Air Brake
A braking system that uses compressed air to apply the service brakes on commercial vehicles.
Practice related concepts →
Start PracticeCDL Glossary
Clear explanations of the terminology you will encounter during CDL study, vehicle inspection and professional driving.
Air Compressor
The engine-driven component that supplies compressed air to the brake system.
Practice related concepts →Air Governor
A device that controls when the air compressor loads and unloads.
Practice related concepts →Alley Dock
A backing maneuver that positions a commercial vehicle into a space approached from an angle.
Practice related concepts →Axle Weight
The amount of vehicle weight supported by one axle or axle group.
Practice related concepts →Backing
Moving a commercial vehicle in reverse using careful setup, mirror use and corrections.
Practice related concepts →Blind Spot
An area around the vehicle that cannot be seen directly or through the mirrors.
Practice related concepts →CDL
A Commercial Driver’s License required to operate specified commercial motor vehicles.
Practice related concepts →CLP
A Commercial Learner’s Permit allowing supervised commercial-driving practice.
Practice related concepts →Danger Zone
The area around a school bus where children may be difficult for the driver to see.
Practice related concepts →Doubles and Triples
Combinations involving two or three trailers and requiring the appropriate endorsement.
Practice related concepts →ELDT
Entry-Level Driver Training required for certain first-time CDL and endorsement applicants.
Practice related concepts →Fifth Wheel
The coupling platform on a tractor that locks around the trailer kingpin.
Practice related concepts →Gross Combination Weight Rating
The manufacturer’s maximum loaded rating for a combination of vehicles.
Practice related concepts →Gross Vehicle Weight Rating
The manufacturer’s maximum loaded rating for a single vehicle.
Practice related concepts →Hazard Perception
Recognizing developing road hazards early enough to respond safely.
Practice related concepts →Hours of Service
Federal limits and requirements governing a commercial driver’s working and driving time.
Practice related concepts →Kingpin
The trailer pin captured by the fifth-wheel locking jaws during coupling.
Practice related concepts →Offtracking
The tendency of rear wheels to follow a shorter path than the front wheels in a turn.
Practice related concepts →Placard
A diamond-shaped sign identifying the hazard class of regulated cargo.
Practice related concepts →Pre-Trip Inspection
A systematic safety inspection completed before operating a commercial vehicle.
Practice related concepts →Rearward Amplification
The increased side-to-side movement experienced by trailers farther back in a combination.
Practice related concepts →Space Management
Maintaining safe space around the vehicle to preserve visibility and escape options.
Practice related concepts →Spring Brake
A mechanically applied brake held in the released position by air pressure.
Practice related concepts →Surge
The movement of liquid cargo inside a tank as speed or direction changes.
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