But what exactly makes a truck an “18-wheeler”?
The term generally refers to a tractor-trailer combination with 18 wheels. The front portion, called the tractor, provides the power. The trailer is attached behind it and carries the cargo.
Understanding those basic parts can also be useful after a serious truck accident because the tractor, trailer, driver, and cargo may involve different companies and different types of evidence.
What Are the Main Parts of an 18-Wheeler?
An 18-wheeler generally has two major sections: the tractor and the trailer.
The tractor is the front section containing the engine and driver’s cab. Federal vehicle definitions describe a truck tractor as a truck designed primarily to pull other motor vehicles rather than carry its own cargo load.
The trailer is the section behind the tractor that carries cargo. Many common tractor-trailer combinations have five axles and 18 wheel positions, which is where the familiar name “18-wheeler” comes from.
You may also hear people use terms such as semi-truck, semi, big rig, tractor-trailer, and 18-wheeler when discussing these vehicles. The terms can overlap in everyday conversation, although technical definitions can differ depending on the vehicle configuration.
Is Every Commercial Truck an 18-Wheeler?
No.
Commercial motor vehicles come in many different forms. Delivery trucks, box trucks, buses, work trucks, and other vehicles may qualify as commercial motor vehicles without being 18-wheelers.
The Federal Motor Carrier Safety Administration, or FMCSA, uses specific criteria to determine when vehicles operating in interstate commerce qualify as commercial motor vehicles under federal regulations. Those criteria can involve the vehicle’s weight, passenger capacity, or transportation of certain hazardous materials.
That distinction matters because different vehicles and operations may be subject to different requirements.
Are 18-Wheelers Subject to Special Safety Rules?
Many interstate commercial trucking operations are subject to federal safety regulations administered by the Federal Motor Carrier Safety Administration.
Those regulations can address subjects such as driver qualifications, vehicle inspection and maintenance, records of duty status, and how long certain commercial drivers may drive.
For example, property-carrying drivers subject to FMCSA’s general hours-of-service rules may drive a maximum of 11 hours after 10 consecutive hours off duty and generally may not drive beyond the 14th consecutive hour after coming on duty. Exceptions can apply.
These rules are designed to regulate commercial operations, but the existence of a rule does not mean every truck accident involves a violation.
Why Does It Matter After an Accident?
An accident involving an 18-wheeler can create evidence and legal questions that may not exist after an ordinary two-car collision.
For example, an investigation may need to determine:
- Who employed or contracted with the driver
- Who operated the motor carrier
- Who owned the tractor
- Who owned the trailer
- Who maintained the equipment
- Who loaded or controlled the cargo
- What commercial records exist
Depending on the truck and operation, relevant evidence may include driver records, electronic logging information, dispatch communications, maintenance records, inspection documents, cargo records, electronic vehicle data, and insurance policies.
The presence of an 18-wheeler does not automatically mean the truck driver or trucking company caused an accident. The evidence still has to establish what happened and whether another party may be legally responsible.
At Jacqueline A. Scott & Associates, we investigate truck and 18-wheeler accidents by looking beyond the size of the vehicle and examining the people, businesses, records, and other evidence connected to the collision.
Frequently Asked Questions
Why is it called an 18-wheeler?
The name comes from a common tractor-trailer configuration with 18 wheel positions. Other large commercial trucks can have different axle and wheel configurations.
Is an 18-wheeler the same as a semi-truck?
The terms are often used interchangeably in everyday conversation. “18-wheeler” usually describes the complete tractor-trailer combination, while “semi-truck” is commonly used for the tractor or combination. Our next educational article explains the tractor-trailer terminology in more detail.
Are all 18-wheelers regulated by the FMCSA?
Not necessarily. Whether particular federal motor-carrier regulations apply depends on factors such as the vehicle, operation, cargo, and whether the transportation involves interstate commerce. FMCSA defines interstate and intrastate operations differently.
This article is general information about Louisiana law and is not legal advice. Laws and deadlines can change, and every case depends on its own facts. Past results do not guarantee or predict future outcomes. Reading this page or contacting the firm does not by itself create an attorney-client relationship.
