Tractor & Construction Plant Wiki

A semi-trailer truck, also known as tractor-trailer or (in the United Kingdom and Ireland a articulated truck or articulated lorry), often abbreviated to artic, is an articulated vehicle consisting of a tractor unit (tractor in the United States, prime mover in Australia, tractor unit in Ireland and truck/tractor unit in the UK, Canada and New Zealand), and a semi-trailer (plus possible additional trailers) that carries the freight.

Colloquial terms for semi-trailer truck include truck and trailer, transfer truck, 18-wheeler, semi, Diesel, Mack truck (named for a prominent brand), big rig (US), transport (Canada), artic (UK and Ireland), and juggernaut (UK).

Regional Configurations


An articulated lorry (Renault Magnum) in London, England.

The noticeable difference between tractor units in the U.S. and Europe is that most European models are "cab over engine" (COE or forward control), while most U.S. trucks are conventional (or normal control). For repairs, the entire cab hinges forward to allow maintenance access. European trucks, whether small rigid or fully articulated, have a sheer face on the front. This allows greater manoeuvrability, as the driver need only gauge distances behind his seating point, and this allows for shorter trucks with longer trailers (with larger freight capacity) within the legal maximum total length. In Europe the entire length of the vehicle is measured as total length, while in U.S. the cabin of the truck is normally not part of the measurement.

Most artic tractors have two axles, again with the front, steer, having two wheels, and rear, drive, having twin wheels on each side. Thus, the most common configuration has six wheels. The cargo trailer usually has three axles at the rear, with single wheels, or six wheels in total. The entire vehicle thus usually has five axles and 12 wheels in total, although the trailers can vary in number of wheels.

United Kingdom

In the UK, to carry the maximum permitted gross weight of 44,000 kg (97,000 lb), both tractor and semi-trailer must have 3 or more axles each [2].[dead link] In practice, there is no legal height limit; however, bridges over 16.5 ft (5.03 m) do not have the height marked on them. No heavier vehicles are permitted on the UK road network, except for indivisible loads, which would be classed as abnormal (or oversize); these vehicles are required to display an STGO (Special Types General Order) plate on the front of the prime mover and, under certain circumstances, are required to travel by an authorised route and have an escort.

In the UK, some articulated trucks have 8 tyres on 3 axles on the tractor; these are known as 6-wheelers or "6 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). Some trailers have 2 axles which have twin wheels on each axle; other trailers have 3 axles, of which 1 axle can be a TAG 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 artic truck tractors which have 6 tyres on 2 axles; these are known as 4-wheelers.

Most UK trailers are 45 feet (13.5 meters) 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 50 and 55 feet (15.25 and 16.75 meters). Although the Construction and Use Regulations allow a maximum rigid length of 60 feet (18.2 meters), 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 75 feet (22.75 meters), although combinations of this length are usually used only to carry steel or concrete beams. 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 authorised 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.

Continental Europe

The maximum overall length applying in the EU and EEA member states are 18.75 meters with a maximum weight of 40 ton, or 44 ton if carrying a ISO container.[1] However, rules limits the semi-trailers to 16.5 meters and 18.75 is met with trucks carrying a standardized 7.82 meter body with one additional 7.82 meter body on tow as a trailer.[2] Since 1996, when Sweden and Finland formally got a final exemption from the European Economic Area rules with 60 ton and 25.25 meter combinations all other member states got the ability to adopt the same rules.

The 25,25 metres 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 with an average of 20% with a corresponding relative decrease in carbon emissions and with the added benefit of a third less trucks on the road.[1] 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 routes in other EU member states.

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 have allowed 25.25 meter combinations on select routes. Like in Sweden and Finland, these vehicles in continental Europe will run a 60 ton weight limit. Two types are to be used:

  1. a 26 ton truck pulling a dolly and semi-trailer, or
  2. an articulated tractor unit pulling a b-double.

The UK government has so far decided not to have its own trial of these 60 ton vehicles, but to keep an eye on the other countries' trials.

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, manoeuvring a trailer hooked to a dolly is different from manoeuvring a fifth wheel trailer. Backing the vehicle requires same technique as backing an ordinary truck/full trailer combination, though the dolly/semi setup is probably longer, thus requiring more space for manoeuvring. The tractor-semi-trailer configuration is rarely used on timber trucks, since these will use the two big 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 + mid-axle trailer configuration instead of the tractor + semi-trailer setup.

The largest trailer manufacturer in Europe is Schmitz Cargobull.[citation (source) needed]

Sweden and Finland

In Sweden the allowed length is 24 metres (78.7 ft) since 1967. Before that, the maximum lenght 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.[1] 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 Loader crane on the 6x4 truck, and two additional stacks on a four axle trailer. The allowed gross weight in both countries is up to 60 tonnes (130,000 lb) depending on the distance between the first and last axle.

In the negotiations starting in the late 80's preceding the two countries 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 Sweden and Finland's entry to the union, the rules changed again, this time to allow trucks carrying a standard CEN unit of 7.82 meter to draw a 13.6 meters standard semi-trailer on a dolly, a total overall length of 25.25 metres (82.8 ft). Later B-double combinations came into use, often with one 20 ft container on the b-link and a 40 ft container (or two 20 ft containers) on a semi-trailer bed. In allowing the longer truck combinations, what would take two 16.5 meter semi-trailer trucks and one 18.75 meter truck and trailer to haul on the continent now could be handled by just two 25.25 meter trucks - greatly reducing overall costs and emissions.

However, even longer trucks exists. Special transports can be exempted from the rules, with 28 meter long semi-trailer trucks in common use for hauling wind turbine parts. Even longer trucks are a part of the ongoing project En Trave Till (lit. One more pile/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 30 meter long truck trailer combination with a gross weight exceeding 90 tonnes (200,000 lb). It's estimated that this will give a 20% lower cost and 20-25% CO2 emissions reduction compared to if the timber instead would have been transported with regular 60 ton truck combinations. The braking distance, road wear, and traffic safety will be either the same or improved with the 90 ton truck-trailer. In the same program two types of 74 tonnes (160,000 lb) combinations will be tested in Dalsland and Bohuslän counties in western Sweden. A enhanced truck and trailer combination for use in the forest and a b-double for plain highway transportation to the mill in Skoghall. However, all such transports are carried out under exemption rules.


Main article: Road transport in 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 4 tires on each axle. This means that Australian single semi-trailer trucks will usually have 22 wheels which is generally more than their counterparts in other countries. 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.[3] B-Triples are set up differently to 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 53.5 metres (175.5 ft), its maximum load may be up to 164 tons (361,558 lb) gross and may have up to 4 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 day time, especially 4 trailer road trains.

In most areas a truck is generally limited to two trailers and a total length of 26 metres (85 ft) and in urban areas this length limit is further reduced to 19 metres (62 ft). 25 metre (82 ft), 62.5 ton (137,788 lb) B-doubles are very common in all parts of Australia including state capitals and on major routes may outnumber single trailer configurations.

In Australia, both conventional tractor units 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.

Super single tires 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 tire 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 tires requires a permit.

North America

In North America, semi tractors usually have 3 axles, the front, or "steer", axle having two wheels, and each of the two rear, "drive", axles having a pair of "dualies" (double) wheels on each side. Thus, the most common configuration of tractor has 10 wheels, however in some cases dual wheels are replaced by tires known as "super singles" (see below), or wide-base singles, to reduce the weight of the tractor. (The weight reduction is about 180 lbs per axle when using super singles). In this case the tractor will only have six wheels. A smaller tractor, having a single drive axle (six wheeler) is often used to pull shorter trailers in tight urban environments, such as downtown areas where a 60-foot rig would be too difficult to manoeuvre. These tractors are referred to as day cabs and do not have sleepers.

The cargo trailer usually has two "tandem" axles at the rear, each of which has dual wheels, or 8 wheels on the trailer. Many trailers are equipped with movable tandems and fifth wheels that can be set to adjust the weight on each axle to stay within legal limits.

Although the cargo's weight added to the semi's weight can equal a certain amount of gross some roads are marked with a different gross restriction so the roads are not damaged. Cargoes that exceed allowed weights are usually marked with overweight load and must obtain a permit to use certain roads.

Rules governing the maximum size and weight of vehicles differ between states in the US. However, since the majority of hauling is done on the interstate system, the vast majority of trucks and trailers made in the US are built to the specifications of the Department of Transportation (D.O.T.), which governs the use of the interstate system. The D.O.T. has established these vehicle limits: 102 inches wide, 13.5 feet in height, and 80,000 lbs gross weight. [3] These limits can be exceeded as individual states have the right to issue temporary oversize and/or overweight permits.

Trailer dimensions vary greatly, depending on the amount and type of cargo it was designed to haul. (See types of trailers under Construction, below.)

Although dual wheels are most common, use of two single, wider tires (known as "super singles") on each axle is becoming popular, particularly among bulk cargo carriers and other weight-sensitive operators. The three advantages of this configuration are : (1) the lighter tire weight allows a truck to be loaded with more freight (2) the single wheel covers less of the brake unit, which allows faster cooling and reduces brake fade. (3) super singles reduce fuel consumption. Testing on an oval track showed 5% fuel savings when using super singles. The savings come from less energy wasted flexing tire side walls. Fewer tire side walls equates to less wasted energy.

The biggest disadvantage is that when a tire becomes deflated or destroyed, it is not possible to drive the vehicle to a service location without risking damage to the rim, as it is with dual wheels.

The United States also allows 2-axle tractors to tow two 1-axle 28.5-foot (8.7 m) semi-trailers known officially as STAA doubles and colloquially as doubles, a set, or a set of joints on all highways that are part of the National Network. The second trailer in a set of doubles uses a converter gear, also known as a con-gear or dolly. This apparatus supports the front half of the second trailer. Individual states may further allow longer vehicles (known as "longer combination vehicles" or LCVs), and may allow them to operate on roads other than those part of the National Network.

LCV types include:

  • Triples: Three 28.5-foot (8.7 m) trailers; maximum weight up to 129,000 pounds (58.5 t).
  • Turnpike Doubles: Two 48-foot (14.6 m) trailers; maximum weight up to 147,000 pounds (66.7 t)
  • Rocky Mountain Doubles: One 40 (12.2 m) to 53 (16.2 m) foot trailer (though usually no more than 48 feet) and one 28.5-foot (8.7 m) trailer (known as a "pup"); maximum weight up to 129,000 pounds (58.5 t)
  • In Canada, a Turnpike Double is two 53-foot trailers and a Rocky Mountain Double is a 50-foot trailer with 24-foot "pup"

Regulations on LCVs vary widely from state to state. No state allows more than three trailers without a special permit. Reasons for limiting the legal trailer configurations include both 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.

Most states restrict operation of larger tandem trailer setups such as triple units, the "Turnpike Double" (twin 48-53 ft units) or the "Rocky Mountain Double." (A full 48-53 ft unit and a shorter 28 ft unit) In general, these types of setups are restricted to tolled turnpikes such as I-80 through Ohio and Indiana, and select Western states. Tandem setups are not restricted to certain roads any more than a single setup. The exception are the units listed above. They are also not restricted because of weather or "difficulty" of operation.

The long-haul tractors used in interstate travel are often equipped with a "sleeper" behind the driver's cab, which can be anything from a small bunk to a rather elaborate miniature apartment.

Semi-Truck Manufacturers

These are for semi-trailer tractors, not straight, rigid, box or other heavy vehicles.

Used in the United States:

Used in Europe:

Used in Japan and some other Asia Pacific regions:

See also: List of dump truck manufacturers.


Side view and underside view of a conventional 18-wheeler semi-trailer truck with an enclosed cargo space. The underside view shows the arrangement of the 18 tires (wheels). Shown in blue in the underside view are the axles, drive shaft, and differentials. The legend for labeled parts of the truck is as follows:
1. tractor unit
2. semi-trailer (detachable)
3. engine compartment
4. cabin
5. sleeper (not present in all trucks)
6. air dam
7. fuel tanks
8. fifth wheel coupling
9. enclosed cargo space
10. landing gear - legs for when semi-trailer is detached

Types of trailers

There are many types of semi-trailers in use, designed to haul a wide range of products. See Semi-trailer for more detail.

Coupling and uncoupling

The cargo trailer is, by means of a nipple called the king pin, hooked to a horseshoe-shaped quick-release coupling device called a fifth wheel or a turntable hitch at the rear of the towing engine that allows easy hook up and release. The truck trailer cannot move by itself because it only has wheels at the rear end, hence the name semi-trailer: it only carries half its own weight. The vehicle has a tendency to fold at the pivot point between the semi and the trailer when braking hard at high speeds. Such a truck accident is called a 'trailer swing', although it is commonly described as a 'jackknife'. 'Jackknifing' is a condition where the tractive unit swings round against the trailer: not vice-versa. See: jackknifing.


Semi trucks use air pressure, rather than hydraulic fluid, to actuate the brakes mainly due to the much larger braking forces required. This also allows for ease of coupling and uncoupling of trailers from the tractor unit, as well as reducing the potential for problems common to hydraulic systems, such as leakage or brake failure caused when overheated brake fluid vaporizes in the hydraulic lines. The most common failure is "brake fade" usually caused when the "drums" or "discs" and the "linings" of the brakes overheat from excessive use.

The "parking brake" of the tractor unit and the "emergency brakes" of the trailer are spring brakes that require air pressure in order to be released. They are applied when air pressure is released from the system, and disengaged when air pressure is supplied. This is an emergency feature which ensures that if air pressure to either unit is lost, that unit will not lose all braking capacity and become uncontrollable.

The trailer controls are coupled to the tractor through two "glad-hand" connectors, which provide air pressure, and an electrical cable, which provides power to the lights and any specialized features of the trailer.

"Glad-hand" connectors (also known as "palm couplings,") are air hose connectors, each of which has a flat engaging face and retaining tabs. The faces are placed together, and the units are rotated so that the tabs engage each other to hold the connectors together. This arrangement provides a secure connection, but allows the couplers to break away without damaging the equipment if they are pulled, as may happen when the tractor and trailer are separated without first uncoupling the air lines. These connectors are similar in design to the ones used for a similar purpose between railroad cars. Two air lines control the trailer unit. An "emergency" or main air supply line pressurizes the trailer's air tank and disengages the emergency brake, and a second "service" line controls the brake application.

In the UK male/female quick release connectors "red line" or emergency, have a female on the truck and male on the trailer and a "yellow line" or service has a male on the truck and female on the trailer. This avoids coupling errors (causing no brakes) plus the connections will not come apart if pulled by accident. The three electrical lines will fit one way round a primary "black" a secondary "green" and an ABS lead, all of these lines are collectively known as "suzies" or "suzie coils".

Another braking feature of semi-trucks is the engine braking, which could be either compression brake (usually shortened to "Jake brake") or exhaust brake or combination of both. The use of compression brake alone however produces a loud and distinctive noise, and owing to noise pollution, some local municipalities have prohibited or restricted the use of engine brake systems inside their jurisdictions, particularly in residential areas. The advantage to using this instead of conventional brakes is that a truck can travel down a long grade without overheating its wheel brakes. Some vehicles can also be equipped with hydraulic or electric retarders which have an advantage of near silent operation.


Because of the wide variety of loads the "semi" may carry, they usually have a manual transmission to allow the driver to have as much control as possible. However, all truck manufacturers now offer semi automatic transmissions (manual gearboxes with automated gear change) as well as automatic transmissions.

"Semi" truck transmissions usually provide at least nine or ten gear ratios, but possibly as many as eighteen (e.g. Australian Road Trains). A large number of transmission ratios means the engine itself can operate within a narrow range of speeds. The range of speeds over which an engine is expected to perform well has implications for the design — the narrower the range, the more the engine can be optimised for that range. Also, having so many gears allows fine-grained control of engine braking for better control on downhills and in curves.

A ten speed manual transmission is controlled via a six-slot H-Box pattern similar to that in five-speed cars — five forward and one reverse gear. Gears six to ten (and high speed reverse) are accessed by toggling a selector control for the range change low/high, so that first gear becomes sixth, second becomes seventh, etc.

Another difference between semi-trucks and cars is the way the clutch is set up. On a regular car the clutch pedal is depressed full stroke to the floor for every gear shift to ensure the gearbox is disengaged from the engine. On a semi-truck with constant mesh transmission (non synchronized), such as by the Eaton Roadranger series, not only is double clutching required, but a clutch brake is required as well. The clutch brake stops the rotation of the gears and allows the truck to be put into gear without grinding when stationary. The bottom of the clutch pedal stroke is where the clutch brake activates and as a result only partial or "half" clutch pedal stroke is used when a vehicle is in motion.


An electrical connection is made between the tractor and the trailer through a cable often referred to as a "pigtail." This cable is a bundle of wires in a single casing. Each wire controls one of the electrical circuits on the trailer, such as running lights, brake lights, turn signals, etc. A standard cable would break when the rig went around corners so it is coiled and retains these coils when not under tension. It is these coils that cause the cable to look like a pigtail.

In most countries a trailer or semi-trailer must have minimum

  • 2 rear lights (red)
  • 2 stop lights (red)
  • 2 turning lights; one for right and one for left, flashing (yellow, orange or red)
  • 2 marking lights behind if wider than certain specifications (red; 3 lights in North America)
  • 2 marking lights front if wider than the truck or wider than certain specifications (white; 3 amber lights in North America)

Drivers license

A special driver's license is required to operate various commercial vehicles.


Regulations vary by province. A license to operate a vehicle with air brakes is required, normally a Class I commercial license. In Ontario, a "Z" endorsement [4] is required to drive any vehicle using air brakes. Anyone holding an Ontario "Z" endorsement can drive a heavy truck with up to one towed vehicle, weighing no more than 4.6 metric tons if he or she also holds a Class A (tractor-trailer), B (school bus), C (regular bus) or D (heavy trucks other than tractor trailers) licence. [5] Anyone holding an Ontario Class A licence or equivalent can drive a tractor-trailer combination with at least 2 towed vehicles (Ibid.).
In Manitoba, one requires a class 1 license, with an "A" or "S" endorsement to operate a semi-truck. An "A" endorsement is for air brakes, and an "S" endorsement is operation of air brakes, plus adjustment of them.

United States

Drivers of semi-trailer trucks generally require a Class A commercial driver's license to operate any combination vehicles with a Gross Vehicle Weight Rating (or GVWR) in excess of 26,000 pounds (11.8 t). Some states (such as North Dakota) provide exemptions for farmers, allowing non-commercial license holders to operate semis within a certain range of their farm within the state. Also a person under the age of 21 cannot operate a commercial vehicle outside the state where the commercial license was issued. A person must be at least 18 in order to be issued a commercial license.

In addition, Endorsements are necessary for certain cargo and vehicle arrangements and types;

  • H - Hazardous Materials (HazMat or HM) - necessary if materials require HM placards.
  • N - Tankers - the driver is acquainted with the unique handling characteristics of liquids tankers.
  • X - Signifies Hazardous Materials and Tanker endorsements, combined.
  • T - Doubles & Triples - the licensee may pull more than one trailer.


Taiwanese sign prohibiting heavy trailers

The Road Traffic Security Rules (zh:道路交通安全規則) require a combination vehicle driver license (

中文: 聯結車駕駛執照

) to drive a combination vehicle (

中文: 聯結車

). These rules define a combination vehicle as a motor vehicle towing a heavy trailer, i.e., a trailer with a gross weight of more than 750 kilograms (1,653 lb).

European Union including UK

A category C+E driver's license is required to drive an articulated lorry.


Truck drivers in Australia require an endorsed license. These endorsements are gained through training and experience. The minimum age to hold an endorsed license is 18 years, and/or must have held open (full) driver's license for minimum 12 months. The following are the heavy vehicle license classes in Australia:

  • LR- A Light Rigid 'Class LR' covers a rigid vehicle with a GVM of more than 4.5 tons but not more than 8 tons. Any towed trailer must not weigh more than 9 tons GVM. Also includes vehicles with a GVM up to 8 tons which carry more than 12 adult including the driver and vehicles in class 'C'.
  • MR- A Medium Rigid 'Class MR' covers a rigid vehicle with 2 axles and a GVM of more than 8 tons. Any towed trailer must not weigh more than 9 tons GVM. Also includes vehicles in class 'LR'.
  • HR- A Heavy Rigid 'Class HR' covers a rigid vehicle with 3 or more axles and a GVM of more than 15 tons. Any towed trailer must not weigh more than 9 tons GVM. Also includes articulated buses and vehicles in class 'MR'.
  • HC (Heavy Combination)- A 'Class HC' Licence covers heavy combination vehicles like a prime mover towing a semi-trailer, or rigid vehicles towing a trailer with a GVM of more than 9 tons. Also includes vehicles in class 'HR'.
  • MC (Multi Combination)- A 'Class MC' Licence covers multi-combination vehicles like Road Trains and B-Double Vehicles. Also includes vehicles in class 'HC'.

New Zealand

In New Zealand drivers of heavy vehicles require specific licenses, termed as 'classes'. A Class 1 Drivers License (aka a Car License) will allow the driving of any vehicle with Gross Laden Weight (GLW) or Gross Combination Weight (GCW) of 4500 kg or less. For other types of vehicles the Classes are separately licensed as follows:

  • `Class 2 - Medium Rigid Vehicle' - Any rigid vehicle with GLW less than 18,001 kg (with Light Trailer up to 3500 kg or less), any combination vehicle with GCW less than 12,001 kg, any rigid vehicle of any weight with no more than 2 axles, or any Class 1 vehicle.
  • 'Class 3 - Medium Combination Vehicle' - Any combination vehicle of GCW less than 25,001 kg or any Class 2 vehicle.
  • 'Class 4 - Heavy Rigid Vehicle' - Any rigid vehicle of any weight, any Combination vehicle which consists of a heavy vehicle and a light trailer, or any vehicle of Class 1 or 2 (but not 3).
  • 'Class 5 - Heavy Combination Vehicle' - Any combination vehicle of any weight, and any vehicle covered by previous classes.
  • 'Class 6' is a Motorcycle License.

Further information on the New Zealand Licensing system for Heavy Vehicles can be found at Land Transport New Zealand.

Role in industry

Modern day semi-trailer trucks often operate as a part of a domestic or international transport infrastructure to support containerized cargo shipment. Various types of rail flat bed train cars are modified to hold the cargo trailer or container with wheels or without. This is called "Intermodal" or "piggy-back" or "piggyback". The system allows the cargo to switch from the highway to railway or vice versa with relative ease by using gantry cranes.

The large trailers pulled by a tractor unit come in many styles, lengths, and shapes. Some common types are: vans, reefers, flatbeds, sidelifts and tankers. These trailers may be refrigerated, heated, ventilated, or pressurized, depending on climate and cargo. Some trailers have movable wheel axles that can be adjusted by moving them on a track underneath the trailer body and securing them in place with large pins. The purpose of this is to help adjust weight distribution over the various axles, to comply with local laws.


  • NBC ran two popular TV series about truck drivers in the 1970s, Movin' On (1974-1976) and B.J. and the Bear (1978-1981). Each featured actor Claude Akins in major roles.
  • A pop song by C.W. McCall called "Convoy" spurred sales of CB radios, with an imaginary trucking story.
  • The "trucker's movie" Smokey and the Bandit was second only to Star Wars in box office gross when released in 1977.
  • Another "trucker's movie" Black Dog (film) features an ex-trucker who takes an illegal load of guns to save his family's home. There are Carjacking attempts and stunt driving action scenes.
  • Steven Spielberg's 1971 film "Duel" features a Peterbilt 281 tanker truck as the villain.
  • Stephen King's 1986 film Maximum Overdrive featured big rigs as its primary homicidal villains.
  • Tractor-trailers appear in the 1980s cartoon The Transformers as the Autobots' leader Optimus Prime (Convoy in Japanese version), their second-in-command Ultra Magnus, and as the Stunticons' leader Motormaster. (The latter considers himself Optimus Prime's rival for the title "King of the Road".) Optimus Prime returned in the 2007 film.
  • The eighteen-wheeled truck was immortalized in numerous country music songs.
  • William Henkin, actor from a suburb of Chicago, had the stage name "Big Rig" when he appeared in various featurettes on Broadway.
  • CMT has a TV show called Trick My Truck where truckers get their trucks 'tricked out'.
  • The History Channel's Ice Road Truckers charts two months in the lives of six men who haul supplies to diamond mines over frozen lakes that double as roads.
  • The American television show Knight Rider featured a semi-trailer truck called 'The Semi', operated by the Foundation for Law & Government (F.L.A.G.) as a mobile support facility for KITT. Also, in two episodes KITT faced off against an armoured semi called Goliath.

See also


  1. 1.0 1.1 1.2 Ramberg, K "Fewer Trucks Improve the Environment" (PDF) Svenskt Näringsliv October 2004
  2. Wideberg, J et al [ "Study Of Stability Measures And Legislation Of Heavy Articulated Vehicles In Different OECD Countries" (PDF)] University of Seville, KTH and Scania May 2006
  4. "Z" endorsement
  5. Ontario drivers classes

External links

  • Truck.Net is a website dedicated to US Trucking Information started in 1996.
  • is a website dedicated to Trucking Information in UK and Europe.
  • Ol' Blue, USA is a website for Safety and Education in and around big trucks in the US as well as an AskTheLaw section also in print and on radio where questions can be directed to commercial law enforcement.

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