DC CDL General Knowledge key terms

A systematic check of a commercial vehicle's critical parts, including brakes, tires, lights, steering, and coupling devices, performed before driving to confirm the vehicle is safe and legally roadworthy.

A physical circuit around the vehicle during which the driver checks lights, tires, wheels, hoses, and body components for damage, looseness, or missing parts before and during a trip.

A procedure that checks whether air pressure holds steady with the engine off and brakes applied, revealing leaks in the system that could reduce stopping power.

A device that alerts the driver with a light and buzzer when air tank pressure drops below a safe level, signaling that brakes may soon apply or fail to release.

A parking and emergency brake that uses a powerful spring to apply the brakes when air pressure is lost, releasing only when air pressure builds again.

The linkage between the brake chamber pushrod and the brake shoe that transfers force; excessive pushrod travel means brakes are out of adjustment and stopping distance increases.

The distance a brake chamber pushrod extends when the brakes are applied; too much travel indicates misadjustment or worn components and must be corrected before driving.

The measured depth of grooves in a tire's tread; front steer tires need at least 4/32 inch and all other tires at least 2/32 inch to maintain traction and resist hydroplaning.

A swelling in a tire's sidewall or tread that signals internal damage such as separated belts or cords; a bulging tire is unsafe and must be replaced, not just inflated.

A defined list of vehicle defects, such as bad brakes, cracked frames, or missing lights, that make a commercial vehicle illegal to operate until repaired.

Loss of traction in which tires slide instead of rolling, caused by braking too hard, accelerating too fast, or turning too sharply on a low-traction surface.

A skid in which the trailer swings out of line with the tractor, folding the combination vehicle at the coupling; common when drive wheels lose traction under braking.

A condition where water on the road lifts the tires off the surface, eliminating steering and braking control; it is more likely at higher speeds and with worn or underinflated tires.

Steering in the direction the rear of the vehicle is sliding to regain control during a skid, rather than steering against the slide.

Loss of braking power caused by overheating brakes from prolonged or repeated use, often on long downgrades; the cure is controlled speed and proper gear selection, not harder braking.

Using the engine's compression to slow the vehicle by downshifting and releasing the accelerator, reducing reliance on wheel brakes on long or steep downgrades.

An escape lane of deep gravel or sand built into a steep downgrade for drivers who lose braking ability, designed to stop a vehicle before it reaches a hazard.

The total distance a vehicle travels from the moment a hazard is seen until it stops, combining perception distance, reaction distance, and braking distance.

The distance traveled while the driver recognizes a hazard and decides to act; it grows with speed and with fatigue or distraction.

The gap kept behind the vehicle ahead, commonly measured in seconds; larger gaps are needed at higher speeds, in poor weather, and when carrying heavy loads.

The safety margin kept around the vehicle on all sides, including front, rear, and lateral gaps, so there is room to react and maneuver if a hazard appears.

The blind spots around a large commercial vehicle where other drivers cannot be seen by the truck driver; passing drivers should avoid lingering in these areas.

A hazard in which a large vehicle swings left before turning right, and a passing driver on the right may be trapped or crushed against the curb.

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 check mirrors to avoid hitting curbs or objects.

Driving in reverse, which is the most dangerous maneuver for large vehicles; it should be avoided when possible and done slowly with mirrors, a spotter, or a walk-around check first.

A person outside the vehicle who guides a driver during backing or tight maneuvers using agreed hand signals, positioned where the driver can see them in the mirror.

A shifting technique for non-synchronized transmissions in which the clutch is pressed twice, once to shift to neutral and once to engage the next gear, matching engine and road speed.

Shifting a non-synchronized transmission without using the clutch, relying on matching engine rpm to gear speeds; it requires skill and is not recommended for inexperienced drivers.

A technique of upshifting at lower engine rpm as the vehicle gains speed, saving fuel and reducing wear; it is used with some automated and manual transmissions.

Side-to-side movement of a trailer, often caused by improper weight distribution, crosswinds, or sudden steering; the driver should slow gradually and avoid hard corrections.

The use of tiedowns, straps, chains, and blocking to keep cargo from shifting or falling; requirements depend on the load's weight, length, and type.

A strap, chain, or other device that anchors cargo to the vehicle; the number and strength required depend on the cargo's weight and length.

The combined strength rating of all tiedowns used for a load; it must be at least half the weight of the cargo being secured.

Placing cargo so that weight is balanced across axles and kept low, protecting steering and braking and helping prevent trailer sway and axle overload.

The maximum load allowed on a single axle or axle group, set by law; exceeding it can cause damage and penalties and affects steering and braking performance.

The maximum safe total weight of a vehicle including its cargo, fuel, and passengers, as specified by the manufacturer; it must never be exceeded.

A diamond-shaped sign placed on a vehicle to identify the class of hazardous cargo it carries, warning responders and other drivers of the risk.

One of the numbered categories, such as flammable liquid or corrosive, used to group hazardous materials by their primary danger for labeling, placarding, and emergency response.

The document that describes hazardous cargo, including proper shipping name, class, quantity, and emergency contact; it must be kept within reach while driving.

A place where a road crosses train tracks; drivers must slow, look both ways, and never stop on the tracks, and must know clearance before proceeding.

A location where a school bus loads or unloads children; drivers must stop for flashing red lights and extended stop arms and watch for children crossing.

Physical and mental tiredness that slows reaction time and judgment; it is a major crash cause and is managed with rest, breaks, and limits on driving hours.

Federal rules limiting driving time and requiring rest breaks for commercial drivers, designed to reduce fatigue-related crashes.

Any activity that takes a driver's eyes, hands, or attention away from the road, such as phone use, eating, or adjusting devices; it sharply increases crash risk.

The percentage of alcohol in a person's blood, used to define legal impairment; commercial drivers are held to a stricter limit than other drivers.

A written record of a crash that documents time, location, parties, injuries, and vehicle damage, often required by law and by the carrier after certain incidents.

Supplies carried in a commercial vehicle, such as warning triangles, a fire extinguisher, and first aid items, used to protect the scene and respond to injuries after a crash.