Call Us: 
Email Us: 
The name semi truck comes from the type of trailer it pulls. The trailer is not built to stand fully on its own. It has wheels at the rear but none at the front, so part of its weight rests on the tractor through a coupling called the fifth wheel. In trucking terms, the trailer is only partially supported by itself, which is where the prefix “semi” comes from.
A full trailer carries its weight on both front and rear axles. A semi-trailer shares its weight with the towing vehicle. When a semi-trailer is disconnected, retractable landing gear supports the front so it does not tip forward. This structural difference is the reason the vehicle combination is called a semi-trailer truck rather than simply a truck with a trailer.
Over time, semi-trailer truck was shortened to semi truck, and eventually just semi, which is now the most common term in North American trucking.
The Two Parts of a Semi Truck
A semi truck works because two separate machines operate as a single unit once connected.
Tractor
The tractor is the powered unit. It contains the engine, transmission, steering axle, and the driver’s cab. Mounted behind the cab is the fifth wheel, a heavy steel plate that locks onto the trailer’s kingpin.
This connection allows the trailer to pivot when the truck turns while keeping the load securely attached. Tractors usually fall into two practical categories:
Day cabs are built for local or regional routes. They have no sleeping space and are lighter and more maneuverable.
Sleeper cabs include a berth behind the driver’s seat so drivers can rest during long-distance hauls.
Semi-Trailer
The semi-trailer carries the freight. It supports its load on rear axles while transferring a portion of that weight onto the tractor through the fifth wheel. That shared weight improves traction and stability when hauling heavy cargo.
When the trailer is detached, landing gear supports the front section until another tractor connects.
Semi trucks also rely on air brake systems rather than hydraulic brakes. The tractor and trailer connect through flexible air lines, and the system automatically engages the brakes if air pressure drops. That fail-safe design is a major safety feature in heavy commercial vehicles.
Where the First Semi Truck Came From
The concept dates back to the early days of the automobile industry. In 1898, inventor Alexander Winton built a vehicle designed to transport cars from his factory to buyers. Driving each new car hundreds of miles to customers created unnecessary wear, so Winton created a trailer system that could carry the vehicles instead.
His invention, often called an automobile hauler, used a powered vehicle to support the front of a trailer that carried another car. By 1899 he began producing these haulers commercially, helping establish the early concept of the semi-truck.
As trucking expanded, the design proved useful for far more than automobiles.
The Trailer Design That Shaped Modern Trucking
In 1914, Detroit blacksmith August Fruehauf built a trailer to transport a boat behind a Ford Model T. He recognized that the trailer shared its weight with the towing vehicle and referred to it as a semi-trailer. That terminology became standard across the trucking industry.
Another key innovation came in 1918 when carriage builder John C. Endebrock introduced the Trailmobile, which simplified the process of connecting and disconnecting trailers. One operator could now handle the job, making tractor-trailer transport far more practical for commercial use.
The fifth wheel itself also evolved during this period. Early designs added a rocking mechanism that allowed trailers to tilt safely on uneven roads. That improvement made heavy freight transport more stable and helped standardize the tractor-trailer combination still used today.
Common Names for a Semi Truck
Several terms describe the same basic vehicle:
Tractor-trailer highlights the two connected components.
18-wheeler refers to a typical configuration with eighteen wheels, though actual setups can vary depending on axles and trailers.
Big rig and rig are informal names widely used by drivers.
Semi is simply the shortened form of semi-truck or semi-trailer truck.
Industry terminology lists these names interchangeably when describing heavy highway freight vehicles.
Semi Truck vs. 18-Wheeler
People often use the terms interchangeably, but they are not identical.
A semi truck refers to any tractor pulling a semi-trailer. An 18-wheeler describes a specific configuration. A typical setup includes:
Two wheels on the steering axle
Eight wheels on the tractor’s drive axles
Eight wheels on the trailer’s axles
Federal highway agencies classify trucks by axle configurations because those layouts affect traffic monitoring, safety regulations, and road wear.
Trailer Types Built for Different Freight
The trailer determines what cargo a semi truck can haul. Over time, the industry developed specialized trailer designs for different types of freight.
Dry vans carry general goods and consumer products.
Refrigerated trailers maintain temperature-controlled environments for food or pharmaceuticals.
Flatbeds transport oversized cargo such as construction materials and machinery.
Lowboy trailers handle tall or heavy equipment.
Tanker trailers move liquids and gases.
Car haulers transport multiple vehicles on stacked platforms.
These designs allow the same tractor to handle many different freight roles depending on the trailer attached.
Why Semi Trucks Matter to the Economy
Semi trucks move the majority of freight across the United States. The trucking industry generated about $906 billion in freight revenue in 2024 and transported roughly 11.27 billion tons of goods, according to the American Trucking Associations’ industry data.
Federal surveys show the scale of the equipment involved. The Bureau of Transportation Statistics estimates that about 2.9 million truck tractors operate in the United States, based on findings from the Vehicle Inventory and Use Survey.
Trucks also dominate cross-border trade. They carry a large share of freight between the United States, Canada, and Mexico, making them essential to North American supply chains. In practical terms, most products people buy have likely spent part of their journey on a semi truck.
Major Semi Truck Manufacturers in the United States
Several manufacturers dominate the heavy-duty truck market in North America.
Freightliner produces a large share of highway tractors used by commercial fleets.
International, built by Navistar, focuses on integrated fleet technology and efficiency.
Kenworth is known for durable long-haul trucks and aerodynamic designs.
Mack Trucks has produced heavy-duty vehicles for more than a century.
Peterbilt is recognized for driver comfort and distinctive styling.
Volvo Trucks North America emphasizes safety technology and engineering innovation.
Western Star builds premium heavy-duty trucks designed for demanding work environments.
Shipping a Car With AmeriFreight Auto Transport
Vehicle shipping relies on specialized tractor-trailer equipment, especially multi-level car hauler trailers designed to transport several vehicles at once.
AmeriFreight Auto Transport coordinates vehicle shipments through a network of vetted carriers. Customer service agents assist with scheduling, pickup coordination, and delivery planning. Optional gap protection plans are available for additional peace of mind during transport. Request a quote now!
Overview of major U.S. manufacturers.
Overview
What is a Semi-Trailer Truck?
A semi-truck, also known as a semi-trailer truck, is a combination vehicle designed for carrying freight.
It consists of two main parts:
Tractor Unit (or Truck): This is the front end of a semi-truck, containing the engine, cab (where the driver sits), and the steering axle. It provides the power to move the entire vehicle. The tractor unit has a fifth-wheel coupling, a horseshoe-shaped device at the rear, which connects to the semi-trailer. Importantly, it can operate independently without a trailer.
Semi-Trailer: This cargo-carrying part attaches to the tractor unit via the fifth wheel. Unlike a full trailer, a semi-trailer only has rear wheels and relies on the tractor for support at the front. It cannot move on its own when detached from its base.
The word "semi" in semi-truck refers to the fact that the trailer is "semi-supported" by the tractor unit, as it lacks a front axle.
Other Names for Semi Truck
Tractor-trailer: This term emphasizes the two main components.
18-wheeler: Refers to the typical number of wheels on a tractor with a single-axle trailer (though configurations can vary).
Big rig: A general term for a large semi-truck.
Semi: A shortened version of semi-truck.
Rig: Another informal term for a semi-truck.
Trailer truck: Highlights the truck pulling a trailer.
Truck and trailer: Similar to the tractor-trailer.
Historical Context of the Name
The term “semi-trailer” emerged in the early 1900s. August Fruehauf is credited with attaching a semi-trailer to a Ford around 1914 to haul boats. The term “semi-trailer truck” came into use to describe the tractor unit pulling a semi-trailer.
Over time, the phrase was shortened to “semi-truck” for simplicity, much like the term “automobile” evolved into “car.” The shorter version has become a catch-all term for a tractor pulling one or more semi-trailers. It is now the most used term in North America and Australia, although “tractor-trailer” remains technically accurate.
Types and Variations of the Semi-Trailers
For Tractor Unit Variations (Sleeper and Day Cabs, Slope-Nosed):
The tractor unit's configuration impacts the operational efficiency and driver comfort. Different semi-trailer designs exist to meet the unique demands of drivers and the types of freight they haul.
Sleeper Cabs
Sleeper cabs are used in long-haul trucking. They are equipped with a sleeping area located behind the driver's seat. They provide a rest space for truck drivers who cover long distances. There are multiple sleeper cab types:
Flat Roof Sleeper: A basic and cost-effective option for shorter hauls requiring overnight stays. It has limited headroom but offers essential sleeping area amenities.
Mid-Roof Sleeper: This variation enhances comfort by providing more headroom and storage space. It is suitable for regional or medium-length routes.
Raised Roof Sleeper: The most spacious design. This offers generous headroom, with additional features such as compact living spaces. It’s commonly used on extended routes where truck drivers spend multiple nights on the road.
Day Cabs
A day cab lacks a sleeping compartment. These tractors are ideal for short-haul work or local deliveries. They offer improved maneuverability and better fuel economy. Since they don't require added weight from living features, they help reduce overall load and fuel consumption.
Slope-Nosed Trucks (Aerodynamic Cabs)
These trucks are designed to cut through the air more efficiently. These slope-nosed or aerodynamic tractor-trailers feature rounded hoods and streamlined cab designs. They are often paired with sleeper or day cab configurations. They are commonly used for pulling heavy loads or semi-trailers across long distances.
For Semi-Trailer Variations:
The type of semi-trailer connected to a tractor determines the kind of cargo it can haul. There’s a wide range of trailer designs built for specific needs:
Flatbeds: Open trailers without sides or roofs. They are perfect for transporting oversized or oddly shaped loads.
Reefer Trailers: Refrigerated units designed to maintain a specific temperature. They are ideal for transporting perishable goods such as food and pharmaceuticals.
Dry Vans: Fully enclosed trailers that shield general freight.
Tanker Trailers: Cylindrical trailers built to move liquids and gases.
Lowboys: Trailers with an extra-low deck height. They are used for hauling tall or heavy equipment.
Car Haulers: Multi-level trailers are explicitly designed to transport multiple vehicles securely.
Dump Trailers: Tilting trailers quickly unload bulk materials, such as sand, gravel, and debris.
Step Deck Trailers: Flatbed trailers with a lower rear deck to accommodate taller loads without exceeding legal height limits.
Extendable Flatbed Trailers: Flatbeds that can stretch in length to carry very long cargo, such as pipes, lumber, or poles.
Conestoga Trailers: Flatbeds equipped with a retractable tarp system, combining weather protection with easy loading access.
Side Kit Trailers: Flatbeds with removable side panels to hold loose materials while offering flexible loading and unloading.
Semi-Truck vs. 18-Wheeler: What’s the Difference?
While people often use "semi-truck" and "18-wheeler" to mean the same thing, they’re not identical. A semi-truck is the general term for a tractor unit attached to one or more semi-trailers, which carry cargo and don’t have front wheels. On the other hand, an 18-wheeler is a common type of semi-truck setup with 18 wheels in total:
Two on the steering axle
Four on the drive axles
12 on the trailer’s axles
All 18-wheelers are semi-trucks. However, not all semi-trucks are classified as 18-wheelers. The main difference is that some may possess a different number of wheels. They can also be designed to tow multiple trailers, such as double or triple configurations.
Semi Truck Manufacturers in the U.S.
Trailers and trucks are used for car shipping. That's why choosing the right truck is necessary for specific transportation purposes. Here are the well-known semi truck manufacturers in the trucking industry:
Freightliner: Holds the largest market share in the U.S. and offers a wide range of models.
International: Manufactured by Navistar. Produces a diverse range of trucks renowned for their advanced technology.
Kenworth: Known for its durability, innovation, and fuel-efficient aerodynamic designs.
Mack Trucks: One of the oldest American brands, known for rugged construction and dependability, especially in vocational applications.
Peterbilt: An iconic American brand known for classic designs, quality, and driver comfort.
Volvo Trucks North America: Although a Swedish company, Volvo has a strong presence in the U.S. It is recognized for its commitment to safety and driver comfort.
Western Star: A premium brand under Daimler Truck North America, specializing in heavy-duty, customizable trucks.
Final Thoughts: Understanding Tractor Trailers
Semi-trucks are the backbone of global freight movement, especially in the United States. These powerful vehicles are essential for efficient logistics. They support numerous industries by reliably and safely delivering goods across vast distances. Understanding their fundamental design highlights their crucial role in modern commerce.
Need to Ship a Car?
AmeriFreight Auto Transport provides auto-transportation services tailored to meet your needs. We are a top-rated company with more than 20 years of experience. We offer various services to ensure you have an option best suited for your vehicle.
Get your free quote now, and partner with us.
Frequently Asked Questions (FAQs)
What is the difference between a semi-truck and a full truck?
A semi-truck consists of a tractor unit and a detachable trailer, while a full truck has a single, rigid frame with the cargo space permanently attached.
What is the proper name for a semi-truck?
The proper name for a semi-truck is a semi-trailer truck or tractor-trailer.
What do you call a semi-truck without a trailer?
A semi-truck without a trailer is referred to as a bobtail.
