NV CDL General Knowledge cheat sheet

Total stopping distance = perception distance + reaction distance + brake lag distance + braking distance; only the last term shortens when brakes are applied, so speed raises stopping distance faster than it raises travel time.

At 55 mph a typical loaded rig needs roughly the length of a football field to stop; doubling speed roughly quadruples braking distance because kinetic energy rises with the square of speed.

Perception distance is the distance traveled during the driver's recognition of a hazard; reaction distance is the distance traveled while moving the foot to the brake - both are governed by alertness, not by brake condition.

Brake lag (about 3/4 second for air brakes) is the interval between pressing the pedal and the shoes contacting the drums; it adds distance at every speed and is absent from hydraulic systems.

The most common cause of serious crashes is driving too fast for conditions; posted limits assume good weather, good visibility, and a alert, sober driver.

Use the four-second following rule for speeds under 40 mph and add one second for each additional 10 mph; at night or in rain, double the minimum gap.

Hydroplaning begins at roughly 35 mph with partially worn tires on wet pavement; tires with low tread lose contact earlier, and steering and braking become ineffective until speed drops.

Work-zone and school-zone limits are enforced with doubled fines in most states; a driver must slow to the posted work-zone speed even when workers are not visible unless signs say otherwise.

Before driving, inspect cargo and its tiedowns, and re-check the securement within the first 50 miles and again every 150 miles or 3 hours, whichever comes first.

Aggregate working load limit: the sum of the working load limits of all tiedowns on a piece of cargo must equal at least half the cargo weight for articles over 1,100 lb, and 1.5 times the weight for articles 1,100 lb or less.

Cargo must be secured against tipping and sliding; for a 1,100 lb article, the tiedown system must resist at least 0.5 g forward, 0.5 g rearward, and 0.5 g sideways acceleration.

Front-end structure: cargo must not obscure lights, reflectors, or the plate; it must not extend more than 3 feet in front of the front bumper at any time.

Rear overhang: cargo may extend up to 4 feet behind the rear of the vehicle without a flag; beyond 4 feet and up to 15 feet, a red or orange flag at least 12 inches square is required in daylight, and a red light at night.

A red flag or light must also mark the extreme ends of loads that project beyond the sides of the vehicle.

Convert axle-weight limits, not gross weight alone: an overweight axle is a violation even when the gross combination weight is legal, so scale checks can fail a load that looks fine on paper.

Cover loose aggregate, sand, and gravel with a tarp; spilled material is a hazard and a violation, and many states hold the driver responsible for any spill.

A compressor builds air pressure; a governor cuts the compressor out near 125 psi and cuts it back in near 100 psi, so normal operating pressure sits between those points.

The low-air warning must activate before pressure drops below 60 psi; the spring brakes begin to apply automatically at roughly 45 psi, and the vehicle must stop before pressure reaches zero.

In a dual-circuit system, a leak in one circuit should not drain the other; if one circuit fails, the other still provides braking, but stopping distance increases.

The alcohol evaporator or air dryer removes moisture; water in the air tanks can freeze in winter and cause brake failure, so drain the tanks daily.

The safety valve on the first (supply) tank protects the system from overpressure, usually venting near 150 psi.

The tractor protection valve and relay valve work together: the tractor protection valve closes the tractor's air supply to the trailer if trailer pressure drops, preventing a total loss of tractor brakes.

Test the air system by building pressure to governor cut-out, shutting off the engine, and checking that pressure does not drop more than 3 psi in one minute for a single vehicle (5 psi for a combination).

Check for leaks at the spring-brake chambers by applying the parking brake and listening; a leak-down rate above 3 psi per minute with the brakes released indicates a problem needing repair.

The seven-step inspection covers: vehicle overview, engine compartment, walk-around inspection, brake check, start-engine check, in-cab check, and a final walk-around.

Before the engine is started, check the oil level, coolant level, power steering fluid, and the condition of belts and hoses; a loose belt can cause loss of steering assist or overheating.

The walk-around covers lights, reflectors, tires, wheels, rims, hubs, springs, mud flaps, and the coupling system; a missing lug nut or a cracked rim is an out-of-service defect.

The brake check includes a static leak test, a slack-adjuster check (no more than about 1 inch of free play on a type 30 chamber), and a low-pressure warning test.

The in-cab check verifies the parking brake, service brake, steering play, horn, wipers, mirrors, gauges, and the emergency equipment: fire extinguisher, spare fuses, and warning triangles.

A CDL pre-trip inspection must be performed and passed as a skills test; the same inspection is required by federal rule before each trip and at the start of each day.

Steering wheel free play should not exceed 10 degrees (about 2 inches at the rim) on a vehicle with power steering, or 10 degrees on manual steering.

Tire tread depth minimum is 4/32 inch on front tires and 2/32 inch on all other tires; any cut, bulge, or exposed cord is an out-of-service condition.

Start the engine only with the transmission in neutral and the parking brake set; on a manual transmission, depress the clutch before cranking.

To move from a stop, release the parking brake, select a gear, and release the clutch smoothly while applying light throttle; a heavy rig needs more throttle than a car to overcome inertia.

Steering: keep both hands on the wheel, at roughly 9 and 3 o'clock, and use push-pull steering; do not palm the wheel or let it spin freely.

Backing: use a spotter whenever possible, back toward the driver's side, and get out to check the area if you are unsure; a rig's blind spot behind the trailer is large.

Turning: a tractor-trailer off-tracks, meaning the rear wheels follow a path inside the front wheels; swing wide enough to keep the trailer wheels clear of the curb.

Braking: apply the brakes firmly and progressively; do not pump air brakes, and avoid riding the brakes on long downgrades, which overheats drums and fades the brakes.

Use the engine brake or a lower gear to control speed on a downgrade; a rule of thumb is to descend in the same gear you would need to climb the grade.

Before entering an intersection, check that you can clear it completely; a long combination can block the intersection if the light changes while you are still crossing.

A manual transmission in a heavy truck is usually unsynchronized; you must double-clutch: clutch in, shift to neutral, clutch out, clutch in, shift to gear, clutch out.

Match engine speed to road speed: downshift before the engine lugs, and upshift before it over-revs; the tachometer should stay in the green band.

Progressive shifting means skipping gears as you accelerate, which saves fuel and wear; it is safe only when the load and grade allow it.

Do not coast in neutral or with the clutch disengaged; you lose engine braking and the ability to accelerate out of trouble.

When descending a grade, select a gear low enough that the engine brake alone holds your speed; do not rely on the service brakes to control a long descent.

If you miss a gear, do not force it; return to neutral, match engine speed, and try again - forcing a shift damages the transmission and can cause a loss of control.

An automatic transmission with a retarder should be used on downgrades, but the retarder must be switched off on slippery surfaces to avoid locking the drive wheels.

A splitter or range selector must be shifted only at the proper speed and with the clutch depressed; shifting a range selector while moving too fast can damage the transmission.

Scan 12 to 15 seconds ahead of the vehicle: at 55 mph that is roughly a quarter mile, and it gives time to react to stopped traffic, signals, and road debris.

Look for the three hazard classes: immediate (a car braking ahead), emerging (a car waiting to pull out), and atmospheric (rain, fog, smoke, or sun glare).

Watch for clues: brake lights, turn signals, a driver's head turning, front wheels angled, and pedestrians near the curb; these predict a hazard before it moves.

Use the mirrors every 5 to 8 seconds; a rig's blind spots require a systematic scan, and a vehicle that disappears from the mirror may be alongside the trailer.

At night, look to the right edge of the road when an oncoming vehicle's headlights blind you, and slow down rather than stare at the lights.

In fog, smoke, or heavy rain, reduce speed and use low beams; high beams reflect off the precipitation and reduce visibility.

A hazard is more likely at intersections, railroad crossings, bridges, construction zones, and hills; slow down before these locations rather than in them.

Check the rear before braking hard; a tailgater behind you may need more warning, so tap the brakes early to flash the brake lights.

Signal at least 100 feet before a turn in a city and 300 feet before a turn on a highway; some states require more, so signal early.

Use the four-way flashers when stopped on the shoulder, when driving slowly in a work zone, and when backing; they warn other drivers of an unusual condition.

Flash your headlights only to signal your presence, not to demand the right of way; a headlight flash can be misread as a courtesy.

Use the horn to warn of danger, not to express annoyance; a short tap is a warning, a long blast is aggression and can startle other drivers.

Tap the brakes lightly before a hard stop to flash the brake lights and warn following traffic.

At night, dim your high beams within 500 feet of an oncoming vehicle and within 200 feet when following another vehicle.

Use hand signals when your turn signals fail or when a bicycle or motorcycle may not see your lights: left arm straight out for a left turn, bent up for a right turn, bent down for a stop.

Keep your vehicle's lights, reflectors, and reflective tape clean and functional; a dirty trailer is harder to see and is a common cause of rear-end crashes.

The four-second rule is the minimum following distance at speeds under 40 mph; add one second for each 10 mph above 40, and double the gap in rain, snow, or darkness.

A rig needs more space to the sides: keep at least one lane of space on either side when possible, and never drive alongside another large vehicle in its blind spot.

At a stop on an upgrade, leave enough space ahead to pull away without rolling back into the vehicle behind you; a loaded rig can roll back several feet.

When passing, do not return to the right lane until you can see the passed vehicle's headlights in your mirror; a rig's rear is far behind the cab.

Before changing lanes, check mirrors, signal, and check the blind spot; a trailer's blind spot can hide a whole car.

Leave room to stop when following a motorcycle or bicycle; they can stop faster than a loaded truck, so increase the gap.

Never tailgate a vehicle that is blocking your view of the road ahead; if you cannot see around it, you cannot see hazards in time.

When entering a highway, use the acceleration lane to match speed and merge into a gap; do not force a merge that requires another driver to brake.

Speed must be reduced before a curve, not in it; braking in a curve shifts weight and can cause a rollover, especially with a high center of gravity.

The posted speed limit is a maximum for good conditions, not a target; a driver must slow for rain, fog, curves, heavy traffic, and a downgrade.

On a long downgrade, select a gear low enough that the engine brake holds the speed; use the service brakes only in short applications to avoid fade.

A rule of thumb for downgrades: descend at a speed no higher than the gear you would use to climb the grade.

Ramp and curve advisory speeds (yellow signs) are set for cars; a loaded rig should go slower than the advisory, not faster.

In a work zone, slow to the posted work-zone speed and be ready for stopped traffic; rear-end crashes are the most common work-zone crash.

In fog, rain, or snow, reduce speed to the point where you can stop within the distance you can see; if you cannot see, pull off the road and stop.

A vehicle's speedometer may be inaccurate with a changed tire size; check it against a measured mile or a GPS unit.

Brake failure: downshift, use the engine brake, pump the brakes, and apply the parking brake gradually; do not lock the wheels, and look for an escape ramp or a safe runoff.

Tire blowout: hold the wheel firmly, keep the vehicle straight, and slow gradually; do not brake hard or steer sharply, which can cause a rollover.

Steering failure: slow down, keep the vehicle straight, and use the brakes gently; a sudden loss of steering assist makes the wheel very hard to turn.

Fire: stop, turn off the engine, get everyone out, and call for help; do not open the hood if the fire is in the engine compartment, because the rush of air feeds the flames.

Skid: steer in the direction you want the front of the vehicle to go, and do not brake hard; a drive-wheel skid is corrected by easing off the throttle.

If you must stop on a highway, pull as far off the road as possible, turn on the four-way flashers, and place warning triangles behind the vehicle: 10 feet, 100 feet, and 200 feet back.

A runaway trailer or a jackknife is best prevented by smooth braking and by not braking hard in a curve; if a jackknife starts, release the brakes and steer to straighten.

After any emergency stop, inspect the vehicle and cargo before continuing; a shifted load or a damaged tire can cause a second failure.