Mississippi CDL General Knowledge key terms

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

The distance traveled while your eyes see a hazard and your brain recognizes it as a reason to stop or slow down. It depends on alertness and visibility, not on the brakes.

The distance covered between recognizing a hazard and actually pressing the brake pedal. A tired or distracted driver adds hundreds of feet to this distance at highway speed.

The distance a vehicle travels from the moment the brakes are applied until it stops. It increases with speed, weight, and poor traction, and is longer for vehicles with air brakes.

The gap you keep behind the vehicle ahead, measured in seconds by counting after its rear passes a fixed object. One second per ten feet of vehicle length is the usual minimum, plus one second for speeds above 40 mph.

The safety margin of empty space you keep around your vehicle on all sides. It gives you room to steer or brake when another driver makes a mistake, and it is your best defense against others' errors.

A planned path out of trouble, such as an open lane, shoulder, or ramp you could use if traffic ahead suddenly stops. Good drivers always keep one in mind before trouble develops.

The skill of scanning ahead, to the sides, and behind to spot risks early, such as merging cars, work zones, or slippery pavement. Looking far ahead lets you act smoothly instead of reacting suddenly.

Loss of braking power caused by overheated brake drums and linings, common on long downgrades when brakes are used too much. The pedal feels normal but the vehicle slows poorly, so you must slow down and use engine braking.

Using a lower gear so the engine's compression slows the vehicle instead of the service brakes. It is the preferred way to control speed on long or steep downgrades and helps prevent brake fade.

A downgrade technique where you apply the brakes firmly enough to reduce speed by about 5 mph, then release them to cool. Repeating this keeps brakes from overheating on long hills.

When tires ride on a thin layer of water instead of the road, causing loss of steering and braking control. It happens at higher speeds or with worn tires; ease off the accelerator and avoid hard braking until grip returns.

The actions taken to regain control when tires lose traction: stop braking, steer in the direction you want to go, and avoid overcorrecting. On ice or rain, gentle inputs matter more than fast ones.

The thickness of rubber remaining on a tire, measured in the grooves. Front tires on large trucks need at least 4/32 inch and other tires at least 2/32 inch; too little tread causes poor traction and hydroplaning.

A systematic check of the vehicle before driving, covering tires, brakes, lights, fluid leaks, coupling devices, and cargo securement. It is required by regulation and prevents most breakdowns and roadside violations.

A three-part check of an air brake system: leakage test with engine off, low air pressure warning test, and a check that the spring brakes apply when pressure drops. It confirms the system will stop the vehicle safely.

A light or buzzer that alerts the driver when air pressure falls below a safe level, usually around 60 psi. If it comes on while driving, stop safely and find the leak before continuing.

Parking and emergency brakes held applied by heavy springs and released by air pressure. If air pressure is lost, they apply automatically, which is why a vehicle cannot be moved until pressure builds.

The lever that connects the brake chamber pushrod to the brake shoe, transferring force. Too much free play means weak or delayed braking, so it is checked during pre-trip inspection.

A valve that lets a tractor's air system supply the trailer while protecting each vehicle's air supply. It helps prevent a major leak in one unit from draining the other's brakes.

The coupling fittings that connect the tractor's air lines to the trailer's brake system. They must be locked and free of leaks, and the lines should cross so they do not rub.

A control in the cab that applies only the trailer brakes, used to test trailer braking and to stop a trailer sway. It should not be used as a parking brake.

Side-to-side whipping of a trailer, often caused by poor weight distribution, high speed, or wind. Ease off the accelerator and use the trailer hand valve gently; do not brake hard or steer sharply.

The heavy plate on the tractor that locks onto the trailer's kingpin to connect the two. A secure lock, proper lubrication, and correct jaw adjustment are checked before every trip.

The sturdy pin under the trailer nose that the fifth wheel jaws grip. A worn or damaged kingpin can let the trailer separate, so it is inspected for cracks and looseness.

After coupling, pull gently against the locked trailer brakes to confirm the fifth wheel is fully locked and the trailer will not separate. It takes seconds and catches a costly, dangerous mistake.

A small axle assembly with its own fifth wheel and air lines that links a second trailer to the first in doubles and triples. Its coupling and air connections must be checked like any other trailer hookup.

A hook-and-latch coupling used to tow a converter dolly or full trailer. The latch must be closed and secured with a safety pin, or the towed unit can break away.

Placing cargo so that axle and tire limits are respected and the load is balanced front to back and side to side. Poor distribution causes steering problems, sway, and overloaded axles.

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

The maximum load allowed on a single axle or axle group, set by law and by tire and suspension ratings. Exceeding it damages roads, hurts handling, and brings fines.

The total weight of the vehicle plus its cargo, fuel, and passengers. It must stay under the vehicle's rated limit and any bridge or road posting.

The forward and backward movement of liquid in a partly filled tank as the vehicle speeds up, stops, or turns. It shifts the center of gravity and can push a truck through a stop or tip it in a curve.

A partition inside a tank that divides the liquid into smaller sections to reduce surge. Baffles improve stability but do not remove the need to slow down and brake gently.

The empty space left at the top of a tank so liquid has room to expand with heat. Filling a tank completely can cause it to overflow or rupture.

A special marking on a commercial license, earned by passing a knowledge test and a security threat assessment, that allows driving vehicles carrying placarded hazardous loads. It requires extra training and background checks.

A diamond-shaped warning sign placed on the outside of a vehicle to show the class of hazardous material carried. Placards warn emergency responders and must match the shipping paper.

The document describing a hazardous load, including proper shipping name, hazard class, quantity, and emergency contact. It must be kept within reach and given to responders after a crash.

The swing-out sign on the driver's side that signals children and traffic to stop while students board or leave. It is used with flashing red lights and must be retracted before moving.

The area around a school bus, roughly ten feet in every direction, where children are hardest to see. Drivers must account for every student and never move until they are clear of it.

The short talk given to riders before a trip covering seat belts, emergency exits, and rules for a safe ride. It is required before carrying passengers and reduces panic in an emergency.

A marked line on the floor of a bus showing where standing passengers may not go. Keeping riders behind it protects the driver's view and keeps weight off the front axle.

A door, window, or roof hatch marked for quick escape from a bus or coach. Drivers must know how each one opens and ensure they are unobstructed before every trip.

Shifting a non-synchronized manual transmission by pressing the clutch, shifting to neutral, releasing, then pressing again to engage the next gear. It matches engine and transmission speeds for smoother, damage-free shifts.

Resting a foot on the clutch pedal while driving, which causes slipping and premature wear. The clutch should be fully engaged or fully pressed, never held partway.