On this page
- What Are the Main Parts of a Semi-Truck?
- Is a Semi-Truck the Same as an 18-Wheeler?
- Is a Semi-Truck a Commercial Motor Vehicle?
- What Safety Rules Can Apply to Semi-Trucks?
- Why Can Semi-Truck Accidents Be Complicated?
- What Evidence Can Exist After a Semi-Truck Accident?
- Why Does It Matter After an Accident?
- Frequently Asked Questions About Semi-Trucks
You may hear people call these vehicles semi-trucks, semis, tractor-trailers, big rigs, or 18-wheelers. Those terms are often used to describe the same general type of vehicle, but they do not always mean exactly the same thing.
A semi-truck generally refers to the powered truck, or tractor, that is designed to pull a separate trailer. When the tractor and trailer are connected, they form the large combination vehicle most people picture when they hear "18-wheeler."
Understanding the basic parts of a semi-truck can also help explain why an accident involving one may be more complicated than an ordinary passenger-vehicle crash.
What Are the Main Parts of a Semi-Truck?
A typical semi-truck combination has two major parts: the tractor and the trailer.
The tractor is the powered portion at the front. It contains the engine and the cab where the driver sits. The Federal Motor Carrier Safety Administration (FMCSA) defines a truck tractor as a self-propelled motor vehicle designed and primarily used to pull other vehicles.
The trailer is the separate section being pulled behind the tractor. It normally carries the freight.
This differs from a straight truck, where the power unit and cargo box are not detachable. FMCSA specifically distinguishes straight trucks from commercial vehicles consisting of a truck tractor and detachable trailer.
That means the tractor and trailer can be separated. A tractor may pull one trailer during one trip and a different trailer during another.
Is a Semi-Truck the Same as an 18-Wheeler?
The terms are often used interchangeably in everyday conversation, but there is a small difference in what they describe.
Semi-truck commonly refers to the tractor or the tractor-trailer combination.
18-wheeler refers to a common tractor-trailer configuration that has 18 wheel positions.
Tractor-trailer describes how the vehicle is built: a powered tractor pulling a detachable trailer.
Big rig is an informal term commonly used for large commercial trucks.
Not every commercial truck is a semi-truck or 18-wheeler. Box trucks, delivery vehicles, buses, and other large vehicles can qualify as commercial motor vehicles without having the traditional tractor-trailer design.
Is a Semi-Truck a Commercial Motor Vehicle?
Many semi-trucks qualify as commercial motor vehicles, or CMVs, under federal law.
For interstate commerce, FMCSA's definition includes vehicles meeting certain weight, passenger, or hazardous-material criteria. For example, a vehicle used on a highway in interstate commerce to transport property or passengers can fall within the federal CMV definition when it has a gross vehicle weight rating or gross combination weight rating of 10,001 pounds or more. Other parts of the definition address passenger vehicles and transportation of hazardous materials requiring placarding.
Whether a particular federal rule applies can depend on the truck, cargo, weight, type of operation, and whether the transportation is interstate or intrastate.
That is why it is important not to assume every truck on the road is governed by exactly the same regulations.
What Safety Rules Can Apply to Semi-Trucks?
Commercial trucking can be subject to federal safety requirements covering drivers, vehicles, working hours, inspections, maintenance, and other parts of the operation.
For example, FMCSA's general hours-of-service rules for covered property-carrying drivers provide an 11-hour driving limit after 10 consecutive hours off duty. Covered drivers generally cannot drive beyond the 14th consecutive hour after coming on duty following the required 10 hours off. The regulations also contain a 30-minute break requirement after eight cumulative hours of driving without a qualifying interruption. Exceptions and special provisions can apply.
Vehicle condition is another important area. FMCSA requires motor carriers subject to the rule to systematically inspect, repair, and maintain commercial motor vehicles under their control. Parts and accessories must be kept in safe and proper operating condition.
The existence of these regulations does not mean that every semi-truck accident involves a violation. The records and circumstances of the particular trip have to be examined.
Why Can Semi-Truck Accidents Be Complicated?
A typical car accident might primarily involve two drivers and their insurance companies.
A semi-truck accident can involve additional people and businesses.
Depending on the circumstances, an investigation may need to determine who:
- Drove the tractor
- Employed or contracted with the driver
- Operated the motor carrier
- Owned the tractor
- Owned or leased the trailer
- Maintained the equipment
- Loaded or secured the cargo
- Dispatched the driver
These roles do not automatically make every person or company legally responsible for an accident. Instead, identifying them helps investigators understand how the trucking operation worked and where relevant evidence may exist.
What Evidence Can Exist After a Semi-Truck Accident?
Commercial trucking operations can create records that would not normally exist after an accident between two personal vehicles.
Depending on the truck and operation, potentially relevant information may include:
- Driver qualification records
- Hours-of-service information
- Electronic logging device records
- Dispatch communications
- GPS or telematics information
- Inspection records
- Repair and maintenance records
- Cargo or shipping documents
- Dash-camera footage
- Electronic vehicle information
- Insurance documents
Some records may help show where the truck traveled, how long a driver had been working, how the vehicle was maintained, or which businesses were involved.
But a record should not be treated as proof of fault without understanding what it actually shows.
Why Does It Matter After an Accident?
Knowing that a vehicle was a semi-truck rather than simply describing it as a "big truck" can help identify what evidence should be investigated and which people or companies may have relevant information.
For example, the tractor and trailer may not necessarily have the same owner. The driver may work for one business while hauling cargo for another. A separate company may have performed maintenance or loaded the trailer.
Those relationships can make preserving records particularly important after a serious collision.
At our firm handles truck and 18-wheeler accident cases in Louisiana. When we investigate a commercial truck collision, we can examine the driver, vehicle, companies involved, available records, and other evidence rather than assuming what happened simply because a semi-truck was involved. The firm's published information confirms that it represents clients throughout Louisiana and handles serious 18-wheeler accident matters.
Frequently Asked Questions About Semi-Trucks
Is a semi-truck the same thing as a tractor-trailer?
The terms are commonly used interchangeably. More specifically, the tractor is the powered vehicle that pulls the detachable trailer, while "tractor-trailer" describes the combined vehicle.
Are all semi-trucks 18-wheelers?
Not necessarily. "18-wheeler" describes a common wheel configuration. Commercial tractor-trailer combinations can have different configurations, including combinations involving more than one trailer. FMCSA, for example, separately identifies single, double, and triple trailer configurations.
Are semi-truck drivers required to follow hours-of-service rules?
Many commercial property-carrying drivers are subject to federal hours-of-service regulations, including driving and duty-time limits. However, exceptions and different rules can apply depending on the driver and operation, so the circumstances must be examined individually. Can more than one company be involved in a semi-truck accident?
Yes. A trucking operation can involve a driver, motor carrier, tractor owner, trailer owner, maintenance provider, cargo company, or other businesses. Their involvement alone does not establish liability. The evidence must show what role each party had and whether that role is legally relevant.
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.
