TWNA Glossary - Trucking Terms
[A] [B] [C] [D]
[E] [F] [G] [H]
[I] [J] [K] [L]
[O] [P] [R] [S]
[T] [U] [V] [W]
- A -
- 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. Helps the driver retain control of the vehicle during heavy
braking on slippery roads.
- AFV (Alternative Fueled Vehicle)
- Vehicle powered by a fuel other than gasoline or diesel.
- 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
- ATC (Automatic Traction Control)
- Usually an optional feature based on ABS, it prevents spinning
of the drive wheels under power on slippery surfaces by braking
individual wheels and/or reducing engine throttle. Also called ASR,
an acronym sometimes loosely translated from the German as anti-spin
- ATV (All Terrain Vehicle)
- Vehicle designed for any type of terrain.
- AVI (Automatic Vehicle Identification)
- System combining an on-board transponder with roadside receivers
to automate identification of vehicles. Uses include electronic
toll collection and stolen vehicle detection. (see IVHS)
- AVL (Automated Vehicle Location)
- Class of technologies designed to locate vehicles for fleet management
purposes and for stolen vehicle recovery. Infrastructure can be
land-based radio towers or satellites. (see IVHS)
- Structural component to which wheels, brakes and suspension are
- Drive axles are those with powered wheels.
- Front axle is usually called the steer axle.
- Pusher axles are unpowered and go ahead of drive axles.
- Rear axles may be drive, tag or pusher types.
- Tag axles are unpowered and go behind drive axles.
- B -
- Distance from a truck's front bumper to the back of its cab.
- Bill of Lading
- Itemized list of goods contained in a shipment.
- Blind Spot
- Areas around a commercial vehicle that are not visible to the
driver either through the windshield, side windows or mirrors.
- Tractor operating without a trailer. Also refers to straight truck.
- Bogie (also spelled bogey)
- Assembly of two or more axles, usually a pair in tandem.
- Brake Horsepower (bhp)
- 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.
- See Sleeper.
- C -
- Cabover (Cab-Over-Engine, COE)
- 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.
- Cartage Company
- Company that provides local (within a town, city or municipality)
pick-up and delivery.
- Cast Spoke Wheel
- Wheel with five or six spokes originating from a center hub. The
spoked portion, usually made of cast steel, is bolted to a multiple-piece
steel rim (see Demountable Rim; Disc Wheel).
- CB (Citizens Band Radio)
- Two-way radio for which no license is required by the Federal
Communications Commission (FCC). Long beyond its heyday in the '70s,
CB is still used by truckers and motorists for everything from traffic
condition reports to emergency calls to idle chatter.
- CDL (Commercial Driver's License)
- License which authorizes an individual to operate commercial motor
vehicles and buses over 26,000 pounds gross vehicle weight. For
operators of freight-hauling trucks, the maximum size which may
be driven without a CDL is Class 6 (maximum 26,000 pounds gross
- CE (CF, LP)
- Distance from back of a truck's cab to the end of its frame.
- CG (Center of Gravity)
- Weight center or balance point of an object, such as a truck body.
Calculated to help determine optimum placement of truck bodies on
- Chassis Weight (Curb Weight, Tare Weight)
- Weight of the empty truck, without occupants or load.
- Compressed natural gas.
- See Cabover.
- COFC (Container On Flat Car)
- Method of moving shipping containers which involves transporting
them on railroad flat cars.
- Common Carrier
- Freight transportation company which serves the general public.
May be regular route service (over designated highways on a regular
basis) or irregular route (between various points on an unscheduled
- Compensated Intracorporate Hauling
- Freight transportation service provided by one company for a sister
- Container (Shipping Container)
- Standard-sized rectangular box used to transport freight by ship,
rail and highway. International shipping containers are 20 or 40
feet long, conform to International Standards Organization (ISO)
standards and are designed to fit in ships' holds. Containers are
transported on public roads atop a container chassis towed by a
tractor. Domestic containers, up to 53 feet long and of lighter
construction, are designed for rail and highway use only.
- Container Chassis
- Single-purpose semitrailer designed to carry a shipping container.
- Contract Carrier
- Company that transports freight under contract with one or a limited
number of shippers.
- Converter Dolly (Dolly)
- Auxiliary axle assembly equipped with a fifth wheel (coupling
device), towed by a semitrailer and supporting the front of, and
towing, another semitrailer.
- Cube (Cubic Capacity)
- Interior volume of a truck body, semitrailer or trailer, measured
in cubic feet.
- Curb Weight
- See Chassis Weight.
- D -
- Operating a truck without cargo.
- Demountable Rim
- Multi-piece steel wheel rim assembly which is bolted to a spoke
hub. Demountable rims are still in use, though they have been replaced
in many applications by the simpler disc wheel. (see Cast Spoke
- Disc Wheel
- Single-piece rim/wheel assembly of stamped and welded steel or
forged aluminum, anchored by 8 or 10 nuts to a hub. A "Budd
wheel" is a ten-hole, stud-piloted disc wheel; a design originated
by the Budd Corporation.
- Displacement (Piston Displacement)
- Sum of the volumes swept by an engine's pistons as they travel
up and down in their cylinders. Based upon bore (diameter of cylinder)
and stroke (distance traveled by piston). Expressed in liters or
- See Converter Dolly.
- Doubles (Twins, Twin Trailers)
- Combination of a tractor and two semitrailers connected in tandem
by a converter dolly. (see Converter Dolly;
- All the components which together transmit power from the transmission
to the drive axle(s). These consist of at least one driveshaft (propeller
shaft) with a universal joint at each end.
- Drivetrain (Powertrain)
- All the components, excluding engine, which transmit the engine's
power to the rear wheels: clutch, transmission, driveline and drive
axle(s). (See Powertrain)
- DRL (Daytime Running Lights)
- System that automatically turns on a vehicle's low beam headlights
when the parking brake is released and the ignition is on.
- E -
- 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.
- Escape Ramp
- See Runaway Truck Ramp.
- 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
- F -
- Fifth Wheel
- Coupling device attached to a tractor or dolly which supports
the front of a semitrailer and locks it to the tractor or dolly.
The fifth wheel's center is designed to accept a trailer's kingpin,
around which the trailer and tractor or dolly pivot in turns.
- Fixed Tandem
- Assembly of two axles and suspension that is attached to the chassis
in one place, and cannot be moved fore and aft. (see Sliding
- For-Hire Carrier
- Company in the business of transporting freight belonging to others
(see Private Carrier).
- G -
- 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-semitrailer
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. Applies to transmissions, power takeoffs, power
dividers and rear axles. Example: If 2.5 revolutions of an input
shaft cause one revolution of the output shaft, the gear ratio is
- Steepness of a grade, expressed as a percentage. Example: A vehicle
climbing a 5% grade rises 5 feet for every 100 feet of forward travel.
- Vehicle's ability to climb a grade at a given speed. Example:
A truck with a gradeability of 5% at 60 mph can maintain 60 mph
on a grade with a rise of 5%.
- GVW (Gross Vehicle Weight)
- Total weight of a vehicle and everything aboard, including its
- 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.
- H -
- Hazardous materials, as classified by the U.S. Environmental Protection
Agency (EPA). Transport of hazardous materials is strictly regulated
by the U.S. Department of Transportation.
- Headache Rack
- Heavy protective barrier mounted behind the tractor's cab. Designed
to prevent "headaches" caused by load shifting forward
from the trailer and crushing the 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. Example: Lifting 33,000 pounds one foot in
one minute, or lifting 3300 pounds ten feet in one minute.
- Horsepower, Gross Laboratory
- Tested horsepower of a "bare" engine without fan, water
pump, alternator, exhaust system or any other accessories.
- Horsepower, SAE Net
- Horsepower capability of an engine with full accessories and exhaust
system. Test procedures per standards of Society of Automotive Engineers
- U.S. Department of Transportation safety regulations which govern
the hours of service of commercial vehicle drivers engaged in interstate
- I -
- Independent Trucker
- See Owner Operator.
- ITS (Intelligent Transportation Systems)
- See IVHS.
- IVHS (Intelligent Vehicle Highway Systems)
- Blanket term for a wide array of technologies, including electronic
sensors, computer hardware and software and radio communications.
The purpose of IVHS is to increase efficiency of use of existing
highways, reducing travel time, fuel consumption, air pollution
and accidents. There are five functional areas:
- Advanced Public Transportation Systems (APTS)
- Advance Traffic Management Systems (ATMS)
- Advance Traveler Information Systems (ATIS)
- Advanced Vehicle Control Systems (AVCS)
- Commercial Vehicle Operations (CVO)
A more recently coined term, Intelligent Transportation Systems
(ITS), encompasses both IVHS and modes of transportation other
than highway, such as rail. (see AVI, AVL, WIM)
- J -
- To place the trailer at a very sharp angle to the tractor.
- Jake Brake
- See Retarder.
- JIT (Just-In-Time)
- Manufacturing system which depends on frequent, small deliveries
of parts and supplies to keep on-site inventory to a minimum.
- K -
- Kingpin (axle)
- Pin around which a steer axle's wheels pivot.
- Kingpin (trailer)
- Anchor pin at the center of a semitrailer's upper coupler which
is captured by the locking jaws of a tractor's fifth wheel to attach
the tractor to the semitrailer.
- L -
- Landing Gear
- Retracting legs which support the front of a semitrailer when
it is not coupled to a tractor.
- LCV (Long Combination Vehicle)
- In general, vehicles longer than a standard doubles rig (tractor
and two 28-foot semitrailers). Examples of LCVs which are permitted
in some U.S. western states and eastern toll roads: Twin 48-foot
trailers; triple 28-foot 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.
- Liquid propane gas.
- Load Range (Tires)
- Letter code system for the weight carrying capacity of tires.
Comparable ply ratings are shown below.
LR PR LR PR A
.... 2 E .... 10 B .... 4 F .... 12 C .... 6 G .... 14 D ....
8 H .... 16 (LR = Load Range PR = Ply Rating)
- Book carried by truck drivers in which they record their hours
of service and duty status for each 24-hour period. Required in
interstate commercial trucking by the U.S. Department of Transportation.
- Open flat-bed trailer with a deck height very low to the ground,
used to haul construction equipment or bulky or heavy loads.
- LTL (Less-Than-Truckload)
- A quantity of freight less than that required for the application
of a truckload (TL) rate; usually less than 10,000 pounds. (see
- LTL Carrier
- Trucking company which consolidates less-than-truckload cargo
for multiple destinations on one vehicle. (see TL
- O -
- On-Board Computer
- See Trip Recorder.
- Gearing in which less than one revolution of a transmission's
input shaft causes one turn of the output shaft. The purpose of
overdrive is to reduce engine rpm in high gear for better fuel economy.
Example: A transmission with an overdrive top gear has a ratio of
0.70 to one. Turning the input shaft 0.7 revolutions causes 1.0
revolution of the output shaft.
- Trucker who owns and operates his own truck(s).
- P -
- Pickup and delivery.
- Weight of the cargo being hauled.
- Peddle Run
- Truck route with frequent delivery stops.
- Cable used to transmit electrical power from the tractor to the
trailer. So named because it is coiled like a pig's tail.
- Semitrailer built with reinforcements to withstand transport by
a railroad flatcar. (see TOFC)
- Pintle Hook
- Coupling device used in double trailer, triple trailer and truck-trailer
combinations. It has a curved, fixed towing horn and an upper latch
that opens to accept the drawbar eye of a trailer or dolly.
- Piston Displacement
- See Displacement.
- Ply Rating (PR)
- Relative measure of tire casing strength. (see Load Range)
- See Drivetrain.
- Private Carrier
- Business which operates trucks primarily for the purpose of transporting
its own products and raw materials. The principle business activity
of a private carrier is not transportation. (see For-Hire Carrier)
- PSI (Pounds Per Square Inch)
- In trucking, 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. Some designs mount to a standard
opening on the transmission, while others attach at the front or
rear of the engine.
- Pull Trailer
- Short, full trailer (supported by axles front and rear) with an
- Pup Trailer
- Short semitrailer, usually between 26 and 32 feet long, with a
- Pusher Axle
- See Axle.
- R -
- Relay (Relay Driving)
- Common practice in the less-than-truckload industry, in which
one driver takes a truck for 8 to 10 hours, then turns the truck
over to another driver, pony express style.
- 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" because the predominant manufacturer
is Jacobs Vehicle Equipment Co.) Other types of retarders include
exhaust retarders, transmission-mounted hydraulic retarders and
axle-mounted electromagnetic retarders.
- RFG (Reformulated Gasoline)
- Gasoline blended with pollution reducing additives.
- Semitrailer specially designed to travel both on highway and on
rails. Manufactured by Wabash Corp.
- Rolling Radius
- Tire dimension from center of the axle to the ground; measured
with tire loaded to rated capacity. Used in calculating geared speed.
- RPM (Revolutions Per Minute)
- Measure of the speed at which a shaft spins. Most often used to
describe engine crankshaft speed. Indicated by a tachometer.
- Runaway Truck Ramp
- Emergency area adjacent to a steep downgrade that a heavy truck
can steer into after losing braking power. Usually two or three
lanes wide and several hundred feet long, the ramp is a soft, gravel-filled
pathway which absorbs the truck's forward momentum, bringing it
to a safe stop. Depending on the surrounding terrain, the ramp may
be level or run up or down hill.
- S -
- 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. Advantages: Shorter turning radius and more of
a vehicle's weight shifted to front axle.
- Shipping Weight
- "Dry" weight of a truck including all standard equipment,
but excluding fuel and coolant.
- Single-Source Leasing
- Service in which companies can lease drivers and trucks from the
same source, rather than having to procure them from different companies.
- Sleeping compartment mounted behind a truck cab, sometimes attached
to the cab or even designed to be an integral part of it.
- Sleeper Team
- See Team.
- 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. Also provides the capability to vary
vehicle combination lengths.
- 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.
- Spoke Wheel
- See Cast Spoke Wheel.
- Spread Axle (Spread Tandem)
- Tandem axle assembly spaced further apart than the standard spacing
of 54 inches. The U.S. federal bridge formula favors trailer axles
with an eight or nine foot spread by allowing higher weight than
on tandems with standard spacing.
- Straight Truck
- See Truck.
- Sport/utility vehicle.
- Synchronized Transmission
- Transmission with built-in mechanisms to automatically "equalize"
the speed of its gears to allow smooth shifting without the need
- T -
- Tag Axle
- See Axle.
- Tare Weight
- See Chassis Weight.
- Tandem Axle (Tandems)
- Pair of axles and associated suspension usually located close
together. (see Spread Axle)
- Team (Driver Team)
- Team of two drivers who alternative driving and resting.
- TEU (Twenty-Foot Equivalent Unit)
- Standardized unit for measuring container capacity on ships, railcars,
- TL (Truckload)
- The quantity of freight required to fill a trailer; usually more
than 10,000 pounds. (see LTL)
- TL Carrier
- Trucking company which dedicates trailers to a single shipper's
cargo, as opposed to an LTL (Less Than Truckload) carrier which
transports the consolidated cargo of several shippers and makes
multiple deliveries. (see LTL Carrier)
- TOFC (Trailer On Flatcar)
- Method of moving cargo which involves transporting semitrailers
on railroad flat cars. (see Piggyback)
- Truck designed primarily to pull a semitrailer by means of a fifth
wheel mounted over the rear axle(s). Sometimes called a truck tractor
or highway tractor to differentiate from it from a farm tractor.
- Tractor Trailer
- Tractor and semitrailer combination.
- Truck, tractor or trailer with three axles grouped together at
the rear. (see Tridem)
- Group of three axles on a truck, tractor or trailer. Tridems are
most common on European semitrailers.
- Trip Leasing
- Leasing a company's vehicle to another transportation provider
for a single trip.
- Trip Recorder (On-Board Computer)
- Cab-mounted device which electronically or mechanically records
data such as truck speed, engine rpm, idle time and other information
useful to trucking management.
- Vehicle which carries cargo in a body mounted to its chassis,
rather than on a trailer towed by the vehicle.
- Twins (Twin Trailers)
- See Doubles.
- U -
- Ultra-low emissions vehicle.
- Upper Coupler
- Load bearing surface on the underside of the front of a semitrailer.
It rests on the fifth wheel of a tractor or dolly and has a downward-protruding
kingpin which is captured by the locking jaws of the fifth wheel.
- V -
- 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. Established and maintained
by the American Trucking Associations.
- W -
- 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
- WIM (Weigh-In-Motion)
- Technology for determining a vehicle's weight without requiring
it to come to a complete stop.
- Y -
- Yard Jockey
- Person who operates a yard tractor.
- Yard Tractor (Yard Mule)
- Special tractor used to move trailers around a terminal, warehouse,
distribution center, etc.