Georgia CDL Combination Vehicles Test key terms

A power unit towing one or more trailers, such as a tractor-semitrailer or a truck pulling a full trailer. The added weight, length, and articulation change how the vehicle turns, stops, and backs.

Any joint where a combination vehicle pivots, such as the fifth wheel coupling or a converter dolly. Each joint adds a place where the trailer can swing out or fold during turns and backing.

The horseshoe-shaped plate mounted on the tractor that locks onto the trailer kingpin and carries the trailer's weight. It pivots to let the trailer turn and must be greased and latched correctly.

The vertical steel pin under the front of a semitrailer that drops into the fifth wheel and holds the trailer to the tractor. Its condition and the locking jaws around it are critical safety checks.

The mechanism inside the fifth wheel that closes around the kingpin to secure the trailer. The release handle must be in the locked position, and a pull test confirms the jaws have fully closed.

A check performed after coupling where you pull the tractor forward gently with the trailer brakes still set. If the trailer holds and the tractor does not move, the kingpin and jaws are properly engaged.

An adjustable fifth wheel or trailer axle assembly that can be moved forward or backward to shift weight between axles. Repositioning it changes axle loads and must keep the vehicle within legal weight limits.

The retractable legs under the front of a semitrailer that support it when uncoupled. They must be fully raised before moving and lowered onto firm ground before releasing the fifth wheel.

A small axle-and-frame unit with its own fifth wheel that couples a second trailer behind a semitrailer. It adds another articulation point and must be secured with safety chains and air lines.

Combination configurations pulling two or three trailers. Each extra trailer increases off-tracking, rearward amplification, and stopping distance, and requires specific driving privileges and inspection attention.

Chains that connect the trailer to the towing vehicle as a backup if the coupling fails. They should be crossed under the tongue and tight enough to hold the trailer without dragging on the road.

A system that applies the trailer's brakes automatically if the trailer separates from the tractor and the air lines part. It is powered by the trailer's emergency air supply or a charged reservoir.

The line that carries air pressure from the tractor to apply and release the trailer brakes during normal driving. It usually connects to the trailer's blue gladhand and must be free of leaks.

The line that supplies air to the trailer's emergency system and signals a breakaway or pressure loss. It connects to the red gladhand, and losing pressure in it triggers the trailer's spring brakes.

The quick-coupling fitting at the end of a trailer air line. Red and blue gladhands must be matched to the correct lines and sealed with good rubber gaskets to prevent leaks.

The tractor-mounted control, often the red button on the dash, that charges or shuts off air to the trailer. Pulling it out applies the trailer parking brakes; pushing it in charges the trailer system.

Brakes held on by heavy springs and released by air pressure. If air pressure drops or the trailer breaks away, the springs apply the brakes automatically, so they also serve as parking brakes.

A test where you charge the trailer system, shut off the engine, and watch the gauge for pressure loss. A steady drop indicates a leak in the lines, fittings, or brake chambers that must be fixed.

The procedure of connecting a tractor to a trailer: aligning the fifth wheel and kingpin, backing under, locking the jaws, connecting air lines and electrical cord, raising landing gear, and testing the connection.

The procedure for separating a tractor from a trailer: parking on firm level ground, setting brakes, lowering landing gear, disconnecting lines, releasing the fifth wheel, and pulling forward slowly.

The systematic walk-around check of the tractor, trailer, coupling, brakes, lights, tires, and cargo before driving. For combination vehicles it must cover every articulation point and air connection.

The tendency of a trailer's rear wheels to cut inside the path of the front wheels during a turn. Longer wheelbases and multiple trailers increase it, so you must swing wide and watch mirrors.

The total width of road a vehicle covers as it moves through a turn, including the trailer's inside cut and any rear overhang swing outside. Planning for swept path prevents curb strikes and side collisions.

The way side-to-side motion at the tractor is magnified at the rear of each following trailer, especially in doubles and triples. Small steering inputs can whip the last trailer, so steer smoothly at speed.

Side-to-side fishtailing of a trailer caused by speed, crosswinds, uneven loading, or abrupt steering. Ease off the accelerator and hold the wheel steady rather than braking hard or overcorrecting.

Approaching a right turn by moving into the proper lane position, often swinging left first, so the trailer clears the curb. Turning too tight causes the trailer's rear wheels to strike or climb the curb.

The point around which a vehicle rotates during a turn, roughly the rear axle of the tractor. Tracking where it sits helps you judge how far the trailer will cut inside or swing outside.

A loss of control where the tractor and trailer fold against each other at a sharp angle. It can result from locking the drive wheels under hard braking or from driving too fast on slippery roads.

The technique of releasing hard braking, looking and steering where you want to go, and avoiding overcorrection when wheels lose traction. With a trailer, smooth inputs matter more because the trailer magnifies them.

The setting that keeps brake shoes close enough to the drum for full stopping power. Poorly adjusted trailer brakes lengthen stopping distance and can cause the tractor's brakes to overheat.

The total distance traveled from recognizing a hazard to a full stop, including perception, reaction, and braking. A loaded combination vehicle needs far more room than a car, especially on downgrades or wet pavement.

The gap you keep behind the vehicle ahead, measured in seconds. Combination vehicles need at least one second per ten feet of vehicle length plus extra time in rain, fog, or darkness.

The margin of clear space kept around the vehicle on all sides. With limited maneuverability and long stopping distances, combination drivers must protect front, side, and rear space continuously.

Choosing a speed that matches road, weather, load, and curve conditions rather than the posted limit alone. Enter curves and downgrades slowly, since a combination vehicle cannot shed speed quickly.

Areas around the vehicle that mirrors do not show, notably beside the trailer, directly behind, and along the right side. Long trailers create large no-zones, so signal early and check mirrors before lane changes.

Keeping the entire combination vehicle, including the trailer, centered in its lane through curves and lane changes. Because the trailer tracks differently, you must check mirrors often and avoid cutting corners.

Setting the flat and convex mirrors so the trailer sides, wheels, and adjacent lanes are visible from the driver's seat. Properly aimed mirrors are the main tool for judging trailer position while turning and backing.

Moving a combination vehicle in reverse, where steering reverses the trailer's direction and small errors grow quickly. Use a spotter, GOAL (get out and look), and gentle corrections to keep the trailer straight.

Get Out And Look: stopping to walk around and check the area before continuing a difficult maneuver. It is the simplest way to avoid hitting objects, people, or other vehicles while backing.

A person who stands where the driver can see them and signals during backing or tight maneuvers. Agree on hand signals beforehand and stop immediately if the spotter disappears from view.

The system of tiedowns, straps, chains, and blocking that keeps a load from shifting or falling. Loads must be secured to standards, with enough tiedowns and working devices inspected before each trip.

How a load's weight is spread across the tractor and trailer axles. Placing heavy freight too far back or forward can overload axles, lighten the steering axle, and make the vehicle unstable.

Movement of cargo during driving caused by weak securement, poor blocking, or sudden maneuvers. A shifting load can change axle weights, damage the trailer, or cause a rollover, so loads need restraint and periodic checks.

A place where the road crosses train tracks, requiring a combination vehicle to slow, look, and listen before proceeding. Never stop on the tracks, and check that the trailer will clear before starting across.

What a driver does when a breakdown, crash, or fire occurs, such as pulling off the road, warning traffic, calling for help, and protecting the scene. Placards and cargo type determine the hazards to report.