Pennsylvania CDL General Knowledge key terms

A systematic walk-around and in-cab check of a commercial vehicle performed before each trip to confirm that critical parts are present, secure, and working, and that defects are corrected before driving.

A written record that a driver prepares after each pre-trip or post-trip inspection listing any defects found, which must be reviewed and signed by the carrier's maintenance staff before repairs are made.

A safety defect serious enough that a vehicle or driver must not be operated until it is repaired or resolved, such as faulty brakes, a missing light, or a driver over the hours limit.

The measured thickness of rubber remaining above the tire's wear indicators; front steer tires generally need at least 4/32 inch of tread and all other tires at least 2/32 inch.

Cuts, bulges, cracks, or exposed cords on a tire's side wall that weaken the tire and make it unsafe to run, even if the tread still looks adequate.

The maximum permitted pushrod travel for air-brake chambers; too much travel means the brake is out of adjustment and the vehicle must be placed out of service until corrected.

The lever arm that transfers pushrod force from a brake chamber to the brake shoe or caliper; its angle and free play indicate whether the brake is properly adjusted.

A braking system powered by compressed air stored in tanks; it includes a compressor, governor, reservoirs, valves, and chambers, and must hold pressure without excessive leakage.

A buzzer and light that activate when air pressure falls below roughly 60 psi, warning the driver to stop before service brakes are lost; below about 45 psi the spring brakes apply.

A check with the engine off and brakes applied that measures how fast air pressure drops; excessive leakage, such as more than 3 psi per minute, means the system needs repair.

A fail-safe parking brake held in the applied position by a strong spring and released by air pressure; it sets automatically if air pressure is lost or the parking valve is pulled.

A test that the parking brake will hold the vehicle stationary, often done by pulling the valve with the transmission in gear and confirming the vehicle does not move.

A green traffic signal that has been green for a long time and may change to yellow before you reach it, so you should anticipate stopping rather than accelerate.

The safety margin of clear space kept around a vehicle, including ahead, behind, and to both sides, which gives time to react and room to maneuver when hazards appear.

The gap between your vehicle and the one ahead, measured in time; at highway speeds large trucks need at least one second per ten feet of vehicle length.

A driver who follows too closely behind you; the safest response is to increase your own following distance ahead so you can slow gradually and avoid forcing that driver to rear-end you.

Where a vehicle sits within a traffic lane; large vehicles often need to occupy a full lane and may use a slightly offset position to create room from hazards or to prepare a turn.

The tendency of a vehicle's rear wheels to follow a path inside the front wheels during a turn, so a long truck may swing wide or clip a curb if the turn is set up poorly.

The outward sweep of a long vehicle's rear end when the front is turned sharply, which can strike nearby objects or vehicles and requires extra clearance during turns.

Changing gears without jerking or grinding by matching engine speed to road speed and releasing the clutch properly; it protects the drivetrain and keeps the vehicle stable.

A shifting method for non-synchronized transmissions in which the clutch is pressed twice, once to leave a gear and once to engage the next, matching engine and gear speeds.

Shifting without using the clutch by matching engine rpm to the next gear; it is possible only with certain transmissions and requires skill to avoid damaging gears.

Resting a foot on the clutch pedal while driving, which partially disengages the clutch, causes slipping, heat, and premature wear, and reduces control.

An area around a large vehicle that the driver cannot see in the mirrors, especially along both sides and directly behind, where other vehicles can disappear from view.

A term for the blind spots around a large truck or bus where a car driver may be hidden; staying in these areas increases the risk of a sideswipe or rear-end crash.

Setting mirrors so that the sides of the vehicle are just visible and the road behind is covered; mirrors should be checked often and readjusted after coupling or loading changes.

Signaling early enough before a turn or lane change, commonly at least 100 feet in city driving and 300 feet on the highway, so others can react.

Hazard warning lights used to warn others when a vehicle is stopped, moving slowly, or disabled; they do not replace required turn signals or clearance lights.

Reflective devices placed behind a disabled vehicle to warn traffic; typically placed 10 feet, 100 feet, and 200 feet back, or closer on a divided highway.

Steps after a crash such as stopping, checking injuries, calling for help, setting out warning devices, and moving the vehicle only when it is safe to do so.

A place where a road meets train tracks; drivers must slow, look and listen, avoid stopping on the tracks, and never try to beat a train or cross when signals are active.

The space needed to fully clear the tracks before stopping; a driver must not enter a crossing unless there is room on the far side for the whole vehicle.

A vehicle that stops or breaks down on railroad tracks; occupants should get out and move away from the tracks immediately, then call for help and warn oncoming trains if possible.

The reduced ability to see detail and color in low light; at night drivers should slow down, increase following distance, and avoid looking directly into oncoming headlights.

The time needed for eyes to readjust after bright light, such as oncoming headlights; to limit it, look toward the right edge of your lane rather than at the lights.

Driving with low or high beams as conditions require; use low beams in fog, rain, or snow and when following or meeting traffic, and dim high beams within about 500 feet of oncoming vehicles.

Loss of tire contact with the road because a layer of water builds between them; it causes steering and braking to fade, so ease off the accelerator and avoid hard braking.

Regaining control when tires lose grip by releasing the brakes or accelerator, steering in the direction the rear of the vehicle is sliding, and avoiding sudden inputs.

Less grip between tires and the road caused by rain, snow, ice, gravel, or worn tires; it requires slower speeds, gentler steering, and longer stopping distances.

Slowing a vehicle by downshifting and letting engine compression resist motion; it helps control speed on long downgrades and reduces reliance on service brakes.

Loss of braking power caused by heat buildup from overuse, common on long downgrades; gearing down and using engine braking helps prevent it.

An escape lane filled with gravel or sand on a steep downgrade where a driver who loses brakes can steer to stop safely instead of crashing.

Tying down a load with rated straps, chains, or binders so it cannot shift, slide, or fall off; the number and strength of tiedowns depend on the load's length and weight.

Movement of cargo during driving that can change weight distribution, destabilize the vehicle, or damage the trailer; proper blocking and bracing prevent it.

The maximum weight allowed on a single axle or axle group, set by law and by the vehicle's rating; exceeding it overloads tires and brakes and may be a violation.

The skill of scanning ahead, recognizing developing risks early, and deciding what to do before a situation becomes an emergency.