Illinois CDL General Knowledge key terms

A systematic check of a commercial vehicle's critical parts, including tires, brakes, lights, fluids, and coupling devices, performed before driving to catch defects that could cause a breakdown or crash.

The skills-test portion in which a driver must identify and explain specific vehicle parts and demonstrate that each is in safe operating condition, memorizing items rather than relying on a checklist.

A defect severe enough that a vehicle must not be driven until it is repaired; inspectors place the vehicle out of service for items such as bad brakes, cracked frames, or inoperative lights.

The lever connecting a brake chamber pushrod to the brake camshaft; excessive travel or a loose adjustment means the brakes are out of adjustment and the vehicle should not be operated.

A braking system that uses compressed air to apply the brakes and spring pressure to release them, requiring the driver to watch air pressure gauges and listen for low-pressure warnings.

A test in which the driver builds full pressure, shuts off the engine, and observes the gauges to confirm air loss stays within allowed limits, indicating the system is not leaking dangerously.

The measured depth of grooves on a tire; front tires of commercial vehicles need at least 4/32 inch and other tires at least 2/32 inch to maintain traction and resist hydroplaning.

Checking a tire's side for cuts, bulges, and exposed cords, and confirming it is properly inflated and matched in size and load rating to the other tires on the vehicle.

The gap between two tires mounted side by side; tires touching or debris wedged between them can cause overheating and blowouts and must be corrected before driving.

The locking plate on a tractor that grips the trailer kingpin; a driver must verify the jaws are closed and a pull test confirms the trailer is locked before moving.

The vertical pin under a trailer that locks into the tractor's fifth wheel; an improperly seated kingpin allows the trailer to separate from the tractor while driving.

The hoses, usually color-coded, that supply air and electrical signals between tractor and trailer; they must be connected correctly and not rubbing or dangling.

The continuous scanning of the road ahead, to the sides, and behind the vehicle so the driver spots changing conditions early enough to react smoothly.

Looking far down the roadway rather than at the hood, which helps a driver hold a steady lane position and see hazards sooner on curves and hills.

The gap between your vehicle and the one ahead; commercial drivers should allow at least one second per ten feet of vehicle length plus one second at speeds above 40 mph.

The safety margin kept around the vehicle on all sides, enlarged when traffic is heavy, the load is heavy, or road and weather conditions reduce stopping ability.

The total distance traveled from perception to a full stop, combining perception distance, reaction distance, and braking distance, all of which grow with speed and weight.

The distance covered while the driver's eyes see a hazard and the brain recognizes it as a reason to act, typically before the foot moves to the brake.

The distance traveled between recognizing a hazard and actually applying the brake, which lengthens when the driver is tired, distracted, or impaired.

Selecting a gear whose engine speed keeps the vehicle in a safe range for the grade and load, downshifting before a hill rather than after the engine starts to lug.

Using the retarding force of a low gear and closed throttle to slow a heavy vehicle on a downgrade, sparing the service brakes from overheating and fading.

Keeping light, continuous pressure on the brake pedal down a long grade, which overheats the brakes and can lead to fading or complete loss of stopping power.

The loss of braking effectiveness when brakes overheat from prolonged use, often felt as a spongy pedal or a vehicle that will not slow as expected on a downgrade.

A specially built gravel or sand ramp on a steep downgrade where a driver with failed brakes can steer off the road and be stopped by the deep, loose surface.

A downhill braking technique of applying the brakes firmly to reduce speed by a set amount, then releasing them to cool, repeated as needed instead of continuous light pressure.

Loss of tire contact with the road when water builds up under the tires; it worsens with speed, worn tread, and low tire pressure, and steering and braking become ineffective.

The response to a skid: stop braking, steer in the direction you want the vehicle to go, and avoid hard acceleration until the tires regain traction.

Signaling well before a turn or lane change, at least 100 feet in advance in urban areas and 200 feet on highways, then canceling the signal afterward.

Hazard warning lights used to warn other drivers when your vehicle is stopped, moving slowly, or disabled, but never as a substitute for turn signals while driving normally.

An area beside or behind the vehicle that mirrors do not show; a driver must check it before lane changes and keep other vehicles from lingering there.

The time the eyes need to readjust after glare from oncoming headlights; drivers should look toward the right edge of their lane until the glare passes.

Driving so fast that the stopping distance exceeds the distance lit by the headlights, leaving no room to stop for an object that appears in the beam.

A thin, nearly invisible layer of ice on the road, common on bridges, overpasses, and shaded areas, which offers almost no traction and is easy to overlook.

The tendency of bridges and overpasses to freeze before the rest of the roadway because cold air circulates beneath them, so drivers should slow down before crossing.

When a tire fails, hold the wheel firmly, keep the vehicle straight, ease off the accelerator, and avoid hard braking until speed drops and you can pull off safely.

Tying down a load with enough tiedowns and working devices to keep it from shifting or falling; aggregate working load limits and tiedown counts depend on cargo weight and length.

Placing cargo so weight is spread properly over the axles and kept low, avoiding an overloaded axle, poor steering traction, or a raised center of gravity.

The maximum gross and axle weights set by law and by the vehicle's ratings; exceeding them strains brakes and tires and is illegal even when the load is secured.

A diamond-shaped warning sign placed on a vehicle carrying regulated hazardous materials, showing the hazard class and identifying the load to emergency responders.

The document describing a hazardous materials shipment, including proper shipping name, hazard class, and quantity; it must be kept accessible to drivers and emergency personnel.

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