CDL General Knowledge Practice Test 2026

Not quiteCorrect answer: C — Walk the area on foot first and check what hangs above the trailer's path

Overhanging objects sit outside the mirror's field of view and are easy to lose against the sky, so the only reliable check is a look from outside the vehicle before the trailer ever moves.

The belief that mirrors show everything that matters while backing, when the hazards that take off a trailer roof are precisely the ones mirrors do not cover.

Not quiteCorrect answer: B — Do whatever you safely can to let them get away from you, avoid eye contact, and refuse to respond to the gestures

An aggressive driver is looking for a partner in the conflict, and any response that engages them keeps a loaded commercial vehicle in the middle of it. Removing yourself ends the interaction, and the vehicle description, plate, and location can be reported to the authorities afterward.

The belief that yielding rewards the behavior and that a professional driver should hold their ground. Holding your own turns a one-sided provocation into a two-vehicle duel, and the heaviest vehicle in that duel does the most damage.

Not quiteCorrect answer: C — Class B, because the towed unit is not rated above 10,000 pounds

A heavy single vehicle stays in Class B as long as anything it tows is rated at 10,000 pounds or less. Coupling on a light trailer does not by itself move the driver into the combination class.

The belief that pulling any trailer at all makes the vehicle a Class A combination, regardless of how light the towed unit is rated.

Not quiteCorrect answer: C — Non-excepted interstate, so that he is qualified for both kinds of interstate driving

Excepted status only holds when the excepted activities are all the driver does. As soon as any ordinary interstate work is mixed in, the stricter certification is the only one that keeps him legal across the whole range of his driving.

Believing that qualifying for an exception in part of your work extends the exception to the rest of it.

Not quiteCorrect answer: B — No, because a tint takes away light, and at night there is too little light to spare, whatever it does for glare

At night there is very little light to begin with, and anything that darkens the view takes away detail you need to identify hazards. Trading a little less glare for a lot less light is a losing bargain after dark, which is also why sunglasses have no place in the cab at night.

Equating glare reduction with better night vision. The comfort of a dimmer scene is mistaken for improved seeing, while pedestrians, animals, and unlit road users disappear into the dark sooner.

Not quiteCorrect answer: A — In the first few minutes, before the rain has had time to flush the oil film off the pavement

Traffic leaves oil on the pavement all through a dry spell. The first water to fall floats and spreads that oil rather than carrying it away, and the result is a slick film. Keep the rain going and the oil is washed clear, so the surface actually improves from a low point at the very start.

Believing that danger rises steadily with how hard and how long it rains. That model has drivers relaxing during the opening minutes, which is exactly the window with the least grip, and treating prolonged rain as the peak hazard when the oil has already been washed clear.

Not quiteCorrect answer: B — 4/32 inch on the front tires and 2/32 inch on the other tires.

Front tires get the deeper minimum because they carry the vehicle's directional control; a steer tire that loses grip or blows takes the driver's ability to steer with it.

Applying the familiar 2/32 inch passenger-car figure to every position, which leaves the two tires that steer a loaded combination with the least reserve of any on the vehicle.

Not quiteCorrect answer: C — Stop at the nearest safe place and sleep, or at minimum take a 15 to 20 minute nap before going on

Losing track of the miles behind you is a recognized warning sign of fatigue, and the only thing that reverses sleep debt is sleep. Trying to push on when you are tired is far more dangerous than most drivers believe and is a major cause of fatal crashes.

The belief that cold air, loud music, or caffeine can substitute for rest. They mask the symptom for a short while and then wear off, often leaving the driver more impaired and now further from a safe place to stop.

Not quiteCorrect answer: B — Clearance lamps and reflectors at the rear have to show red; amber back there tells a following driver he is looking at the front of a vehicle.

Lamp colour is information, not decoration: amber toward the front, red at the rear. An amber clearance lamp at the back of a trailer at night tells an approaching driver the vehicle is facing him, which is exactly the wrong conclusion.

Believing that a lamp which lights is a lamp which passes, so colour errors are dismissed as cosmetic when they actively misinform other drivers.

Not quiteCorrect answer: A — Count the seconds between the vehicle ahead passing a fixed landmark and your reaching it

Counting from a fixed point measures the actual time gap, which is what matters, while a distance guess ignores how fast that gap is being closed.

The belief that following distance can be judged as a distance in feet or vehicle lengths, when the whole point of the rule is elapsed time.

Not quiteCorrect answer: B — A support reaching from high on the cargo down to the deck, or outward against the sidewalls

Blocking works at deck level, wedged tight against the cargo so it cannot slide. Bracing works from the top of the cargo down or outward to the floor and walls, resisting the load tipping or pushing over.

Using blocking and bracing as interchangeable words, so a driver installs only deck-level blocking and leaves a tall load free to topple forward.

Not quiteCorrect answer: C — Glance at them briefly and often, putting your eyes back on the road in between

Your vehicle keeps covering ground while you are looking backwards, so a long study of the mirror is bought with a long stretch of road travelled blind. Short, frequent glances build the same picture without ever giving up the view ahead for more than an instant.

Assuming a careful, thorough look is safer than a quick one. In a moving vehicle the cost of a mirror check is measured in distance travelled unseen, which makes frequency the safer choice over duration.

Not quiteCorrect answer: B — Once engine speed has dropped close to idle

Holding the clutch out while the engine is still turning above idle keeps the driveline connected, so the engine helps slow the vehicle and you keep the ability to power out of trouble. Disconnecting it only at the point where the engine would otherwise stall gives you that benefit without stalling.

The habit of pushing the clutch in as soon as braking starts, or coasting out of gear. A disconnected driveline throws away engine braking and leaves the brakes to do all of the work of a heavy vehicle alone.

Not quiteCorrect answer: A — The empty van rides higher than it did loaded, so yesterday's clearance proves nothing

Weight compresses the suspension and tires, so removing the load lets the body rise, and a vehicle that just fit when loaded can strike the same structure when empty.

The belief that a vehicle's height is a fixed specification, when the loaded and unloaded heights of the same van are genuinely different.

Not quiteCorrect answer: A — Taking a bend at speed, or making a sudden swerve around an obstacle

Rollover is driven by sideways force, and sideways force comes from turning. A curve or an emergency swerve supplies it; straight-line braking loads the vehicle forward instead, which does not tip it.

Thinking rollover is mainly a braking problem, so a driver with a top-heavy load believes gentle stopping is protection enough and does not also slow for curves and ramps.

Not quiteCorrect answer: A — Signal well before the turn, keep it running until the turn is finished, and switch it off afterwards if it does not cancel on its own

An early signal is what discourages a following driver from starting a pass just as you slow and swing, and leaving it running through the turn keeps that message alive while both of your hands stay on the wheel. Cancelling matters too, because a signal left on after the turn tells the next drivers something untrue about your intentions.

Signalling late to avoid confusing anyone, or cancelling early to "tidy up." Late signals invite exactly the pass that a wide, slow turn cannot accommodate, and cancelling mid-turn removes the warning while the vehicle is still occupying two lanes.

Not quiteCorrect answer: A — Go back to neutral, let the clutch out, bring the revs up until they suit the speed you are travelling, then make the shift again

The gear refuses because engine speed and road speed have drifted apart while you were in neutral. Reconnecting the engine in neutral and setting the rpm to match the road speed rebuilds the condition the gear needs, and then it goes in normally. Nothing is wrong with the transmission that speed matching does not fix.

Forcing the lever when a gear will not take. The obstruction is a speed mismatch inside the box, and force damages the very components that would otherwise let you have a gear again.

Not quiteCorrect answer: A — Assume it could be holding something solid and plan an early, gradual move around it if that can be done safely

You cannot read weight off the outside of a box or a sack, and a loaded one can cut a tire, damage a rim, wedge between duals, or tear out brake and electrical lines. Because you cannot rule that out, the object earns an early and unhurried avoidance rather than a last-second one.

Judging an object's danger by how light it looks. That assumption is what turns a routine avoidance into a blown steer tire, and it is also why drivers leave the decision until swerving is the only option left.

Not quiteCorrect answer: A — Come off the throttle and disengage the clutch, so the wheels spin freely while the vehicle slows itself

While hydroplaning, the tires are riding on a film of water, so anything that stops them turning leaves them with no grip to recover with. Coming off the throttle and freeing the wheels lets speed bleed away until the tires can find the surface again, and it is the same move if the drive wheels start to skid.

The reflex that a vehicle out of control should be braked. On water, braking is what locks the wheels and removes the last chance of regaining steering; the wheels have to be allowed to spin freely, not stopped.

Not quiteCorrect answer: C — 40 mph

Forty mph is the point at which the manual treats the plain one-second-per-ten-feet count as no longer sufficient, so a single second is added for every speed above it.

The belief that the extra second is tied to highway speed limits, so drivers only start adding it near 55 mph and follow too closely everywhere in between.

Not quiteCorrect answer: B — Too much of the cargo weight is riding on the steering axle

Extra weight over the front presses the steer tires hard into the road, so the driver has to fight the wheel to turn them, and the same pressure grinds the tires and punishes the axle itself.

Assuming heavy steering must be a mechanical fault in the steering gear, when where the load sits front to rear is the more common cause.

Not quiteCorrect answer: A — The most that one vehicle, cargo included, is built and rated to weigh

GVWR is a ceiling set by the manufacturer for one loaded vehicle, so it never moves. The scale reading is the actual gross weight and can sit anywhere below that ceiling, which is why the two numbers rarely match.

The belief that GVWR is a measurement that rises and falls with the load, rather than a fixed manufacturer's rating you must stay under.

Not quiteCorrect answer: C — Warn the traffic behind you as you slow, with your four-way flashers or a touch on the brake pedal

The traffic behind you is the immediate threat when a heavy vehicle slows in a compressed lane, and drivers near work zones are already distracted. A flasher or brake-light signal gives them the notice your deceleration alone will not.

Thinking the traffic behind is somebody else's problem, or that clearing the zone quickly is the safer trade. Speed inside a work zone raises both the risk to workers and the odds of the rear-end collision you were trying to escape.

Not quiteCorrect answer: C — The left side of the vehicle strikes a vehicle beside or ahead of it because the rear wheels track inside the front wheels

Off-tracking means the rear of a long vehicle follows a tighter arc than the front, so an early turn sweeps the left side of the unit through space the driver believed was already cleared.

The belief that if the front of the vehicle clears an obstacle the rest of the vehicle will follow the same path, when the rear consistently cuts the corner.

Not quiteCorrect answer: A — It puts the faults the driver found in front of the people who repair the vehicle.

The report is the mechanism by which what the driver noticed becomes work the shop actually performs. It is a repair order written by the person who was closest to the failure.

Treating the report as the driver's personal liability shield rather than the carrier's repair order, which leads to vague entries that no mechanic can act on.

Not quiteCorrect answer: A — A run between midnight and 6 a.m. after six hours of sleep or less, in a week where the driver has worked more than 60 hours

Each factor multiplies the others: six hours of sleep or less roughly triples crash risk, working more than 60 hours a week raises it by about 40 percent, and many heavy vehicle crashes fall between midnight and 6 a.m. when alertness bottoms out. Stacked together they describe the highest-risk trip a driver can take.

The belief that being an experienced night driver adapts you to the schedule. Body clock and sleep debt are physiological, not habits, so long-haul drivers on night runs are one of the highest-risk groups rather than an exempt one.

Not quiteCorrect answer: C — It should climb from 50 psi to 90 psi in no more than three minutes.

The build-up rate, not just the final pressure, tells you whether the compressor can keep up. A system that fills slowly will still reach cut-out in the yard but cannot replace the air that repeated brake applications take out on a long grade.

Judging the air system solely by whether it eventually reaches cut-out pressure, which hides a weak compressor until the moment you need air faster than it can make it.

Not quiteCorrect answer: B — Alternate your attention between what is far down the road and what is happening just in front of you

The far view tells you what is developing and gives you time to plan; the near view tells you what is happening now, including brake lights, lane position, and vehicles moving in beside you. Safe driving needs both, so the eyes keep moving between them rather than settling at one distance.

Taking a long visual lead to mean staring at the horizon. A driver fixed on a far point misses the car that has just stopped two lengths ahead.

Not quiteCorrect answer: C — Stay in the right lane and let the faster traffic go around you

Heavy vehicles get tailgated mainly when they cannot keep pace, and keeping right leaves the passing lane open so the queue behind you can clear instead of crowding your bumper.

The belief that a slow-moving heavy vehicle is entitled to any lane it can hold, when occupying a passing lane at reduced speed is what creates the tailgating pressure in the first place.

Not quiteCorrect answer: C — Press it, so the revs come up to where the lower gear will engage at your current road speed

A lower gear spins the engine faster at the same road speed. Raising the rpm while the transmission is in neutral is what brings the two sides of the clutch to the same speed, so the gear engages instead of grinding or refusing. Waiting for rpm to fall widens the mismatch you are trying to close.

Assuming downshifting is upshifting in reverse order with the same throttle behaviour. The pedal work is what actually differs between the two, and getting it wrong on a downgrade can leave you with no gear at all.

Not quiteCorrect answer: A — One hand on each side of the wheel, both holding it tightly

Hitting a curb or a deep pothole sends a violent kick back through the steering. Two firm hands placed opposite each other give you leverage on both sides of that kick, so the wheel cannot be torn out of your grip and the vehicle cannot be steered for you.

Carrying over relaxed car habits, where a light one-handed grip is survivable. Heavy steer axles transmit far more force to the wheel, and a hand that is not there when the kick comes cannot catch it.

Not quiteCorrect answer: B — The work zone limit binds you throughout, and bad weather or workers near the lane call for slower still

More people are hurt and killed in work zones by vehicles going too fast than by any other cause, and the hazard does not switch off when a crew steps behind a barrier. On a long stretch of construction the real danger is drift: speed climbs a few miles an hour at a time without the driver noticing, which is why the speedometer, not the feel of the road, is what you check.

Treating a work zone limit as conditional, in force only when a crew is in sight or only when traffic agrees to it. The limit is set for the geometry of the zone, narrowed lanes, shifted alignment, equipment entering, and none of that depends on whether a worker happens to be standing there.

Not quiteCorrect answer: C — Moving out of the seated, belted driving position to reach for the phone, even if you meant to use it hands-free

The federal restriction names three acts: holding the phone with at least one hand for a voice call, dialing by pressing more than a single button, and moving out of the belted driving position to reach for it. That last one stands on its own, regardless of what you planned to do once you had the phone.

The 'as long as I never hold it to my ear I'm compliant' rule of thumb. It ignores the reach itself, which is exactly the moment the driver is unbelted, twisted, and not looking at the road.

Not quiteCorrect answer: C — Becomes higher as you move up through the gears

The lower gears cover very little road speed each, so they can be left early; as the gears get taller, more rpm is needed before the next one will pull the load. The shift point therefore climbs as you work up the box, which is why the manufacturer's figures for your specific vehicle matter rather than one habitual number.

Assuming a single shift rpm applies to the whole gearbox. A driver who shifts every gear at the same point either lugs the engine low in the range or over-revs it higher up.

Not quiteCorrect answer: A — That the parking brakes are applied, the wheels chocked, or both.

You are about to stand in front of a loaded vehicle with your hands inside it. Securing it against rolling protects the inspector, which is why this comes before anything is opened.

Thinking of the parking brake and chocks as yard equipment for parked trailers, rather than personal protection for whoever is standing ahead of the front wheels.

Not quiteCorrect answer: A — As a ceiling you do not exceed, whatever the traffic around you is doing

That number is the ceiling for the descent, and it is posted before the crest for a reason: once the vehicle is over the top, the choices about speed and gear have already been made. Read the signs alongside it that give the length and steepness of the grade too, because those tell you what you are committing to.

Treating a "safe speed" sign as a softer suggestion because it is not a standard black-and-white speed limit sign. The wording describes what the road can tolerate, and traffic moving faster does not change what your combination can tolerate.

Not quiteCorrect answer: C — The driver is placed out of service for 24 hours

Below the prosecution threshold the law still refuses to let the driver continue, so it removes him from the road for a full day. It is a separate consequence from the one-year disqualification, not a lesser version of it.

The belief that any reading under 0.04 percent carries no consequence at all, so a small amount of alcohol is treated as safe to drive on.

Not quiteCorrect answer: C — A single day, long enough to pass what you found to whoever drives it next.

The in-cab copy exists for one job: handing your findings to whoever climbs into this seat next. A day is long enough for that handoff, and the carrier keeps its own copy for the record.

Confusing the copy carried in the cab, which is a handoff between drivers, with the carrier's file copy kept for record-keeping.

Not quiteCorrect answer: B — When one-fourth or more of the leaves are missing.

One-fourth is the line at which an inspector will stop the vehicle. It is not the line at which the spring became dangerous, and a lower count is no licence to keep driving.

Reading the out-of-service threshold as the point where the defect becomes dangerous. It is only the point where someone else will stop you; a single broken leaf can still shift and strike a tire.

Not quiteCorrect answer: C — The vehicle is placed out of service and may not be driven until the defect is corrected.

An out-of-service order is not a penalty to be paid and driven away from. It is a prohibition on moving the vehicle, and it stays in force until the condition that earned it has been corrected.

Treating an out-of-service order like a citation or a deadline to comply with later, rather than an immediate ban on operating that vehicle.

Not quiteCorrect answer: B — The nuts are loose and have been working against the wheel.

Rust streaking radiating from a fastener is produced by movement: the nut has been shifting and grinding, pumping rusty debris out from under itself. The nuts must be tested for tightness, not merely cleaned.

Reading rust as cosmetic surface corrosion, so the driver wipes away the only visible evidence that a wheel is about to come off.

Not quiteCorrect answer: B — Repetition fixes the whole route in memory, so a step left out is one you notice.

A repeated routine turns coverage into a habit. When the sequence is always the same, an omission feels wrong, which is the only reliable defence against a distracted morning.

Reading a standard inspection routine as a legally mandated sequence rather than a memory discipline. What is required is that nothing gets missed, and repetition is what delivers that.

Not quiteCorrect answer: A — Flash the brake lights with a few light touches on the pedal, then bring your speed down gradually

Your vehicle is the reason the drivers behind cannot see the problem, so the warning has to come from your vehicle. A few taps flash the brake lights before you actually need to slow, which starts their reaction early and stops your eventual braking from arriving as a surprise.

Assuming other drivers can see whatever you can see. The size that gives you a better view forward is the same size that blocks theirs, so a hazard you have spotted is often one only you know about.

Not quiteCorrect answer: C — 12 to 15 seconds — around a city block at town speeds, something like a quarter of a mile on the highway

The lead has to cover far more than reaction time: a heavy vehicle needs a great deal of road to shed speed, and just as much to move sideways into a gap. Picking a problem up twelve to fifteen seconds out is what lets you answer it with a gentle adjustment instead of an emergency one.

Confusing visual lead time with following distance. Following distance is the gap you keep from the vehicle in front; the visual lead is how far past that vehicle your eyes are working.

Not quiteCorrect answer: C — Re-grooved, recapped, or retreaded tires.

A retread carries a bonded tread that can separate from the casing. On a bus steer axle that separation takes away steering control with a full load of passengers aboard, so those tires are barred from that position outright.

Assuming a retread that passes a tread-depth and condition check is fine anywhere on the vehicle, when the prohibition is about how retreads fail, not how they look.

Not quiteCorrect answer: B — Whenever the accelerator is released all the way

A retarder is tied to the accelerator, not the brake pedal: releasing the throttle all the way is the signal that you want the vehicle slowed. That is why simply lifting off in a vehicle with the retarder engaged produces noticeably more deceleration than the same lift with it switched off.

Expecting the retarder to work like an assist to the service brakes, activated by the pedal. Drivers who believe that are surprised by the deceleration that arrives the moment they lift off.

Not quiteCorrect answer: C — Being in the right gear lets you pull lightly through the bend, which settles the vehicle, and accelerate again the moment it opens out

Light, steady power through a curve keeps the drivetrain loaded and the vehicle settled, while braking or shifting mid-curve upsets a load that is already leaning. Having the gear chosen beforehand also means you are not taking a hand off the wheel at the point where steering demands the most from you.

Believing speed can be sorted out inside the curve. Every adjustment made while turning competes for the same limited tire grip that is already being spent on cornering.

Not quiteCorrect answer: C — The driver, who must spot an overload or a badly distributed load even when other hands did the loading

The rules attach the duty to the person who takes the vehicle onto the road, because that is who will have to control it. Who physically stacked the freight changes nothing about who answers for it.

The belief that having someone else load and sign for the freight transfers the legal responsibility for weight and securement away from the driver.

Not quiteCorrect answer: B — Headlights on low beam

Poor visibility runs both ways: whatever is hiding other traffic from you is hiding you from them, and marker lights alone do not lift a vehicle out of a grey background. Low-beam headlights do. High beams throw their light back at you off rain and snow, and they bother other drivers in daylight as much as at night.

Believing high beams cut through precipitation and that dazzle is only a night-time concern. Water in the air throws high-beam light straight back at you, and oncoming drivers are affected in poor daytime visibility too.

Not quiteCorrect answer: A — Tires, wheels and rims, brakes, lights and reflectors, trailer brake and electrical lines, coupling and cargo securement.

The stop-along-the-way check targets what changes while the vehicle is working: components loaded by heat, weight and vibration. Those are the parts that were sound this morning and may not be sound now.

Repeating the engine-compartment inspection at every stop, when the fluids checked cold in the yard are not what fails between here and the next town.