Why are 18-Wheelers Called ‘Semi-Trucks’?

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We thought we’d do a blog today about a question that has little to do with personal injury, but seems to come up often in truck accident law: the etymology of the word “semi-truck.” Specifically, “why are they called semi-trucks if they’re so big?”

Trucking Etymology

It seems to be a misnomer to title an 80,000 pound vehicle semi-anything. After all, “semi” usually means that it’s “part of” something…right? Since semi-trucks completely dwarf your everyday pickup truck, how can an 18-wheeler ever be considered “part-of” a truck?
The answer is pretty simple: semi-truck or semi is actually short for semi-trailer truck. The “semi” part of the title has nothing to do with the size of the big rig, but everything to do with what the tractor is pulling behind it.

Then how is it HALF of a Trailer?

Now that we’ve defined it as a semi-trailer we seem to have hit another road-bump. That simple wooden box with two wheels you can buy at the hardware store is called a trailer, but the giant big rig that makes you nervous when you’re in the lane next to it is a semi-trailer?  Again, this seems wrong.
To get into the mechanics of it, a “full trailer” has both front and rear axles, and is towed by a tractor or truck. Conversely, a big rig’s semi-trailer has no front wheels, and the front of the semi-trailer (and about half its weight) rests on the rear of the tractor.  Thus, you get the term “semi-trailer”
Americans, liking to keep words short and sweet, have gradually shortened the semi-trailer truck word down to simply “semi-truck.”

Trucking through Dialects

18-wheelers seem to have a long list of words used to describe them. What you call it depends a lot on where you come from. Most likely, if you’re from the United States, you call these vehicles semi-trucks or semis, but if you live in Louisiana, you might me more likely to call it an “18-wheeler.” You’ll probably say “Tractor-Trailers” if you’re from New England.”
In Britain, they’re known as “articulated lorries” or “artics” for short.
As experts in semi-truck accident law, our attorneys have to know the law, the medicine, and the mechanics when working a case. If you have a question for our St. Louis personal injury lawyers, feel free to shoot us an email using our online contact form.

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