This MedLibrary.org supplementary page on Tractor unit is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
A tractor unit, traction unit, road tractor or prime mover (Australian English) is a heavy-duty vehicle, usually with a large diesel engine and several axles. The tractor unit serves as a method of moving trailers. Trailers can be swaped between tractor units quickly so the unit does not stand idle whilst the load is unloaded or loaded, unlike a rigid, and is not restricted to one type of goods as trailer types can be swaped e.g Bulk tipper to a box van. The tractor-trailer combination also means that a load can be shared across many axles, yet be more manuverable than a equivalently sized rigid truck (see trucks). The tractor unit couples to the trailer using some sort of mechanical lock system, usually a fifth wheel. A tractor unit is primarily designated a freight vehicle and is most common in the heavy goods vehicle class of vehicles although smaller van based tractor units do exist.
A tractor unit can have many axles depending on axle load legislation. The most common varieties are those of 4x2, 6x2 and 6x4 types, were a 6x4 has 3 axles with 2 of the axles driven. 6x4 units are more common in long distance haulage in larger countries such as the USA and Australia. In Europe, the 4x2 and 6x2 variants are more commonplace. Those with 3 axles or more can have more than one steering axle, which can be also driven. The axle configurations are usually based upon axle load legislation and maximum GVWs. Heavier versions of tractor units, such as those used in heavy haulage and road trains, tend to have 4 or more axles with more than one axle driven. In certain countries (such as Switzerland), a certain amount of weight must be spread over driven axles which lead to heavier varieties having all wheel drive, otherwise another tractor unit would have to be used. The heavy haulage variants of tractor-units are often turned into a ballast tractor by fitting temporary ballast because their chassis allows a high GVW which may go beyond the legal limit, hence requiring special permits.
A tractor unit can sometimes have a mounted crane located behind the cab. The tractor unit can still pull a trailer using its fifth wheel although it will carry less payload due to the extra bulk of the crane. A crane truck is able to lift its load on site, and usually comes with stabilizers like those on mobile cranes. These cranes can come in sizes from a few tones up to special heavy duty ones that can lift in excess of 80 ton/mtr for lifting containers and office units.
In the USA and Australia in particular, owner drivers, and even fleet operators go to great lengths to customize their vehicle. This involves fitting larger exhausts, extra lights and custom paint among other things. Such tractor units attract lots of attention and can be beneficial for promoting their business, such tractors can be matched with a customized trailer. Some companies have one custom truck, or at least one tractor unit that is different or more powerful than the rest to act as a flag ship.
Regional variations
In the United Kingdom this type of "tractor" is often called an "artic",short for articulated lorry.
In the United States and Canada they are referred to as a Semi-trailer trucks .
See also
References
 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (November 2008) |
Wikipedia content modification information:
- This page was last modified on 14 November 2008, at 22:05.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Tractor unit".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.