ND CDL General Knowledge key terms

The maximum total weight a single vehicle is designed to carry, including the vehicle itself, fuel, passengers, and cargo, as specified by the manufacturer. Exceeding it can overload tires, brakes, and axles.

The maximum allowable combined weight of a towing vehicle plus its trailer(s), including all cargo and fluids, set by the manufacturer. It caps what the whole rig may weigh when loaded and ready to drive.

The portion of a vehicle's total weight carried by a single axle or axle group. Bridge formula and per-axle limits are enforced at weigh stations, so load distribution matters as much as total weight.

A license category covering combination vehicles with a gross combination weight rating of 26,001 pounds or more, provided the towed unit exceeds 10,000 pounds. It permits driving most tractor-trailers.

A license category for single vehicles with a gross vehicle weight rating of 26,001 pounds or more, or any such vehicle towing a unit not exceeding 10,000 pounds. Typical examples are straight trucks and dump trucks.

A license category for single vehicles under 26,001 pounds GVWR that either carry 16 or more passengers or are placarded for hazardous materials. Small hazmat trucks and passenger vans often fall here.

An addition to a CDL that authorizes a specific type of vehicle or cargo, such as air brakes, doubles/triples, tank vehicles, hazardous materials, or passenger transport. Each requires passing the matching knowledge or skills test.

A systematic walk-around check of the vehicle before driving, covering lights, tires, brakes, coupling devices, fluid levels, and cargo securement. Defects found here prevent breakdowns and are part of the CDL skills test.

The use of tiedowns, straps, chains, and blocking to keep cargo from shifting, falling, or spilling during transport. Rules specify minimum tiedown counts and working load limits based on cargo weight and length.

The combined strength rating of all tiedowns used to secure a load, found by adding each tiedown's working load limit. The total must equal at least half the cargo weight for most loads.

The total distance a vehicle travels from the moment a hazard is seen until it comes to rest. It combines perception distance, reaction distance, and braking distance, and grows quickly as speed increases.

The gap kept between your vehicle and the one ahead, commonly at least one second for each ten feet of vehicle length at speeds under 40 mph, plus one extra second above that. It allows time to react.

The safety margin of clear space kept around all sides of your vehicle so you can steer or stop if another driver makes a mistake. It is managed by lane position, speed choice, and following distance.

An area around a large vehicle that the driver cannot see in the mirrors. In tractor-trailers the zones beside and behind the trailer are large, so other drivers should never linger there.

The tendency of a vehicle's rear wheels to follow a path inside the front wheels during a turn. Long combination vehicles track off more, so drivers must swing wide and watch the trailer's rear in the mirrors.

A CDL endorsement (letter H) required to drive a vehicle carrying placarded amounts of hazardous materials. Applicants must pass a knowledge test and a federal security threat assessment with fingerprinting.

A diamond-shaped warning sign placed on the outside of a vehicle or bulk package to identify the hazard class of the contents. Placards alert emergency responders and trigger many driving and parking restrictions.

The document that accompanies a hazardous materials shipment and lists the proper shipping name, hazard class, UN identification number, quantity, and emergency response information. It must be within reach while driving.

A reference carried by hazmat drivers that lists, by UN number or material name, the initial isolation distances and protective actions to take in a spill or fire. It is organized into numbered guides by hazard.

One of nine categories used to group hazardous materials by the kind of risk they pose, such as flammable liquid, corrosive, or radioactive. The class number appears on placards and shipping papers.

A four-digit code, often preceded by the letters UN, that identifies a specific hazardous material worldwide. It appears on shipping papers and on placards, letting responders look up the correct emergency guide.

A restriction or endorsement on a CDL that must be obtained to drive a vehicle equipped with air brakes. It requires passing a separate knowledge test on the air brake system and how to inspect it.

The engine-driven pump that builds and maintains air pressure in the brake system, typically cycling between a cut-out pressure near 125 psi and a cut-in pressure near 100 psi. It supplies the reservoirs used for braking.

A storage cylinder that holds compressed air for the brake system so brakes can be applied repeatedly without waiting for the compressor. Tanks must be drained of moisture and oil during pre-trip inspection.

A device between the compressor and the reservoirs that removes moisture and oil from compressed air. Keeping water out of the system prevents corrosion and freeze-ups that could disable the brakes in cold weather.

A buzzer and light that activate when system pressure drops below a set level, usually around 60 psi, warning that brakes may soon fail. Driving with the warning on is unsafe and a test failure.

A parking and emergency brake that uses a powerful spring to apply the brakes when air pressure is released. Losing air pressure causes the spring brakes to engage automatically, stopping the vehicle.

The linkage that connects the brake chamber pushrod to the brake shoe, transferring force to apply the brake. Too much free play means poor braking, so it is checked by pulling the pushrod by hand.

An air cylinder that converts air pressure into mechanical force on the pushrod to apply the brakes. A ruptured diaphragm or cracked housing causes air loss and weak braking, so it is inspected before each trip.

A check of the air brake system for leaks with the engine off and brakes released, watching the gauge for pressure loss over one minute. Excessive drop indicates a leak that must be repaired.

A leak check performed with the engine off and the brake pedal held fully down for one minute, watching for pressure loss beyond the allowed amount. It confirms the system holds air while brakes are engaged.

A vehicle made of a power unit towing one or more trailers, such as a tractor-semitrailer. Its handling, braking, and turning differ from a straight truck, so they are tested as a separate CDL unit.

The horseshoe-shaped coupling plate on the tractor that locks onto the trailer's kingpin. It carries the trailer's weight and allows pivoting, and must be checked for proper locking before driving.

The sturdy vertical pin under the front of a semitrailer that locks into the tractor's fifth wheel. A visible gap between the trailer apron and the fifth wheel after coupling signals an incomplete hookup.

A coupling check where the driver pulls gently forward with the trailer brakes set to confirm the kingpin is locked in the fifth wheel. If the trailer moves, it is not properly secured.

A control in the cab, also called the trolley valve, that applies only the trailer brakes. It is used to test trailer brakes and to help straighten a skid or control speed on downgrades.

The tendency of the last trailer in a multi-trailer combination to swing wider and faster than the tractor during a lane change. It makes doubles and triples prone to rollover if steered abruptly.