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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. Helps the driver retain control of the vehicle during heavy braking on slippery roads.
Air Control System, Suspension
An arrangement of valves and tubing connected to the trailer air system which is designed to regulate the ride height (or mounting height) of an air suspension.
Air Leveling Valve
See Valve, Air Leveling
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.
Anti-lock
See Brake, Anti-lock
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 regulation.
Auto Transporter
See Trailer, Auto Transporter
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.
Axle
Structural component to which wheels, brakes and suspension are attached. • 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.
Axle Spindle
The machine steel journal or shaft (usually heat treated and hardened) at each end of an axle which is contoured to accept wheel bearings and seals and around which the wheels rotate.
Axle, Air Lift
A single air operated axle which when lowered will convert a vehicle into a multi-axle unit and provide the vehicle with a greater load carrying capacity.
Axle, Camber
The controlled convexity of a trailer axle designed to compensate for deflection of the axle under load, to compensate for the curvature or crown of certain roads and to minimize tire wear thereby.
Axle, Drop
An axle in which the centerline of the beam portion is lower than the centerline of the spindles.
Axle, Flip or Removable
A frame and axle which can be rigidly pinned or pivoted at the rear of a trailer or an axle assembly that can be flipped up and onto the rear of the trailer to which it is attached.
Axle, Multi
A grouping of axles along the length of a trailer designed to distribute the load over as large an area of road surface as possible.
Axle, Single
One axle mounted independently of any other axle.
Axle, Spread Tandem
A two-axle assembly in which the axles are separated beyond the spacing of a normal tandem assembly in order to qualify for maximum axle loads allowed by regulations.
Axle, Tandem
A two-axle assembly having a means of distributing or transferring weight between the two axles.
Axle, Tri (Tridem)
A three-axle assembly having a means of distributing or transferring weight between the three axles.
Axle, Trunnion
A short axle pivoted at or near its mid-point about a horizontal axis transverse to its own centerline. Normally used in pairs in conjunction with a walking beam in order to achieve two axis of oscillation.
See Trailer, B-Train
Bar Spreader
A transverse rigid member attached at intervals between the side walls of a trailer, commonly employed on open top van trailers to stabilize the upper rails.
BBC
Distance from a truck’s front bumper to the back of its cab.
Beam, Main
A main structural member of a lowbed, platform or chassis trailer, usually one of a pair.
Beam, Meat Rail Support
A transverse load carrying member installed between the upper side walls of refrigerated van trailers and containers to which meat rails are attached.
Beaver Tail
The rearmost section of a trailer sloped downward to facilitate loading and unloading from the rear.
Bill of Lading
Itemized list of goods contained in a shipment.
Binder, Load
A mechanical device, consisting of a lever-operated toggle and lock, generally used to tighten a cargo securing system. Winches are sometimes used as load binders.
Blind Spot
Areas around a commercial vehicle that are not visible to the driver either through the windshield, side windows, or mirror.
Bobtail
Tractor operating without a trailer.
Bogie (also spelled bogey)
Assembly of two or more axles, usually a pair in tandem. See Undercarriage.
Bolster, Container Chassis
Transverse structure with locks on each end for securing a container to the chassis. Also provides vertical load support for a container.
Booster
A mechanism which attaches additional axles to the rear of a trailer. The trailer to booster connection may rely on mechanical, air (or other gas), or hydraulic means to provide load transfer.
Box, Connection
Contains fittings for trailer emergency and service brake connections and electrical connector to which the lines from the towing vehicle may be connected.
Brake Caliper Assembly, Disc
The nonrotational components of a disc brake, including its actuating mechanism and pads which generate friction forces on the disc.
Brake Chamber
A mechanical device mounted near either end of an axle, adjacent to the wheel, which receives pressurized air from a valve and exerts force through the slack adjuster and camshaft to the foundation brake.
Brake Control, Load Proportioning
A system or device which regulates the input force to the brakes on an axle in proportion to the load on that axle.
Brake Drum
The cylindrical rotational member of a drum-brake assembly attached to the wheel and acted upon by the brake shoe and lining assemblies.
Brake Dust Shield
See Dust Shield, Brake
Brake Hop
See Wheel Hop
Brake Horsepower (bhp)
Engine horsepower rating as determined by brake dynamometer testing. See Horsepower.
Brake Hose
A flexible tube (usually rubber or coiled synthetic) used to conduct pressurized air in and air brake system (may pertain also to conduit for other fluids).
Brake Hose Coupler
See Gladhand
Brake Line, Trailer Control (Service)
The conduit or tube which transmits the brake actuating signal from the tractor to the trailer air brake valve (this line is normally not pressurized).
Brake Line, Trailer Supply (Emergency)
The conduit or tube which carries air from the tractor compressor through the trailer brake valve to the reservoir(s) (this line is normally pressurized).
Brake Lines, Trailer Air
The system of conduit or tubes carrying compressed air from the gladhands to the trailer brake system. There are two separate lines: supply (emergency) and control (service).
Brake Rotor, Disc
The flat, circular rotational member of a disc brake assembly which is attached to the spoke wheel, or hub, and is acted upon by the caliper and friction pads assembly.
Brake Slack Adjuster
See Slack Adjuster
Brake Spider
That portion of the foundation brake which is anchored to either end of the axle bar, variously bolted or welded.
Brake System, Air
A type of brake system which uses compressed air to transmit operator signals and to provide the motive force required for actuation.
Brake System, Emergency
A wheel brake system used for stopping a vehicle in the event of a malfunction in the operation and/or control of the service brake system.
Brake System, FMVSS 121
A trailer air brake system composed of, but not limited to, drums or disks, foundation brakes, brake lining, slack adjusters, brake chambers, air tanks, air lines, gladhands, appropriate pneumatic fittings and parking brake system, an air supply control valve, protective devices, and the mechanically actuated part of the brake chamber.
Brake, Anti-lock
Device, which, when incorporated into a conventional service brake system, automatically controls the degree of rotational wheel slip at one or more wheels of an undercarriage during braking.
Brake, Parking
A mechanism designed to prevent the movement of a stationary motor vehicle.
Brake, Service
The primary system or mechanism designed to retard or stop a motor vehicle.
Brake, Spring
A mechanism (usually integral with or attaché directly to a service brake chamber) which employs the stored energy of a coil spring to actuate the foundation brake.
Brakes, Disc
A type of wheel brake in which the brake linings or pads are squeezed against either side of a flat, circular disc by means of a caliper-type clamp assembly.
Brakes, Drum
The cylindrical rotation member of a drum-brake assembly attached to the spoke wheel or hub and acted upon by the brake shoe and lining assemblies.
Brakes, Foundation
The non-rotational components of a brake, including the actuating mechanism for development of retarding forces.
Brakes, Wedge
A type of wheel brake in which the brake shoe and lining assemblies are spread apart by forcing a wedge between opposing ends of the assemblies pushing them outward against the brake drum.
Bridge
On a double drop lowbed or drop frame trailer, that portion of the structure beginning with the rear drop and extending to the rear end.
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.
Bridge Weight Formula, Federal
The Federal standard specifying the relationship between axle (or groups of axles) spacing the gross weight those axles may carry, expressed by the formula: • W = 500 (LN/N-1 + 12N + 36) • W = Overall gross weight on any group of two or more consecutive axles • L = Distance in feet between the extreme of any group of two or more consecutive axles • N = Number of axles in group under consideration
Bulkhead
A structure (fixed or removable) installed across a trailer’s width to compartmentalize a trailer and/or to protect against damage caused by shifting cargo.
Bull Boards
Wooden boards installed across the width of a van trailer or container generally stacked one on the other in slots located on either side of the rear door opening used to protect doors from shifting cargo.
Bull Nose
A type of trailer front end construction in which the front corners are beveled (usually 45° in order to provide additional swing clearance on trailers with longer than normal kingpin locations (for example, 56-inch swing radius with a 48-inch kingpin location).
Bumper
A structure designed to provide rear end protection.
Bunk
See Sleeper.
Cabover (Cab-Over-Engine, COE) Truck or tractor design in which the cab sits over the engine on the chassis.
Caging, Spring Brake
To compress the parking/emergency brake spring by trapping it between its pressure plate and the spring brake housing using air pressure or manually by tightening the release bolt until heavy resistance occurs.
Capacity, Cubic
Usable internal load-carrying space as related to van trailers, bulk trailers, tank trailers, containers, etc. (usually express in cubic feet and sometimes referred to as “cube”).
Capacity, Rated Trailer
The rated trailer capacity does not indicate trailer payload capability, but rather the total of the payload and the vehicle weight. The assignment of the rated capacity value is the responsibility of the trailer manufacturer taking into account all factors relating to the intended usage including (but not limited to) payload and its location and distribution, method of loading and unloading, safety factor, operating environment, handling characteristics, center of gravity, etc.
Capacity, Towing
See Towing Capacity
Cargo Control Post
See Post, Cargo Control
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 vehicle weight).
Certification Label
See Label, Certification
Chain, Safety (Safety Cable)
A back-up device consisting of chains or cables between the towing and towed vehicles used to prevent separation of the vehicles in the event of malfunction or loss of the primary towing connection.
Chain, Spreader
A chain connected at intervals between the side walls of a trailer to prevent their being pushed out by the cargo.
Chassis
The structural framework comprising the load carrying elements on all trailers other than those of monocoque construction.
Chassis Weight (Curb Weight, Tare Weight)
Weight of the empty truck, without occupants or load.
Chock
See Wheel Chock
Clearance, Road
Distance between a trailer component and the road surface.
Clearance, Support
See Support Clearance
Clearance, Swing
The minimum distance between a trailer and its power unit or tractor while turning.
COE
See Cabover.
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 basis).
Compensated Intracorporate Hauling
Freight transportation service provided by one company for a sister company.
Connection Box
See Box, Connection
Connector, Electrical, Female
That component part of a trailer electrical system usually attached to the front of a trailer and designed to accept the male electrical connector on the tractor jumper cable. Female connectors are also located on the rear of trailers used in doubles and triples operations and at various locations on oilfield and lowbed trailers.
Connector, Electrical, Male
That component part of a tractor or converter dolly electrical system attached to an electrical jumper cable and designed to plug into a mating female connector on a trailer.
Construction, Beam
A frame-type trailer consisting of two mainbeams, with short crossmembers between, designed to transport mobile equipment of various types by supporting its undercarriage at points between the wheel or track assemblies.
Construction, Full Frame
See Chassis
Construction, Monocoque
That type of structural design employed in frameless van trailers, tanks, and other trailers such in which the trailer body or shell is the principal load carrying element.
Construction, Perimeter Frame
A type of chassis design in which the two main load carrying members are spread apart so that they constitute the side frames of the trailer.
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.
Controller Logic, Anti-lock
That part of an electro-mechanical anti-lock system which receives and processes electrical signals from the wheel sensors and in turn transmits electrical controlling signals to the anti-lock air valve.
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.
Coupler Assembly, Rocking Upper
An upper coupler plate and pin structure pivoted about an axis parallel to the longitudinal axis of the trailer.
Coupler Assembly, Upper
The structural element at the front of a trailer, including the kingpin, which receives and transfers the load from the forward portion of the trailer’s load carrying elements to the tractor fifth wheel.
Coupler Height
The nominal design dimension from the ground, or road surface, to the bottom of the upper coupler plate with the trailer unladen.
Coupler Pickup Plate, Upper
See Plate, Pickup
Coupler TOFC Plate, Upper
See TOFC Plate
Coupler, Air Hose Dummy
Metal fittings, usually attached to the rear of a tractor or to a converter dolly, and used to store the loose ends of air brake hoses when not in use. They also provide an effective seal preventing the entry of contaminates into the gladhand openings.
Coupler, Plate, Upper (Upper Fifth Wheel Plate)
The flat plate on the underside of the upper coupler through which the kingpin protrudes and which rests directly on the tractor fifth wheel.
Crossmember
A transverse member in a trailer chassis or underframe.
Crossmember Spacing
Distance between crossmember centers.
Crossmember, Rear
The transverse member at the extreme rear of a trailer to which the bumper is normally mounted and on which the stop, tail, and turn lights are often installed.
Cube (Cubic Capacity)
Interior volume of a truck body, semitrailer or trailer, measured in cubic feet.
Cubic Capacity (Cube)
See Capacity, Cubic
Curb Weight
See Chassis Weight.
Curbside
That side of a trailer nearest the curb when the trailer is traveling in a normal forward direction. Opposite to “roadside” and “driver side.”
System that automatically turns on a vehicle’s low beam headlights when the parking brake is released and the ignition is on.
Dead-Heading
Operating a truck without cargo.
Deck
The load carrying area on a platform, lowbed, or chassis-type trailer.
Deck, Drop Side
That portion of the loading deck on a lowbed or drop deck trailer which falls outside the main frames and which is several inches lower than the top of the main frames.
Decking, Double
A removable secondary floor with supporting members, located between the permanent flooring and the roof to permit separate loading compartments when full height stacking is not desired.
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 Wheel.
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 cubic inches.
Dolly
See Converter Dolly.
Dolly Load Divider
A short frame-type trailer complete with upper coupler, fifth wheel, and undercarriage assembly and designed in such a manner that when coupled to a semitrailer and tractor it carries a portion of the trailer kingpin load while transferring the remainder to the tractor fifth wheel.
Dolly, Converter
An auxiliary undercarriage assembly consisting of a chassis, fifth wheel, and towbar used to convert a semitrailer to a full trailer.
Dolly, Permanent
An undercarriage assembly with a permanently attached turntable and a towbar and which, in aggregate, comprises the forward axle(s) of a full trailer.
Door Header
The transverse structural member comprising the top of a door opening.
Door Hinge
The movable joint or device by which a door is articulated.
Door Hold Back
A device used to temporarily hold doors in the open position along the sides of a trailer.
Door Lock
A device used to secure doors in their closed position by means of mating parts on the door and the trailer door frame. Most door locks are designed to accept a seal or padlock for security purposes.
Door Sill
A transverse frame member at the bottom of a door opening.
Door, Roll-Up (sometimes referred to as “Overhead Door”)
An assembly of counterbalanced, hinged panels mounted in tracks on either side of the door opening designed to allow the door to be raised or lowered to control access to the loading area.
Door, Swinging
A door panel articulated by means of hinges along one vertical side.
Doors (Rear or Side)
Panels provided on the sides or at the rear of a trailer or container and articulated in any of several ways to allow access to the cargo area when opened.
Doors (Rear or Side)
Panels provided on the sides or at the rear of a trailer or container and articulated in any of several ways to allow access to the cargo area when opened.
Doors, Vent
Small doors used to provide and/or control air circulation.
Doubles
A trailer combination consisting of a truck tractor, semitrailer, and a full trailer coupled together (also called double trailer or double bottom).
Doubles (Twins, Twin Trailers)
Combination of a tractor and two semitrailers connected in tandem by a converter dolly. See Converter Dolly; Pintle Hook.
Doubles, Rocky Mountain
A trailer combination consisting of a truck tractor, a standard length semitrailer, and a shorter full trailer coupled together.
Doubles, Turnpike
A trailer combination consisting of a truck tractor, a standard length semitrailer, and a standard length full trailer coupled together.
Drain Gutter
A trough across the front and/or rear of an insulated trailer floor used to accumulate and drain liquids from the interior of the trailer.
Drain, Kazoo
A self-opening and closing rubber bladder used for the collection and drainage of liquids from drain gutters or troughs in insulated trailers.
Driveline
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.
Duct-Six Fingers
An assembly consisting of six flexible passages, usually of different length and suspended from the ceiling, which is used to distribute air from a trailer refrigeration system.
Duct-Straight Chute
A single passage suspended from the ceiling and used for the distribution of air from a trailer refrigeration system.
Ductboards
Loose over-the-floor sections which permit air circulation or drainage beneath the cargo.
Ducts
Passageways installed within a trailer or incorporated into the linings, floor, or insulated envelope for the purpose of transmitting air or other gases.
Dust Shield, Brake
A non-rotating plastic or metal cover bolted to the brake spider on either end of an axle, to restrict the entry of foreign material into the brake drum.
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.
Plastic or metal shields or deflectors fixed to the trailer above the wheel assemblies principally to control spray thrown from the rotating tires.
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 tract or dolly pivots in turns.
Fifth Wheel Pickup Ramp
See Ramp, Fifty Wheel Pickup
Fifth Wheel Spacer
A type of adapter or spacer designed to incorporate a kingpin and plate on the bottom and a rigid fifth wheel on top. Used to lower the effective upper coupler height of a gooseneck in some lowbed applications designed to operate normally in connection with a load divider dolly or “jeep.”
Fifth Wheel, Full Oscillating
A fifth wheel assembly whose trunnion mechanism allows freedom of movement about both the transverse and longitudinal axis.
Fifth Wheel, Sliding
An assembly designed to incorporate a manual adjusting and locking feature which allows the fifth wheel to be moved or relocated forward or backward. Most commonly used on truck tractors to affect changes in weight distribution and/or overall combination length.
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 Tandem.
Floor
The cargo-carrying surface (also called the “deck).
Floor Loading Height
The unladen height of a trailer floor above the ground measured at the rear of the trailer.
Floor Loading Height
The unladen height of a trailer floor above the ground measured at the rear of the trailer.
Floor System
A floor system consisting of three principal structural elements: (1) the loading deck material; (2) the crossmembers to which the deck material is connected; and (3) the fastening system at either end of the crossmembers.
Floor System Load Rating
See Rating, Floor System Load
Floor, Composite
Flooring consisting of alternate narrow metal sections (generally “hat-shaped”) and wood floorboards.
Floor, Laminated
A floor consisting of trailer-length boards manufactured by bonding small pieces of wood together.
Floor, Shiplap
A floor consisting of shiplap boards, the term “shiplap” referring to the practice of alternately offsetting or rabbeting opposing edges of a board so that when joined to others of its kind, adjacent boards “lap” one another.
Floor, Tongue & Groove
A floor consisting of tongue and groove boards, the term “tongue & groove” referring to the practice of alternately placing a tongue and a groove on opposing edges of a board so that when joined to others of its kind, the tongue on one board engages the groove on the adjacent board.
For-Hire Carrier
Company in the business of transporting freight belonging to others. See Private Carrier.
Frame Beam
See Construction, Beam
Frame Trailer, Extendable (Extendable Flatbed)
A frame or flatbed whose length may be readily increased or decreased within prescribed limits and with prescribed variations in load carrying capability.
FRP
An acronym taken from the words “Fiberglass Reinforced Plastics.” The term as used to describe the composite panels utilized in truck trailer construction should be written FRP/Plywood, FRP/Honeycomb, FRP/Road, etc., to properly describe the core construction.
A chain gate with a canvas or plastic curtain attached.
Gate, Chain
A movable barrier, composed of horizontal and vertical straight link steel chains, usually installed across the rear door openings of van trailers with or without conventional doors.
Gate, Lift
A powered platform, usually installed at the rear of a trailer, used to load and unload cargo.
Gate, Scissors
A scissor-action folding metal gate usually used across the rear door openings of van trailers with or without conventional doors.
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).
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 2.5:1.
Geared Speed
Calculated vehicle speed at the engine’s governed rpm in each transmission gear, or (commonly) in top gear.
Gladhand
A paired mechanical joining device used to connect flexible air brake hoses to one another or to portions of trailers or towing vehicles.
Gladhands, Polarized
A variation in gladhand design incorporating a feature which prevents the crossing or improper connection of supply or control lines.
Gooseneck
On a drop frame trailer, that portion of the trailer which extends upward and forward from the front of the loading deck to, and including, the upper coupler and front crossmember.
Gooseneck, Folding
A gooseneck which is articulated in such a manner that it may be extended flat upon the ground upon being disconnected from the tractor. The motive force required to operate such goosenecks is usually obtained through the use of the tractor winch line or hydraulic cylinders.
Gooseneck, Full Width
A gooseneck the same width as the trailer deck.
Gooseneck, Removable
A gooseneck which can be separated from the trailer and reconnected, usually through the use of large hooks or removable pins. The motive force required to remove such goosenecks is usually obtained through the use of the tractor winch line or hydraulic cylinders.
Gooseneck, Stinger
A variation of the conventional gooseneck, not normally used on trailers designed to be pulled by truck tractors.
Grade
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.
Gradeability
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%.
Gross Axle Weight Rating
See Weight Rating, Gross Axle
Gross Combination Weight Rating
See Weight Rating, Gross Combination
Gross Vehicle Weight Rating
See Weight Rating, Gross Vehicle
Gross Weight
See Weight, Gross
Guide, Container Chassis
Structure at the nose of a container chassis which guides the container into place and may retain the container from forward movement (also called “horn”).
Gutter, Drain
See Drain Gutter
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.
The response or controllability of the vehicle to driver steering and braking inputs experienced in normal highway maneuvers.
Hat Box
See Fifth Wheel Spacer
Hazmat
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.
Headerboards
Wooden boards installed across the width of a trailer, generally stacked one on top of the other in slots located in either front corner of a van trailer or container.
Height, Floor Loading
See Floor Loading Height
Height, Inside
The unobstructed inside loading height measured from the floor to the lowest point of roof construction.
Height, Overall
The nominal design dimension from the ground to the highest point on the trailer, based on a specified coupler height, with the trailer unladen.
Hitch
A connecting device at the rear of a vehicle used to pull a full trailer with provision for easy coupling and uncoupling. See Tow Bar, Pintle Hook.
Holder, Certificate
A moisture proof container provided for storage and easy access to trailer related literature such as licenses, registration, defect and maintenance information (also called Registration Holder and Defect Card Holder).
Hook, Pintle
A kind of hitch, normally employing a vertical horn or hook, sized to accept a lunette eye, and equipped with a safety latch. See Hitch.
Horsepower
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 (SAE).
Hose, Brake
See Brake Hose
Hours-of-Service
U.S. Department of Transportation safety regulations which govern the hours of service of commercial vehicle drivers engaged in interstate trucking operations.
Ice Hatch and Ice Hatch Door An opening and its cover located in or near the front corners of an insulated van or truck body through which ice is loaded.
Ice Pan
That portion of the floor designed to accept and store ice in front of an insulated van.
Independent Trucker
See Owner Operator.
Insulation
Any of several materials, or classes of materials, used in the construction of trailers and containers whose function it is to control the transfer of heat in or out of the vehicle.
ITS (Intelligent Transportation Systems)
Formerly called 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.
A device, variously designed, to provide temporary support to the front or rear of a parked vehicle and used to prevent nosediving and taildiving when loading and unloading.
Jackknife
A condition existing in a truck or truck tractor trailer(s) combination when the longitudinal axis of the combination moves from a relatively straight line to one having one or more exaggerated angles on the orders of 90&#t176; kingpin or pintle connections. Usually occurs in connection with loss of traction while operating over-the-road or when maneuvering or backing in close quarters.
Jake Brake
See Retarder.
Jeep
See Dolly, Load Divider
Just-In-Time
Manufacturing system which depends on frequent, small deliveries of parts and supplies to keep on-site inventory to a minimum.
An especially machined stub shaft which extends vertically from the lower surface of an upper coupler assembly and which locks into a fifth wheel.
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.
Kingpin Plate
See Coupler Plate, Upper
Kingpin, Removable
A special adaptation of the standard kingpin shape which allows it to be readily removed and relocated to other positions or settings in the upper coupler assembly. Screw-in and drop-in types are commonly used.
Label, Certification – (National Highway Traffic Safety Administration) A label or plate permanently affixed to the forward left side of a trailer providing specific information required by law relating to that vehicle.
Lamp
A lamp is a light emitting device permanently attached to the vehicle and energized by the tractor electrical system.
Lamp, Combination Stop & Tail
A single red lamp having to separately energized filaments which fulfills the requirements of both a stop lamp and tail lamps.
Lamp, License Plate
A clear lamp or lamps used to illuminate the license plate on the rear of a vehicle.
Lamps, Clearance
Lamps mounted on the front and rear of a vehicle which show to the front or to the rear of a vehicle permanently mounted as near as practically possible to the left and right extreme edges to indicate the overall width (amber to the front, red to the rear).
Lamps, Identification
Red lamps deployed horizontally in a group of three, spaced within specified limits, and used on the rear of trailers usually located as high as possible on the longitudinal centerline.
Lamps, Side Marker
Lamps which show to the side of a vehicle, permanently mounted as near as practicably possible to the front and rear edges to indicate the overall length, and also midway along the side on vehicles 30 feet long and over (amber on front and midway along the side, red on the rear).
Lamps, Stop
Red lamps spaced as far apart as practicable on the rear of a vehicle and designed to operate upon application of the service brakes with greater brightness than tail lamps.
Lamps, Tail
Red lamps spaced as far apart as practicable on the rear of a vehicle and designed to operate when tractor headlamps are illuminated.
Lamps, Turn Signal
Lamps spaced as far apart as practicable on the rear of a vehicle and designed to operate intermittently upon activation of a hand control mounted on the tractor.
Landing Gear
Retracting legs which support the front of a semitrailer when it is not coupled to a tractor. See Supports.
Landing Gear Clearance
See Support Clearance
Landing Gear Cross Shaft
The transverse shaft connecting the gear mechanism of the landing gear legs.
Landing Gear Extended Length
The maximum length which each leg is designed to extend to provide maximum upper coupler elevation.
Landing Gear Foot Member
A device attached either directly or indirectly to each lower leg to serve as ground contact support for the trailer.
Landing Gear Location
See Support Location
Landing Gear Retracted Length
The minimum collapsed length which each leg is designed to retract to provide the maximum clearance between the bottom of the foot member and the road surface.
Landing Gear Sandshoe
A pivoted flat plate attached to the bottom of each leg which affords increased bearing surface on the ground (a type of foot member).
Landing Gear Stiff Leg
A variation in leg design employing non-powered telescoping tubes adjusted by means of mating holes and a through shear pin.
Landing Gear Travel
The distance which the lower leg is designed to travel from a fully retracted position to a fully extended position.
Landing Gear Wheels
Dual wheels attached to the bottom of each lower leg providing ground contact for the supports (a type of foot member).
Ledge Loading
A projection or slot on the back or sides of a lowbed trailer which is used to temporarily attach loading ramps.
Length, Inside
The unobstructed inside loading length measured at the floor of a van trailer or container.
Length, Outside Trailer
The length measured from the front vertical plane of the foremost transverse load carrying structure to the rear vertical plans of the rearmost transverse load carrying structure, including door hardware.
Lessee
Company or individual which leases vehicles.
Lessor
Company which leases vehicles.
Life 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.
Lift Gate
See Gate, Lift
Lift Pads
See Pads, Lift
Lift Shoe
A lift shoe is the device used by lifting equipment which contacts and transmits the lifting forces to the trailer through the trailer lift pads.
Lifting Equipment
The term “Lifting Equipment” refers to straddle carriers, traveling and fixed gantry cranes, counter-balanced lift trucks, derricks, and similar types of equipment used in transporting trailers from one place to another by lifting.
Lights, Running
Marker, clearance, tail, and identification lights as required by regulations.
Load Binder
See Binder, Load
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)
Logbook
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.
Logbook
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.
Long Combination Vehicle
In general, vehicles longer than a standard double 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.
Lowboy
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 TL.
LTL Carrier
Trucking company which consolidates less-than-truckload cargo for multiple destinations on one vehicle. See TL Carrier.
Lunette Eye
A steel eye mounted on the drawbar of a trailer or dolly designed to couple with a pulling vehicle having a pintle hook.
The tipping down at the front end of an uncoupled trailer resting on its supports while being loaded or unloaded.
An acronym taken from the words “Original Equipment Manufacturer.”
On-Board Computer
See Trip Recorder.
Outrigger
Structural load-carrying members attached to and extending outward from the main longitudinal frame members of a trailer. See Side Bracket.
Over-the-Road Service
The transportation of goods by vehicles designed and manufactured for use over improved highways and city streets which are maintained in good condition, and in terminal yard or parking areas which are maintained in relatively hard and smooth condition.
Overdrive
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.
Owner-Operator
Trucker who owns and operates his own truck(s).
A lift pad is a structural reinforcement attached to the lower rails of a van trailer or container and intended to prevent localized mechanical damage to the vehicle when engaged by lifting equipment.
Panel
Material used to cover the interior and exterior surfaces of a trailer.
Payload
The net weight of the cargo carried by a vehicle.
Peddle Run
Truck route with frequent delivery stops.
Piggyback
Semitrailer built with reinforcements to withstand transport by a railroad flatcar. See TOFC.
Pigtail
Cable used to transmit electrical power from the tractor to the trailer. So named because it is coiled like a pig’s tail.
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. See Hook, Pintle.
Piston Displacement
See Displacement.
Planks, Widening
Planks used in connection with side brackets or extensions to temporarily widen the deck on a drop frame or lowbed trailer.
Plate, Pickup
That portion of the upper coupler plate forward of the kingpin which initially encounters the fifth wheel and guides it toward the kingpin.
Plate, TOFC
See TOFC Plate
Ply Rating (PR)
Relative measure of tire casing strength. See Load Range.
Pockets, Stake
Rectangular openings or enclosures installed at intervals around the perimeter of platform trailers to accept removable stakes and/or stake sides.
Pogo Stick
A flexible, vertical springwound tube installed on a truck tractor frame behind the cab providing an elevated support for longer than normal tractor air hoses and electrical cable.
Pole or Rope Ridge
A rigid member or rope installed down the centerline or an open top van trailer to lend support to the tarpaulin and provide good damage.
Post
A vertical structural member utilized in the construction of van trailers and containers to which panels, side sheets and, in some instances, doors are attached.
Post, Cargo Control
A specialized variation wherein a steel post is provided with one or two rows of punched slots along the length of the post designed to accept various cargo control fittings.
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. 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 extended tongue.
Pup Trailer
Short semitrailer, usually between 26 and 32 feet long, with a single axle.
Pusher Axle
See Axle.
Removable wood or metal wall sections (usually slatted) held in place on flatbeds normally by stake pockets.
Rail, Rub
An exterior protector bar or strip extending horizontally along the sides (on some types of trailers across the front and rear) and intended to provide scuff protection for the trailer. On some van trailers there may be more than one row extending horizontally along either side.
Rails, Lower Side (Chassis Rails)
The main longitudinal frame members on vans and containers used to connect the side wall and floor structures. Lower rails comprise the principal tensile structural elements used in frameless (monocoque) construction.
Rails, Meat
Supports suspended longitudinally beneath the ceiling of an insulated van or container of which meat is hung for transport by means of hooks or other devices.
Rails, Upper Side (Roof Rails)
The main longitudinal frame members on vans and containers used to connect the roof and the side wall structures. Upper rails comprise the principal compressive structural elements used in frameless (monocoque) construction.
Ramp, Fifth Wheel Pickup
A sloping structure permanently attached behind the fifth wheel on a truck tractor and intended to lift and guide the upper coupler assembly of a trailer being coupled.
Ramp, Flip
A ramp hinged in such a manner that it may be folded aboard the trailer when not in use (usually installed on the rear of lowbed or drop frame trailers).
Ramp, Motor Grader
A ramp attached to either side of a lowbed gooseneck designed to support the front wheels of a motor grader being carried.
Ramps
Articulated or removable bridge-type structures used to load or unload lowbed or drop frame trailers.
Rating, Floor System Load
A load rating for trailer or container floors expressed in terms of the maximum gross load which may be imposed by a fork truck front axle having specific wheel “prints” or load areas.
Rating, Gross Axle Weight
See Weight Rating, Gross Axle
Rating, Gross Vehicle Weight
See Weight Rating, Gross Vehicle
Reefer
Refrigerated trailer with insulated walls and a self-powered refrigeration unit. Most commonly used for transporting food. See Trailer, Refrigerated.
Reflector, Reflex
Device used on vehicles to give a warning indication to the driver of an approaching vehicle by means of incident light reflected from the headlights of the approaching vehicle.
Refrigeration Unit
A mechanical device designed to be mounted on a refrigerated trailer or container for the purpose of cooling the cargo area.
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.
Remak
The remanufacture of a trailer utilizing certain components salvaged from existing vehicles as provided for in Title 49 Code of Federal Regulations Part 571.7(f).
Reservoir, Air
A container or tank used to store compressed air.
Retarder
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.
Ridge Pole
See Pole, Ridge
Ridge Strap
See Strap, Ridge
Rim
A metal ring uniquely designed and manufactured to receive a pneumatic tire (or tire-tube assembly) and transfer its operational loads to a wheel assembly or disc.
Ring, Bull (“D” Ring)
A heavy articulated fitting installed at or near floor level and used as a cargo tie-off. On lowbeds, commonly installed at intervals along the side frames.
Ring, Lashing
A device permanently attached to a trailer underframe and designed to accept tiedown equipment.
Ring, Tie
A particular kind of cargo tie-off consisting of an articulated ring, usually installed in a recessed pocket in the sides or floor.
Riser
Vertical mounting brackets or struts employed in some types of running gears to transfer suspension loads to the trailer sub-frame.
RO/RO
An acronym taken from the words “Roll-On/Roll-Off” and used to describe a particular type of trailer-on-ship operation.
RoadRailer
Semitrailer specially designed to travel both on highway and on rails. Manufactured by Wabash Corp.
Roadside
The side of the trailer farthest from the curb when traveling in a normal forward direction. Opposite to “curbside” (sometimes called “driver side”).
Rolling Radius
Tire dimension from center of the axle to the ground; measured with tire loaded to rated capacity. Used in calculating geared speed.
Rolling Tail Pipe
A full width cylindrical member located at the rear of the bed of a platform or drop frame trailer and level with or projecting slightly above the floor. Its purpose is to facilitate the loading of cargo such as skid mounted equipment through use of a cable passing over the rolling tail pipe so that the tail pipe may rotate and facilitate loading by reducing friction and scuffing by either the cable or the cargo. See TTMA RP No. 64.
Roof Bow
A transverse member in the roof of a van trailer or container which is connected at either end to the roof rails (upper rails) and which supports the roof sheet.
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.
Running Gear
See Undercarriage
See Landing Gear Sandshoe
Seal, Oil
A device used to retain liquid lubricant in the bearing area of a wheel or hub assembly. The seal normally rotates with the wheel and “wipes” a mating stationary part on the spindle inboard of the inside bearing.
Semitrailer
Truck trailer supported at the rear by its own wheels and at the front by a fifth wheel mounted to a tractor or dolly. See Trailer, Semi.
Sensor, Wheel
That part of an electro-mechanical anti-lock system installed in the hub of a wheel, which generates and transmits to the logic controller an electric current proportional in strength to the rotational speed of the wheel.
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.
Shut-Off Cock
A type of valve used to control or stop the flow of air in a line.
Sideboards
Removable boards used in conjunction with swinging or pivoted side brackets to increase the effective width of the loading deck on lowbed or drop deck trailers.
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.
Skylight
A panel of clear or translucent material installed in the roof, nose, or sides of van-type trailers to admit light to the cargo area.
Slack adjuster
An adjustable mechanical lever fixed to the brake camshaft on one end, to the brake chamber push rod on the other, and designed to transmit brake chamber energy to the camshaft.
Sleeper
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.
Slider
See Undercarriage, Sliding
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.
Sockets, Pipe
Short sections of pipe installed at intervals usually along the top of trailer or sides to receive tarp bows or spreaders. Sometimes used on flatbeds in lieu of stake pockets.
Spacer, Rim
A device used in connection with spoke wheel assemblies to produce the desired dual tire spacing with demountable rims.
Span
See Wheelbase
Speedability
Top speed a vehicle can attain as determined by engine power, engine governed speed, gross weight, driveline efficiency, air resistance, grade, and load.
Spider, Brake
See Brake Spider
Splash Guard (Mudflaps)
A flexible plastic or rubber deflecting shield installed behind running gear tires to control spray.
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.
Spring Deflection
The reduction in effective suspension spring height brought about by imposed load.
Spring Set (Axle Seat)
A suspension component affixed to a trailer axle and used to position and support a suspension spring.
Spring, Air (Air Bag)
A flexible pneumatic cushion pressurized by trailer system air and regulated by leveling valves to provide the desired performance in an air suspension.
Stake pockets
See Pockets, Stake
Stanchion, Free Standing
A trailer support which accommodates the trailer’s kingpin, but is not locked or rigidly attached to the transporter.
Stanchion, Locking
A trailer support that locks the trailer kingpin and is rigidly attached to the transporter’s deck.
Stinger Steered Vehicle Combination
A truck tractor or truck towbar semitrailer combination where the towbar connection is located just to the rear and below the top of the rear tires of the towing vehicle.
Strap, Ridge
See Rope Ridge
Stretch, Over-the-Road Van
The lengthening of a van trailer from its original manufactured overall length to a longer specified overall length.
Stretch, TOFC Van
The lengthening of a previously certified TOFC van trailer which is in structurally sound operating condition.
Strip, Scuff
Material installed inside van trailers and containers to minimize mechanical damage from within to lower side walls and nose.
Structure, Permanent Front End
See Bulkhead
Support Clearance
The distance between the rearmost interference point of a truck tractor or dolly and the trailer landing gear or its supporting structure during any decree of turning or maneuvering of the tractor.
Support Location
The distance from front of the trailer to the vertical centerline of the landing gear legs.
Supports
Structure generally adjustable in height, used to support the front end of a semitrailer in an approximately level attitude when disconnected from towing vehicle. Includes landing gear legs, foot members, mounting brackets, braces, and related fasteners. See Landing Gear.
Suspension
Any one of several types of articulated mechanical assemblies used to position and secure axle and wheel assemblies to a trailer frame or sub-frame.
Suspension Mounting Height
The vertical distance from, and perpendicular to, the horizontal centerline of the axle(s) in a suspension to the horizontal line representing the lower surface of the suspension sub-frame. Normally taken with the suspension in the unladen condition.
Suspension Setting
The distance from the rear extreme of the trailer (or dolly) to the vertical centerline of the axle, if single axle, or to the vertical centerline of the axle arrangement when two or more axles are employed in the suspension.
Suspension Subframe
A structural assembly, usually employed in frameless (monocoque) construction, to which the suspension and axle assemblies are attached.
Suspension, Air Ride
A suspension employing flexible pneumatic cushioning devices, or air springs, which are pressurized by tractor air and regulated by height control valves or variable pressure regulators.
Suspension, Four Spring (3-Point Suspension)
A two-axle suspension equipped with elliptical (or plate type) springs wherein the springs on one axle are caused to interact with the springs on the other by pivotal rockers or equalizer beams. 1. Front Hanger: The forward most frame mounting bracket which normally incorporates a progressive spring seat and an anchor point for one torque arm. 2. Rocker Hanger (Equalizer Hanger): An intermediate frame mounting bracket which incorporates a pivoted rocker, or equalizer beam, and an anchor point for one torque arm. 3. Rear Hanger: The rearmost frame mounting bracket which normally incorporates a progressive spring seat. 4. Torque Arm, Adjustable (Adjustable Radius Rod): An articulated, adjustable member which is attached to an axle bar at one end and anchored (usually through another suspension part) to the trailer frame or sub-frame at the other end. Its function is to absorb certain dynamic axle loads and to provide the means for axle alignment. 5. Torque Arm, Non-Adjustable (Fixed Radius Rod): Same as (4) except it is of a fixed length. 6. Rocker (Equalizer Beam): A suspension part containing a progressive spring seat on either end and a transverse pivot connection in between, allowing vertical translation of the wheel and axle assemblies it connects.
Suspension, Overslung
A suspension employing flat plate or tapered springs wherein the springs are attached above the top of the axle bar.
Suspension, Single Axle
A suspension usually employing two springs and designed to accommodate one axle.
Suspension, Single Point (sometimes referred to as a 2-spring tandem)
A tandem two-axle suspension consisting of two springs deployed much in the same manner as walking beams between the axles and pivoted halfway between the axles on a trunnion shaft at the connection to the trailer frame.
Suspension, Spring Beam
A type of two-axle suspension which employs a spring beneath each walking beam to enhance ride when the trailer is traveling in the unladen condition.
Suspension, Steel Spring
Any one of several types of suspensions which employ either flat plate or tapered steel springs to reduce shock loads from the axle and wheel assemblies.
Suspension, Underslung
A suspension wherein the springs or air beams are attached below the bottom of the axle bar.
Suspension, Walking Beam
A type of unsprung suspension comprised of parallel beams pivoted on a common transverse axle or trunnion between the axles and attached at the ends to axle and wheel assemblies. Most commonly used in two-axle assemblies but also to a lesser degree in three and four-axle variations.
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.
See Axle.
Tandem Axle (Tandems)
Pair of axles and associated suspension usually located close together. See Spread Axle, Axle, Tandem.
Tare Weight
See Chassis Weight.
Tarp (Tarpaulin)
A water resistant fabric cover used to protect the cargo on an open trailer.
Tarp Basket
An open framework rack or storage compartment attached across the front of a trailer and used to store a tarpaulin when not in use.
Tarp Bow
A transverse support installed at intervals along the top rails of open top trailers, or removable side panels, and designed to elevate and support a tarpaulin or tarp.
Tarp Hook
Any one of several types of fittings attached at intervals around the outside of open top trailers, or trailers with removable side panels, and used as anchor points for securing a tarpaulin or tarp.
Tarp Tie Rod
Rods or tubes attached horizontally around the outside of open top trailers, or trailers with removable sides, and used in lieu of tarp hooks.
Team (Driver Team)
Team of two drivers who alternate driving and resting.
Tie-Down Assembly
A system of chains, cables, or straps along with the accompanying attachment hardware used to secure cargo in or on trailers for support.
Tire
A device made of rubber, fabric, steel, or other materials which, when mounted on the rim at a wheel and filled with air, cushions and sustains the load.
Tire Carrier
A rack or other device for carrying a spare tire.
Tire Clearance
The distance or dimension between a tire or tires and the nearest point of interference or contact on the trailer. Normally taken as the vertical distance above the periphery of a tire, but may also be construed to mean lateral clearance.
TOFC (Piggyback)
An acronym taken from the words “Trailer-on-Flat-Car” and used to describe the transport of highway trailers on the rail system.
TOFC Plate
On trailers for TOFC service, a structural extension of approximately 24 inches on the rear of the upper coupler assembly.
Tow Bar
A strut or column-like device temporarily attached between the rear of a towing vehicle and the front of the vehicle being towed. Its purpose is to maintain the interval or distance between the two (not commonly used with truck trailers).
Towing Capacity
The total weight of the trailer or trailers towed.
Track, Axle
The projected nominal wheel track for a given axle bar and spindle combination as used in specifying trailer axles.
Track, Cargo Control
A vertical or horizontal structural member, normally attached to the inside of sidewall posts, having pierced slots for use with cargo tie-off straps or double decking components.
Track, Wheel Tread
The distance or dimension between the vertical centerlines of single tires or dual tire combinations as measured transverse to the longitudinal centerline of the trailer.
Tractor
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 it from a farm tractor.
Tractor Trailer
Tractor and semitrailer combination.
Trailer
A vehicle without motive power designed for carrying property and for being drawn by a motor vehicle. The term “trailer” includes full trailers and semitrailers as sub-groups.
Trailer Body
A trailer body is that portion of the assembly whose function it is to contain or accommodate the cargo.
Trailer Chassis
See Chassis.
Trailer on Flatcar
Method of moving cargo which involves transporting semitrailers on railroad flat cars. See Piggyback.
Trailer Tank
A trailer equipped with a liquid tight vessel for carrying liquids or dry bulk products.
Trailer Tank
A trailer equipped with a liquid tight vessel for carrying liquids or dry bulk products.
Trailer, Agricultural Commodity
A trailer that is designed to transport bulk agricultural commodities in off-road harvesting sites and to processing plants or storage locations.
Trailer, Auto Transporter
The semitrailer portion of an auto transporter truck and trailer combination designed and manufactured expressly for the loading, transportation, and unloading of automobiles.
Trailer, B-Train
A type of double semitrailer incorporating a uniquely designed suspension subframe-fifth-wheel combination which obviates the need for a converter dolly when towing a full trailer.
Trailer, Carryall
See Trailer, Lowbed.
Trailer, Container Chassis
A semitrailer chassis designed especially to transport one or two containers over the highway.
Trailer, Converted Semi
A semitrailer and converter dolly combination.
Trailer, Desert Float
See Trailer, Oilfield Float.
Trailer, Dolly
See Dolly, Converter.
Trailer, Doubles
See Doubles.
Trailer, Drop Center (Double Drop)
A trailer design employing an offset or drop in the cargo deck immediately behind the supports and another immediately in front of the suspension, the purpose of which is to lower the cargo deck and/or to provide the greatest height possible for cargo in the dropped area.
Trailer, Drop Frame
A trailer design employing one offset or drop in the cargo deck immediately behind the supports.
Trailer, Extendable Platform
See Frame Trailer, Extendable.
Trailer, Flat Bed
See Trailer, Platform.
Trailer, Full
A load carrying vehicle equipped with two or more axles and constructed with a front towbar coupled to a swiveling or steerable undercarriage assembly at the front of the trailer.
Trailer, Heavy Hauler
See Trailer, Lowbed.
Trailer, Industrial
A general purpose trailer, sometimes equipped with a tilt bed or ramps and towed by means other than a truck tractor.
Trailer, Insulated Van
A van trailer constructed with (or without) insulation in the floor, and with insulation in the walls, nose, and roof.
Trailer, Lowbed
A platform trailer constructed to provide minimal ground clearance beneath the loading deck and designed to transport heavy, oftentimes concentrated loads with high centers of gravity.
Trailer, Lowbed, Level Deck
A lowbed trailer with the deck level from the back of the gooseneck to the rear of the trailer.
Trailer, Oilfield Float (Oilfield Flatbed)
A flatbed equipped with a pick-up loop at the front for a winch line and with provision in the area of the supports to allow the nose of the trailer to be lowered to the ground for loading of unloading. Oilfield floats are normally equipped with a rolling tailpipe across the rear.
Trailer, Open Top Van
A van trailer constructed with tarp bows or spreaders in lieu of a conventional closed roof.
Trailer, Piggyback
See Trailer, TOFC.
Trailer, Platform (Flatbed)
A trailer chassis consisting of load carrying main frames and a flat loading deck without permanent sides or roof.
Trailer, Platform, Extendable
See Frame Trailer, Extendable.
Trailer, Pole
A trailer consisting of an upper coupler assembly connected by a tube (or pole) to a running gear assembly and designed to carry long loads capable of supporting their own length.
Trailer, Pulpwood
Any of several types of chassis trailers designed exclusively for transporting pulpwood.
Trailer, Pup (Pull)
A short trailer typically less than 30 feet long and typically pulled behind a trailer or truck (see Trailer, Full).
Trailer, Refrigerated
An insulated van trailer designed to possess specific thermal properties and intended for use with self-contained refrigeration systems.
Trailer, Semi
A load-carrying vehicle equipped with one or more axles and constructed so that its front end is connected to and supported by a vehicle which pulls it.
Trailer, Straddle
A trailer that is driven or backed over the cargo it is to carry in order that lifting devices integral with the trailer can position and secure the cargo for transport.
Trailer, Tag-a-Long
See Trailer, Industrial.
Trailer, Thermal
See Trailer, Refrigerated.
Trailer, TOFC
A trailer designed for carriage on a railcar and which, if built after January 1, 1973 for straight floor van trailers or after June 1, 1975 for container chassis, containers an Association of American Railroads certification plaque described in AAR Specification M 931 or M-943. Visually a TOFC trailer may be identified by the AAR certification plaque near the DOT certification label, lift pads located along the bottom sides of the trailer (except for container chassis and tank trailers) and a plate extending about two feet to the rear of the upper coupler assembly.
Trailer, Van
A trailer designed to have a totally enclosed cargo space comprised of fixed sides, nose, roof, and with articulated panels across the rear and sometimes at selected places in the sides.
Trailer, Wedge Van
A van trailer having a straight floor in which the inside clear height at the rear is greater than at the front.
Tri-Axle
Truck, tractor, or trailer with three axles grouped together at the rear. See Tridem and Axle,Tri.
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.
Triple
A combination consisting of a tractor pulling a semitrailer plus two full trailers.
Truck
Big vehicle that moves items.
Truck
Vehicle which carries cargo in a body mounted to its chassis, rather than on a trailer towed by the vehicle, for the purpose of transporting cargo.
Truck Tractor
A motor vehicle designed primarily for the purpose of pulling semitrailers.
Truckload
The quantity of freight required to fill a trailer; usually more than 10,000 pounds. See LTL.
Truckload 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.
Trunnion Axle
See Axle, Trunnion.
Twins (Twin Trailers)
See Double.
Type of Trailer
The first separation within the Trailer Classification. Truck Trailers comprise one type of trailer, recreational trailers another, etc.
Type of Trailer Body
The second separation with the Trailer Classification. Van Trailers comprise one body type, Tanks another, etc.
Type of Vehicle
A broad separation intended to classify vehicles into groups possessing common traits, including design and purpose. Trucks comprise one group, trailers another, etc.
Undercarriage (Running Gear, Bogie) A structural subframe complete with suspension and axle-wheel assemblies.
Undercarriage Body Rail
A longitudinal member attached to a series of crossmembers which provides guide and location features for a sliding undercarriage.
Undercarriage Locator Bar
A removable round tubular or solid bar inserted through the positioning holes of the body rail to assist in locating the sliding undercarriage at a predetermined location.
Undercarriage Stop Bar
A round tubular or solid fixed bar installed near the extreme ends of a slider body rail usually through the positioning holes to serve as a safety stop when moving the sliding undercarriage from one position to another.
Undercarriage, Removable
An undercarriage capable of being separated from the trailer structure.
Undercarriage, Sliding (Slider)
A specialized undercarriage design which incorporates provisions for readily moving it to new locations forward and backward to affect changes in weight distribution and/or wheelbase.
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. See Coupler Plate, Upper.
Upper Coupler, Rocking
See Coupler Assembly, Rocking Upper.
An automatic control device used on air suspensions to regulate the flow of air in and out of the air springs to maintain the predetermined ride or mounting height. There are normally two leveling valves employed in each air suspension, one on either side of the trailer.
Valve, Anti-lock
That part of an electro-mechanical anti-lock system which receives electrical signals from the logic controller and releases air from or admits air to the brake chambers on a given axle to adjust the brake actuation force.
Valve, Booster Relay
A relay type valve used to accelerate the application and releases of pressurized air to the towed vehicle(s) relay or relay emergency valve.
Valve, Check
An automatic control device designed to provide free fluid flow in one direction only.
Valve, Quick Release
A valve placed in the trailer control (service) brake line to accelerate the release of pressurized air in the line.
Valve, Relay
A secondary control unit used in an air brake system to accelerate the application and release of pressurized air to and from brake chambers.
Valve, Relay Emergency
A combination valve which incorporates the features of a relay valve along with additional provisions for the automatic application of the trailer brakes in the event pressure is lost in the trailer supply (emergency) air flow.
Valve, Tractor Protection
An automatic control device used on truck tractor air systems which (a) permits driver control of pressurized air passing through the air brake lines to the towed vehicle whenever the air pressure in the towing vehicle exceeds a predetermined value, (b) closes off the flow of air to the trailer automatically when the tractor brake system pressure falls below predetermined value, and (c) vents the trailer supply (emergency) line when flow in this line is stopped either manually or automatically.
Valve, Trailer Control (Hand Control Valve)
A manually-operated control device mounted in the cab of a truck tractor with which a driver can apply and release trailer brakes independent of tractor brakes.
Vehicle Identification Number (VIN)
An arrangement of 17 Arabic numerals and Capital letters uniquely differentiating a motor vehicle from any other so identified. (Reference: TTMA Recommended Practice No. 56 and Title 49 Code of Federal Regulations 565 and 571.115).
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.
VIN (Vehicle Identification Number)
Assigned by the manufacturer, this number is unique to each vehicle and appears on the vehicle’s registration and title.
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.
Weevil Pins and Sockets
Pins and sockets located on both sides of a platform trailer outboard of the rolling tail pipe. Its purpose is to contain or guide the winch cable when winching cargo such as skid-mounted equipment aboard the trailer (see TTMA RP No. 64).
Weight Rating, Gross Axle (GAWR)
The Rated load-carrying capacity of an individual axle and wheel assembly.
Weight Rating, Gross Combination
The maximum combined weight rating for a truck tractor and trailer(s) combination.
Weight Rating, Gross Vehicle (GVWR)
The maximum rated combined weight of a vehicle and its payload based upon structural capability alone.
Weight, Axle
The weight transmitted to the ground by the trailer axles.
Weight, Gross
The combined weight of a trailer and its payload.
Weight, Payload
See Payload.
Weight, Sprung
That portion of the vehicle weight supported by the suspension springs.
Weight, Tare (Unloaded)
The weight of an empty vehicle.
Weight, Unsprung
The weight of the axles, wheel assemblies, and all other trailer parts whose weight is not borne by the suspension springs.
Wells, Coil
Recessed areas between the main beams of platform trailers designed to carry steel coils.
Wheel Bearings
An assembly of hardened precision rollers and races designed to minimize friction at the spindle and wheel hub interface.
Wheel Boxes
Enclosures permanently attached above the tires and wheels to protect the cargo area from road spray and debris which may be thrown upward by the tires. Generally found on furniture vans and other trailers having deep drops.
Wheel Chock
A wedge-shaped stop applied in front of or behind the wheels of parked trailers to prevent rolling.
Wheel Rim
See Rim.
Wheel Track
See Track, Wheel Tread.
Wheel, Disc
A type of wheel consisting of a rim permanently affixed to a round metal plate (or disc) and designed to mate with an axle and hub assembly. The disc may be flat but is most commonly “dished” or offset in order that the wheel may be used either singly or in pairs for dual wheels.
Wheel, Spoke
A type of wheel consisting of integral hub and spokes designed to accept demountable rims either singly or in pairs with a spacer for dual tires.
Wheelbase
The distance from the kingpin to the centerline of suspension.
Width, Inside
The unobstructed inside loading width of a van-type trailer or container.
Width, Outside Trailer
The width measured across the sidemost load-carrying structures, support members, and structural fasteners.
WIM (Weight-in-Motion)
Technology for determining a vehicle’s weight without requiring it to come to a complete stop.
Wire Color Coding
The practice of using electrical conductors with variously colored insulating coatings to identify the different circuits in trailer electrical systems, usually in accordance with a recognized industry standard such as Society of Automotive Engineers (SAE), American Trucking Association (ATA), etc.
Person who operates a yard tractor.
Yard Tractor or Yard Dog
Special tractor used to move trailers around a terminal, warehouse, distribution center, etc.
