Semi-trailer

[1] A large proportion of a semi-trailer's weight is supported by a tractor unit, or a detachable front-axle assembly known as a dolly, or the tail of another trailer.

Some popular manufacturers are Kenworth, Iveco, Freightliner, MAN, Scania, Mercedes-Benz, DAF, Renault Trucks, Volvo, Peterbilt, and Mack.

The trailers can be coupled and uncoupled quickly, allowing them to be shunted for loading and to be trucked between depots.

Because of this, a semi-trailer can haul longer objects, (logs, pipe, beams, railway track).

For heavy haulage or for increased manoeuvrability, some semi-trailers are fitted with rear-wheel steering, controlled electro-hydraulically.

In some applications, no separable coupling is fitted, and the trailer is bolted to the tractor unit, using a bearing, and rocker feet as are used under a fifth wheel skid plate.

The driver has to raise the trailer legs manually and couple the airbrake lines and electrical cables.

A tank trailer is a semi-trailer specifically designed to carry liquids, fluids and gases.