18 Wheeler, 16 Wheeler, Tractor Trailer

Tractor trailer trucks are referred to by several names. These include “semi-trailer,” “semi-tractor trailer,” “big rig,” “18 wheeler,” or simply “semi.” These vehicles consist of a truck, which is also referred to as a tractor. This truck contains the vehicle and the cab in which the driver sits to operate the vehicle. A semi-trailer is then attached to the back of the truck in order to tow cargo. The term “semi” originates from the fact that the trailer does not contain front wheels, as opposed to a standard trailer. In this application, the term semi indicates that this particular trailer is a partial trailer.

Anatomy of a Tractor Trailer

The term 18 wheeler arises from the combination of ten tractor wheels and eight trailer wheels. Sixteen wheeler trucks are less common. As indicated by the name, 16 wheeler trucks have 16 wheels as opposed to 18. Tractor trailer engines can be as high as six times as large as the size and weight of a car engine. These heavy-duty elements allow for tractor trailers to legally travel with up to 80,000 pounds of cargo without a permit.


The tractor is the front, powered portion of the truck which contains the engine and the driver. The tractor typically has two or three axles. Axles are central shafts that facilitate rotating gears or wheels. On vehicles such as tractor trailers, an axle runs the full width of the vehicle and supports two wheels. The wheels are attached to both ends of the axle. Tractors built for hauling heavy-duty machinery such as equipment for commercial construction may feature up to five axles.


Cargo trailers typically feature a pair of axles at the rear. These “tandem” axels typically have dual wheels. This totals four wheels on each axle, for a total of eight wheels. In some trailers, the tandem is movable. This allows for adjustment of the trailer’s weight distribution. A typical trailer is 53 feet long.

Tractor Trailer Facts

It is estimated that there are roughly 5.6 million registered tractor trailers in the United States. On average, tractor trailers are estimated to travel 140 billion miles each year. One tractor trailer averages about 45,000 miles of travel a year. Tractor trailers are an important means for transporting goods. In fact, roughly 68 percent of U.S. goods are delivered through the use of tractor trailers. Tractor trailers are not particularly fuel efficient, as the average tractor trailer’s fuel economy is roughly 6.5 miles per gallon.


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