Kentucky CDL General Knowledge key terms

The total ground covered from the moment a hazard is recognized until the vehicle comes to a complete halt, combining perception distance, reaction distance, and braking distance.

The distance a vehicle travels while the driver's eyes and brain notice and identify a hazard before any physical response begins. Typically about one second of travel at highway speed.

The ground covered between the instant the driver decides to act and the moment the foot actually reaches and presses the brake pedal, usually three-quarters of a second.

The distance needed to stop once the brakes are applied, affected by speed, vehicle weight, brake condition, and road surface traction. It increases with the square of speed.

The sum of perception distance, reaction distance, and braking distance. At 55 mph a loaded tractor-trailer needs roughly the length of a football field to stop.

Loss of tire contact with the road because water builds up under the tread. It can begin at speeds as low as 30 mph, and steering and braking become ineffective until speed drops.

The safety margin of empty road kept around the vehicle so there is room to stop or maneuver when traffic ahead slows suddenly or a hazard appears.

The gap maintained behind the vehicle ahead. Under 40 mph a minimum of one second per 10 feet of vehicle length is required; at higher speeds add one extra second.

Because mirrors leave blind spots, a heavy vehicle should change lanes slowly, signal early, and check mirrors on both sides repeatedly. If you must back up, get out and look first.

The area beside and behind a large vehicle that cannot be seen in the mirrors, including the deep zone directly behind a trailer and the right side of a tractor-trailer.

A curved mirror that widens the field of view but makes objects appear smaller and farther away than they really are, so it must not be relied on for judging distance.

A systematic walk-around check of the vehicle before driving, covering tires, brakes, lights, coupling devices, cargo securement, and emergency equipment, documented in the driver's daily report.

The skills-test portion in which the driver must name and demonstrate the inspection of key vehicle parts and explain what defects would make the vehicle unsafe to operate.

A three-part check of an air brake system: static leak test with engine off, applied-pressure leak test, and a check that the low-pressure warning and spring brakes engage.

A buzzer and light that must activate before air pressure drops below 60 psi, warning the driver that braking power is being lost and that the vehicle must be stopped safely.

A parking and emergency brake held released by air pressure and applied by a heavy spring when pressure is lost, automatically stopping the vehicle if the system fails.

Pressing the brake pedal harder and harder without releasing it, which wastes air and can leave too little pressure to stop. Release and reapply when braking on a long downgrade.

Loss of braking power caused by overheated brake drums and linings, common on long downgrades when brakes are used continuously instead of being controlled by gearing.

A technique for long downgrades in which the driver applies the brakes firmly to slow several mph, then releases them to cool, repeating as needed while staying in a low gear.

The horseshoe-shaped coupling plate on the tractor that locks onto the trailer's kingpin, carrying the trailer's weight and allowing it to pivot during turns.

The sturdy vertical pin mounted under the front of a semitrailer that locks into the tractor's fifth wheel. It must be fully seated and the locking jaws closed.

A valve that closes the air supply to the trailer lines if a trailer breaks away or a line fails, keeping enough air in the tractor to stop it and setting the trailer brakes.

A small frame with a fifth wheel and one or two axles used to connect a second trailer to the rear of the first when pulling doubles or triples.

A hook-and-latch coupling on the rear of a vehicle used together with safety chains and air lines to tow a trailer, common on converter dollies and full trailers.

Combinations of two or three trailers pulled by one tractor. They require extra care because they are prone to sway, off-tracking, and rapid rearward amplification.

The tendency of the last trailer in a multi-trailer combination to swing wider and faster than the tractor during a quick lane change or steering correction, risking a rollover.

The tendency of the rear wheels of a long vehicle to follow a path inside the front wheels when turning, so the driver must swing wide and watch the mirrors.

The forward or sideward movement of liquid cargo inside a partly filled tank, which shifts weight suddenly and can make the vehicle hard to steer or stop.

An internal wall or partition inside a tank that slows the movement of liquid, reducing surge. Baffles do not eliminate surge entirely and tanks still need smooth handling.

The empty space left above the liquid in a tank so the product can expand with heat without overflowing. Never fill a tank completely; leave the required outage.

The H endorsement added to a CDL after a background check, required to drive vehicles carrying placarded quantities of hazardous materials.

A diamond-shaped warning sign placed on the outside of a vehicle to identify the class or division of hazardous material being carried, so emergency responders know what is aboard.

The document describing hazardous cargo, including the proper shipping name, hazard class, UN identification number, quantity, and emergency response information. It must be within reach while driving.

The use of tiedowns, straps, chains, and blocking to keep cargo from shifting or falling. The system must withstand the forces of braking and turning.

The combined load rating of all tiedowns holding a piece of cargo. The total must be at least half the cargo weight, and the working load limit of each part counts.

A strong barrier placed behind the cab of a flatbed or in front of cargo to stop forward movement of the load during a sudden stop, protecting the driver.

The area within about 10 feet around a school bus where children are hardest to see. Drivers must account for students who may cross behind or in front of the bus.

The procedure for stopping, securing the bus, and letting students on or off, including using warning lights and the stop arm and making sure students reach safety before moving.

The process of stopping safely, setting the parking brake, and supervising riders as they board or exit, ensuring they are clear before the bus moves again.

A marking on the floor of a bus showing where standing passengers may not go, keeping the aisle and the area near the driver clear for safety.

A shifting method for non-synchronized manual transmissions: press the clutch, shift to neutral, release the clutch, then press it again and shift to the next gear.

Shifting a manual transmission without using the clutch, matching engine speed to road speed. It can be used by skilled drivers but is not recommended for beginners.

Moving up or down through the gears one at a time in the correct order rather than skipping gears, which keeps engine speed and vehicle control within safe limits.

Loss of tire grip that lets the vehicle slide, often caused by speeding, hard braking, or abrupt steering on wet or icy pavement. Correct by releasing the brake and steering as needed.

The grip between tires and the road surface that allows steering, accelerating, and stopping. It decreases on wet, icy, or loose surfaces and with worn tires.