Maryland CDL General Knowledge key terms

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

The total ground covered from the moment a hazard is recognized until the vehicle halts, made up of perception distance, reaction distance, and braking distance added together.

The gap you keep behind the vehicle ahead, measured in seconds by counting from when that vehicle passes a fixed object until your front bumper reaches it.

The buffer of empty roadway kept on all four sides of your vehicle so that a sudden stop or swerve by another driver leaves you room to react safely.

Any area around the vehicle that cannot be seen in the mirrors or through the windows, requiring a direct glance over the shoulder before changing lanes.

A technique for manual transmissions in which each upshift is made at progressively higher engine rpm, keeping the engine in its efficient power band and reducing wear.

A shifting method for non-synchronized manual transmissions: press the clutch, shift to neutral, release the clutch, press it again, then engage the next gear to match gear speeds.

A backing maneuver into a tight dock or alley performed by sighting along the driver's side of the trailer, using pull-ups and GOAL to keep the trailer aligned.

An acronym meaning Get Out And Look; the practice of stopping and walking around the vehicle during a difficult backing maneuver to verify clearance before continuing.

A person positioned outside the vehicle who guides a backing or docking maneuver with agreed hand signals, remaining visible in the mirrors at all times.

An engine control that limits maximum vehicle speed, usually by cutting fuel at a set rpm, so the truck cannot exceed its programmed top speed.

A retarding device that uses engine compression to slow the vehicle on downgrades, saving service brakes from overheating; it must be switched off on slippery surfaces.

Loss of stopping power caused by overheating brake drums and linings during prolonged or repeated braking, such as riding the brakes down a long grade.

A mountain-driving method of braking firmly to reduce speed by about 5 mph, then releasing the brakes to cool, rather than applying light continuous pressure down a grade.

A gravel or sand-filled ramp built beside a steep downgrade so a driver who loses braking can steer into it and be stopped by the deep, loose surface.

A place where the roadway intersects train tracks; commercial drivers must slow, look both ways, listen, and ensure there is room to clear the tracks completely before proceeding.

The mental and physical slowing caused by insufficient sleep or long hours of driving, which impairs judgment and reaction time and is a leading factor in truck crashes.

The body's internal 24-hour clock that produces natural drowsiness at night and in the early afternoon, making those periods especially risky for long-haul driving.

Federal rules limiting driving and on-duty time and requiring rest breaks, designed to prevent fatigue-related crashes by capping consecutive hours behind the wheel.

The percentage of alcohol in a person's blood; for commercial drivers a level of 0.04 or higher is prohibited, and any measurable alcohol requires removal from driving duty.

The legal principle that by driving on public roads a commercial driver agrees to submit to alcohol or drug testing when requested by an authorized officer.

A test with the engine off and system charged that measures air pressure loss over one minute with brakes released and applied, confirming the system holds pressure.

A check that the compressor builds pressure within a set time and that the governor cuts out and cuts in at the specified pressures, confirming proper charging.

The device that senses reservoir pressure and cycles the compressor on and off, cutting out near 120-125 psi and cutting back in around 100 psi.

A buzzer and light that activate when reservoir pressure falls below roughly 60 psi, warning the driver that braking power is nearly exhausted.

A parking and emergency brake held released by air pressure and applied by a heavy spring when pressure is lost, bringing the vehicle to a stop automatically.

The fraction of a second between pressing the pedal and the brakes actually engaging on an air brake system, which lengthens total stopping distance compared with hydraulic brakes.

The linkage that transfers pushrod force to the brake shoes; if its travel is too long, brakes are out of adjustment and stopping power is reduced.

A valve that closes the tractor's air lines when trailer pressure is lost, trapping enough air in the tractor to stop it and preventing a trailer breakaway from draining the system.

The couplers that join the tractor's service and emergency air lines to the trailer; they must be locked and checked for leaks after coupling.

The trailer air supply line that charges the trailer reservoirs and applies the trailer spring brakes when pressure is lost or the line is disconnected.

The horseshoe-shaped coupling plate on the tractor that locks around the trailer kingpin; its jaws must be closed and the release handle secured before driving.

The vertical pin mounted under the trailer nose that locks into the fifth wheel jaws, forming the pivot point between tractor and trailer.

The tendency of the rear wheels of a long vehicle to follow a shorter path than the front wheels, causing the trailer to cut corners on turns.

The outward sweep of the rear end of a long vehicle during a turn, which can strike pedestrians, poles, or parked cars on the outside of the curve.

A hook-and-eye coupling used to tow a full trailer behind a truck, requiring safety chains or cables and a separate air connection for trailer brakes.

A small axle unit with its own fifth wheel and air lines that couples a second trailer to the rear of a first trailer in a doubles combination.

A special endorsement on a commercial license required to haul placarded quantities of hazardous materials, obtained after a background check and a knowledge test.

A diamond-shaped warning sign affixed to a vehicle showing the hazard class and material carried, required in specified quantities so responders can identify the danger.

The transport document listing the hazardous material's proper shipping name, hazard class, quantity, and emergency response information; it must stay within reach while driving.

A reference carried by hazmat drivers that gives initial isolation distances and first-aid guidance keyed to a material's four-digit identification number.

The use of tiedowns, straps, chains, and blocking to keep cargo from shifting, falling, or spilling; specific aggregate working-load limits apply to the tiedown system.

The maximum load a tiedown or securement device is rated to hold, marked on the device and used to calculate whether the total tiedown capacity meets requirements.

Placing cargo so weight is spread correctly across axles and kept low, respecting axle and gross weight limits and avoiding an overloaded or unstable vehicle.

A marking on the floor of a passenger bus showing where standing passengers may not cross, keeping the aisle and front area clear for the driver.

The maximum number of seated and standing riders a bus is designed to carry; exceeding it is unsafe and prohibited, and the driver must count passengers when necessary.

The location where a school bus loads or unloads children; the driver activates warning lights, extends the stop arm, and ensures students are clear before moving.

The area within roughly ten feet around a school bus where children are hardest to see; drivers must account for every student before pulling away.

The orderly removal of students from a bus in an emergency, practiced so riders know exits, the danger zone, and where to assemble safely away from traffic.

The forward and backward movement of liquid inside a partly filled tank as the vehicle accelerates or stops, which shifts weight and can destabilize the rig.

A partition inside a tank that divides the liquid into smaller compartments, reducing surge and helping keep the vehicle stable during stops and turns.

The empty space left above the liquid in a tank to allow for expansion and to limit surge; tanks are not filled completely for this reason.

The endorsement required to drive a vehicle carrying liquid or gaseous cargo in a permanently mounted tank, added after passing the tank vehicle knowledge test.

The endorsement required to tow two or three trailers, granted after passing a knowledge test on coupling, converter dollies, and combination stability.