Home truck accident definitions

Truck Accident Definitions

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ABS (Antilock Braking System)

Computer, sensors and solenoid valves which together monitor wheel speed and modulate braking force if wheel lockup is sensed during braking.

Air Ride Suspension

Suspension which supports the load on air-filled rubber bags rather than steel springs. Compressed air is supplied by the same engine-driven air compressor and reservoir tanks which provide air to the air brake system.

ATC (Automatic Traction Control)

Feature based on ABS that prevents spinning of the drive wheels under power on slippery surfaces by braking individual wheels and/or reducing engine throttle.

AVI (Automatic Vehicle Identification)

System combining an on-board transponder with roadside receivers to automate identification of vehicles.

AVL (Automated Vehicle Location)

Helps locate vehicles for fleet management purposes and for stolen vehicle recovery. Infrastructure can be land-based radio towers or satellites.


Structural component to which wheels, brakes and suspension are attached.

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Bill of Lading

Itemized list of goods contained in a shipment.

Blind Spot

Areas around a tractor trailer that are not visible to the driver either through the windshield, side windows or mirrors.


Tractor operating without a trailer.


Assembly of two or more axles, usually a pair in tandem.

Brake Horsepower

Engine horsepower rating as determined by brake dynamometer testing.

Bridge Formula

A bridge protection formula used by federal and state governments to regulate the amount of weight that can be put on each of a vehicle’s axles, and how far apart the axles (or groups of axles) must be to legally carry a given weight.


Sleeper portion of the tractor.

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Truck or tractor design in which the cab sits over the engine on the chassis.

Cargo Weight

Combined weight of all loads, gear and supplies on a vehicle.

CB (Citizens Band Radio)

Two-way radio for which no license is required by the Federal Communications Commission (FCC).

CDL (Commercial Driver’s License)

License which authorizes an individual to operate commercial motor vehicles and buses over 26,000 pounds gross vehicle weight.

Chassis Weight (Curb Weight, Tare Weight)

Weight of the empty truck, without occupants or load.

Common Carrier

Freight transportation company which serves the general public.

Container (Shipping Container)

Standard-sized rectangular box used to transport freight by ship, rail and highway.

Contract Carrier

Company that transports freight under contract with one or a limited number of shippers.

Converter Dolly

Auxiliary axle assembly equipped with a fifth wheel (coupling device), towed by a semi-trailer and supporting the front of, and towing, another semi-trailer.

Cube (Cubic Capacity)

Interior volume of a truck body, semi-trailer or trailer, measured in cubic feet.

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Operating a truck without cargo.

Demountable Rim

Multi-piece steel wheel rim assembly which is bolted to a spoke hub.

Disc Wheel

Single-piece rim/wheel assembly of stamped and welded steel or forged aluminum, anchored by 8 or 10 nuts to a hub.


All the components which together transmit power from the transmission to the drive axle(s).


All the components, excluding engine, which transmit the engine’s power to the rear wheels: clutch, transmission, driveline and drive axle(s).

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EDI (Electronic Data Interchange)

The business-to-business interconnection of computers for the rapid exchange of a wide variety of documents, from bills of lading to build tickets at auto plants.

Exempt Carrier

Company which transports commodities exempted from Interstate Commerce Commission (ICC) economic regulation.

EV (Electric Vehicle)

Vehicle powered by electric motor(s) rather than by an internal combustion engine. Most common source of electricity is chemical storage batteries.

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Fifth Wheel

Coupling device attached to a tractor or dolly which supports the front of a semi-trailer and locks it to the tractor or dolly.

Fixed Tandem

Assembly of two axles and suspension that is attached to the chassis in one place, and cannot be moved fore and aft.

For-Hire Carrier

Company in the business of transporting freight belonging to others.

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GAWR (Gross Axle Weight Rating)

Maximum weight an axle is rated to carry by the manufacturer. Includes both the weight of the axle and the portion of a vehicle’s weight carried by the axle.

GCW (Gross Combination Weight)

Total weight of a loaded combination vehicle, such as a tractor-semi-trailer or truck and full trailer(s).

Geared Speed

Calculated vehicle speed at the engine’s governed rpm in each transmission gear, or (commonly) in top gear.

Gear Ratio

Number, usually expressed as a decimal fraction, representing how many turns of the input shaft cause exactly one revolution of the output shaft.


Steepness of a grade, expressed as a percentage.


Vehicle’s ability to climb a grade at a given speed.

GVW (Gross Vehicle Weight)

Total weight of a vehicle and everything aboard, including its load.

GVWR (Gross Vehicle Weight Rating)

Total weight a vehicle is rated to carry by the manufacturer, including its own weight and the weight of its load.

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Hazardous materials, as classified by the U.S. Environmental Protection Agency (EPA).

Headache Rack

Heavy protective barrier mounted behind the tractor’s cab.

Horsepower (hp)

Measure of power (the amount of work that can be done over a given amount of time). One horsepower is defined as 33,000 foot-pounds of work in one minute.


U.S. Department of Transportation safety regulations which govern the hours of service of commercial vehicle drivers engaged in interstate trucking operations.

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To place the trailer at a very sharp angle to the tractor.

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Kingpin (axle)

Pin around which a steer axle’s wheels pivot.

Kingpin (trailer)

Anchor pin at the center of a semi-trailer’s upper coupler which is captured by the locking jaws of a tractor’s fifth wheel to attach the tractor to the semi-trailer.

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LCV (Long Combination Vehicle)

In general, vehicles longer than a standard doubles rig (tractor and two 28-foot semi-trailers).


Company or individual which leases vehicles.


Company which leases vehicles.

Lift Axle

Extra, unpowered axle needed only when the vehicle is loaded, allowing it to meet federal and state vehicle weight standards. The lift axle is mounted to an air spring suspension that raises the axle when it is not required.


Book carried by truck drivers in which they record their hours of service and duty status for each 24-hour period. Requirement of the Federal Motor Carrier Safety Regulations.


Open flat-bed trailer with a deck height very low to the ground, used to haul construction equipment or bulky or heavy loads.

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Gearing in which less than one revolution of a transmission’s input shaft causes one turn of the output shaft.


Trucker who owns and operates his own truck(s).

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Pickup and delivery.


Weight of the cargo being hauled.


Semi-trailer built with reinforcements to withstand transport by a railroad flatcar.

Powertrain (Drivetrain)

All the components, including engine, which transmit the engine’s power to the rear wheels: clutch, transmission, driveline and drive axle(s).

Private Carrier

Business which operates trucks primarily for the purpose of transporting its own products and raw materials.

PSI (Pounds Per Square Inch)

Unit of measurement for tire air pressure, air brake system pressure and turbocharger boost.

PTO (Power Takeoff)

Device used to transmit engine power to auxiliary equipment. A PTO often drives a hydraulic pump, which can power a dump body, concrete mixer or refuse packer.

Pull Trailer

Short, full trailer with an extended tongue.

Pup Trailer

Short semi-trailer, usually between 26 and 32 feet long, with a single axle.

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Relay (Relay Driving)

One driver takes a truck for 8 to 10 hours, then turns the truck over to another driver.


Refrigerated trailer with insulated walls and a self-powered refrigeration unit. Most commonly used for transporting food.


Device used to assist brakes in slowing the vehicle. The most common type of retarder on over-the-road trucks manipulates the engine’s valves to create engine drag. (This type is commonly referred to as “Jake Brake.”

RPM (Revolutions Per Minute)

Measure of the speed at which a shaft spins.

Runaway Truck Ramp

Emergency area adjacent to a steep downgrade that a heavy truck can steer into after losing braking power.

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Truck trailer supported at the rear by its own wheels and at the front by a fifth wheel mounted to a tractor or dolly.

Setback Axle

Front steering axle moved rearward from the generally accepted standard position.

Shipping Weight

Dry weight of a truck including all standard equipment, but excluding fuel and coolant.


Sleeping compartment mounted behind a truck cab.

Sliding Fifth Wheel

Fifth wheel mounted to a mechanism that allows it to be moved back and forth for the purpose of adjusting the distribution of weight on the tractor’s axles.

Sliding Tandem (Slider)

Mechanism that allows a tandem axle suspension to be moved back and forth at the rear of a semitrailer, for the purpose of adjusting the distribution of weight between the axles and fifth wheel.


Top speed a vehicle can attain as determined by engine power, engine governed speed, gross weight, driveline efficiency, air resistance, grade and load.

Synchronized Transmission

Transmission with built-in mechanisms to automatically equalize the speed of its gears to allow smooth shifting without the need to double-clutch.

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Tandem Axle

Pair of axles and associated suspension usually located close together.


Team of two drivers who alternative driving and resting.


Truck designed primarily to pull a semi-trailer by means of a fifth wheel mounted over the rear axle(s).

Tractor Trailer

Tractor and semi-trailer combination.

Trip Leasing

Leasing a company’s vehicle to another transportation provider for a single trip.

Trip Recorder

Cab-mounted device which electronically or mechanically records data such as truck speed, engine rpm, idle time and other information useful to trucking management.

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VIN (Vehicle Identification Number)

Assigned by the manufacturer, this number is unique to each vehicle and appears on the vehicle’s registration and title.

VMRS (Vehicle Maintenance Reporting Standards)

Set of codes developed to facilitate computerized tracking of parts and labor used in equipment repair.

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Walking Beam Suspension

Type of truck and tractor rear suspension consisting of two beams, one at each side of the chassis, which pivot in the center and connect at the front to one axle of a tandem and at the rear to the other axle.

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Yard Jockey

Person who operates a yard tractor.

Yard Tractor

Special tractor used to move trailers around a terminal, warehouse, distribution center.

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