Colorado CDL General Knowledge key terms

The maximum total weight a single vehicle is designed and rated to carry, including the vehicle itself, fuel, passengers, and cargo, as specified by the manufacturer. Exceeding it can affect braking, handling, and legal operation.

The maximum total weight allowed for a towing vehicle plus its towed trailer or trailers, including all cargo and fluids, as rated by the manufacturer. It sets the upper limit for a loaded combination.

The portion of a vehicle's total weight carried by a single axle or axle group. Overloading one axle is a common cause of failed inspections and unstable braking, even when total weight is legal.

How a load's mass is spread among axles and between tractor and trailer. Poor distribution overloads tires and brakes, lightens steering axles, and can make a combination vehicle hard to control or stop.

The downward force a trailer exerts on the hitch ball or coupler of the towing vehicle. Too little causes sway; too much overloads the rear axle and lifts weight off the front steering tires.

A systematic check of a vehicle's critical parts, including brakes, tires, lights, fluids, and coupling, performed before driving. It is required by regulation and is the driver's main defense against breakdowns and out-of-service violations.

A sequence of checks, including static leak, applied leak, and low-pressure warning tests, that confirms an air brake system holds pressure and warns the driver before pressure is lost. It is performed during the pre-trip inspection.

An engine-driven pump that builds and maintains air pressure in the brake system. It must recover pressure quickly enough that the vehicle can be driven safely after normal brake use.

A valve that controls the compressor, letting it build pressure until the cut-out point and restarting it at the cut-in point. It keeps system pressure within the designed operating range.

Storage tanks that hold compressed air for braking. They are drained of moisture and oil during the pre-trip inspection, and each tank has a drain valve that must be opened to check for contamination.

A device that removes moisture from compressed air before it reaches the brake reservoirs. Moisture in the system can freeze in cold weather or corrode valves, causing brake failure.

A buzzer and light that activate when system pressure drops below a set threshold, typically around 60 psi. It warns the driver that brakes may soon be insufficient and that stopping is required.

A parking and emergency brake that uses a powerful spring to apply the brakes when air pressure is lost. It releases only when air pressure is restored, so a pressure failure brings the vehicle to a stop.

A mechanism that holds a stopped vehicle in place. On air-braked vehicles it is usually spring-applied and released by air pressure, and it must be tested during the pre-trip inspection.

A lever that links the brake chamber pushrod to the brake shoe, multiplying force and taking up adjustment as linings wear. Excessive pushrod travel means brakes are out of adjustment and may fail inspection.

A cylinder where air pressure pushes a diaphragm and pushrod to apply the brakes. A torn diaphragm or leaking chamber reduces braking force and is a common defect found in inspections.

Loss of braking power caused by overheating, usually from repeated or prolonged braking on downgrades. It can be avoided by using engine braking and controlled, intermittent brake applications.

A device that uses engine compression or a driveline retarder to slow the vehicle without using the service brakes. It helps control speed on long downgrades and reduces brake fade.

Changing to a lower gear to increase engine braking and control speed, especially on downgrades. The shift should be made before the vehicle gains too much speed, not after.

The total distance a vehicle travels from the moment a hazard appears until it stops, combining perception, reaction, and braking distance. It grows with speed, weight, and poor road conditions.

The gap a driver keeps behind the vehicle ahead, measured in seconds. Large vehicles need at least one second per ten feet of vehicle length at speeds under 40 mph, plus extra time in poor conditions.

The safety margin of empty space kept around a vehicle so there is time to react to hazards. It includes following distance, side room, and clearance overhead and ahead.

Areas around a large vehicle that the driver cannot see in mirrors, including directly behind and along both sides. Other drivers should avoid lingering there, and the truck driver must check mirrors carefully before turning or changing lanes.

The tendency of a vehicle's rear wheels to follow a tighter path than the front wheels in a turn. Drivers must swing wide and watch mirrors so the trailer does not strike curbs, poles, or pedestrians.

The outward sweep of a vehicle's rear end during a turn, opposite the direction of the front. It can strike nearby objects or people, so drivers must check mirrors and allow extra room before turning.

The horseshoe-shaped plate on a tractor that locks onto the trailer's kingpin to connect the two. It must be greased, properly latched, and checked for securement before driving.

The vertical pin under a trailer that locks into the tractor's fifth wheel. The locking jaws must fully close around it, and a visible gap or missing lock is a serious defect.

A visual and physical inspection that the fifth wheel jaws are locked on the kingpin, the release handle is in place, and the trailer is supported. A failed coupling can drop a trailer.

The retractable legs that support a trailer when it is not attached to a tractor. They must be fully raised and secured before driving, and checked for damage during inspection.

An adjustable fifth wheel mounting that lets a driver move the pivot point forward or back to redistribute weight between tractor axles. It is locked with pins that must be checked before driving.

Side-to-side fishtailing of a trailer, often caused by too little tongue weight, excessive speed, or sudden steering. The driver should ease off the accelerator and avoid hard braking or sharp steering.

A loss of control in which the tractor and trailer fold toward each other at an angle. It is often caused by locking the drive wheels or trailer wheels during hard braking on slippery surfaces.

An electronic system that rapidly modulates brake pressure to prevent wheel lockup, helping the driver keep steering control during hard braking. A functioning ABS does not shorten stopping distance on all surfaces.

A CDL endorsement required to drive vehicles carrying placarded amounts of hazardous materials. It requires a background check, knowledge testing, and compliance with federal hazmat rules.

A diamond-shaped warning sign placed on vehicles and containers to identify the hazard class of the material being carried. Placards must match the shipping paper and be visible from all sides.

One of nine categories, such as flammable liquid, corrosive, or radioactive, used to classify hazardous materials by their primary risk. The class determines placarding, packaging, and handling requirements.

The document that accompanies a hazardous materials shipment and lists the material, quantity, class, and emergency response information. It must be kept within reach and shown to inspectors or emergency responders.

A reference book carried by hazmat drivers that gives initial response guidance for incidents involving hazardous materials, organized by material identification number and hazard class.

The forward or backward movement of liquid inside a partly filled tank during acceleration, braking, or turning. It shifts weight suddenly and can push a tank vehicle out of control or over a stop line.

An internal wall inside a tank that divides the liquid into compartments to reduce surge and side-to-side movement. Baffled tanks handle better than smooth bore tanks when partly loaded.

A tank with no internal baffles, so liquid can surge freely from end to end. These tanks require extra care with braking, acceleration, and turning, especially when partially filled.

The empty space left above the liquid in a tank to allow for expansion as temperature rises. Filling beyond the outage limit can cause liquid to overflow through vents.

A tank mounted on a vehicle for carrying liquid or gaseous cargo. It must be inspected, marked, and operated according to its specification, and its valves and hatches must be secure before moving.