The term tractor-trailer is used to describe a vehicle that is made up of two or more components. The first component is the tractor, sometimes referred to as the semi or main rig. This is a vehicle that can be driven on the roads with or without a trailer. The trailer is a unit that is attached to the tractor, and in some areas, you are allowed to couple several of these units together behind the one tractor. In some countries, you can have tractor-trailer combinations that include the tractor and up to four trailers – that makes for a long train that can be difficult to control.
So what is the trailer? There are generally three different types of trailer in use today. These are:
- Box – as the name suggests, this is a big empty box – at least, until it’s full of cargo. Box trailers can carry virtually anything, and almost all of your supermarket items will have spent some time in a box trailer. A variation of the box trailer is the flat top (not to be confused with a flat bed) that has soft side curtains rather than solid walls. Curtains allow for side access for loading and unloading whilst solid box trailers generally only have rear access. Box trailers can also have refrigeration units for the transportation of goods that need to be kept at low temperatures.
- Tanker – tankers are used to transport liquids, gases, and fine materials such as wheat. Tankers require special truck handling skills because of the fluid nature of their cargo.
- Flat Bed – flat bed trailers are generally used to transport heavy equipment and lumber. The flat bed is generally quite low to the ground in comparison to other trucks. Variations include double decker flat beds that are used to transport new cars.
There are many other different types of tractor-trailers in use, however, those three are the most common. All require drivers to have a Class A Commercial Drivers License and to have undertaken truck driver training.