NH CDL General Knowledge key terms

A systematic check of a commercial vehicle's critical parts and systems performed before driving, covering tires, brakes, lights, coupling devices, and emergency equipment, so defects are found while the vehicle is stationary rather than while moving.

A stationary check in which the system is charged, the engine shut off, and pressure loss observed over one minute with brakes released and then applied; excessive drop signals a leak that must be fixed before driving.

A buzzer and light that must activate before air pressure falls below a set threshold, warning the driver that braking power is fading and that the vehicle should be stopped safely before spring brakes apply automatically.

Parking and emergency brakes held engaged by heavy springs and released by air pressure; if system pressure drops too low they apply on their own, which is why a vehicle with a serious air loss can lock up suddenly.

The lever linking the brake chamber pushrod to the brake shoe; its angle and travel show whether brakes are properly adjusted, and too much pushrod travel means weak or delayed braking.

Setting brake shoes close enough to the drum that the pushrod stroke stays within limits; out-of-adjustment brakes on a commercial vehicle are a serious defect and a common roadside inspection violation.

The measured groove depth on a tire; commercial vehicle front tires and other tires must meet minimum legal depths, and shallow tread worsens traction, hydroplaning risk, and stopping distance on wet roads.

The fifth wheel, kingpin, pintle hook, or other connection between tractor and trailer; it must be inspected for secure locking, wear, and proper gap because a failed coupling separates the units while moving.

A valve that closes off the tractor's air supply if a trailer breaks away or a line ruptures, keeping enough air to stop the power unit and causing the trailer brakes to apply.

The total distance a vehicle travels from the moment a hazard is noticed until it halts, made up of perception distance, reaction distance, and braking distance, and growing rapidly as speed increases.

The distance covered while the driver's eyes see a hazard but the brain has not yet recognized it as something requiring action; it lengthens with fatigue, distraction, and poor visibility.

The distance traveled between recognizing a hazard and actually pressing the brake pedal; it depends on alertness and is much longer for a tired, impaired, or distracted driver.

The distance needed to stop once the brakes are applied; it rises with the square of speed, so doubling speed roughly quadruples braking distance, and it is further stretched by poor traction or worn brakes.

The gap kept behind the vehicle ahead, commonly measured in seconds by counting after the leader passes a fixed object; heavy vehicles need at least one second per ten feet of length under good conditions.

The safety margin kept around the vehicle on all sides, including front, rear, and lateral gaps, so there is room to steer or stop if another road user makes a sudden move.

Where the vehicle sits within its lane; large vehicles often need to occupy more than one lane or shift within a lane to complete turns without letting the rear wheels off the pavement or over a curb.

The tendency of a vehicle's rear wheels to follow a tighter path than the front wheels in a turn, so the trailer cuts the corner; the longer the wheelbase, the greater the effect.

The outward sweep of a vehicle's rear end or trailer during a turn, which can strike pedestrians, signs, or parked vehicles; the driver must check mirrors and allow extra room before turning.

A shifting method using the clutch twice per gear change, once to move to neutral and once to engage the next gear, matching engine and transmission speed so gears engage without grinding in a non-synchronized transmission.

Shifting without using the clutch by matching engine speed to road speed at the moment of the change; it requires skill and is not recommended for inexperienced drivers because a mismatch damages the transmission.

Adjusting engine speed so the transmission input speed matches the gear being selected, which allows smooth engagement and prevents jerking, grinding, and wear on the drivetrain.

Loss of traction in which tires slide instead of rolling, caused by braking too hard, accelerating too fast, or turning too sharply for the road surface and speed.

A condition where brakes stop the wheels from rotating, so the tires slide and steering control is lost; releasing brake pressure to let wheels roll again is the standard recovery.

Turning the steering wheel in the direction the rear of the vehicle is sliding to bring it back in line; a driver must look and steer where they want to go rather than at the obstacle.

Riding on a thin layer of water so tires lose contact with the pavement, causing loss of steering and braking; it happens more easily at higher speeds, with low tread, or with underinflated tires.

An electronic system that rapidly releases and reapplies brake pressure to prevent wheel lockup, helping the driver keep steering control during hard stops on slippery surfaces.

Slowing below the posted limit when rain, snow, ice, fog, or wind makes the road unsafe; the posted maximum is meant for ideal conditions, and driving too fast for conditions can itself be a violation.

How far down the road a driver scans for hazards; at highway speeds a large vehicle should look well beyond the vehicle ahead so problems are spotted early enough to react smoothly.

The skill of reading traffic, road, and weather cues to anticipate problems before they force evasive action, such as noticing brake lights far ahead or a driver who may pull out.

A specially built gravel or sand ramp beside a steep downgrade that lets a driver with failing brakes stop safely by driving up the incline instead of continuing downhill out of control.

Loss of braking power when brakes overheat from repeated or prolonged use, common on long downgrades; drivers prevent it by using a lower gear and controlled braking rather than riding the brakes.

Using a lower gear so compression slows the vehicle, reducing reliance on the service brakes on downgrades and helping prevent overheating and fade.

A vehicle that cannot be slowed or stopped on a grade, often from brake failure or fade; the driver should look for an escape ramp, use gears and available braking, and warn others.

The required steps after a crash: stop, protect the scene with warning devices, check for injuries, call for help, exchange information, and report the incident as required by law.

Reflective triangles or flares placed behind a stopped vehicle to alert approaching traffic; placement distance depends on road type and speed, and they must be set out promptly after a breakdown.

The use of tiedowns, straps, chains, and blocking to keep a load from shifting, sliding, or falling; the number and strength of tiedowns must meet rules based on cargo weight and length.

Arranging cargo so weight is spread properly across axles and kept within axle and gross weight limits; poor distribution overloads tires and brakes and can make steering or handling unsafe.

The point where a vehicle's and load's weight is concentrated; raising it by loading heavy cargo high makes a rollover more likely in turns and evasive maneuvers.

The combined strength rating of all tiedowns used to secure a load; the total must be at least half the cargo weight, and each tiedown must be rated and in good condition.

A crash in which the vehicle tips onto its side or roof, often triggered by high speed in a curve, a high center of gravity, or a sudden swerve; it is among the most deadly outcomes for large vehicles.

Federal limits on driving and on-duty time for commercial drivers, including maximum driving hours, required off-duty periods, and break rules, designed to prevent fatigue-related crashes.

The record of a driver's duty status, driving time, and rest periods; it must be accurate and current because inspectors use it to verify compliance with hours-of-service limits.

Physical and mental tiredness that slows reaction time, impairs judgment, and can cause a driver to fall asleep at the wheel; it is managed with rest, breaks, and honest reporting of duty status.

The body's internal clock that creates natural drowsy periods, especially at night and in early afternoon; drivers should plan rest around these low-alertness windows rather than fight them.

The percentage of alcohol in the bloodstream; commercial drivers are held to a stricter limit than other drivers, and a violation can end a driving career even without a crash.

The legal rule that holding a commercial license means agreeing to submit to alcohol or drug testing when lawfully requested; refusing can bring penalties as severe as a failed test.

Loss of the privilege to drive a commercial vehicle, triggered by serious traffic violations, alcohol or drug offenses, or certain crashes, and lasting for a set period or permanently.

A place where tracks cross a road; drivers must slow, look both ways, listen, and never start across unless there is room to clear the tracks completely on the far side.

A crossing signal that reacts to approaching trains, such as flashing lights, bells, or gates; drivers must obey them and never drive around lowered gates.

A fixed crossing warning that does not change with train traffic, such as a crossbuck sign, pavement markings, or a stop sign; it still requires slowing and looking carefully.

The legal priority to proceed at an intersection or merge; failing to yield it, especially when turning across traffic or entering from a stop, is a leading cause of crashes involving large vehicles.

The blind spots around a large vehicle where a car can disappear from the driver's mirrors; drivers must check mirrors and signal early, and other motorists should avoid lingering there.

Rules requiring drivers to stop for a school bus with flashing red lights and an extended stop arm, often in both directions, unless separated by a physical median or barrier.