What Exactly is a Semitruck?
The term “semitruck” is a bit of a misnomer. It specifically refers to the powerful front part of the vehicle, the tractor (or “cab”). This is the part with the engine and the driver. The “semi” part comes from the type of trailer it pulls—a semi-trailer.
A semi-trailer doesn’t have front wheels; its front end rests on a hinged plate on the tractor called the fifth wheel. This means the tractor carries a significant portion of the trailer’s weight.
Key Components of a Semitruck (Tractor-Trailer)
The Tractor (The Truck):
Cab: Where the driver works and often sleeps (in a “sleeper cab”).
Engine: A very large, powerful diesel engine, often 13-15 liters in size.
Transmission: Typically has 10, 13, or 18 gears to handle heavy loads.
Fifth Wheel: The pivoting plate on the back of the tractor that hooks onto the trailer.
The Trailer:
Semi-Trailer: The most common type, supported by the tractor.
Axles: Typically have 2 or 3 axles with dual wheels (“dualies”) on each side.
Types: There are many kinds of trailers:
Dry Van: The enclosed box you see most often.
Flatbed: An open, flat platform for large or unusual cargo.
Refrigerated (“Reefer”): An insulated van with a cooling unit.
Tanker: For hauling liquids like fuel or milk.
Dump Trailer: For hauling and dumping loose material like gravel.
Why “18-Wheeler”?
This nickname comes from the total number of wheels on a standard tractor-trailer combination:
Tractor: 10 wheels (2 front steering wheels + 4 sets of dual wheels on 2 axles)
Trailer: 8 wheels (4 sets of dual wheels on 2 axles)
Total: 18 wheels
The Role of Semitrucks
Semitrucks are the backbone of the freight and logistics industry. In the United States alone, they move over 70% of all freight by weight. Virtually every physical product you buy spent some time on a semitruck.
If You’re Interested in Driving or Buying One
Commercial Driver’s License (CDL): Operating a semitruck requires a special license, a Class A CDL, which involves knowledge tests and a skills test.
Cost: A new tractor can cost $130,000 to $180,000+. A new trailer can be $30,000 to $80,000+. Used equipment is a significant market.
Career: Truck driving is a major profession. It can be a long-haul (over-the-road) or local delivery job, with pay often based on miles driven or percentage of load value.
Safety
Semitrucks are essential but require extreme caution around them due to their size and weight.
Large Blind Spots (“No-Zones”): The areas directly in front, closely behind, and along the sides of the trailer are critical to avoid.
Long Stopping Distances: A fully loaded semitruck can take the length of a football field or more to come to a complete stop.
Wide Turns: They often need to swing wide to the left to make a right turn safely. Never squeeze in between a turning truck and the curb.