Alabama CDL General Knowledge key terms

The total distance a vehicle travels from the moment the driver perceives a hazard until the vehicle comes to a complete stop, combining perception distance, reaction distance, and braking distance.

The distance a vehicle travels while the driver is recognizing that a hazard exists ahead and deciding what to do about it.

The distance traveled between the moment a driver decides to act and the moment the foot actually reaches the brake pedal or the hands begin to steer.

The distance a vehicle travels from the instant the brakes are applied until it stops, affected by speed, weight, brake condition, and road surface traction.

The grip between tires and the road surface that allows steering, accelerating, and stopping; it is reduced by rain, ice, snow, oil, and loose gravel.

A loss of tire grip in which the wheels slide instead of rolling, often caused by braking too hard, accelerating too fast, or turning too sharply on a slippery surface.

A condition in which tires ride up on a layer of water and lose contact with the road, causing loss of steering and braking control at higher speeds.

The gap maintained behind the vehicle ahead, commonly measured in seconds by counting from when that vehicle passes a fixed object until your vehicle reaches it.

The safety margin of clear space kept around a vehicle on all sides so there is room to stop or maneuver if traffic ahead changes suddenly.

Any road, traffic, weather, or load condition that could require a driver to change speed or direction to avoid a crash.

The maximum total weight a single vehicle is designed to carry, including the vehicle itself, fuel, passengers, and cargo, as specified by the manufacturer.

The maximum allowable total weight of a towing vehicle plus its trailer(s) and all cargo, as specified by the manufacturer.

The amount of weight carried by a single axle or axle group, which must stay within legal limits to avoid overloading and damage to roads and tires.

The system of tiedowns, straps, chains, and blocking used to keep cargo from shifting, sliding, or falling off the vehicle during travel.

A strap, chain, rope, or other device used to fasten cargo to a vehicle; the number and strength required depend on the cargo's weight and length.

Movement of cargo during travel, which can change axle weights, affect steering and braking, and cause loss of control or spilled cargo.

The point at which a vehicle's or load's weight is balanced; keeping it low and centered improves stability, especially in turns.

A crash in which a vehicle tips onto its side or roof, most often caused by taking a curve too fast, especially with a high center of gravity.

A braking system that uses compressed air to apply the brakes, common on heavy trucks and buses, and which requires an understanding of air pressure and reservoir capacity.

A pump driven by the engine that builds and maintains air pressure in the brake system's reservoirs.

A reservoir that stores compressed air for the brake system; drains are used to remove moisture and oil that collect inside.

A device that controls when the air compressor pumps air into the tanks and when it stops, keeping system pressure within a set range.

A light and buzzer that activate when air pressure in the brake system drops below a safe level, warning the driver to stop and find the problem.

A parking brake that uses a strong spring to apply the brakes automatically when air pressure is lost, so the vehicle fails safe rather than rolling freely.

The linkage that connects the brake chamber pushrod to the brake shoes; too much free play means the brakes are out of adjustment and slow to apply.

A temporary loss of braking power caused by overheating, often from repeated hard braking on long downgrades, which can be avoided by using a lower gear.

A power unit towing one or more trailers, such as a tractor-semitrailer, which requires different handling and braking techniques than a single vehicle.

The horseshoe-shaped coupling plate on a tractor that locks onto the trailer's kingpin to connect the trailer and support its front weight.

The pin mounted under a trailer's front that locks into the tractor's fifth wheel to hold the trailer in place.

A fifth wheel that can be moved forward or backward on the tractor frame to shift weight between axles and meet legal weight limits.

A small axle and frame with its own fifth wheel and hitch that connects a second trailer to a tractor-trailer combination.

Side-to-side fishtailing of a trailer, often started by steering too sharply, uneven load, or speed, and countered by slowing gradually and not braking hard.

The tendency of a trailer's rear wheels to cut a shorter path than the tractor's front wheels in a turn, requiring the driver to swing wider.

A systematic check of a vehicle's tires, brakes, lights, fluids, couplings, and load before driving, required to catch defects that could cause breakdowns or crashes.

A step-by-step visual check made by walking completely around the vehicle, looking at each component in a fixed order so nothing is missed.

A check performed at low speed after starting that confirms the brakes stop the vehicle squarely and that the parking brake holds.

A brake that holds a parked vehicle in place; it must be set whenever the vehicle is left unattended and released before driving.

A shifting technique using two clutch presses, one to shift to neutral and one to engage the next gear, to match engine speed in a non-synchronized transmission.

Changing to a higher gear as speed increases, done at the right engine speed so the vehicle does not lose power or jerk.

Changing to a lower gear, used to slow the vehicle and control speed on downgrades, and done before the engine lugs or the vehicle loses power.

Operating a vehicle while attention is taken away by texting, eating, adjusting controls, or other tasks, increasing the risk of missing hazards and crashing.

A place where a road crosses train tracks; drivers must slow down, look and listen, and never stop on the tracks.