If you are joining the trucking industry or want to, it’s good to brush up on your skills … and your trucking vocab.

A semi-truck isn’t the same as a box truck, so you definitely don’t want to confuse these two terms. So just why is a semi-truck called a semi-truck?  

A semi-truck, also called a semi, semi-tractor-trailer, semi-trailer-truck, 18-wheeler, big rig, or trailer truck, is made of two parts: the trailer that doesn’t have a front axle and only rear wheels that need to be hitched to a tractor, which hauls that trailer.  

We’ve got all the details about semi-trucks for you, including information about their origin. 

What Is the Real Name of a Semi-Truck?

The real name of a semi-truck is a semi-tractor-trailer or a semi-trailer truck. 

A semi-truck also goes by a few other names in North America: 

  • Semi 
  • Semi trailer 
  • Tractor trailer
  • 18-wheeler 
  • Big rig
  • Trailer truck 
  • Truck

What Is a Semi-Truck? 

The term “semi-truck” sounds really confusing, so let’s get into the nitty gritty of what this commercial vehicle is. The name will then (hopefully) make sense. 

A semi-truck has two parts: 

  1. The semi-trailer that carries the load or cargo 
  2. The semi-tractor that is the powered vehicle (with a heavy-duty engine) to pull or haul the trailer 

A semi-trailer or semi-truck isn’t the same thing as a trailer. A semi doesn’t have a front axle, while a trailer does have a front axle. 

Thus, a semi-trailer’s weight is partially supported by the wheels and the rest of the weight is supported by the tractor unit that hauls the semi-trailer. It has only rear wheels, while the wheel-less front of the semi-trailer is hitched (via fifth-wheel coupling, or a hitch) on the back wheels of the tractor.    

If you have a tandem tractor-trailer configuration, then the weight can also be supported by the back end of the other trailer or dolly. 

A regular trailer bears its own weight, even though it is attached to another vehicle via a drawbar or something similar. 

Also, it’s essential to note that not all semis are 18-wheelers. Only the ones that have 18 wheels are 18-wheelers. 

Why is it called a semi-truck?

Why is it called a semi-truck

The use of the term semi-truck can be very misleading. After all, the prefix, semi, means half or not complete. If you look at a semi-truck, it seems pretty complete to most people.


A standard semi-truck has 18 wheels. This is why another name for them is an 18-wheeler.

There are four axles on a semi-truck, and each axle has four wheels (two on each side). Then, there is another, fifth axle, meant for steering, which has two more wheels on it.

The reason there are so many wheels on a semi-truck is that the immense weight of the truck needs to be distributed.

If there are fewer wheels, it means more weight on each wheel, which can wreak havoc on the nation’s infrastructure.

In some states, you will see trailers with 6 or even more axles. This is all to spare the roads from the effect of heavy loads.

Already you may see shallow grooves along highways. These are a result of the great weight that semi-trucks carry.

If semi-trucks go down to fewer wheels or carry more weight, the grooves will become deeper and necessitate more maintenance.

Trailer Configuration

A semi-truck relies on the truck’s cab to prop up the front part of it. Without this support, the trailer simply wouldn’t be able to move.

Unlike traditional trailers, which can be towed independently, a semi-truck’s trailer has the front part connected to the cab for stability. The wheels on the front axles are actually attached to the truck and not the trailer.

It is this half-ability to stand on its own that gives the semi-truck its name. It has everything to do with how the trailer part of the truck is designed, and nothing with the truck’s cab area.

Types of Semi-Trucks 

There are many subcategories of semi-trucks but they still share the same common thread. They need a truck to tow them.

Flat-Roof Sleeper

This semi-truck has a sleeping compartment that is smaller than other types of semi-trucks. The roof is flat, which means less headroom.

Mid-Roof Sleeper

Inside the cab of this semi-truck, you will find a larger living space. In addition to a bed, you will also find storage compartments and in never models, room for a TV. The roof is rounded for a bit of extra height.

Raised-Roof Sleeper

As the name suggests, this type of semi-truck has more headspace, at least 12 inches more. The cab has a bed and storage area and is quite spacious.

Day Cab

If you only drive your semi-truck for short hauls, made during the day, then you can save money with a day cab. While still roomy, it doesn’t have a sleeping area as it is not used for overnight shipping.

Slope-Nose Truck

Perfect for bumpy terrain, this is the kind of semi-truck you want if you are traversing more rural areas. The front is shorter and rounder but can still haul large and heavy loads.

Conventional Nose Truck

While less common today, there was once a huge demand for this style. The design allowed for easier access to the engine but the shape resulted in lower fuel mileage.

There are also a variety of commercial trailers that can be hitched to the tractor to make a semi-trailer: 

  • Reefer trailer 
  • Lowboy trailer 
  • Flatbed trailer 
  • Step deck trailer 
  • Dry van trailer 
  • Power only trailer
  • Conestoga trailer 
  • Extendable double drop trailer 
  • Stretch single drop trailer 
  • Stretch double drop trailer 
  • Stretch removable gooseneck trailer
  • Removable gooseneck trailer
  • Specialty trailer 
  • Multi-car trailer 
  • Sidekit trailer 
  • Belt trailer 
  • Dump trailer 
  • Grain hopper 
  • Tank trailer

Semi-Truck History and Origin

Semi-Truck History and Origin

Semi-trucks haul more than 70% of commodities and goods in the United States alone. But where and when did it all start? 

Semis have been around for more than 120 years. 

1989: The Start of Car Haulers (aka Semi-Trucks) 

It all started in the late 19th century. Alexander Winton was a Scottish-American inventor, engineer, and designer, and he is credited for inventing the semi-truck. 

In 1896 in Cleveland, Ohio, Winton built his first motor, and a year after that, he established the Winton Motor Carriage Company.

When Winton was manufacturing cars, he wanted to ship the vehicles to his customers without putting any miles on the car (and to avoid any wear and tear to get the cars to the buyers).

Thus, he invented a car hauler – called an automobile hauler – for his company in 1989. 

The first semi-trucks comprised a tractor, which was a modified short-wheeled touring vehicle and a trailer, which was a cart.

The front end of the trailer sat on top of part of the tractor, while the rest of the trailer was on wheels.     

1914 and World War I 

In 1914, August Charles Fruehauf, a blacksmith from Detroit, Michigan, officially called his hauler a semi-trailer.

Fruehauf built a carriage to transport a boat for a customer. 

The boat-hauling semi-trailer was a success, so Fruehauf developed semis to meet other uses, like hauling lumber.

In 1918, he incorporated the Fruehauf Trailer Corporation, which became the Fruehauf Trailer Company in 1963. 

To this day, Fruehauf Trailer Company is a leading manufacturer of semi-trailers.  

In 1915, John C Endebrock designed the trailmobile (aka truck trailer), an iron chassis frame that could be hooked onto a car (a Ford Model T, to be precise) by only one person.

Earlier trailers needed three people to hook one up to a car. 

Semi-trucks became popular during World War I.

The military used these vehicles because they were flexible and speedy – two characteristics that horse-drawn trailers and trains didn’t offer. 

1929 to 1960

In 1929, Freightliner was established.

The company used Fageol trucks as inspiration for their semi-trucks. The tractor was shorter, allowing for the trailer to be longer.   

When it comes to heavy-duty commercial vehicles, Mack Trucks are credited as one of the first innovators.

The company was established in 1900. For 15 years, from 1929, Mack manufactured more than 2,600 semi trucks.

The brand today is known for its durable commercial vehicles. 

George Cassens helped semi-trucks gain even more popularity in the 1930s.

The shipping costs for new cars to their owners were too expensive, so Cassens hauled the vehicles from the manufacturer to the buyers with a four-car auto trailer, which was hitched to a two-ton Dodge truck.

In the 1930s, semi-trucks became even more useful as more and more roads were paved.

And then again in the 1950s and 60s, semis became the cornerstone of the trucking and cargo transportation industry with the development of the Interstate Highway System.

The Present 

Since Winton invented the first semi-trailer, the vehicle has evolved quite a bit.

These days, many semi-trucks are 18-wheelers with three axles. 

In 2019, trucks hauled 11.84 billion tons of cargo and goods in the USA. 

The job growth rate for semi-truck drivers is expected at 6% between 2020 and 2030. 

None of this would be possible without Winton’s invention.  

What’s the Difference Between a Semi and a Truck?

The main difference between a semi-truck and a regular truck (straight truck or box truck) is: 

The semi-truck has a trailer that’s hitched onto the truck or tractor, while the regular truck is one whole vehicle. 

The truck is connected by one chassis, and it’s used to carry freight – mostly large items like furniture or appliances. 

The semi is bigger, and gives truck drivers more versatility and cargo load options.  

What are other names for a semi-truck?

If you live in England or other parts of the United Kingdom, the term articulated lorry is often used for a semi-truck. Lorry is another word for truck, and adding the articulated part shows that it is hauling a trailer.

Kids in the United States and Canada will often call semi-trucks big rigs. This is an informal term but is fun for younger kids as they start to be more aware of different vehicles on the road.

Finally, you can also hear the term 18-wheeler used to call a semi-trailer. This is because they have 18 wheels in total. There are 10 wheels on the truck part and 8 wheels on the trailer.  

Why are tractor-trailers called semi-trucks?

A tractor-trailer is another word for a semi-truck. The word semi comes from the fact that only the back set of wheels is on the trailer. This is to better distribute the load and to have more steering power. A semi-truck’s trailer can not be towed on its own without first attaching it to the truck.

The term is more common for those in North America and is not used as frequently in England.

My Last Thoughts on Semis 

And there you have it. All the names for a semi-truck, why it is called a semi-truck, and the history. 

One thing’s for sure – semi-trucks play an essential role in transporting goods in America and around the world, and it’s all thanks to wonderful inventors.