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Glossary of Truck Industry Terms A – D


10-Year Average Accident Rate.
For each State, the aggregate number of large truck-involved fatal crashes (as reported in the Fatality Analysis Reporting System (FARS)) for a 10-year period divided by the aggregate vehicle miles traveled (VMT) (as defined by the Federal Highway Administration (FHWA)) for the same 10-year period.

The most familiar combination rig. The tractor has ten wheels and the semi-trailer has eight.

2-Axle Dolly.
Is attached to the trailer using the actual cargo. One end of the cargo rests on the dolly. The other end rests on the trailer.

2-Axle Float.
Has a flat bed frame with two rear axles and no landing gear. It is used mostly in oil fields for hauling drilling equipment, pipes, and so on.

2-Axle Jeep Dolly.
Can be attached to the fifth wheel. The fifth wheel is between the tractor and trailer.

2-Axle, Double Drop, Low Bed with Outriggers.
Has a double-top frame and two rear axles. Outriggers are attached to each side of the trailer to support wider loads.

45-Degree Angle Parking.
An alley dock backing technique in which the rig is pulled forward at a 45-degree angle to the target, then backed in.

49 CFR Part 166.
Specification for hazardous materials that require special equipment or protection.

5-Axle Removable Gooseneck, Low Bed Detachable, Two Axle Dolly.
This low bed frame has three rear trailer axles. A two-axle dolly is attached to the rear of the trailer.

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A Train.
Combination of vehicles composed of a tractor and a semi-trailer towing a full trailer:
1) connected with an A dolly; or
2) without a converter dolly.

Abate or Abatement.
To discontinue regulatory violations by refraining from or taking actions identified in a notice to correct non-compliance.

ABS (Antilock Braking System).
System that electronically controls wheel slip, thereby preventing sustained wheel locking when braking and stopping on surfaces with low friction.

Accelerator or Accelerator Pedal.
Located just under the steering wheel, this pedal can be operated with your right foot to control engine speed. Make sure there is no looseness or sticking.

Continuous or repeated exposure to the same conditions resulting in public liability which the insured neither expected nor intended.

(1) Except as provided in paragraph(2) of this definition, an occurrence involving a commercial motor vehicle operating on a highway in interstate or intrastate commerce which results in:(i) A fatality;(ii) Bodily injury to a person who, as a result of the injury, immediately receives medical treatment away from the scene of the accident; or(iii) One or more motor vehicles incurring disabling damage as a result of the accident, requiring the motor vehicle(s) to be transported away from the scene by a tow truck or other motor vehicle.
(2) The term accident does not include:(i) An occurrence involving only boarding and alighting from a stationary motor vehicle; or(ii) An occurrence involving only the loading or unloading of cargo.

Accident packet.
Given by most companies to drivers to help them handle their responsibilities at the scene of an accident. Packets usually contain basic instructions for handling the scene of an accident, a preliminary accident report or memo, and witness cards.

Accident rate.
For each State, the total number of fatal crashes involving large trucks (as measured by the FARS for each State) divided by the total VMT as defined by the FHWA for each State for all vehicles.

Statutes granting the Secretary authority to regulate motor carrier safety.

Actual knowledge.
Actual knowledge by an employer that a driver has used alcohol or controlled substances based on the employer’s direct observation of the employee, information provided by the driver’s previous employer(s), a traffic citation for driving a CMV while under the influence of alcohol or controlled substances or an employee’s admission of alcohol or controlled substance use, except as provided in 382.121. Direct observation as used in this definition means observation of alcohol or controlled substances use and does not include observation of employee behavior or physical characteristics sufficient to warrant reasonable suspicion testing under 382.307.

Adaptive Cruise Control.
Radar based system relying on radar sensing and on on-board computer that adjusts a vehicle’s cruise speed automatically to accommodate changing traffic conditions.

Administrative Law Judge.
An administrative law judge appointed pursuant to the provisions of 5 U.S.C. 3105

Administrative Takedown Funds.
Funds deducted by the FMCSA each fiscal year from the amount made available for the MCSAP for expenses incurred in the administration of the MCSAP, including expenses to train State and local government employees.

The Federal Highway Administrator, who is the chief executive of the Federal Highway Administration, an agency within the United States Department of Transportation, or his/her designate.

Adulterated Specimen.
A urine specimen containing a substance that is not a normal constituent or containing an endogenous substance at a concentration that is not a normal physiological concentration.

Adverse Driving Conditions.
Snow, sleet, fog, other adverse weather conditions, a highway covered with snow or ice, or unusual road and traffic conditions, none of which were apparent on the basis of information known to the person dispatching the run at the time it was begun.

Any communication to the public in connection with an offer or sale of any interstate household goods transportation service. This includes written or electronic database listings of your name, address, and telephone number in an online database. This excludes listings of your name, address, and telephone number in a telephone directory or similar publication. However, Yellow Pages advertising is included in this definition.

Persons are affiliates of one another if, directly or indirectly, one controls or has the power to control the other, or a third party controls or has the power to control both. Indicators of control include, but are not limited to: interlocking management or ownership; shared interest among family members; shared facilities or equipment; or common use of employees. Following the issuance of a public interest exclusion, an organization having the same or similar management, ownership, or principal employees as the service agent concerning whom a public interest exclusion is in effect is regarded as an affiliate. This definition is used in connection with the public interest exclusion procedures of Subpart R of this part.

Often referred to as an intercooler, this device is a heat exchanger which cools the induction air before it enters the cylinders of an engine. It is most often used in diesels downstream of the turbo charger. If used properly, it can lead to longer engine life.

A person or company that acts as the official representative of another, such as a consignee’s agent.

Aggregate Working Load Limit.
The summation of the working load limits or restraining capacity of all devices used to secure an article of cargo on a vehicle.

Aggregated Shipments.
Several shipments from different shippers to one consignee that are consolidated and treated as a single consignment.

Agitator Body.
Truck body designed and equipped to mix concrete in transit.

Agreed Valuation.
Freight value mutually agreed upon by shipper and carrier as a basis for transportation charges. It also may represent an agreed maximum amount that can be recovered in case of loss or damage.

Agricultural Commodity Trailer.
A trailer that is designed to transport bulk agricultural commodities in off-road harvesting sites and to a processing plant or storage location, as evidenced by skeletal construction that accommodates harvest containers, a maximum length of 28 feet, and an arrangement of air control lines and reservoirs that minimizes damage in field operations.

Air Application Gauge.
A gauge designed to read the amount of pressure applied during air brake operation.

Air Application Pressure Gauge.
Shows the amount of air pressure being applied to the brakes. When the brakes are not in use, the gauge will read zero psi.

Air Blank.
In evidential breath testing devices (EBTs) using gas chromatography technology, a reading of the device’s internal standard. In all other EBTs, a reading of ambient air containing no alcohol.

Air Blockage.
When air cannot reach the brakes. This is usually caused by water freezing in the air system.

Air Brake.
A brake in which compressed air actuates the braking mechanism by pushing on a diaphragm within a brake chamber.

Air Brake Application Gauge.
Indicates in psi the amount of air pressure used when the brake pedal is pushed.

Air Brake System.
In an air brake system, pressure is used to increase the braking force. The compressed air can multiply the force of mechanical braking many times.

Air Cleaner.
Air or filter device for cleaning air entering engine. There may be two, one on each side of the tractor.

Air Compressor.
Device designed to build-up and maintain the necessary air pressure in the brake system reservoir.

Air Deflector.
Contoured panel typically positioned on the roof of a commercial vehicle cab that minimizes air flow between the truck cab and body or trailer.

Air Dryer.
Device designed to remove moisture from the compressed air of the braking system. It is normally installed between the compressor and service reservoir.

Air Filter Restriction Gauge.
Indicates how dirty the air filter is and when maintenance is needed.

Air Gauges.
Dashboard mounted gauges (reservoir pressure, application, manifold pressure) which indicate the air pressure in pounds per square inch.

Air Intake Manifold.
Distributes air to the various cylinders of the engine. It attaches to the cylinder heads at the intake ports.

Air Intake System.
Delivers fresh air to the cylinders. An air cleaner removes dirt, dust, and water from the fresh air.

Air Line.
Pressure tubing used to circulate the compressed air of the air brake system.

Air Operated Release.
The device on a fifth wheel that allows you to release the locking mechanism on the sliding fifth wheel by moving the fifth-wheel release lever in the cab to the unlocked position.

Air Pressure Gauge.
Tells the amount of pressure in the tanks. The maximum pressure is around 120 psi. The air compressor will build whenever the pressure falls below 90 psi (pounds per square inch).

Air Reservoir.
Provides air to your braking system. You should always bleed them each day to remove moisture.

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

Air Slide Fifth Wheel.
A fifth wheel design that utilizes a switch on the dashboard to activate an air cylinder mounted to the fifth wheel slide plate which moves and locks the position of the fifth wheel.

Air Slider.
A cab-controlled sliding fifth wheel that can be unlocked by air to be moved backward or forward.

Air Starter.
Using another vehicle’s air supply to charge your starter.

Air Suspension.
Uses bags of air placed between the axle and frame.

Air Tag.
A tag axle that has two bellows-like air bags that, when filled, forces the tractor’s rear axle harder against the ground for a smoother ride and for weight distribution between the two axles of the tractor.

The intoxicating agent in beverage alcohol, ethyl alcohol, or other low molecular weight alcohols including methyl and isopropyl alcohol.

Alcohol Concentration.
The alcohol in a volume of breath expressed in terms of grams of alcohol per 210 liters of breath as indicated by a breath test under this part.

Alcohol Concentration (Or Content).
The alcohol in a volume of breath expressed in terms of grams of alcohol per 210 liters of breath as indicated by an evidential breath test under this part.

Alcohol Confirmation Test.
A subsequent test using an EBT, following a screening test with a result of 0.02 or greater, that provides quantitative data about the alcohol concentration.

Alcohol or Alcoholic Beverage.
Beer as defined in 26 U.S.C. 5052
(a), of the Internal Revenue Code of 1954,
(b) Wine of not less than one-half of one per centum of alcohol by volume, or
(c) Distilled spirits as defined in section 5002(a)(8), of such Code.

Alcohol Screening Device (ASD).
A breath or saliva device, other than an EBT, that is approved by the National Highway Traffic Safety Administration (NHTSA) and placed on a conforming products list (CPL) for such devices.

Alcohol Screening Test.
An analytic procedure to determine whether an employee may have a prohibited concentration of alcohol in a breath or saliva specimen.

Alcohol Testing Site.
A place selected by the employer where employees present themselves for the purpose of providing breath or saliva for an alcohol test.

Alcohol Use.
The drinking or swallowing of any beverage, liquid mixture or preparation (including any medication), containing alcohol.

Any person not a citizen or national of the United States.

A fractional part of a specimen used for testing. It is taken as a sample representing the whole specimen.

A gauge on the instrument panel that shows the current output of the alternator. It indicates whether the alternator is being charged by the battery or is discharging.

Anchor Point.
Part of the structure, fitting or attachment on a vehicle or article of cargo to which a tiedown is attached.

Antilock Brake System or ABS.
A portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by:
(1) Sensing the rate of angular rotation of the wheels;
(2) Transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals; and
(3) Transmitting those controlling signals to one or more modulators which adjust brake actuating forces in response to those signals.

Applicable Safety Regulations or Requirements.
49 CFR subtitle B, chapter III, Subchapter B-Federal Motor Carrier Safety Regulations; and 49 CFR subtitle B, chapter I, Subchapter C-Hazardous Materials Regulations.

Arrester Beds.
An escape ramp, 300-700 feet long, made of loose material (usually pea gravel).

Article of Cargo.
A unit of cargo, other than a liquid, gas or aggregate that lacks physical structure (e.g., grain, gravel, etc.) including articles grouped together so that they can be handled as a single unit or unitized by wrapping, strapping, banding or edge protection device(s).

Articulated Vehicle.
A vehicle consisting of two or more separable wheeled units connected so as to allow flexibility of movement, such as a vehicle towing a trailer or tractor and semi-trailer combination.

Movement between two separate parts, such as a trader and a trailer.

Aspect Ratio.
The relationship between the tire sidewall height and the section width.

Assistant Administrator.
The Assistant Administrator of the Federal Motor Carrier Safety Administration. The Assistant Administrator is the Chief Safety Officer of the agency pursuant to 49 U.S.C. 113 (d).

American Trucking Association.

ATC (Automatic Traction Control).
Optional feature based on ABS which prevents spinning of the drive wheels under power on slippery surfaces by braking individual wheels and/or reducing engine throttle.

Consists of maps of states, major cities, and areas. Some atlases may also include the location of permanent scales, low underpasses, size and weight limits, fuel taxes, designated routes and state laws for access to the designated highway system.

Operating rights granted to for-hire, common, and contract carriers by the FMCSA.

Authorized Carrier.
Person/company granted common or contract carrier operating rights by the FMCSA.

Automatic On-Board Recording Device.
An electric, electronic, electromechanical, or mechanical device capable of recording driver’s duty status information accurately and automatically as required by 395.15. The device must be integrally synchronized with specific operations of the commercial motor vehicle in which it is installed. At a minimum, the device must record engine use, road speed, miles driven, the date and the time of day.

Automatic Transmission.
One that, when set for a certain speed range, will not exceed that speed and the engine automatically shifts through the gears until it reaches that speed.

Automobile Transporter Body.
Truck or trailer body with ramps for loading and low-road clearance, designed for the transportation of vehicles, also known as a car carrier.

Auxiliary Brakes or Speed Retarders.
Devices that reduce the rig’s speed without using the service brakes.

Auxiliary (lift) Axles.
Axles which are lowered to the ground when heavy loads are carried, such as on dump trucks.

Auxiliary Lights.
Include reflectors, marker lights, clearance lights, taillights, ID lights, and brake lights. When working, auxiliary lights make the rig visible to other highway users.

Auxiliary Starter Button.
Available on some cab-over-engine (COE) models. It lets you start the engine with the cab tilted.

Auxiliary Transmission.
Second transmission connected with the main transmission to provide a wider range of speeds and gear ratios.

Average Speed Formula.
Average speed = Distance divided by time.

AVI (Automatic Vehicle Identification).
System combining an on-board transponder and 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.

Horizontally aligned structural member to which the wheels, brakes and suspension are attached.

Axle Group.
Any number of consecutive axles on a vehicle through which weight is 1) intended to be equally distributed for transmission to a public highway; and 2) transmitted to a public highway.

Device designed to raise and lower the liftable axle of a vehicle.

Axle Load.
Weight existing on a motor vehicle’s axle; an axle weight limit on a highway refers to the maximum weight allowed on the truck’s heaviest axle.

Axle Ratings.
Rear axles on a truck generally carry three ratings: 1) carrying capacity rated at the ground; 2) total weight the axle is capable of carrying/pulling in service, gross combined weight; 3) the maximum horsepower limit the axle is capable of carrying in normal service.

Axle Ratio.
Ratio of axle to drive line; the number of turns of the drive line in relation to one full turn of the drive wheels. The higher the numerical ratio, the slower the road speed.

Axle Spread.
The distance between the extreme axle centers of an axle group.

Axle Temperature Gauge.
Shows the temperature of the lubricant in the front and rear drive axles. The normal reading is 150-200 degrees, but it can reach higher readings, up to 230-250 degrees for a short period of time.

Axle Weight.
The load each axle is supporting. It can either be checked with portable scales by adding the weight of the wheel or at a weight station by driving each axle over the scale.

Connect the wheels to the rest of the rig and support the weight of the vehicle and its cargo.

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B Train.
A combination of vehicles composed of a tractor and a semi-trailer towing another semi-trailer attached to a fifth wheel mounted on the rear of the first semi-trailer.

1) Return transportation movement, usually at less revenue than the original move (headhaul);
2) Movement in the direction of lighter traffic flow when traffic is generally heavier in the opposite direction; or
3) to move a shipment back over part of a route already traveled.

A plate or wall for restricting movement of fluids.

A wall that has holes in it through which the liquid can flow in a tanker.

Bail-Out Area.
Places you can use to avoid a crash.

Ball Joint.
A mechanical joint in which a spherical end moves freely in a recessed socket. It is also called a ball and socket.

Barn Doors.
Rear doors on a trailer that swings open.

Basic Program Funds.
The total MCSAP funds less the High Priority Activity, Border Activity, Administrative Takedown and Incentive Funds.

Creates or receives and stores electrical energy.

Battery Fluid.
On some vehicles the fluid level in the batteries needs to be checked or maintained.

Distance from a truck’s front bumper to the back of its cab

The inner edge of the outer wall of a rubber tire, fitting on the rim. The “foundation” of a tire. It is made of high tensile steel wires and wrapped and reinforced by the plies.

Bell Pipe Concrete.
Pipe whose flanged end is of larger diameter than its barrel.

Belly Dump.
Trailer that unloads by opening an air-operated gate in its bed; bulk materials like sand, grain, coal or other dry products are usually belly-dumped.

Belly Mount Trailer.
A refrigerated trailer that has the refrigeration unit under the trailer.

Belted Bias Tires.
Have body cords that run across the tread at an angle.

The shoulder of the road.

Tire construction where the cords run diagonally to the tire’s bead or directional rotation.

Bill of Lading.
A contract between a shipper and a carrier.

Bill of Sale.
Formal document issued by a seller to a buyer as evidence of transfer of title to an item of personal property.

Used to bind down loads on flatbed trailers. It is important to make sure that all cargo is packaged correctly.

Bingo Card.
Slang term for authority cab card; designed with open squares on the back where driver places vehicle’s authority identification stamps (or PSC#) as received from various states. Card is to be carried in the cab of the power unit to which it has been assigned.

Black Ice.
A thin layer of ice clear enough to let you see the road underneath.

Blanket Permit.
A master type permit issued to a carrier by a state or province and which does not have any particular vehicle identification indicated. The permit may be photocopied, with a copy placed in the carrier’s vehicles as the required permit for those vehicles in that state.

Blanket Waybill.
A waybill covering two or more consignments of freight.

Bleed the Air Tanks.
To drain the accumulated water out of the air tanks of a tractor to prevent the condensed water from reducing air tank capacity and thus cutting braking efficiency.

Bleed the Fuel Lines.
To remove trapped air from the fuel lines.

Bleeding Tar.
Tar in the road that rises to the top, causing the road to be slippery.

Blind Sample or Blind Performance Test Specimen.
A urine specimen submitted to a laboratory for quality control testing purposes, with a fictitious identifier, so that the laboratory cannot distinguish it from employee specimens, and which is spiked with known quantities of specific drugs or which is blank, containing no drugs.

Blind-Side Backing.
Backing toward the right (blind) side of the rig.

Blind Specimen or Blind Performance Test Specimen.
A specimen submitted to a laboratory for quality control testing purposes, with a fictitious identifier, so that the laboratory cannot distinguish it from an employee specimen.

A structure, device or another substantial article placed against or around an article of cargo to prevent horizontal movement of the article of cargo.

Pieces of wood nailed to the floor.

Blood Alcohol Content (BAC).
The amount of alcohol in the bloodstream. Determines the level of intoxication.

A device that forces additional air into the engine to increase its efficiency and horsepower.

When a tire suddenly loses air.

Slang term for a tractor driven without its trailer, can also refer to a straight truck or a truck with a short rear overhang.

Bodily Injury.
Injury to the body, sickness or disease including death resulting from any of these.

1) An assembly of two or more axles; or
2) Removable set of rear axles and wheels used to support a van container.

Bogie or Bogey.
Assembly of two or more axles, usually a pair in tandem mechanically linked and suspended as one unit. Normally added to carry more weight.

Bogie truck.
Low skeleton platform mounted on two centrally located load-carrying wheels and fitted with two or four smaller diameter stabilizing wheels; also known as a restless dolly

Slang term for the binder devices used to tighten chains around cargo on flatbed trailers.

Booster Axles.
An axle generally having an air or hydraulic cylinder suspension system that can be actuated independently to assume a portion of the load that would otherwise be carried by adjacent axles.

Border Activity Funds.
Funds provided to States, local governments, and other person carrying out program, activities and projects relating to CMV safety and regulatory enforcement supporting the North American Free Trade Agreement (NAFTA) at the U.S. border. Up to 5 percent of total MCSAP funds are available for these activities.

Bottom Dump.
Trailer that unloads through bottom gates; same as belly dump.

Box Trailer.
Enclosed trailer for transporting freight.

Braces and Support.
Methods used to prevent loads fro moving. Whether flat bed or drybox, a load must be blocked or braced to prevent movement on all sides.

A structure, device, or another substantial article placed against an article of cargo to prevent it from tipping that may also prevent it from shifting.

Pieces cut to fit and nailed or otherwise secured.

An energy conversion mechanism used to stop, or hold a vehicle stationary.

Brake Backing Plate.
A circular plate in a hydraulic braking system to which the brake shoes, brake adjuster and wheel cylinder are mounted.

Brake Blocks.
Friction material or lining attached to a brake shoe.

Brake Chamber.
Chamber in which air pressure is converted to mechanical force for actuation of the air brakes.

Brake Chamber.
Air chamber mounted near each wheel and connected to the brake itself by a push rod and slack adjuster (cam brake) or a push rod (wedge brake).

Brake Chamber Diaphragm.
Diaphragm within the brake chamber designed to convert air pressure into mechanical force via a push rod.

Brake Compounding.
The result of stepping on the treadle valve with the spring brakes applied. If too much pressure is applied, the brake components can be damaged.

Brake Drum.
A bowl-shaped component of the braking system that is attached to the hub. When the brake shoes, with a friction material lining, expand against the inner surface of the drum, braking force is produced.

Brake Drum.
Metal, drum-shaped compartment that revolves with the wheel and provides a friction surface for the brake lining.

Brake Fade.
Decline of braking effectiveness which results from overheating of the brake shoes.

Brake Fade.
Occurs when the brakes overheat and lose their ability to stop the truck on a downgrade.

Brake Horsepower (bhp).
See Horsepower. Engine horsepower rating as determined by brake dynamometer testing. Gives actual or useful horsepower.

Brake Horsepower.
The actual horsepower of an engine, measured by a brake attached to the drive shaft and recorded on a dynamometer.

Brake Lining.
Material designed to create friction when pressed against the brake drum. It is fastened to the brake shoe and contacts the drum during the braking process.

Brake Shoe.
The non-rotating unit of the brake (to which the brake shoe is attached) that contacts the rotating unit to supply braking force.

Brake Tubing/Hose.
Metallic brake tubing, nonmetallic brake tubing and brake hose are conduits or lines used in a brake system to transit or contain the medium (fluid or vacuum) used to apply the motor vehicle’s brakes.

Used to stop the vehicle. Make sure that you maintain air pressure and don’t have any leaks in brake lines. If the brakes are pulling, have them checked right away. Bad brakes are dangerous to you and other motorists.

Braking System.
Used to slow or stop the rig. The braking system uses service brakes, secondary brakes, and parking brakes.

Break Down the Unit.
Slang term for the process of uncoupling a tractor from a trailer.

Breakaway Protection.
Process which applies brakes on the trailer(s) in case of a broken air hose or some other emergency.

Breath Alcohol Technician (BAT).
A person who instructs and assists employees in the alcohol testing process and operates an evidential breath testing device.

The distance between one axle and another, or between two sets of axles. Used in some states to ascertain the permissible gross weight for the vehicle. Also called spread.

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 Formula.
Formula used to determine maximum gross weight that can be carried on any given arrangement of consecutive axles.

A person who, for compensation, arranges or offers to arrange the transportation of property by an authorized motor carrier. A motor carrier, or person who is an employee or bona fide agent of a carrier, is not a broker within the meaning of this section when it arranges or offers to arrange the transportation of shipments which it is authorized to transport and which it has accepted and legally bound itself to transport.

Brokerage License.
Granted by the Federal Motor Carrier Safety Administration to allow licensee to arrange for transportation in interstate commerce.

Budd System.
A bolt and nut combination for holding disc wheels on to the hub. The design was originated by the Budd Corporation.

Budd Wheel.
See Disc Wheel. A single or dual mounted ten-hole disc wheel.

Build Sheet.
See Line Sheet.

A large trailer used for hauling low density bulk products which are pumped on and off.

A panel attached to the front of a trailer used for storing chains and binders and to protect the driver in a cab from heavy cargo shifting forward.

A solid wall or steel divider that divides a large tank into smaller tanks.

Bulk Cargo Container.
Shipping container employed in handling/hauling dry fluid materials.

Bulk Freight.
Dry or liquid freight not in packages/containers and transported in bulk, e.g., potatoes, grain, citrus, ore, etc.

Any motor vehicle designed, constructed and used for the transportation of passengers: except passenger automobiles or station wagons other than taxicabs.

A vehicle designed to carry more than 15 passengers, including the driver.

Any motor vehicle designed for transporting passengers, including taxi cabs.

Business District.
The territory contiguous to and including a highway when within any 600 feet along such highway there are buildings in use for business or industrial purposes, including but not limited to hotels, banks, or office buildings which occupy at least 300 feet of frontage on one side or 300 feet collectively on both sides of the highway.

Buttonhook Turn.
A right turn that allows you to clear the corner by proceeding straight ahead until the trailer tires clear the corner then turning right.

Bypass System.
Filters a small amount of the oil flow. It is normally used with the full flow system.

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C Dolly.
A converter dolly with two parallel arms which connect to two hitches located on a towing unit so as to prevent any rotation in a horizontal plane through the hitch points.

C Train.
A combination of vehicles composed of a tractor and a semi-trailer towing a full trailer connected with a C dolly.

The dimension from the center line of the back of the cab to the center line of the rear axle which determines how long the trailer can be.

The driver’s compartment of a commercial vehicle.

Cab Air Suspension.
Pneumatic suspension system of the driver’s compartment of the commercial vehicle.

Cab Cards.
Official identification cards to which permit stamps and state operating permits are attached. They are referred to as “bingo cards” by drivers.

Cab card.
Registration document issued by base jurisdiction for a vehicle in an apportioned/prorated fleet which identifies vehicle, base plate, registered weight by jurisdiction (if IRP); also shows jurisdictions where vehicle is registered.

Cable Anti-Jackknife Devices.
Area mounted on the trailer and connected to the tractor. The y keep the trailer and tractor in line.

Cabover (Cab-Over-Engine, COE).
Truck or tractor design in which the cab sits over the engine on the chassis.

Cab-Over-Engine (COE).
A truck or truck-tractor having all, or the front portion of the engine under the cab.

Cab Protector.
See Headache Rack

The process in which a person compresses the parking brake spring manually to release the spring brakes without the use of air pressure.

A hydraulic unit which, when pressurized by a brake application, squeezes the friction pads against a rotating disc.

Cam Brakes.
A drum brake in which the brake shoes are actuated by the rotation of a camshaft.

An alignment feature that is the amount the front wheels are tilted outward at the top. It is best for trucks to have positive camber.

Long, straight shaft covered with elliptical knobs called cams; as the camshaft turns, cams push the push rods and open the cylinder valves.

Camshaft (Brake).
Located on the axle, the cam rod creates a rotating force. One end of the rod is an “s” shaped cam which expands the brake shoes against the rotating drum.

Cancelled Test.
A drug or alcohol test that has a problem identified that cannot be or has not been corrected, or which this part otherwise requires to be cancelled. A cancelled test is neither a positive nor a negative test.

Cancellation of Insurance.
The withdrawal of insurance coverage by either the insurer or the insured.

Carbon Monoxide (CO).
A colorless, odorless, highly poisonous gas, produced by the incomplete combustion of fuel. It is usually expelled by the exhaust system.

Device in an engine to mix air with gasoline spray; mixture is then distributed to cylinders by intake manifold so it can be ignited by a spark.

Freight transported in a vehicle.

Cargo Doors.
Doors at the back or side of trailer where cargo may be loaded or unloaded. All hinges should be secure and rust and damage free.

Cargo Manifest.
Document listing all consignments on a truck, vessel or aircraft and giving quantity, identifying marks, consignor/consignee of each item.

Cargo Retainer Bars.
Used to secure cargo and keep loose cargo from moving.

Cargo Securement Devices.
Tie-downs, chains, tarps, and other methods of securing cargo in a flatbed. During inspection, make sure there is no damage and that they can withstand 1 ½ times any pressure from the load.

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

An organization that hauls cargo by truck.

Individual, partnership or corporation engaged in the business of transporting goods or passengers.

Carrier Bearings.
On trucks with a long wheel base, they join two drive shafts.

Carrier of Migrant Workers by Motor Vehicle.
Any person, including any “contract carrier by motor vehicle,” but not including any “common carrier by motor vehicle,” who or which transports in interstate or foreign commerce at any one time three or more migrant workers to or from their employment by any motor vehicle other than a passenger automobile or station wagon, except a migrant worker transporting himself/herself or his/her immediate family.

Carrier’s Time Record.
A record maintained by the carrier that records a driver’s duty status.

Cartage Company.
A Company that provides local pick-up and delivery, within a town, city or municipality.

Cashier’s Check.
A check that has all four of the following characteristics:
(1) Drawn on a bank as defined in 12 CFR 229.2
(2) Signed by an officer or employee of the bank on behalf of the bank as drawer.
(3) A direct obligation of the bank.
(4) Provided to a customer of the bank or acquired from the bank for remittance purposes.

The tire structure, excepting tread and sidewall rubber.

An alignment feature that is the amount the axle kingpin is tilted backward at the top. It is measured in degrees. The axle should have a positive caster or tilt forward.

Cast Spoke Wheel.
Wheel with five or six spokes origination from a center hub. The spoked portion, usually made of cast steel, is bolted to a multiple-piece steel rim.

Cast Steel Top Plate.
One type of manufactured fifth wheel top plate. See Fifth Wheel Plate.

CDL (Commercial Driver’s License).
License which authorizes an individual to operate commercial motor vehicles and buses over 26,000 pound gross vehicle weight. For operators of any trucks, the maximum size which may be driven without a CDL is Class 6 (maximum 26,000 pounds gross vehicle weight).

CE (CF, LP).
Distance from back of a truck’s cab to the end of its frame.

Centers for Disease Control (CDC).
Agency to be notified if a cargo spill is a disease-causing agent.

Center of Gravity.
The point where weight acts as a force. Center of gravity affects the vehicle’s stability.

Centrifugal Filter.
A type of bypass filter in which the oil enters the permanent housing, spins the filter at a high speed, forcing the dirt and particles out of the oil for more efficient cleaning of the oil.

Centrifugal Force.
The force that pushes objects away from the center of rotation. This force has the ability to push a vehicle off the road in a curve.

Certified Scale.
Any scale inspected and certified by an authorized scale inspection and licensing authority, and designed for weighing motor vehicles, including trailers or semi-trailers not attached to a tractor, or designed as a platform or warehouse type scale.

A legislative acronym, Code of Federal Regulations.

CG (Center of Gravity).
The point within the length and width of a vehicle around which its weight is evenly distributed or balanced.

Chain Binders.
A device used to remove slack from chains used to tie down loads.

Chain Control Area.
A highway area on which it is illegal to drive chains.

Chain of Custody.
The procedure used to document the handling of the urine specimen from the time the employee gives the specimen to the collector until the specimen is destroyed. This procedure uses the Federal Drug Testing Custody and Control Form (CCF).

Charging Circuit.
Produces electricity to keep the battery charged and run the electrical circuits which include battery, alternator or generator, voltage regulator, ammeter or voltmeter, electrical wires, and battery cables.

Charter Transportation of Passengers.
Transportation, using a bus, of a group of persons who pursuant to a common purpose, under a single contract, at a fixed charge for the motor vehicle, have acquired the exclusive use of the motor vehicle to travel together under an itinerary either specified in advance or modified after having left the place of origin.

The section of a commercial vehicle which includes the frame, suspension, wheels and brakes, steering mechanism, etc., but not the vehicle body or engine.

Chassis. The load-supporting frame in a truck or trailer, exclusive of any appurtenances which might be added to accommodate cargo.

Chassis Weight (Curb Weight, Tare Weight).
Weight of the empty truck including fluids, but minus occupants or load.

Check Valve.
Valve designed to prevent a loss of air pressure.

Check Valve.
Device to automatically isolate one part of the air brake system from another. A one-way check valve provides free air flow in one direction only. A two-way check valve permits actuation of the brake system by either of two brake application valves.

List of parts of the vehicle to check or inspect.

Chemical Transportation Emergency Center (CHEMTREC).
Tells emergency personnel what they need to know to take care of a chemical problem. It also helps make the proper notifications and supplies the emergency personnel with expert technical assistance.

Blocking equipment used to restrain movement of the wheels of a tractor or trailer.

Circuit Breaker. Breaks an electrical circuit during an overload.

Civil Forfeiture Proceedings.
Proceedings to collect civil penalties for violations under the Commercial Motor Vehicle Safety Act of 1986 (49 U.S.C. Chapter 313); the Hazardous Materials Transportation Act of 1975, as amended (49 U.S.C. Chapter 51); the Motor Carrier Safety Act of 1984 (49 U.S. C. Chapter 311, Subchapter III); section 18 of the Bus Regulatory Reform Act of 1982 (49 U.S.C. 31138); section 30 of the Motor Carrier Act of 1980 (49 U.S.C. 31139) and the ICC Termination Act of 1995 (49 U.S.C. Chapters 131-149).

The representative of the Federal Motor Carrier Safety Administration authorized to make claims.

Class 8.
Trucks in 60,000 to 80,000 pound range.

Class A Fire.
A fire in ordinary combustibles such as wood, paper and cloth.

Class B Fire.
A fire in flammable or combustible liquids and gases such as gasoline, diesel fuel, alcohol, paint, acetylene, hydrogen.

Class C Fire.
A fire in live electrical equipment. You must put it out with something that does not conduct electricity. After the electricity is cut off, extinguishers suitable for Class A or Class B fires may be used.

Class D Fire.
A fire in combustible metals such as magnesium and sodium. These fires can only be put out with special chemicals or powders.

Clearance Lamp.
A lamp used on the front and the rear of a motor vehicle to indicate its overall width and height.

Clearance Lights.
Also referred to as marker or running lights, these lights outline a vehicle’s length and breadth.

A “U” shaped yoke that screws onto the pushrod and is pinned to the slack adjuster.

Connects or disconnects the engine from the rest of the power train.

Device used for engaging or disengaging the engine’s power to the drive line.

Clutch Brake.
Stops the gears from turning. To engage it, push the clutch pedal all the way to the floor.

Clutch Brake.
Mechanism that slows the rotating clutch during disengagement which allows the driver to engage a gear while the motor is at idle.

Clutch Pedal.
Used when you start the engine or shift the gears. It has three basic positions – disengaged, free play, and engaged.

Clutchless Shifting.
Shifting a manual transmission without depressing the clutch. Also called slip shifting.

A commercial motor vehicle.

See Bus. Single deck multi-passenger vehicle used for long distance operation.

COD Shipments.
Shipments in which the driver collects payment on delivery for freight or cargo and freight.

Coefficient of Friction.
The interaction of an object (e.g. a tire) and a particular surface (e.g. roadway) calculated by dividing the force required to overcome friction on the object by the object’s weight. A higher number means greater friction, and greater stopping ability in the case of a vehicle on a roadway.

COE-High Profile.
A COE having the door sill step above the height of the front tires.

Code of Federal Regulations (CFR).
U.S. Government Printing Office publications containing regulations various federal agencies have created/promulgated.

Collection Container.
A container into which the employee urinates to provide the specimen for a drug test.

Collection Site.
A place selected by the employer where employees present themselves for the purpose of providing a urine specimen for a drug test.

A person who instructs and assists employees at a collection site, who receives and makes an initial inspection of the specimen provided by those employees, and who initiates and completes the CCF.

Combination Bypass/Full Flow Filter.
Oil from the full flow filter goes to the bearings, and the oil from the bypass filter returns to the oil pan.

Combination Ramp and Arrester Bed.
This escape ramp relies on loose surface material to stop a rig. It has a grade of 1.5% – 6% and is 500-2,200 feet long.

Combination Vehicle.
A power unit, typically a tractor, pulling one or more cargo units.

Combination Vehicle.
When you add a trailer to a tractor or a straight truck. it is also called a combination rig.

Combined Gross Vehicle Weight.
The total unladen weight of a combination of vehicles plus the weight of the load carried on that combination of vehicles.

(1) Any trade, traffic or transportation within the jurisdiction of the United States between a place in a State and a place outside of such State, including a place outside of the United States and
(2) Trade, traffic and transportation in the United States which affects any trade, traffic and transportation described in paragraph (1) of this definition.

Commercial Carrier.
Any motor carrier transporting persons or property for-hire on the public highways.

Commercial Driver’s License (CDL).
A license issued by a State or other jurisdiction, in accordance with the standards contained in 49 CFR part 383, to an individual which authorizes the individual to operate a class of a commercial motor vehicle.

Commercial Driver’s License Information System (CDLIS).
The CDLIS established by FHWA pursuant to section 12007 of the Commercial Motor Vehicle Safety Act of 1986.

Commercial Motor Vehicle.
Any self-propelled or towed motor vehicle used on a highway in interstate commerce to transport passengers or property when the vehicle-
(1) Has a gross vehicle weight rating or gross combination weight rating, or gross vehicle weight or gross combination weight, of 4,536 kg (10,001 pounds) or more, whichever is greater; or
(2) Is designed or used to transport more than 8 passengers (including the driver) for compensation; or
(3) Is designed or used to transport more than 15 passengers including the driver, and is not used to transport passengers for compensation; or
(4) Is used in transporting material found by the Secretary of Transportation to be hazardous under 49 U.S.C. 5103 and transported in a quantity requiring placarding under regulations prescribed by the Secretary under 49 CFR, subtitle B, chapter I subchapter C.

Commercial Motor Vehicle (CMV).
A motor vehicle or combination of motor vehicles used in commerce to transport passengers or property if the motor vehicle –
(a) Has a gross combination weight rating of 11,794 kilograms or more (26,001 pounds or more) inclusive of a towed unit(s) with a gross vehicle weight rating of more than 4,536 kilograms (10,000 pounds); or
(b) Has a gross vehicle weight rating of 11,794 or more kilograms (26,001 pounds or more); or
(c) Is designed to transport 16 or more passengers, including the driver; or
(d) Is of any size and is used in the transportation of hazardous materials as defined in this section.

Commercial Motor Vehicle.
Any motor vehicle that meets the definition of “commercial motor vehicle” found at 49 CFR 382.107 concerning controlled substances and alcohol use and testing, 49 CFR 383.5 concerning commercial driver’s license standards, or 49 CFR 390.5 concerning parts 390 through 399 of the FMCSRs.

Commercial Motor Vehicle (CMV).
A motor vehicle that has any of the following characteristics:
(1) A gross vehicle weight (GVW), gross vehicle weight rating (GVWR), gross combination weight (GCW), or gross combination weight rating (GCWR) of 4,537 kilograms (10,001 pounds) or more.
(2) Regardless of weight, is designed or used to transport 16 or more passengers, including driver.
(3) Regardless of weight, is used in the transportation of hazardous materials and is required to be placarded pursuant to 49 CFR part 172, subpart F.

Commercial Regulations.
Statutes and regulations that apply to persons providing or arranging transportation for compensation subject to the Secretary’s jurisdiction under 49 U.S.C. Chapter 135. The statutes are codified in Part B of Subtitle IV, Title 49, U.S.C(49 U.S.C. 13101 through 14913). The regulations include those issued by the Federal Motor Carrier Safety Administration or its predecessors under authority provided in 49 U.S.C. 13301 or a predecessor statute.

Commercial Shipper. Any person who is named as the consignor or consignee in a bill of lading contract who is not the owner of the goods being transported but who assumes the responsibility for payment of the transportation and other tariff charges for the account of the beneficial owner of the goods. The beneficial owner of the goods is normally an employee of the consignor and/or consignee. A freight forwarder tendering a shipment to a carrier in furtherance of freight forwarder operations is also a commercial shipper. The Federal government is a government bill of lading shipper, not a commercial shipper.

Commercial Vehicle Safety Act of 1986 (CMVSA/86).
Was passed to make sure all CMV drivers were qualified.

Commercial Vehicle Safety Plan (CVSP).
The document outlining the State’s CMV safety objectives, strategies, activities and performance measures.

Mixing types of goods from separate shipments and sending them as a combined shipment.

1) Articles, goods or merchandise; or 2) Goods shipped.

Common Carrier.
A term for a transportation company which serves the general public. It may be regular route service over designated highways on a regular basis or an irregular route between various points on an unscheduled basis.

Common Carrier.
A motor carrier that offers its services to all individuals and businesses.

Compatible or Compatibility.
The State laws and regulations applicable to interstate commerce and to intrastate movement of hazardous materials are identical to the FMCSRs and the HMRs or have the same effect as the FMCSRs; and that State laws applicable to intrastate commerce are either identical to, or have the same effect as, the FMCSRs or fall within the established limited variances under 350.341, 350. 343, and 350.345 of this subchapter.

Compliance Order.
A written direction to a respondent under this part requiring the performance of certain acts which, based upon the findings in the proceeding, are considered necessary to bring respondent into compliance with the regulations found to have been violated.

Compliance Review.
An on-site examination of motor carrier operations, such as driver’ hours of service, maintenance and inspection, driver qualification, commercial drivers license requirements, financial responsibility, accidents, hazardous materials, and other safety and transportation records to determine whether a motor carrier meets the safety fitness standard. A compliance review may be conducted in response to a request to change a safety rating, to investigate potential violations of safety regulations by motor carriers, or to investigate complaints or other evidence of safety violations. The compliance review may result in the initiation of an enforcement action.

Compression Pin.
Hardware used to join two 20-foot containers into a single 40-foot unit.

Compression Ratio.
Volume of air above the piston at bottom dead center compared with volume of air at top dead center.

Compression Stroke.
A phase of the four-stroke cycle when the air-fuel mix is compressed.

Squeezes the air into a smaller space. This increases the force the air exerts.

A device designed to create and maintain the necessary air in the brake system reserve and air ride suspension. It may be belt or gear driven.

Compressor Belt.
Belt running between engine pulley and air compressor that uses power of engine to operate air compressor.

Computerized Idle Timer.
A function of the engine’s electronic controls, it will shut down the engine in a prescribed amount of time after the truck has come to a halt.

Condensation Type Air Dryer.
A type of air dryer in an air brake system that accepts hot air from the compressor and cools it. The water and other impurities condense and are expelled out the purge valve.

Confirmatory Drug Test.
A second analytical procedure to identify the presence of a specific drug or metabolite which is independent of the initial test and which uses a different technique and chemical principle from that of the initial test in order to ensure reliability and accuracy. (Gas chromatography/ mass spectrometry (GC/MS) is the only authorized confirmation method for cocaine, marijuana, opiates, amphetamines, and phencyclidine).

Confirmatory Validity Test.
A second test performed on a different aliquot of the original urine specimen to further support a validity test result.

Confirmed Drug Test.
A confirmation test result received by an MRO from a laboratory.

Connecting Carrier.
Any carrier that transports freight to an interchange location and then transfers the cargo to another company to continue the shipment.

Connecting Rod.
Rod that connects the piston to the crankshaft.

Consent Order.
A compliance order which has been agreed to by respondent in the settlement of a civil forfeiture proceeding.

To send goods to purchaser or agent to sell.

Person who receives goods shipped from the owner.

Goods shipped when an actual purchase has not been made, but when the consignee agrees to sell the goods.

The person or company (usually the owner) that ships goods to customers.

Practice of combining less-than-carload (LCL) or less-than-truckload (LTL) shipments to make carload/truckload movements.

Consortium/Third-party Administrator (C/TPA).
A service agent that provides or coordinates one or more drug and/or alcohol testing services to DOT-regulated employers. C/TPAs typically provide or coordinate the provision of a number of such services and perform administrative tasks concerning the operation of the employer’s drug and alcohol testing programs. This term includes, but is not limited to, groups of employers who join together to administer, as a single entity, the DOT drug and alcohol testing programs of its members. (e.g., having a combined random testing pool). C/TPAs are not “employers” for purposes of this part.

Constant Mesh Gearbox.
All forward gear pairs remain in mesh for the transmission with the driving gear pair being engaged by a clutch.

Container (Shipping Container).
Standard-sized rectangular box, flat or tank used to transport product by ship, rail and highway. International shipping containers generally 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.
A semi trailer of skeleton construction limited to a bottom frame, one or more axles, specially built and fitted with locking devices for the transport of cargo containers, so that when the chassis and container are assembled, the units serve the same function as an over the road trailer.

Container Chassis.
Single-purpose semi-trailer designed to carry a shipping container.

Container (Van Body Type).
A truck or trailer body provided with means for ready removal from and attachment to a vehicle.

1) Practice/technique of using box-like device to store, protect, and handle a number of packages as a unit in transit; or
2) Shipping system based on large cargo-carrying containers (usually 20 or 40 feet in length) that can be interchanged between trucks, trains, and ships without rehandling contents.

Continuing Education.
Training for medical review officers (MROs) and substance abuse professionals (SAPs) who have completed qualification training and are performing MRO or SAP functions, designed to keep MROs and SAPs current on changes and developments in the DOT drug and alcohol testing program.

Continuous Seal.
A term denoting that the seals on a truck remained intact during the movement of the truck from origin to destinations or, if broke in transit, that it was done by proper authority and without opportunity for loss to occur before new seals were applied.

Illegal or prohibited traffic or freight.

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

Contract Carrier.
A motor carrier that is under contract to customers to transport their freight. The contract sets the rates and other terms of service.

Controlled Braking.
Putting on the brakes with a steady pressure just short of wheel lockup.

Controlled substance.
Has the meaning such term has under 21 U.S.C. 802(6) and includes all substances listed on schedules I through V of 21 CFR 1308 (1308.11 through 1308.15), as they may be amended by the United States Department of Justice.

Controlled Substances.
Those substances identified in 40.85 of this title.

A truck or tractor style consisting of a long hood with the driver sitting behind the engine.

Conventional Converter Dollies.
Used to change semitrailers into full trailers. The dolly becomes the front axle of the trailer.

Conventional Tractors.
Have a smoother ride because the driver sits between the front wheels and the rear wheels. Its main drawback is a longer wheel base, making it difficult to maneuver in tight spaces.

Converter Dolly.
Coupling device equipped with a fifth wheel and one or two axles. It allows a trailer to be coupled to a tractor or trailer combination.

Converter Dolly.
A set of wheels with a fifth wheel used to connect a tractor to a trailer or a trailer to a trailer.

Converter Dolly Axle.
Attaches to the front end of the trailer. this axle steers the second trailer in a set of doubles. The entire axle turns for steering.

Convex Mirror.
A curved mirror that gives the driver a wide-angle view to the rear of the rig.

An unvacated adjudication of guilt, or a determination that a person has violated or failed to comply with the law in a court of original jurisdiction or by an authorized administrative tribunal, an unvacated forfeiture of bail or collateral deposited to secure the person’s appearance in court, a plea of guilty or nolo contendere accepted by the court, the payment of a  fine or court cost, or violation of a condition of release without bail, regardless of whether or not the penalty is rebated, suspended, or probated.

A fluid, usually water and antifreeze, that circulates within the system. Coolant helps keep the engine cool and should be checked according to the truck’s operator manual.

Coolant Alarm.
A warning light that indicates if the level of coolant in the engine’s system is too low.

Coolant Filter.
Keeps the coolant system free of impurities.

Coolant Level Alarm.
Lights up when the coolant level starts dropping, indicating a probable leak.

Coolant Temperature Gauge.
Shows the temperature of the coolant in the engine block. The normal operating range is around 170-195 degrees.

Coolant Temperature Warning.
Lights up when the temperature is too high.

The period after stopping a rig but before turning off the engine.

Cooling System.
Keeps the temperature down in the engine.

Turning sharply in one direction and then quickly turning back in the other direction.

The procedure for connecting a tractor to a trailer, creating what is referred to as an articulated vehicle or tractor-trailer combination.

Joining a tractor to a trailer.

Coupling Device.
Device – called a converter gear or dolly – that makes it possible to attach one trailer to another or to a tractor. Check to make sure all parts are not damaged and are properly secured.

Coupling System.
Connects the tractor to the trailer.

Cranking Circuit.
Sends electricity from the battery to a small starter motor.

Creeper Gear.
Lowest gear/combination of gears on a tractor used when extra power is needed.

Wind-currents traveling from side to side – particularly dangerous on mountain roads.

Compliance, Safety, Accountability (CSA) is a Federal Motor Carrier Safety Administration (FMCSA) initiative to improve large truck and bus safety and ultimately reduce crashes, injuries, and fatalities that are related to commercial motor vehicles. It introduces a new enforcement and compliance model that allows FMCSA and its State Partners to contact a larger number of carriers earlier in order to address safety problems before crashes occur. Rolled out in December 2010, the program establishes a new nationwide system for making the roads safer for motor carriers and the public alike.

Cube (Cubic Capacity).
Interior volume of a truck body, semi-trailer or trailer, measured in cubic feet.

Cubic Capacity.
The carrying capacity of a truck measured in cubic feet.

Cubic Foot.
A common measure of the capacity of a truck, 1,728 cubic inches.

Curb Weight.
See Chassis Weight. The weight of a commercial vehicle with fuel, oil, lubricants and coolant and all standard equipment, but minus the driver and cargo.

Curb Weight.
The weight of an empty tractor trailer minus driver and cargo but including fuel, oil, and all standard equipment.

Curtain Sider.
Commercial vehicle trailer with removable sides made of a flexible fabric which can be pulled back for side access to the cargo.

Custom Trailer and Dolly for Hauling Large Diameter and Long Items.
Has a drop frame and two rear axles.

Customer Relations.
How a truck driver gets along with customers.

Commercial Vehicle Safety Alliance.

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Dayton Wheel.
See Cast Spoke Wheel.

Dead Axle.
An axle that is not powered by the engine. Its purpose is to help carry the load.

Dead Axle.
An axle that is not powered. Used to steer and support the load.

Dead Heading.
Operating a truck without a cargo.

Returning to home base without a load after delivery has been made.

Deck Plate.
A horizontal surface designed to provide a person with stable footing for the performance of work such as the connection and disconnection of air and electrical lines, gaining access to permanently-mounted equipment or machinery or for similar needs.

Declared Combined Gross Vehicle Weight.
The total unladen weight of any combination of vehicles plus the maximum load to be carried on that combination of vehicles for which registration fees have been paid.

Defensive Driving.
Driving to avoid or get out of problems that may be created by other drivers.

The act of transferring possession of a shipment. This could be from consignor to carrier, one carrier to another, or carrier to consignee.

Deliver, or Terminal, Carrier.
The carrier that delivers the shipment to the consignee.

Department of Motor Vehicles (DMV).
Assists in making state laws and regulations for motor carriers.

Department of Transportation.
The federal agency responsible for enforcing the Federal Motor Carrier Safety Regulations.

Department of Transportation (DOT).
Administers federal regulations and interstate trucking operations.

Depth Perception.
The ability to judge distances.

Desiccant Air Dryer.
A type of air dryer in an air brake system in which the water is stripped from the air by running the air through a bed of desiccant beads.

Designated Employer Representative (DER).
An individual identified by the employer as able to receive communications and test results from service agents and who is authorized to take immediate actions to remove employees from safety-sensitive duties and to make required decisions in the testing and evaluation processes. The individual must be an employee of that company. Service agents cannot serve as DERs.

Delay of a driver and freight vehicle or container beyond a stipulated time.

Detention Time or Demmurage.
Detaining a vehicle beyond a given time. payment is made to the carrier when delivery is delayed.

See Brake Chamber Diaphragm.

Diesel Engine.
A compression ignition, internal combustion engine.

Diesel Engine.
Has fuel injectors to supply fuel to the cylinders. The air intake system supplies the air to the cylinders. It does not have a carburetor.

The food a person eats.

A gear assembly which permits one axle shaft and wheel to turn at a different speed than the other.

Transfers driving power to the wheels through the drive axle shafts.

Differential Lock, Interaxle Type.
Used on twin-screw tractors, this valve can be set to lock both rear axles together so that they pull as one for off-the-road operation. Never used for over-the-road operation.

Differential Warning.
Flashes when the interaxle differential is in the locked position.

Dilute Specimen.
A urine specimen with creatinine and specific gravity values that are lower than expected for human urine.

Direct Assistance.
Transportation and other relief services provided by a motor carrier or its driver(s) incident to the immediate restoration of essential services (such as, electricity, medial care, sewer, water, telecommunications, and telecommunication transmissions) or essential supplies (such as, food and fuel). It does not include transportation related to long-term rehabilitation of damaged physical infrastructure or routine commercial deliveries after the initial threat to life and property has passed.

Direct Current (D.C.).
Electrical current that always flows in one direction only and is the type used in automotive equipment.

Direct Drive.
A match between the transmission output shaft speed and the transmission input speed.

Direct Drive.
Refers to a condition in which the transmission is in a gear having a 1:1 ratio, that is, when the engine crankshaft is turning at the same rate as the vehicle drive shaft.

Disabling Damage.
Damage which precludes departure of a motor vehicle from the scene of the accident in its usual manner in daylight after simple repairs.
(1) Inclusions. Damage to motor vehicles that could have been driven, but would have been further damaged if so driven.
(2) Exclusions.
(i) Damage which can be remedied temporarily at the scene of the accident without special tools or parts.
(ii) Tire disablement without other damage even if no spare tire is available.
(iii) Headlight or taillight damage.
(iv) Damage to turn signals, horn, or windshield wipers which make them inoperative.

Disc Brakes.
A braking system in which friction pads are brought into contact with the face of the disc brake with the assistance of a caliper.

Disc Brakes.
A modern disc brake system usually has a fixed disc attached to the inside of the wheel. To slow down or stop, the linings are squeezed against each side of the disc. This looks something like a wide-jawed vice closing quickly on a spinning disk. It creates the friction that slows or stops the rig.

Disc Wheel.
Single-piece rim/wheel assembly of pressed steel or forged aluminum, anchored by 8 or 10 nuts to a hub.

Any of the following three actions:
(a) The suspension, revocation, or cancellation of a CDL by the State or jurisdiction of issuance.
(b) Any withdrawal of a person’s privileges to a drive a CMV by a State or other jurisdiction as the result of a violation of State or local law relating to motor vehicle traffic control (other than parking, vehicle weight or vehicle defect violations).
(c) A determination by the FMCSA that a person is not qualified to operate a commercial motor vehicle under part 391 of this chapter.

Person in charge of dispatching trucks and drivers to and from destinations.

The scheduling and control of freight distribution.

Distance Calculation.
Distance traveled can be determined by multiplying driving speed (miles per hour) by time (the number of hours driven).

Distance Formula.
Distance = Speed X Time.

A change made in the route of a shipment in transit.

Divisible Load.
Any load consisting of a product, material or equipment which can be reduced to meet the specified regulatory limits for size and/or weight.

A platform where trucks load and unload.

Dock Plate.
Removable ramp used between dock and trailer/railcar so forklift can drive into unit, used for ease/safety in loading/unloading.

Dock Receipt.
A receipt given for a shipment received or delivered at a pier or dock.

The papers that accompany shipments and provide an accurate record of the cargo. It also serves as a contract for the transportation services.

Door Sill Step.
Any step normally protected from the elements by the cab door when closed.

DOT, The Department, DOT Agency.
These terms encompass all DOT agencies, including, but not limited to, the United States Coast Guard (USCG), the Federal Aviation Administration (FAA), the Federal Railroad Administration (FRA), the Federal Motor Carrier Safety Administration (FMCSA), the Federal Transit Administration (FTA), the National Highway Traffic Safety Administration (NHTSA), the Research and Special Programs Administration (RSPA), and the Office of the Secretary (OST). These terms include any designee of a DOT agency.

DOT agency.
An agency (or “operating administration”) of the United States Department of Transportation administering regulations requiring alcohol and/or drug testing (14 CFR parts 61, 63, 65, 121, and 135; 49 CFR parts 199, 219, 382, and 655), in accordance with part 40 of this title.

A tractor plus semi-trailer plus full trailer having 5 or 6 axles with typically two 26-29 foot trailers.

Double Check Valve.
A valve positioned between the two reservoir air tanks in an air brake system. In the event of a failure, it will seal off the damaged tank, thereby preserving the air in the second tank.

Double Clutching.
Shifting the gears of a non-synchronized truck transmission to keep maximum control of the vehicle by depressing and releasing the clutch pedal twice; the driver must downshift in order to gain enough RPM to reach the next lower gear.

Double Clutching.
A method of shifting in which you shift to neutral, then shift to the desired gears to match the RPM.

Double Drop Deck Trailer.
A trailer bed that is not only lower than the fifth-wheel plate, but is even lower than the trailer axles. The floor of the trailer comes within a few inches of pavement.

Double Drop Frame.
These are low beds that can haul heavy and oversized equipment without going over the height limits. Since these trailers are low to the ground they may have bottom clearance problems at railroad crossings, curbs, and large potholes.

A steep downward slant in the road, usually around mountains or hill country.

When the engine needs more power, moving down the gears increases engine power while giving up some speed.

Drag Link.
The link in a steering system that connects the Pitman arm to the steering arm.

Drag Link.
Transfers movement from the Pitman arm to the left steering arm.

Drain Cocks.
Drains moisture from the air brake system reservoirs; should be drained each day.

A horizontally hinged rigid bar or A-frame by which a full trailer is towed and steered.

Driveaway-Towaway Operation.
Any operation in which a motor vehicle constitutes the commodity being transported and one or more set of wheels of the motor vehicle being transported are on the surface of the roadway during transportation.

Drive Axle.
By way of a differential and transmission arrangement, the drive axle transmits power from the engine to the wheels.

Drive Axle.
An axle that transmits power to the wheels. A drive axle is a powered axle that actively pulls the load.

Drive Shaft.
Is a steel shaft that runs from the transmission to the rear of the vehicle.

Drive Train.
Takes the power generated by the engine and applies it to the tractor’s rear wheels. As the wheels turn, the rig moves.

Drive Wheel Skid (Tractor Jackknife).
A skid that occurs when the tractor drive wheels lose traction.

All the components which together transmit power from the transmission to the drive axle(s). These consist of at least one drive shaft (propeller shaft) with a universal joint at each end.

Any person who operates a commercial motor vehicle. This includes, but is not limited to: Full time, regularly employed drivers; casual, intermittent or occasional drivers; leased drivers and independent owner-operator contractors.

Driver Applicant.
An individual who applies to a State to obtain, transfer, upgrade or renew a CDL.

Driver Awareness.
A driver must be aware of his or her vehicle at all times and be constantly alert.

Driver’s Daily Log.
Daily record required to be kept by driver which shows driving, on-duty/not driving, sleeper berth, and off-duty time.

Driver’s Daily Log, or Driver’s Log.
The most commonly used record of duty status for drivers.

Driver Image.
The impression a truck driver makes on other people.

Driver or Operator.
Any person who drives any motor vehicle.

Driver Qualification Proceeding.
A proceeding commenced under 49 CFR 391.47 or by issuance of a letter of disqualification.

Driver Reaction Distance.
The distance your rig travels during the time it takes to identify a hazard.

Any employee who is employed solely as such by a private carrier of property by commercial motor vehicle, who is engaged both in selling goods, services, or the use of goods, and in delivering by commercial motor vehicle the goods sold or provided or upon which the services are performed, who does so entirely within a radius of 100 miles of the point at which he/she reports for duty, who devotes not more than 50 percent of his/her hours on duty to driving time. the term selling goods for purposes of this section shall include in all cases solicitation or obtaining of reorders or new accounts, and may also include other selling or merchandising activities designed to retain the customer or to increase the sale of goods or services, in addition to solicitation or obtaining of reorders or new accounts.

Driver-Side Backing.
Backing toward the left (driver) side of the rig.

Driver’s License.
A license issued by a State or other jurisdiction, to an individual which authorizes the individual to operate a motor vehicle on the highways.

Driver’s Qualification File.
Includes hiring information, documents concerning the driver’s qualifications to drive, including employment testing, motor vehicle records, citizenship, notice to driver and certificate of compliance, current driver’s license, notices of violations to employer, drug testing, medical statements.

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

Driving a commercial motor vehicle while under the influence of alcohol.
Committing any one or more of the following acts in a CMV –
(a) Driving a CMV while the person’s alcohol concentration is 0.04 percent or more.
(b) Driving under the influence of alcohol as prescribed by State law; or
(c) Refusal to undergo such testing as is required by any State or jurisdiction in the enforcement of 383.51(b) or 392.5(a)(2).

Driving Time.
All time spent at the driving controls of a commercial motor vehicle in operation.

Drop Deck Flatbed Trailer.
A trailer with a flatbed which is lower than the fifth wheel on the tractor.

Drop Frame Trailer.
Open flatbed trailer sometimes equipped with van body (household goods mover) designed with minimum floor-to-highway distance except for raised section for rear wheel housings and raised forward section. This increases cargo capability without increasing the vertical clearance of the vehicle.

The drugs for which tests are required under this part and DOT agency regulations are marijuana, cocaine, amphetamines, phencyclidine (PCP), and opiates.

Drum Brakes.
A metal cylinder that looks something like a drum that is bolted to each end of the axle. To stop the vehicle, the brake shoe linings are forced against the inside surface of the brake drums which creates the friction that slows or stops the rig.

Drum Truck.
Hand truck used to carry drums. Never roll drums to load them.

Dry Bulk Tankers.
Used to haul dry bulk cargo. Dry bulk tankers have a high center of gravity that requires careful speed control, particularly on curves.

Dry Tank.
The air reservoir from which the brake system draws air.

Dry Tank.
Part of brake system. Air passes from wet tank to dry tank. Dry tank is the air reservoir from which the air is drawn for operating the brake system.

Dual Circuit Brake System.
A redundant air brake system designed so the second system will take over in the event of a failure by the first.

Dual Wheels.
Wheel assembly with two wheels on each side of axle, generally found only on rear.

Two wheels mounted together.

Wheels with tires mounted in pairs on each end of the axle.

Dummy Coupler.
A fitting used to seal the opening in an air brake hose connection (glad hands) when the connection is not in use. Sometimes called a dust cap.

Dump body.
Truck body which can be titled to discharge load.

Dump Trailer.
Framed or frameless trailer, used for transporting granular construction materials, coal, etc. Unloaded by use of a hydraulic cylinder that raises the front end of the trailer and dumps the cargo out the rear of the trailer.

All loose materials used to support and protect cargo.

Dunnage and Return.
The weight of the dunnage will be listed on the bill of lading. If the shipper wishes it to be returned, this will be stated on the bill of lading.

Dunnage Bag.
An inflatable bag intended to fill otherwise empty space between articles of cargo, or between articles of cargo and the wall of the vehicle.

A tax levied by a government on imports and exports.

Driver vehicle inspection report.

A device for measuring the work output of an engine.

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