Iowa CDL General Knowledge Test cheat sheet

Total stopping distance = perception distance + reaction distance + braking distance; perception and reaction distance together average about 1 second of travel at any speed.

At 55 mph a vehicle travels about 80 feet per second, so a 1-second reaction gap covers roughly 60 feet before the brakes are applied.

Braking distance grows with the square of speed: doubling speed from 30 to 60 mph roughly quadruples the distance needed to stop.

Stopping distance also increases with vehicle weight and with the number of axles, and is longer on wet, icy, or gravel surfaces than on dry pavement.

A posted speed limit is the maximum for good conditions; in rain, fog, snow, or heavy traffic the safe speed is below the posted limit.

Use the four-second following rule at speeds under 40 mph and add one second for each additional 10 mph; a 55 mph rig needs at least six seconds behind the vehicle ahead.

When a hazard appears, brake firmly and progressively rather than locking wheels; locked wheels lose steering control and lengthen the stop.

If a front tire blows, hold the steering wheel firmly, keep the vehicle straight, and slow gradually before pulling off the road; hard braking on a blown front tire can cause a loss of control.

Cargo must be secured so it cannot shift, leak, spill, or fall; the driver is responsible for inspecting the cargo and its tiedowns before, during, and after the trip.

Aggregate working load limit of tiedowns must be at least 50 percent of the cargo weight for cargo under 1,100 lb, and at least 1,100 lb or 50 percent of the cargo weight (whichever is greater) for heavier cargo.

On flatbed or open cargo, the front tiedown must be within 4 feet of the front of the cargo, and additional tiedowns every 10 feet of cargo length.

Cargo that extends more than 4 feet behind the rear of the vehicle requires a red or orange flag at least 12 inches square during daylight and a red light at night.

Cargo extending more than 4 feet to the rear or more than 3 feet to the front of the vehicle requires an overhang flag or light; anything wider than 8 feet 6 inches needs special permits.

Cargo must not obscure the driver's view, must not interfere with steering or braking, and must not hide required lights, reflectors, or the license plate.

Before driving, check that the cargo is centered and balanced; an off-center load shifts weight to one side and can cause a rollover or uneven braking.

After driving 50 miles, recheck the cargo and tiedowns, and check again after every 150 miles or 3 hours of driving.

A dual air brake system has two separate circuits; a loss of pressure in one circuit leaves the other circuit able to stop the vehicle, and the low-pressure warning must activate before pressure drops below 60 psi.

The warning buzzer or light must come on before pressure falls below 60 psi, and the spring brakes must apply automatically when pressure drops to between 20 and 45 psi.

Build air pressure to the governor cut-out (usually 120-140 psi), then shut off the engine and check that pressure does not drop more than 3 psi in one minute for a single vehicle, or 3 psi in one minute with the engine off and brakes released.

With the engine running and pressure built up, apply the foot brake and hold it; pressure should not drop more than 3 psi in one minute with the brakes applied.

With the engine running, release the parking brake and apply the foot brake; pressure should not drop more than 3 psi in one minute with the brakes applied.

The safety valve releases air at about 150 psi to protect the system from over-pressurization; if it releases air, the system should be checked.

Air pressure must build from 85 to 100 psi within 45 seconds at fast idle; a slower build indicates a compressor or leak problem.

Fan the brakes by applying and releasing the foot brake several times; the low-pressure warning and spring brake application should occur at the specified pressures.

A tractor-trailer has a shorter wheelbase than a straight truck, so it turns more sharply; the rear wheels of the trailer follow a path inside the path of the front wheels (off-tracking).

When backing a trailer, turn the steering wheel toward the side you want the trailer to go; the trailer turns in the direction the bottom of the steering wheel moves.

Before backing, get out and check the area, use a helper if possible, and back slowly; if you lose sight of the helper, stop.

The tractor protection valve closes and keeps air from escaping when the trailer breaks away or the emergency line is disconnected, applying the trailer spring brakes.

The trailer hand valve (trolley valve) should be used only to test the trailer brakes, never to park or to stop the vehicle.

A combination vehicle's bobtail (tractor alone) stopping distance is shorter than a loaded combination; drive a bobtail tractor with extra care because it can jackknife more easily.

The coupling system must be checked after coupling: tug test with the trailer brakes set, check the fifth-wheel jaws, and confirm the safety latch is closed and the release handle is in.

When uncoupling, first lower the landing gear, then pull the air lines and electrical cord, then release the fifth-wheel jaws, and finally pull the tractor forward slowly.

The pre-trip inspection covers three main areas: the engine compartment, the cab and controls, and the walk-around of the exterior (lights, tires, brakes, coupling).

Check tire tread depth: at least 4/32 inch on steering axle tires and at least 2/32 inch on all other tires; check for cuts, bulges, and proper inflation.

Check the engine compartment for fluid levels (oil, coolant, power steering, washer), belt condition and tension, and leaks under the vehicle.

Check that the parking brake holds the vehicle, that the service brake stops it without pulling, and that the air pressure builds and holds as specified.

Check all lights: headlights (high and low beams), turn signals, four-way flashers, brake lights, tail lights, clearance lights, and reflectors.

During the walk-around, check the coupling system, the landing gear, the mud flaps, the exhaust system, and the frame for cracks or loose parts.

The in-cab inspection includes the seat belt, mirrors, horn, wipers, heater and defroster, gauges, and the steering wheel for excessive play.

After the pre-trip inspection, do a brake test: with the engine running and the vehicle stopped, apply the brakes and check that the vehicle does not pull and the pedal does not fade.

To start moving, release the parking brake after the engine is running and the vehicle is in gear, then accelerate gently so the load does not shift.

Use the steering wheel with both hands; keep the hands at the 9 and 3 o'clock positions and do not grip the wheel too tightly.

When turning, slow down before the turn, signal early, and accelerate gently after the turn; do not coast through a turn with the clutch in.

To stop, release the accelerator, apply the brake progressively, and downshift as speed drops so the engine helps slow the vehicle.

Use the mirrors and turn your head to check blind spots before changing lanes; mirrors do not cover the area directly behind or beside the vehicle.

When driving a vehicle with a manual transmission, do not ride the clutch or hold the vehicle on a hill with the clutch; use the parking brake.

When pulling off the road, signal, check mirrors, slow down, and pull as far off as possible; turn on the four-way flashers if the vehicle is a hazard.

When driving through a curve, slow down before entering the curve and accelerate gently after the apex; braking in a curve can cause a skid.

Shift up at the correct engine rpm: too low an rpm causes lugging and too high an rpm wastes fuel and strains the engine.

Double-clutching: press the clutch, shift to neutral, release the clutch, press the clutch again, and shift to the next gear; this matches engine and transmission speeds.

When downshifting, match engine speed to the lower gear before releasing the clutch; releasing the clutch too early can cause the drive wheels to skid.

Do not coast with the clutch in or the transmission in neutral; you lose engine braking and the ability to accelerate quickly.

On a downgrade, select a lower gear before starting down the grade and use the engine brake or retarder; do not rely on the service brakes alone.

If you miss a gear, do not force it; return to neutral, match the speed, and try again.

When starting on a hill, use the parking brake to hold the vehicle while you release the clutch and accelerate, then release the parking brake.

Do not shift gears while crossing railroad tracks or in an intersection; keep the vehicle in gear and proceed steadily.

Scan the road at least 12 to 15 seconds ahead; at highway speed this is about a quarter mile, which gives time to react to changing conditions.

Look for clues such as brake lights, turn signals, and drivers looking over their shoulders; these signal a driver may change lanes or turn.

Watch for road hazards: potholes, loose gravel, standing water, and construction zones; slow down before reaching them rather than braking abruptly.

Check mirrors frequently and scan the sides of the road for pedestrians, cyclists, and animals; hazards can appear from any direction.

When approaching a hill or curve, look as far ahead as possible and be ready for stopped or slow vehicles that may be hidden.

At night, use high beams when there is no oncoming traffic and low beams when following another vehicle or meeting traffic.

In fog, rain, or snow, reduce speed and increase following distance; use low beams, not high beams, because high beams reflect off the precipitation.

When you see a hazard, decide early whether to slow down, change lanes, or stop; waiting until the last moment reduces your options.

Texting or using a hand-held phone while driving is prohibited for commercial drivers; even a momentary glance away from the road at highway speed covers a long distance.

Distractions include eating, drinking, adjusting the radio or GPS, grooming, and interacting with passengers; any of these can take your attention off the road.

Before driving, set the GPS, adjust mirrors and seats, and secure loose items so you do not need to reach for them while moving.

If you must make a call, pull off the road to a safe location and stop before using the phone.

Fatigue is a form of impairment: drowsy driving slows reaction time and judgment much like alcohol; take breaks and do not drive when tired.

Keep your eyes moving and your mind on the driving task; do not stare at one object for more than a moment.

If something in the cab distracts you, pull over and deal with it rather than trying to handle it while driving.

Distracted driving is a leading cause of crashes; the safest practice is to eliminate distractions before the vehicle moves.

The safe following distance is at least one second for each 10 feet of vehicle length at speeds under 40 mph; add one second for speeds above 40 mph.

At 55 mph, a 60-foot combination vehicle needs at least 7 seconds of following distance; increase this in rain, snow, or low visibility.

Stopping distance increases with speed, weight, and road conditions; at 55 mph a loaded truck may need more than 300 feet to stop.

Maintain a space cushion around the vehicle: at least one car length ahead for each 10 mph of speed is a common rule of thumb for light vehicles.

When passing, allow extra space before pulling back in front of the passed vehicle; a heavy truck needs more room to accelerate and stop.

When being passed, maintain speed and keep to the right; do not speed up or move into the passing lane.

When entering a highway, use the acceleration lane to match traffic speed and merge smoothly; do not stop at the end of the ramp unless necessary.

When approaching a work zone or a stopped school bus, slow down and be prepared to stop; obey flaggers and posted reduced speeds.

At night, drive slower than you would in daylight; your headlights let you see only about 250 feet on low beam and about 350 to 500 feet on high beam.

Use high beams when there is no oncoming traffic; switch to low beams when meeting or following another vehicle to avoid blinding the other driver.

If an oncoming vehicle has high beams on, look toward the right edge of your lane and slow down until it passes.

In fog, use low beams and fog lights; high beams reflect off the fog and reduce visibility.

In rain, snow, or ice, reduce speed, increase following distance, and brake gently; avoid sudden steering or braking that can cause a skid.

If you begin to skid, take your foot off the accelerator and steer in the direction you want the vehicle to go; do not brake hard.

In strong wind, slow down and keep both hands on the wheel; be especially careful when passing large vehicles or driving on bridges and open stretches.

If visibility becomes too poor to drive safely, pull off the road as far as possible, turn on the four-way flashers, and wait until conditions improve.

Drivers hauling hazardous materials need a hazardous materials endorsement on their CDL and must follow placarding, packaging, and routing rules.

Placards must be displayed on both sides and both ends of the vehicle for the hazard class being carried; the placard shows the hazard class number and name.

The shipping paper must accompany the shipment and include the proper shipping name, hazard class, UN identification number, and total quantity.

When a hazardous materials incident occurs, stop, keep people away, call for help, and give the dispatcher or emergency responders the placard information and shipping paper details.

Do not smoke or use open flames near hazardous materials, and keep the engine off during loading and unloading unless the product requires it.

If a tire blows or a fire starts, stop as soon as it is safe, get away from the vehicle, and call for help; do not try to fight a large fire.

If the vehicle is involved in a crash with hazardous materials, do not move the vehicle unless it is necessary to prevent further danger, and warn others to stay away.

Emergency equipment required on a hazardous materials vehicle includes a fire extinguisher, warning triangles or flares, and personal protective equipment as specified.