|t}}. It is estimated that this will give a 20% lower cost and 20–25% {{CO2}} emissions reduction compared to the regular  {{convert|60|t|adj=on}} 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  {{convert|90|t|adj=on}} truck-trailer. In the same program two types of  {{convert|76|t|adj=on}} 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  {{convert|90|t|adj=on}} combinations with normal axle load (an extra dolly) for use on the {{convert|150|km|mi|0|abbr=on}} [[Kaunisvaara]]-[[Svappavaara]] route, carrying iron ore.<ref name="Krantz2014">{{cite journal |url=http://issuu.com/irinalau11/docs/uptime__2__2014_-_final_low_res |title=Where Size Matters |journal=Uptime |first=Olivia |last=Krantz |pages=8–15 |date=2014 |issue=2}}</ref><ref>{{cite web |url=http://www.northland.eu/en-us/media/news/-dispensation-for-90-tonnes-truckes-is-favorable-f |title=Dispensation for 90 Tonnes Truckes is Favorable for All Concerned |work=Northland.eu |date=30 October 2012 |archive-url=https://web.archive.org/web/20130128113749/http://www.northland.eu/en-us/media/news/-dispensation-for-90-tonnes-truckes-is-favorable-f |archive-date=28 January 2013}}</ref><ref>[https://www.finlex.fi/fi/lainsaadanto/saadoskokoelma/2013/407 full law text in Finnish language], [http://www.forest.fi/smyforest/foresteng.nsf/allbyid/67462FE1ACF87602C2257B2D00454578?OpenDocument#popupPic explanation by Finnish Forest Association in English], [http://www.trailer.se/news.php?id=9513 76 tons in the newspaper]</ref>

{{As of|2015}}, 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 {{convert|33|m|ft}} long, has 13 axles, and weighs a total of {{convert|104|t}}.<ref name="trailer20151028">{{cite news |url=http://www.trailer.se/104-tons-scania-i-finskt-forsok/ |title=104-tons Scania i finskt försök |language=sv |work=Trailer |first=Stefan |last=Nilsson |date=28 October 2015 |access-date=10 September 2018}}</ref><ref name="smyfi20150826">{{cite web |url=https://smy.fi/en/artikkeli/largest-lorry-in-western-europe-to-start-operating-in-finnish-lapland/ |title=Largest lorry in western Europe to start operating in Finnish Lapland |publisher=Finnish Forest Association |date=26 August 2015 |access-date=10 September 2018}}</ref>

Starting from 21 January 2019 the Government of Finland changed the maximum allowed length of truck from {{convert|25.25 to 34.50|m|ft|1|sp=us}}. 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. [https://valtioneuvosto.fi/en/article/-/asset_publisher/ajoneuvoyhdistelmien-enimmaispituudeksi-34-5-metria Maximum length of a vehicle combination 34.5 metres] [https://www.lvm.fi/-/maximum-length-of-a-vehicle-combination-34.5-metres-995264 Maximum length of a vehicle combination 34.5 metres]

====United Kingdom====
[[File:Renault Sport articulated lorrys with extended tents @ Silverstone for Renault World Series.JPG|thumb|Semi-trailer trucks with extended [[tents]], representing [[Renault]] at [[Silverstone Circuit|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 {{convert|44,000|kg|lb|abbr=on}}. In order for a 44,000&nbsp;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.<ref>{{cite web |url=https://www.returnloads.net/pdfs/haulage-courier-vehicle-types-and-weights/ |title=A Guide to Haulage & Courier Vehicle Types & Weights |publisher=Returnloads.net |access-date=28 July 2016}}</ref> 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 {{convert|5.03|m|ft|order=flip|abbr=on}} do not have the height marked on them. Semi-trailer trucks in continental Europe have a height limit of {{convert|4.0|m|ft|order=flip|abbr=on}}. Vehicles heavier than 44,000&nbsp;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.{{CN|date=October 2024}}

Most UK trailers are {{convert|13.7|m|ft|0|order=flip|abbr=on}} long and, dependent on the position of the fifth wheel and [[kingpin (automotive part)|kingpin]], a coupled tractor unit and trailer will have a combined length of between {{convert|15.25|and|16.75|m|ft|0|order=flip|abbr=on}}. Although the Construction and Use Regulations allow a maximum rigid length of {{convert|18.2|m|ft|0|order=flip|abbr=on}}, 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 {{convert|22.75|m|ft|0|order=flip|abbr=on}}.<ref>{{cite web |url=https://www.gov.uk/guidance/moving-goods-by-road |title=Moving goods by road |publisher=HM (UK) Revenue & Customs |date=5 April 2016 |access-date=28 July 2016}}</ref>

In January 2012, the [[Department for Transport]] began conducting a trial of longer semi-trailers. The trial involves 900 semi-trailers of {{convert|14.6|m|ft|0|order=flip|abbr=on}} in length (i.e. {{convert|1|m|ft|0|order=flip|abbr=on|disp=sqbr}} longer than the current maximum), and a further 900 semi-trailers of {{convert|15.65|m|ft|0|order=flip|abbr=on}} in length (i.e. {{convert|2.05|m|ft|0|order=flip|abbr=on|disp=sqbr}} longer). This will result in the total maximum length of the semi-trailer truck being {{convert|17.5|m|ft|0|order=flip|abbr=on}} for trailers {{convert|14.6|m|ft|0|order=flip|abbr=on|disp=out}} in length, and {{convert|18.55|m|ft|0|order=flip|abbr=on}} for trailers {{convert|15.65|m|ft|0|order=flip|abbr=on|disp=out}} long. The increase in length will not result in the {{convert|44|t|lb|-3|order=flip|abbr=on|disp=out}} 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.{{CN|date=October 2024}}

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.{{CN|date=October 2024}}

In 2009, the operator Denby Transport designed and built a {{convert|25.25|m|ft|0|order=flip|abbr=on|adj=mid| long}} [[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 {{convert|44|t|lb|-3|order=flip|abbr=on}}, 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 {{convert|44|t|lb|-3|order=flip|abbr=on}}, as opposed to {{convert|60|t|lb|-3|order=flip|disp=out|abbr=on}} usually associated with B-Trains, the Eco-Link also exerts less weight per axle on the road compared to the standard six-axle {{convert|44|t|lb|-3|order=flip|abbr=on}} semi-trailer truck.{{CN|date=October 2024}}

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 {{convert|85|ft|m|1|abbr=on}}.{{citation needed|date=June 2014}} 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.{{CN|date=October 2024}}

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 {{convert|41|ft|m|1|abbr=on}}, the same as a conventional semi-trailer truck.{{CN|date=October 2024}}

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.{{CN|date=October 2024}}

===North America===
[[File:FEMA - 13788 - Photograph by Mark Wolfe taken on 07-11-2005 in Alabama.jpg|thumb|right|Various American trucks lined up]]
[[File:HuckepackCrop.JPG|thumb|Tractor unit hauling tractor units in [[Idaho]]]]

In [[North America]], the combination vehicles made up of a powered semi-tractor and one or more semitrailers are known as "semis", "semitrailers",<ref>{{cite web| url = http://www.merriam-webster.com/dictionary/semitrailer| title = Merriam-Webster| date = 28 May 2023}}</ref> "tractor-trailers", "big rigs", "semi-trucks", "eighteen-wheelers", or "semi-tractor-trailers".{{CN|date=October 2024}}

The [[tractor unit]] typically has two or three [[axle]]s; those built for hauling heavy-duty commercial-construction machinery may have as many as five, some often being [[Axle#Lift axle|lift axles]].

The most common tractor-cab layout has a forward engine, one steering axle, and two [[drive axle]]s. 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).{{CN|date=October 2024}}

Ubiquitous in Europe but less common in North America since the 1990s, is the [[Cab over|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.{{CN|date=October 2024}}

{{As of|2016|5|25}}, a truck could cost {{US$|100,000}}, while the diesel fuel cost could be $70,000 per year.<ref>{{cite web |url=http://askthetrucker.com/what-it-really-costs-to-own-a-commercial-truck/ |title=What It Really Costs to Own a Commercial Truck |first=Allen |last=Smith |date=25 May 2016 |publisher=Ask The Trucker |access-date=18 May 2017 |quote=pay over $100,000 for your first commercial vehicle. 18-wheeler drinks .. easily more than $70,000 annually}}</ref> Trucks average from {{convert|4|to|8|mpgus|L/100 km}}, with fuel economy standards requiring better than {{convert|7|mpgus|L/100km}} efficiency by 2014.<ref>{{cite web |last=Dyer |first=Ezra |url=http://www.popularmechanics.com/cars/news/pictures/10-things-you-didnt-know-about-semi-trucks-5#slide-5 |title=10 Things You Didn't Know About Semi Trucks |publisher=Popularmechanics.com |access-date=25 March 2016}}</ref> Power requirements in standard conditions are {{cvt|170|hp}} at {{cvt|55|mph|0}} or {{cvt|280|hp}} at {{cvt|70|mph|0}}<!--plus engine management-->, and somewhat different power usage in other conditions.<ref>{{cite web |url=http://electracold.com/CAT.pdf |title=Understanding Tractor-trailer Performance |publisher=[[Caterpillar Inc.|Caterpillar]] |page=5 |date=2006 |id=LEGT6380}}</ref>

[[File:RoadtrainCrop.JPG|thumb|Rocky Mountain Double]]

The [[semi-trailer|cargo trailer]] usually has [[tandem]] axles at the rear, each of which has [[Glossary of trucking industry terms in the United States#Dual wheels|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.<ref>{{cite web |url=http://www.rsa.ie/Documents/Vehicle%20Std%20Leg/Vehicle%20regs/Weights_Dimensions_Leaflet.pdf |title=Guidelines on Maximum Weights and Dimensions |publisher=Ireland Road Safety Authority |date=February 2013 |access-date=26 June 2014}}</ref><ref>{{cite book |last=Crismon |first=Fred W |title=US Military Wheeled Vehicles |edition=3 |year=2001 |publisher=Victory WWII Pub. |isbn=0-970056-71-0 |page=10}}</ref> 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#Trucks|tandem axles]] to allow adjusting the weight distribution.{{CN|date=October 2024}}

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" ([[road train|LCVs]]), and may allow them to operate on roads other than Interstates.{{CN|date=October 2024}}

[[Long combination vehicle]] types include:
[[File:UPS Freight truck, Motor Cargo & Overnite trailers.jpg|thumbnail|right|[[STAA doubles|STAA double]] pup {{cvt|28.5|ft}} trailers ]]
* Doubles (officially "[[STAA doubles]]", known colloquially as "a set of joints"): Two {{convert|28.5|ft|m|1|abbr=on}} trailers.
* B-Doubles: Twin {{convert|33|ft|m|1|abbr=on}} trailers in B-double configuration (very common in Canada but rarely used in the United States).
[[File:UPS Truck in Beatty Nevada (24.06.2009).jpg|thumb|UPS truck with triples in [[Nevada]]]]
* Triples: Three {{cvt|28.5|ft|1}} trailers.
[[File:Road train (27).jpg|thumb|{{cvt|53|ft}} container turnpike double in [[Canada]]]]
* Turnpike Doubles: Two {{cvt|40|ft|1}} – {{cvt|53|ft|1}} trailers.
* Rocky Mountain Doubles: One {{cvt|40|to|53|ft|1}} trailer (though usually no more than {{cvt|48|ft|1}}) and one {{cvt|28.5|ft|1}} trailer (known as a "[[road train#Dog-trailer (dog trailer)|pup]]").
* In Canada, a Turnpike Double is two {{convert|53|ft|m|1|abbr=on}} trailers, and a Rocky Mountain Double is a {{convert|50|ft|m|1|abbr=on}} trailer with a {{convert|24|ft|m|1|abbr=on}} "pup".<ref>{{cite web| url = http://www.bclaws.ca/civix/document/id/complete/statreg/30_78#section7.08| title = British Columbia, max. dimension of semi-trailer truck}}</ref><ref>{{cite web| url = http://www.manitoba.ca/mit/mcd/resources/pdf/mb_vehicle_weights_and_dimensions_guide.pdf| title = Manitoba, max. dimension of semi-trailer truck}}</ref><ref>{{cite web| url = https://cdn.ymaws.com/www.ctea.ca/resource/resmgr/Docs/2016_VW&D_in_Ontario_Public_.pdf| title = Ontario, max. dimension of semi-trailer truck}}</ref>

The US federal government, which only regulates the [[National Highway System (United States)|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 {{convert|20000|lb|kg|abbr=on}} on a single axle, {{convert|34000|lb|kg|abbr=on}} on a tandem, and {{convert|80000|lb|kg|abbr=on}} total for any vehicle or combination. There is a maximum width of {{convert|8.5|ft|m|abbr=on}} and no maximum height.<ref>{{cite web |url=https://ops.fhwa.dot.gov/Freight/sw/overview/index.htm |title=Commercial Vehicle Size and Weight Program |publisher=US Department of Transportation |series=Freight Management and Operations |date=May 2003 |access-date=7 August 2016 |id=FHWA-OP-03-099}}</ref><ref>{{cite web |url=https://ops.fhwa.dot.gov/freight/publications/size_regs_final_rpt/index.htm#cmv |title=Federal Size Regulations for Commercial Motor Vehicles |publisher=US Department of Transportation |access-date=2 October 2012}}</ref>

Roads other than Interstates are regulated by individual states, and laws vary widely. Maximum weight varies between {{convert|80,000|lb|kg|abbr=on}} to {{convert|171,000|lb|kg|abbr=on}}, depending on the combination.<ref>{{cite web |url=http://www.bigtruckguide.com/heaviest-semi-trucks-in-the-united-states-and-canada/ |title=Top 10 Heaviest Semi Trucks in the United States and Canada |website=BigTruckGuide.com |first=Paul |last=Jakubicek |date=16 January 2015 |access-date=12 July 2016}}</ref> 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.<ref>{{cite web |url=http://www.mto.gov.on.ca/english/trucks/lcv/program-conditions/index.shtml |title=Long Combination Vehicles |access-date=1 June 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130517124815/http://www.mto.gov.on.ca/english/trucks/lcv/program-conditions/index.shtml |archive-date=17 May 2013 }}</ref>

===Oceania===
====Australia====
{{Main|Road transport in Australia}}

[[Australia]]n road transport has a reputation for using very large trucks and [[road train]]s. 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.{{CN|date=October 2024}}

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.<ref>{{cite press release |url=http://www.minister.infrastructure.gov.au/mv/releases/2007/July/114MV_2007.htm |title=Vaile Announces the B-Triple Road Network |publisher=Ministry for the Department of Infrastructure |date=9 July 2007 |archive-url=https://web.archive.org/web/20080602215035/http://www.minister.infrastructure.gov.au/mv/releases/2007/July/114MV_2007.htm |archive-date=2 June 2008}}</ref> B-Triples are set up differently from conventional road trains. The front of their first trailer is supported by the [[Fifth wheel coupling|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.{{CN|date=October 2024}}

In total, the maximum length that any articulated vehicle may be (without a special permit and escort) is {{convert|53.5|m|ft|abbr=on}}, its maximum load may be up to 164&nbsp;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.{{CN|date=October 2024}}

Articulated trucks towing a single trailer or two trailers (commonly known as "short doubles") with a maximum overall length of {{convert|19|m|ft|abbr=on}} 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&nbsp;tonnes and overall length of {{convert|25|m|ft|abbr=on}}, or {{convert|26|m|ft|abbr=on}} 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.{{CN|date=October 2024}}

Maximum width of any vehicle is {{convert|2.5|m|ft|abbr=on}} and a height of {{convert|4.3|m|ft|abbr=on}}. In the past few years, allowance has been made by several states to allow certain designs of heavy vehicles up to {{convert|4.6|m|ft|abbr=on}} high but they are also restricted to designated routes. In effect, a 4.6&nbsp;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&nbsp;meter high vehicles.{{CN|date=October 2024}}

In Australia, both conventional prime movers and [[cabover]]s 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.{{CN|date=October 2024}}

<gallery align="center" mode="packed">
File:B double logging truck in Australia.jpg|An Australian [[Tractor unit|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]]
</gallery>

====New Zealand====
New Zealand legislation governing truck dimensions falls under the Vehicle Dimensions and Mass Rules, published by [[NZ Transport Agency]].<ref>{{cite web |url=https://www.nzta.govt.nz/assets/resources/factsheets/13/docs/13-vehicle-dimensions-and-mass.pdf |title=Vehicle Dimensions and Mass Guide |publisher=[[NZ Transport Agency]]}}</ref> New rules were introduced effective 1 February 2017,<ref>{{cite web |url=https://www.drivingtests.co.nz/resources/vehicle-dimensions-and-mass-vdam-changes/ |title=Vehicle dimensions and mass (VDAM) changes|date=13 February 2017}}</ref> 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.{{CN|date=October 2024}}

Common combinations in New Zealand are a standard semi-trailer, a [[Road train#B-double|B-double]], 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: {{convert|19|m|ft|abbr=on}}
* Simple: {{convert|22|m|ft|abbr=on}}
* Pole: {{convert|20|m|ft|abbr=on}}
Trailers with two axle sets can be {{convert|20|m|ft|abbr=on}} long, including heavy rigid vehicles towing two trailers.
Oversized loads require, at minimum, a permit, and may require one or more pilot vehicles.<ref>{{cite web |url=https://www.nzta.govt.nz/assets/resources/factsheets/53/docs/53-overdimension.pdf |title=Overdimension vehicles and loads |publisher=[[NZ Transport Agency]]}}</ref>

'''High-productivity motor vehicle''' (HPMV) permits are issued for vehicles exceeding 44 tonnes, or the above dimensions.<ref>{{Cite web|date=1 May 2021|title=Land Transport Rule – Vehicle Dimensions and Mass 2016 – Rule 41001/2016|url=https://www.nzta.govt.nz/assets/resources/rules/docs/vehicle-dimensions-and-mass-2016-as-at-1-may-2021.pdf|website=NZTA}}</ref> Trucks up to 62 tonnes were allowed, with an initial bridge strengthening program costing $12.5m.<ref>{{Cite web|date=2013-07-27|title=More monster trucks to thunder along our roads|url=https://www.stuff.co.nz/waikato-times/news/8972026/More-monster-trucks-to-thunder-along-our-roads|access-date=2021-05-04|website=Stuff|language=en}}</ref>