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Glossary of Truck Industry Terms J – M


A type of accident in which the tractor and trailer turn to make a V-shape.

Jake Brake.
An engine compressor brake which builds up back pressure by preventing exhaust from escaping thus the engine slows as the cycle at the top of the power stroke is interrupted, which provides a retarding force.

Jake Brake.
Slang for the Jacobs engine brake. Used as an auxiliary braking device on a tractor.

Jeep Wheel.
Gooseneck dollies used with very heavy or extra long loads. See Joe Dog.

Jiff Lock.
Two fifth wheels on a three axle tractor; a gear set designed to fit into the frame of a two axle tractor converting it to a three axle tractor.

Jifflox Converter Dolly.
Used in the eastern U.S., it is hooked behind the axle of a single axle tractor. This converts it to a tandem axle tractor. The tractor then can pull a loaded trailer.

Joe Dog.
A device with a dead axle that converts a single-axle tractor to a tandem-axle tractor. It hooks over the tractor’s fifth wheel, replacing it with another for the semi to be hooked onto. Also referred to as Jeep Wheel.

Jug Handle Turn.
A right turn where you compensate for off-tracking by moving into another lane of traffic before entering the intersection. This type of turn is dangerous and sloppy.

Using another vehicle battery to start a dead battery. You should always remember to observe safety rules, prepare the truck, and properly hook up the jumper cables when working on the battery.

Just in Time (JIT) Delivery System.
A method of shipping that gets rid of the costly overhead of warehousing stock.

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

Usually a 2” steel pin that is locked into the jaws of the fifth wheel to couple the tractor to the trailer.

Kingpin Weight.
Weight of the trailer at the kingpin or the trailer weight applied to the fifth wheel.

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For hazard class; look very much like small placards and should be placed near the proper shipping name and identification number.

Any U.S. laboratory certified by HHS under the National Laboratory Certification Program as meeting the minimum standards of Subpart C of the HHS Mandatory Guidelines for Federal Workplace Drug Testing Programs; or, in the case of foreign laboratories, a laboratory approved for participation by DOT under this part. (The HHS Mandatory Guidelines for Federal Workplace Drug Testing Programs are available on the Internet at or from the Division of Workplace Programs, 5600 Fishers Lane, Rockwall II Building, Suite 815, Rockville, MD 20857).

Laden Weight.
Weight of vehicle and its load.

That which constitutes a load. The freight in a vehicle.

A device used to produce artificial light.

Landing Gear.
Retractable legs which support the front end of a semi-trailer when it is not coupled to a tractor.

Landing Gear.
On a trailer, used to support the load while it is not under a tractor.

Large Truck.
A truck over 10,000 pounds gross vehicle weight rating including single unit trucks and truck tractors (FARS definition).

Layover Time.
The non-working time that a road driver spends away from his home terminal before being dispatched to some other destination.

LCV (Long Combination Vehicle).
Vehicles longer than a standard doubles rig (tractor and two 28-foot semi-trailers). Some examples are twin 48-foot trailers and triple 28-foot trailers.

Leaf Spring.
Suspension system consisting of superimposed, flat, narrow steel plates.

Leaf Spring Suspension.
Narrow metal strips of varying lengths bolted together and attached to frame hangers.

The company or individual which leases vehicles.

The company which owns the vehicle and leases it to customers.

License Plate Lamp.
A lamp used to illuminate the license plate on the rear of a motor vehicle.

Licensed Medical Practitioner.
A person who is licensed, certified, and/or registered, in accordance with applicable Federal, State, local or foreign laws and regulations, to prescribe controlled substances and other drugs.

Licensing Entity.
The agency of State government that is authorized to issue drivers’ licenses.

Lift Axle.
An un-powered axle used only when the vehicle is loaded in order to meet federal and state standards. It is attached to the undercarriage with an air spring suspension which allows the axle to be raised when it is not in use.

Lift Axle.
Can be raised off the pavement when loaded to reduce tire and axle wear. It is usually kept in the raised position.

Limit of Detection (LOD).
The lowest concentration at which an analyte can be reliably shown to be present under defined conditions.

Line Haul.
The movement of freight between major cities or terminals. Line haul operations do not include pick-UPS or deliveries. Line haul service is also commonly referred to as over-the-road (OTR) operations.

Line Sheet.
A production list of all components that go into the manufacturing of a truck, tractor or trailer.

Liquid Cargo Tankers. Used to carry gasoline, asphalt, milk, juices, or liquefied gas. The smooth interior of the tanks and partial loads make driving very challenging. Drivers should accelerate slowly, avoid braking in turns, turn only at safe speeds.

Liquid Surge. The wave action of the liquid cargo in a tanker.

Live Axle. Supports the vehicle weight, sends power tot he wheels and is hollow.

Livestock Body. Truck or trailer designed for the transportation of farm animals.

Livestock Trailer.
Trailer designed for livestock transport.

Livestock Transport Trailer.
These trailers are either flat floor or double drop frame design. They are used to carry live animals. Live cargo shifts about and that changes the balance and stability. Drivers should drive at the speed that lets them keep the vehicle under control at all times. When braking, tap the brakes lightly to set the animals. Then slowly put on the brakes.

Load Lock.
A bar type device designed to hold the cargo in the trailer.

Local Pickup and Delivery.
The driver operates in and around cities. He or she will usually be delivering freight to its final destination.

Local Truck Routes.
Many cities and towns have designated routes for trucks.

Lock Ring.
In two-piece wheel rims, the lock ring holds the side ring firmly on the rim base.

Locking Main Differential.
A differential that locks both shafts together so equal torque is applied to left and right wheels.

Log Body.
Truck or trailer body designed for the transportation of long items.

Book carried by truck drivers in which they must record their hours-of-service and duty status.

Long-Distance Transport.
Cargo is transported from a point of origin to one or more distant destinations.

Long Ton.
2,240 pounds. Also called a gross ton.

All logs that are not short-wood, i.e., are over 4.9 m (16 feet) long. Such logs are usually described as long logs or tree-length.

Low Air Pressure Warning Alarm.
Sounds or lights up when there is low pressure in the air brake system.

Low Bed.
An open trailer with drop frame construction used primarily to haul heavy equipment. Also known as flat bed or low boy.

Trailer designed with open flat-bed with the deck very low to the ground, most commonly used for hauling heavy machinery for construction, bulky or tall loads.

Low Chassis Vehicle.
(1) A trailer or semitrailer manufactured on or after January 26, 1998, having a chassis which extends behind the rearmost point of the rearmost tires and which has a lower rear surface that meets the guard width, height, and rear surface requirements of 571.224 in effect on the date of manufacture, or a subsequent edition.
(2) A motor vehicle, not described by paragraph (1) of this definition, having a chassis which extends behind the rearmost point of the rearmost tires and which has a lower rear surface that meets the guard configuration requirements of 393.86(b)(1).

Low Pressure Warning Signal.
Tells the driver the air pressure has dropped below 60 psi. a red warning light will turn on, a buzzer will sound, or both will happen.

Low Profile Tires.
Tires with a profile ratio of 80 or less.

LTL Carrier.
A trucking company which consolidates less-than-truckload cargo for multiple destinations on one vehicle.

Lubrication System.
Distributes oil between the moving parts to keep them from rubbing together.

Lug Lever.
The device that unlocks locking lugs on a sliding tandem axle.

Lug Tread.
Deep grooves in the tire shoulders that run perpendicular to the sidewalls. These tires are best for the drive wheels.

Occurs when the driver fails to downshift when the engine speed starts to fall below the normal operating range. In this condition, the tractor produces too little power and lugs, or struggles.

Lumber Body.
Platform truck or trailer body with rollers designed for the transportation of lumber.

Loading and unloading cargo.

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Maintenance policy.
Guidelines companies set up that tell drivers and mechanics what their responsibilities are in servicing and maintaining their vehicles.

When a part of system does not work properly.

Managing Your Speed.
Adjusting your speed for the road, weather, and traffic conditions.

To change direction while moving.

Bill of lading describing the cargo of the vehicle.

The ability of the tractor trailer to change direction while moving.

Manual Sliding Fifth Wheel.
A type of fifth wheel that utilizes a pull lever mounted on the sliding plate that allows repositioning of the fifth wheel or the tractor.

Manual Release.
The device on a fifth wheel that allows you to release, or unlock, the sliding mechanism by pushing or pulling a release handle.

Manual Transmission.
One that must be shifted by the driver through the different gears. A clutch must be used.

See Spring Brakes.

Medical Examiner.
A person who is licensed, certified, and/or registered, in accordance with applicable State laws and regulations, to perform physical examinations. The term includes, but is not limited to, doctors of medicine, doctors of osteopathy, physician assistants, advanced practice nurses, and doctors of chiropractic.

Medical Review Officer (MRO).
A person who is a licensed physician and who is responsible for receiving and reviewing laboratory results generated by an employer’s drug testing program and evaluating medical explanations for certain drug test results.

Meet and Turn.
A type of relay run in which two drives start toward each other from different points and meet at a chosen mid-point. At the meeting place, the drivers exchange complete units or only trailers. Then each driver goes back to his or her starting point.

Mexico-Domiciled Motor Carrier.
A motor carrier of property whose principal place of business is located in Mexico.

See Spring Brakes.

Michigan Special.
Vehicle with 11 axles.

Migrant Worker.
Any individual proceeding to or returning from employment in agriculture as defined in section 3(f) of the Fair Labor Standards Act of 1938, as amended (29 U.S.C. 203(f)) or section 3121(g) of the Internal Revenue Code of 1954 (26 U.S.C. 3121(g)).

Mixed Truckload.
A truckload of different freight articles combined into a single shipment.

Frequently used to refer to the basic divisions of the transportation industry. The principal modes of transportation are truck, rail, air and water.

Motor Carrier (MC).
A for-hire motor carrier or a private motor carrier. The term includes a motor carrier’s agents, officers and representatives as well as employees responsible for hiring, supervising, training, assigning, or dispatching of drivers and employees concerned with the installation, inspection, and maintenance of motor vehicle equipment and/or accessories. For purposes of subchapter B, this definition includes the terms employer, and exempt motor carrier.

Motor Carrier (MC).
A motor carrier, motor private carrier, or motor carrier of migrant workers as defined in 49 U.S.C. 13102 and 31501.

Motor Carrier (MC).
Any carrier of migrant workers by motor vehicle as defined in paragraph (b) of this section.

Motor Carrier (MC).
The person or company that is in the business of transporting goods.

Motor Vehicle.
Any vehicle, machine, tractor, trailer, or semi-trailer propelled or drawn by mechanical power and used to transport property, but does not include any vehicle, locomotive, or car operated exclusively on a rail or rails. The following combinations will be regarded as one motor vehicle:
(1) A tractor that draws a trailer or semi trailer; and
(2) A truck and trailer bearing a single load.

Motor Vehicle.
Any vehicle, machine, tractor, trailer or semi-trailer propelled or drawn by mechanical power and used upon the highways in the transportation of passengers or property, or any combination thereof determined by the Federal Motor carrier Safety Administration, but does not include any vehicle, locomotive, or car operated exclusively on a rail or rails, or a trolley bus operated by electric power derived from a fixed overhead wire, furnishing local passenger transportation similar to street-railway service.

Moving Floor Trailer.
Trailer with a moving floor designed for easy unloading of cargo.

Noise-absorbing chamber used to quiet the engine’s noise.

Multiple Axle Assembly.
Two or more dead axles together. They spread the rig’s weight over more axles. This reduces the amount of weigh ton any one axle.

Multiple-Employer Driver.
A driver, who in any period of 7 consecutive days, is employed or used as a driver by more than one motor carrier.

Multiple Stops.
All stops made in any one village, town or city may be computed as one.

Multi-Wheel Low Bed Trailer with Jeep Dolly.
Has a low bed frame and two rear trailer axles.

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