Space you leave between your truck and the vehicle ahead.
A heavy truck needs far more room to stop than a car, so the manual measures following distance in seconds, not car lengths. The rule is one second for every 10 feet of vehicle length at speeds under 40 mph, plus one more second above 40 mph. Count from when the vehicle ahead passes a fixed mark until you reach it, and add more time on wet or icy roads.
Differs by state: The time rule is the same in more than 40 state manuals. Minnesota adds a statute: at least 500 feet between trucks on highways, except when passing or in a designated truck lane. Serve the time rule nationally; a question keyed to 500 feet is unanswerable outside Minnesota.
Example: On the interstate you watch the car ahead pass an overpass shadow and count; you reach it too soon, so you drop back.
Diagram coming
Also called: safe following distance
How far a vehicle travels while coming to a stop.
It is made of three parts: perception distance, reaction distance and braking distance; with air brakes, brake lag is added. Speed matters most: double your speed and the braking distance grows about four times. Wet roads, worn tires and an empty truck all stretch it.
Differs by state: Most manuals print the same figures at 55 mph on dry pavement: 142 ft perception, 61 ft reaction, 216 ft braking, 419 ft total. Adding air-brake lag makes the total over 450 ft. Pennsylvania still prints an older edition: 3/4-second perception, 60 ft, 390 ft braking, about 450 ft total. Its air-brake total reads 'more than 300 feet'. Serve the majority figures; a Pennsylvania learner sees different numbers in the state manual.
Does not mean: Not the same as braking distance, which is only the part after the brakes start working.
Example: Coming off a rainy exit ramp, you remember the wet road can double your stopping distance and slow well before the light.
Diagram coming
Distance traveled between seeing a hazard and recognizing it as one.
Your eyes can be on a hazard before your mind understands it is a hazard. Fatigue, distraction and poor visibility stretch this time, and the vehicle keeps moving the whole while.
Differs by state: Forty-two manuals give an alert driver's perception time as 1 3/4 seconds, about 142 feet at 55 mph. Pennsylvania's manual still prints the pre-2005 figures of about 3/4 second and 60 feet. Serve the majority and flag any Pennsylvania-keyed item.
Example: A deer stands at the tree line; for a moment it is just a brown shape, and your truck rolls on before you register danger.
Distance covered between recognizing a hazard and hitting the brake.
Once your brain knows there is danger, your foot still has to move from the accelerator to the brake pedal. That takes most drivers under a second, but at highway speed the truck covers a surprising distance.
Example: Brake lights flare ahead; you know you must stop, yet your truck travels several car lengths before your foot reaches the pedal.
Distance traveled from the brakes taking hold to a full stop.
This is the part of stopping distance that speed changes most: go faster and it grows much faster than your speed does. Good brakes, good tires and a dry road keep it short; a wet road or an empty, bouncing truck makes it longer.
Differs by state: Forty-three manuals print about 216 feet of braking distance at 55 mph on dry pavement with good brakes. Pennsylvania prints about 390 feet, a pre-2005 figure that also folds in perception and brake lag. Serve 216 feet nationally.
Does not mean: Not the whole stopping distance; seeing, deciding and moving your foot come before it.
Example: Running empty back to the yard, you leave extra room at every light because a light truck bounces and its braking distance grows.
total stopping distance
총 정지 거리Perception, reaction and braking distances added together; with air brakes, brake lag too.
It is the full distance from the moment a hazard appears to the moment the truck stands still. The manual gives one total in the driving section and a longer one for air-brake vehicles, because air takes time to reach the brakes. Both figures are correct; read the question to see which one it wants.
Differs by state: Most manuals print two totals at 55 mph on dry pavement. The driving section gives a minimum of 419 feet (142 perception + 61 reaction + 216 braking). The air-brake section gives over 450 feet, because about 32 feet of brake lag is added. Pennsylvania's older edition prints about 450 feet for the first total and 'more than 300 feet' for the air-brake total. Never harmonize 419 and 450; they answer different questions.
Example: At highway speed a car cuts in and brakes; by the time your rig stops, you have used more than a football field of road.
Diagram coming
Area around your vehicle that your mirrors cannot show you.
Trucks have big blind spots: directly behind, right beside the cab and trailer, and close in front of the hood. Check mirrors often so you know when a car has slipped into one, and use a helper when backing.
Example: A sedan that was behind you vanishes from the mirror; you assume it is in your blind spot and hold your lane.
Diagram coming
Also called: blind spots
The tires lose their grip and the vehicle slides.
Skids come from braking too hard, steering too sharply, giving the drive wheels too much power, or simply driving too fast for the road. Most are drive-wheel skids; the cure is to stop braking or accelerating, then steer where you want to go.
Example: On a wet curve the trailer starts to swing; you ease off the brakes and the tires grip again before the skid grows.
Also called: skidding
The rear drive wheels lose traction and slide sideways.
It is the most common skid, caused by braking hard enough to lock the drive wheels or by spinning them with too much power. A straight truck spins out; a tractor-trailer can jackknife because the trailer pushes the tractor sideways. Fix it by getting off the brake or accelerator, then countersteering.
Example: Braking hard on ice, you feel the tractor's rear step out; you release the pedal and the drive tires catch again.
Diagram coming
Front tires lose grip and the truck ignores the steering wheel.
Driving too fast for conditions causes most of them; worn front tires or too little weight on the front axle also help cause them. There is only one way out: stop turning or braking so hard and let the truck slow down until the front tires grip.
Example: Entering an icy curve too fast, you turn the wheel but the hood keeps pointing at the ditch until you slow and the tires bite.
Diagram coming
Steering back the opposite way after a swerve or skid.
A vehicle that is turning back on course tends to keep turning. Unless you steer the other way quickly, you skid in the opposite direction; think of swerve and countersteer as one movement. It takes practice, best learned on a skid pad.
Example: You swerve right around a stalled car, then immediately steer left again so the trailer does not keep swinging toward the shoulder.
Diagram coming
Also called: counter-steer, countersteer
Tires ride up on water and lose contact with the road.
It is like water skiing: with no grip you may not be able to steer or brake. It can start at speeds as low as 30 mph where water pools, and worn tread or low tire pressure make it more likely. To recover, release the accelerator and push in the clutch so the wheels turn freely; do not brake.
Example: In heavy rain the steering suddenly feels light and you see clear reflections ahead; you lift off the accelerator and let the truck slow.
Diagram coming
Also called: hydroplane
Thin, clear ice that makes the road look only wet.
You can see the pavement through it, so it is easy to miss. Any time the temperature is near or below freezing and the road looks wet, treat it as ice. Bridges and shaded stretches freeze first; feel the front of your mirror for ice as a check.
Example: At dawn the highway looks damp but the thermometer reads below freezing, so you slow down and avoid any sudden steering.
The grip between the tires and the road surface.
Rain, ice, snow, loose gravel and worn tread all reduce traction, so you must slow down. The manual's rule: cut speed by about a third on a wet road and by half or more on packed snow. An empty truck has less traction because less weight sits on the tires, and retarders or hard braking can break traction on slippery roads.
Example: Snow starts to pack on the highway, so you switch the retarder off and leave extra room; traction is now your limiting factor.
Following another vehicle too closely to stop safely if it brakes.
When a car tailgates your truck, do not speed up and do not tap your brakes or flash your lights to scare it off. Signal early, slow gradually, and open up more room ahead so the tailgater can get around you. Trucks get tailgated most when they are slow, uphill, or in bad weather.
Example: A pickup rides your bumper in the rain; you ease off slightly, add space ahead, and let it pass when it can.
Also called: tailgater
Soft gravel bed or uphill lane that stops a runaway truck.
Ramps sit a few miles below the top of long mountain grades and are marked by signs. The loose material drags the wheels to a stop; some ramps also climb so gravity helps. If your brakes fail on a hill, use the ramp without hesitating; drivers who skip it often crash.
Example: Smoke rises from your brakes halfway down a long grade; you see the escape ramp sign and steer straight into the gravel bed.
Diagram coming
Also called: runaway truck ramp, escape ramps
Downhill stretch of road where gravity speeds the truck up.
Pick a safe speed before the hill, based on the truck's weight, the length and steepness of the grade, the road and the weather. Shift to a low gear at the top and let the engine hold the speed; brake in firm, short applications instead of riding the pedal. Brakes that are used too much overheat and fade.
Does not mean: Not a license downgrade; here it is a hill, though the manual also uses the word for losing CDL privileges.
Example: A sign warns of a long, steep grade ahead; you slow at the top, shift down, and start down with the engine holding you back.
Also called: steep grade, long downgrade
An uphill stretch of road, where gravity slows the truck down.
Heavy trucks lose speed climbing, so stay in the right lane and do not pass another slow vehicle unless you can get by quickly. Starting from a stop on a steep upgrade needs the parking brake or trailer hand valve so you do not roll back.
Does not mean: Not a license upgrade (moving from Class B to Class A); here it is a hill.
Example: Grinding up a long upgrade at a crawl, you keep right and switch on the flashers where that is legal so cars see you early.
Also called: uphill
Safe speed through a curve, below what is posted for cars.
Take a curve too fast and either the tires lose grip and you slide off, or they hold and the truck rolls over. Slow down before the curve, not in it, because braking in a curve can lock the wheels. Be in a gear that lets you accelerate slightly through the turn.
Example: The ramp sign shows a speed meant for cars; with a tall load you slow well below it before the curve begins.
Also called: speed on curves
Moving your vehicle from one traffic lane into the next.
Signal first, then check your mirrors before moving, after signaling, as you start to move, and once you are in the new lane. Change lanes slowly and smoothly so a driver you missed has time to react. With doubles or triples, the extra length means you need a longer gap.
Example: You signal left, wait, check both mirrors twice, and ease across only after the gap behind the trailer is clearly empty.
Also called: changing lanes
Joining moving traffic from an on-ramp or an ending lane.
A loaded truck accelerates slowly, so you need a much bigger gap than a car. Use your mirrors to be sure the gap is big enough before you enter, and expect that merging drivers may not see you.
Example: On the on-ramp you build speed, watch the mirror for a wide gap, and slide in without forcing anyone to brake.
Also called: merge
Overtaking a slower road user and moving ahead of them.
Assume the person you are passing has not seen you; a light horn tap, or a headlight flick at night, warns them. Pass only where it is legal and you can see far enough ahead; a slow truck needs a long way to get by. Going uphill, do not pass a slow vehicle unless you can get around quickly.
Does not mean: Not passing a test; those questions are about the exam, not the maneuver.
Example: Before passing a cyclist on a county road you tap the horn lightly and move fully into the other lane.
Also called: overtaking
The right to proceed first when two road users' paths cross.
A train always has it at a crossing, and you must yield to stopped emergency vehicles by moving over or slowing down. Never assume the other driver will yield to you; many hazards come from drivers who believe they have the right-of-way.
On the test
Questions seldom use the term directly; the manual applies it to trains at crossings and to moving over for stopped emergency vehicles.
Appears in 5 test questions
See 1 question on the Iowa testExample: Lights flash at a crossbuck; you stop short of the tracks because the train has the right-of-way, no matter how long it takes.
Road section where crews are working, often with narrow lanes.
Speeding is the top cause of injury and death in work zones, so hold the posted limit and watch the speedometer on long stretches. Expect uneven pavement, sharp lane shifts, workers close to traffic and construction vehicles pulling in. Use flashers or brake lights to warn drivers behind you.
Example: Orange barrels squeeze the interstate to one lane; you drop to the posted limit, turn on the flashers, and leave extra room ahead.
Also called: construction zone
A place where two or more roads cross or meet.
Intersections are where paths conflict, so slow down and look for drivers who may not stop. Turning left, reach the center of the intersection before you turn, so the trailer does not off-track into another car. With two left-turn lanes, use the right-hand one.
Example: Turning left onto a wide avenue, you roll to the middle of the intersection first so your trailer's wheels clear the car waiting beside you.
Diagram coming
Also called: intersections
Highway whose opposing lanes are separated by a median or barrier.
Traffic on your side all moves one way, so a stopped truck's warning devices go only behind it, toward approaching traffic. Space the three triangles 10, 100 and 200 feet behind the vehicle.
Example: A tire blows on the interstate; you pull to the shoulder and walk back with the triangles, placing them all behind the trailer.
Diagram coming
An undivided road with a single lane in each direction.
Because traffic comes from both directions, a stopped truck needs warning devices both ahead and behind, plus one near the vehicle. Put one within 10 feet of the vehicle, one 100 feet behind and one 100 feet ahead. If a hill or curve hides you from drivers within 500 feet, move the far triangle back so they see it in time.
On the test
Questions ask where to set out reflective triangles after stopping on a straight, level, undivided two-lane road, or beyond a hill or curve.
Appears in 25 test questions
See 2 questions on the New Jersey testExample: Your truck dies on a rural two-lane road; you set one triangle ahead, one behind, and one by the rear corner before calling for help.
Diagram coming
Paved or gravel strip beside the travel lanes for emergency use.
Most shoulders will hold a heavy truck, so steering onto one can be safer than a collision. Once there, avoid braking until you have slowed a lot, keep one set of wheels on the pavement, and stop before pulling back on. If you must return at speed, turn back sharply and then countersteer.
Example: A car swerves into your lane; you steer right onto the clear shoulder, stay off the brakes, and roll to a stop on the gravel.
Headlight setting that throws light farthest down the road.
Use them whenever it is safe and legal, because low beams show far less of the road ahead. Dim them when another vehicle is coming toward you or you are following one, and never answer another driver's glare with your own. In the pre-trip you check them with the dimmer switch during the light check.
Example: On an empty rural highway at night you run on high beams, dropping to low as soon as headlights appear over the rise.
Also called: high beam
Headlight setting aimed low to avoid blinding other drivers.
You see much less of the road on low beams, so slow down enough to stop within the distance they light. Use them in daytime rain, snow, dusk and fog to be seen, and in the pre-trip you turn them on for the walk-around light check.
Example: Fog settles over the valley at noon, so you switch on the low beams, not the high beams, and ease off the speed.
Also called: low beam
All four turn signals flashing together to warn other drivers.
The manual calls them four-way flashers. Turn them on when stopped at the roadside, when driving very slowly, in fog, and near work zones so drivers behind notice you. Laws on using them while moving differ by state, so check where you drive.
Differs by state: The manual itself says laws on using flashers while driving slowly differ from state to state. The divergence catalogue did not test this fact, so no state list is given; treat 'flashers while moving' items as state-sensitive.
Example: Your loaded truck crawls up a long grade far below the speed limit, so you switch on the hazard lights where the state allows it.
Also called: four-way flashers
Straps, chains or ropes that fasten cargo to the vehicle.
On flatbeds they keep the load from shifting or falling off; in closed vans they stop cargo from moving and upsetting the handling. Use at least one tie-down for every 10 feet of cargo, and never fewer than two, however small the load. Their combined strength must be at least half the cargo's weight; see working load limit.
Example: Loading steel beams on a flatbed, you count the chains against the beam length and add one more before tightening the binders.
Diagram coming
Also called: tiedowns
Holding cargo in place with blocking, bracing and tie-downs.
A shifting load can roll a truck, break the cab's header board, or spill onto the road. Inspect it before the trip, again within the first 50 miles, and then every 150 miles or three hours, whichever comes first. The whole system must have enough combined strength for the load's weight; see working load limit.
Example: An hour into the trip you pull into a rest area and walk the flatbed, re-tensioning two straps that have loosened.
Also called: securing cargo
blocking and bracing
받침목과 버팀목 고정Blocks and braces that keep cargo from sliding or tipping.
Blocking is fitted tightly in front of, behind or beside a piece of cargo and fastened to the deck. Bracing is a strut from high on the load to the floor or trailer walls, so the load cannot tip or shift. Hazmat rules also call for blocking or bracing of cylinders and some packages.
Example: A single crate sits mid-deck; you nail blocking tight against all four sides and brace the top so it cannot tip in a hard stop.
Diagram coming
working load limit
작업 하중 한계 (WLL)Maximum load a tie-down or securement part is rated to carry.
Every strap, chain, hook and anchor point has a working load limit (WLL) marked by its maker. Add up the limits of all tie-downs on a load to get the aggregate working load limit. Federal rules say that total must be at least half the weight of the cargo.
Does not mean: Not the breaking strength; the working load limit is well below the point where the strap fails.
Example: The tag on each strap shows its working load limit; you add the tags up before deciding the coil is held down well enough.
Also called: WLL
aggregate working load limit
총 작업 하중 한계The combined working load limits of all tie-downs holding one load.
Federal rules require this total to be at least half the cargo's weight. Count only the tie-downs actually holding that load, and use each one's marked limit.
On the test
Questions ask the minimum aggregate working load limit federal rules require, stated as a share of the cargo weight.
Appears in 2 test questions
See 1 question on the California testExample: Four straps hold a machine; you add their four marked limits and compare the total with the machine's weight before rolling.
A heavy cover tied over open cargo to protect it.
Flatbed loads are often covered with a tarp. It must be tied tight so it cannot flap, tear, or block your view.
On the test
Questions ask how to check that a tarp is secured during inspection and what to watch for in your mirrors while driving.
Appears in 2 test questions
See 1 question on the HazMat testExample: In the mirror you see a corner of the tarp lifting in the wind, so you pull over and tie it down again.
Also called: tarpaulin, tarps
Tiredness that slows your reactions and dulls your judgment.
A tired driver can fall asleep for a few seconds without knowing it. The only real cure is sleep, not coffee or pills.
Example: You cannot stop yawning and do not remember the last few miles, so you pull into a rest area and nap.
Also called: drowsy driving, drowsy
distracted driving
주의 분산 운전Driving with your eyes, hands, or mind off the road.
Texting is the worst distraction because it takes your eyes, hands, and mind at the same time. Using a handheld phone in a commercial motor vehicle (CMV) is a serious traffic violation.
Example: Your phone buzzes on the highway; you leave it until you can park, because one glance at 55 mph covers a long way.
Also called: texting
Pushy, selfish driving that ignores other people's safety and rights.
Speeding, tailgating, and cutting people off are aggressive driving. Road rage goes further: it is anger that turns into threats or violence.
On the test
Questions ask how aggressive driving differs from road rage, which behaviors count as aggressive, and how to respond to an aggressive driver.
Appears in 17 test questions
See 8 questions on the General Knowledge testDoes not mean: Aggressive driving is not road rage: road rage is anger that turns into threats or violence, usually a crime.
Example: A car tailgates you and flashes its lights; you move right, let it pass, and avoid eye contact.
Also called: road rage, aggressive driver
blood alcohol concentration
BAC (혈중 알코올 농도)The amount of alcohol in your blood, a measure of impairment.
Your BAC rises with how much you drink, how fast you drink, and how little you weigh. The limit for driving a CMV is 0.04, and any alcohol below that still means 24 hours out of service. Only time lowers it; coffee and cold showers do not.
Differs by state: The 0.04 limit and the 24-hour out-of-service rule read the same in every manual (49 CFR 392.5). The trigger below 0.04 differs: most states say any detectable amount. Michigan prints a 0.015 floor and Kentucky a 0.01 to 0.039 band. The Michigan figure still needs source verification.
Example: You had two beers with dinner, so you hand the keys to your co-driver and do not move the truck until morning.
Also called: BAC, blood alcohol content, blood alcohol
Driving a commercial motor vehicle (CMV) counts as consent to alcohol testing.
You do not sign anything. By driving a CMV you have already consented. Refusing the test loses your CDL just like failing it.
Example: An officer asks for a breath test at a roadside stop; because you drive a CMV, refusing would mean losing your CDL.
Driving under the influence (DUI) is driving any vehicle while impaired.
Impaired means by alcohol or drugs; states call it DUI, DWI, or OWI. A first conviction costs your CDL for at least one year, three if the CMV was placarded for hazmat. A second conviction costs it for life, and a conviction in your personal car counts too.
Differs by state: The disqualification periods are federal minimums (49 CFR 383.51) and read the same in every manual. Only the name of the offense changes by state: DUI, DWI, OWI, or DWUI.
Does not mean: DUI is not limited to the truck: a conviction in your personal vehicle also disqualifies your CDL.
Example: A driver is convicted of DUI in his own car on a weekend; he loses his CDL too, not only his car license.
Also called: DWI, OWI, driving under the influence, driving while intoxicated
Blocks set against the tires so a parked vehicle cannot roll.
A trailer without spring brakes holds only as long as its air lasts. When the air leaks out, nothing holds it except chocks.
Example: You drop a trailer that has no spring brakes, so you wedge chocks against its tires before pulling the tractor away.
Diagram coming
Also called: chock, chocks
How far and how clearly you can see around you.
Rain, fog, snow, dust, and darkness all cut visibility. When you cannot see far, slow down so you can stop within what you see.
Example: Fog rolls in on the interstate, so you slow down, turn on your low beams, and leave more space ahead.
The highest legal speed on a road, shown on a sign.
Trucks and buses may have a lower limit than cars on the same road. A curve's posted speed is set for cars; a tall, heavy truck can roll over at that speed.
Does not mean: A speed limit is the maximum, not a target; the safe speed can be much lower in bad conditions.
Example: The curve sign says 35, but your tank vehicle is tall and heavy, so you slow well below it before the curve.
Also called: posted speed, posted speed limit
A speed that lets you stop within the distance you can see.
Safe speed is often below the speed limit. Rain, curves, hills, traffic, and poor visibility all lower it. On a downgrade, pick it before you start down.
Does not mean: Safe speed is not the posted speed limit; the limit is a ceiling, and conditions may require much less.
Example: Rain is pounding the windshield, so you slow well below the posted limit and leave extra room ahead.
Loss of braking power from lost hydraulic pressure or overheated brakes.
Good brakes rarely fail. If they do, downshift, pump the pedal, use the parking brake, and look for an escape route or escape ramp. Do not wait.
On the test
Questions ask what to do and what not to do when hydraulic brakes fail, and what to use when brakes fail on a downgrade.
Appears in 13 test questions
See 5 questions on the Air Brakes testExample: Halfway down a mountain grade the pedal goes soft; you downshift, see the escape ramp sign, and take the ramp.
A sudden tire failure, often with a loud bang.
Signs are a bang, heavy vibration, or steering that suddenly feels heavy. Hold the wheel firmly and stay off the brake until the truck slows.
Example: You hear a bang and the wheel jerks; you grip it with both hands, ease off the gas, and brake only once slowed.
Also called: tire blows, blowout
A system that holds a set speed for you.
It is for dry, open roads with steady traffic. Turn it off on wet or icy roads, on downgrades, and in heavy traffic, where you need full control of speed.
Example: Rain starts on the interstate, so you switch cruise control off and control speed with your foot.
