NY CDL Combination key terms

The horseshoe-shaped coupling plate mounted on the tractor that locks around the trailer kingpin to hold the trailer attached and let it pivot while towing.

The vertical steel pin under the front of a trailer that drops into the fifth wheel jaws, forming the pivot point between tractor and trailer.

The full procedure of backing the tractor under a trailer, engaging the fifth wheel, connecting air and electrical lines, raising the landing gear, and testing the connection.

A pull check after coupling in which the driver applies slight forward power against a locked trailer brake to confirm the fifth wheel jaws are closed on the kingpin.

The retractable support legs under a trailer front that hold it level when uncoupled; they must be fully raised before driving away.

The sequence of parking on firm level ground, chocking wheels, lowering landing gear, disconnecting lines, releasing the fifth wheel, and pulling out slowly.

A movable fifth wheel mounting that lets the driver shift the tractor's rear axle position to adjust weight distribution between steering and drive axles.

The interlocking couplers that join the tractor's air supply and service lines to the trailer's brake system; they must be sealed and locked.

A dash-mounted control, often called the trolley valve, that lets the driver apply only the trailer brakes independently for testing and for settling a trailer.

The flexible hoses carrying compressed air between tractor and trailer; they must be supported so they do not drag, kink, or rub.

A valve that closes off the tractor's air supply if a trailer line breaks or separates, keeping enough air to stop the tractor.

A trailer-mounted valve that applies the trailer spring brakes automatically when air pressure drops or the supply line separates.

Parking and emergency brakes held off by air pressure; when pressure is lost, powerful springs apply the brakes automatically.

The air hose that continuously charges the trailer's reservoirs; losing it triggers the trailer's automatic emergency brake application.

The air hose that carries the driver's brake application signal to the trailer's relay valve so trailer brakes match tractor braking.

A trailer valve that uses a small control signal from the service line to release a large volume of stored air to the brake chambers quickly.

The short delay between pressing the pedal and air pressure reaching the trailer brakes; it lengthens stopping distance and requires following farther behind.

A buzzer and light that activate before pressure falls too far to stop safely, typically around 60 psi, warning the driver to stop immediately.

The measured drop in pressure per minute with brakes released and with them applied; excessive leakage means the vehicle must be taken out of service.

The systematic walk-around check of coupling, air lines, brakes, tires, lights, and load security required before every trip in a combination vehicle.

The tendency of a trailer's rear wheels to follow a path inside the tractor's front wheels during a turn, so the trailer cuts the corner.

The total width of road a combination vehicle occupies while turning, including the trailer's inner cut and the front end's outer swing.

The way each trailing unit swings wider than the one ahead during a quick lane change or evasive move, making the last trailer travel farthest sideways.

A visual reference used when turning, such as watching the trailer's rear wheels in the mirror to judge how far inside the corner they will track.

The size of the circle a vehicle needs to complete a turn; a long combination requires a much wider radius than a car.

The point where a vehicle's weight is concentrated; the higher it sits, the more easily the unit tips over in a turn or sudden maneuver.

A tip-over caused mostly by taking a curve or evasive move too fast for the load height and road conditions; it is the deadliest combination vehicle crash type.

How far the cargo's weight sits above the road; tall or heavy-top loads raise the center of gravity and sharply reduce the safe cornering speed.

Choosing a speed that lets you stop within the distance you can see and stay below the rollover threshold on curves, downgrades, and in bad weather.

The gap kept behind the vehicle ahead, measured in seconds; combination vehicles need at least one second per ten feet of length plus extra margin.

The total distance traveled from seeing a hazard to full stop, including perception, reaction, brake lag, and the longer braking distance of a loaded combination.

A skid in which the tractor and trailer fold toward each other, usually after the drive wheels lock or the trailer pushes the tractor during hard braking.

The corrective actions after losing traction: stop braking, steer where you want to go, and avoid hard inputs until the tires roll freely again.

A wheel that stops rotating while the vehicle keeps moving, losing steering and side grip; it is the usual first step toward a jackknife or trailer swing.

A skid where the trailer's rear wheels slide sideways out of line, often from overbraking or a sudden steer; release the brakes and steer to correct.

An antilock braking system that automatically releases and reapplies brake pressure at locking wheels to keep steering control during hard stops.

A retarding device that uses engine compression to slow the vehicle on downgrades, reducing reliance on service brakes and the risk of overheating.

Loss of braking power when overheated drums or pads cannot grip; it is prevented by gearing down and using engine braking on long descents.

An escape lane of deep gravel or sand built on steep grades to stop a vehicle that has lost braking control.