What is a Tractor-Trailer?


A tractor-trailer is the term given to a combination of a trailer and an on-road tractor, or truck. A tractor-trailer is comprised of two entirely separate units so that the truck can be hooked to other trailers and the trailer can be hooked to other trucks. They are connected both with hardware and electronically so that the truck can control the brakes and all the lights on the trailer.

Tractors trailers feature a truck at the front end and a trailer that can be hitched to the truck at the back.
Tractors trailers feature a truck at the front end and a trailer that can be hitched to the truck at the back.

The Tractor-Trailer is used for transporting goods and materials from one place to the other. It is how groceries find their way to the shelves of the grocery store, for one example.

A tractor-trailer may be used to transport produce from the farmer to the grocery store.
A tractor-trailer may be used to transport produce from the farmer to the grocery store.

The truck portion of a tractor-trailer must have enough engine power to pull a significant amount of weight. The weight of the trailer can vary greatly depending on what type of freight it contains. A trailer loaded with empty plastic bottles, for example, will weigh much less than a trailer full of bottled water.

Sometimes the passenger cab of the truck includes a compartment large enough for a bed. This is so the driver of the tractor-trailer can sleep in the truck when delivering freight over long distances. It is common for a driver to own his truck and contract out to companies to transport freight in the company trailers. One driver may haul freight for a number of different companies over a wide geographic area and spend weeks at a time living in his truck.

The trailer portion of the tractor-trailer combination can be one of a variety of designs to serve a variety of different purposes. Probably the most common style is the box trailer. It can vary in length from about 28 feet to 53 feet (8.5 to 16.2 meters) and is totally closed except for the door at rear end and sometimes on the sides.

Another style of trailer is known as a flat bed, which is basically a platform on which freight is strapped. A tractor-trailer with a flatbed is often used to transport lumber, bricks or other construction materials. A third common type of trailer is a tanker, which carries liquids such as water or milk or dry goods such as flour or grain.

Other terms used to describe a tractor-trailer are "eighteen wheeler" and semi-trailer truck." The term "eighteen wheeler" is sometimes used because there is often a total of eighteen wheels in the combination. The term "semi-trailer truck" refers to a trailer in which one end is supported by the truck that it is connected to. The other end of the trailer has its own set of wheels.

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Discussion Comments


Yes, most of them do have eighteen wheels. Some of the smaller ones have less. Count them when you are a passenger!


I hate getting behind those flatbed tractor-trailers that are hauling logs. They are open in the back and on the sides, and even though the logs are strapped in, I'm always afraid that one will get loose and come flying toward my windshield.

If I see a log truck up ahead and I'm driving on a four-lane highway, I will get in the passing lane way before I reach him. I just feel safer off to the side than directly behind him.

Also, leaves and bits of bark chip off in the wind and fly out everywhere around the truck. Because the load is so heavy, they go really slow when they are driving uphill, too.


A tractor-trailer cab without the trailer attached looks so funny to me. Something that was once so very long is suddenly really short, even though it is still very tall.

Somehow, tractor-trailers are a lot less intimidating once their trailers have been detached. They must be a whole lot more easy to maneuver, too. I imagine that it is a little bit of a shock for the driver when he first starts to drive again after unloading.

I don't think that I could ever actually drive one of these. I have trouble parking my small sedan, so I know that I would get into jams with something as big as a tractor-trailer.


@Kristee – I travel a lot, and I can tell you that a tractor-trailer wreck is one of the scariest kind. I have seen one flip before, and though I didn't get hit by it, just watching it get all banged up with someone inside nauseated me.

Miraculously, the driver was okay. He told me that his truck had been flipped by the wind before during a severe thunderstorm that produced a funnel cloud, and he survived that with no major injuries, too.

I have heard of small cars being involved in tractor-trailer wrecks and actually getting lodged up under the trucks. I seem to remember one person getting decapitated in this way.


I've always called tractor-trailers “eighteen-wheelers.” I don't think I have ever actually counted the wheels for myself, but since that is what my parents always called them, I took their word for it.

As a child, I was terrified by eighteen-wheelers. I think when you are very small, big things seem even bigger and scarier.

Now, the only time that I am frightened by eighteen-wheelers is when they are veering into my lane a little. I get quite a rush when this happens, and I generally swerve before I can even think.

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