South Dakota CDL Practice Test 2026

Not quiteCorrect answer: C — The suspension system and the coupling device

Suspensions are rated for the weight they can carry and couplings for the weight they can pull or carry. Both sit directly in the load path, so either one can be overloaded on a truck whose gross and axle weights are perfectly legal.

Assuming that clearing the gross and axle limits proves every load-bearing part of the vehicle is within its own rating.

Not quiteCorrect answer: C — You should wait for a noticeably larger gap than usual

Acceleration falls off as weight goes up, so the loaded vehicle spends more time in the path of approaching traffic and needs more empty road ahead of it before pulling out.

The belief that a driver's habitual gap judgment carries over from an empty run to a loaded one, when the load directly lengthens the time spent getting up to speed.

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 — Hold the trailer's rear in tight to the curb and take the extra lane only at the end of the turn

Both swinging left first and straddling early open a gap on your right that a car will fill, and you then turn into it. Taking the extra room at the end of the turn instead keeps that gap closed while you are still committed to the corner.

The belief that setting up wide to the left is the professional way to handle a tight corner. It invites a driver up your right side exactly where the trailer is about to sweep.

Not quiteCorrect answer: B — Squeezed on smoothly at the pressure your speed and the distance available call for, and held there to a settled stop

The pedal is a control, not a switch: how much you need depends on how fast you are going and how soon you must be stopped. Choosing that pressure early and holding it steady produces a controlled deceleration, keeps the load settled, and leaves you pedal travel in reserve if the situation gets worse.

Treating braking as either-or, or believing firm braking automatically causes a skid. Wheels lock when demand exceeds available traction, which depends on the surface, not on the driver being willing to press the pedal.

Not quiteCorrect answer: B — With the vehicle creeping forward at only about five mph, press the pedal hard and judge whether it stops straight, promptly, and with a normal-feeling pedal

Only a moving test loads the brakes the way the road will. At walking pace a pull to one side, a spongy pedal, or a late response reveals itself harmlessly, which is far better than discovering it during the first real stop in traffic.

Believing that gauges, warning lights, and a static pedal press together prove the brakes work, when problems like uneven application only show up under actual vehicle motion.

Not quiteCorrect answer: C — Pump the pedal three times, then push it down hard and hold it for five seconds; it must not sink.

Pumping removes the reserve assist so the pedal reflects the hydraulic circuit alone, and holding pressure is what exposes a slow leak. A pedal that sinks under steady pressure is losing fluid somewhere.

Accepting a pedal that feels firm on a single press as proof of a sealed system, when only sustained pressure reveals the slow leak that finishes failing on a long downgrade.

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: C — Normal, because front wheel braking helps in all conditions

The valve was meant to prevent front wheel skids, but it cuts your stopping power to do it, and testing showed those skids are unlikely even on ice. Leaving it in the normal position keeps the front brakes doing their share.

Trusting the label: "slippery" sounds like the setting for a slippery road, but using it there costs braking without buying safety.

Not quiteCorrect answer: C — The driver's side, so you can watch the trailer directly out of your own window

Curving to the driver's side keeps the whole trailer in view through your window and mirror instead of hiding it behind the rig. Blind-side backing forces you to guess at exactly the moment corrections have to be small and early.

Choosing the side by where the open space looks bigger. Visibility matters more than clearance, because you cannot correct a drift you never saw.

Not quiteCorrect answer: A — 55 psi

The warning has to appear while you still have enough air to make a controlled stop. 55 psi is the threshold on a typical vehicle; the spring brakes will not grab until pressure falls much further, which is exactly the margin the warning is protecting.

Confusing the warning threshold with the pressure at which spring brakes apply on their own — those are two different numbers, and the gap between them is your time to pull over.

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: 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 — 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 — Hang back, keep a generous following distance, and treat any pass as a high-risk maneuver rather than a routine one

Wandering inside the lane and inconsistent speed are the standard signature of a distracted driver, and a distracted driver does not know you are there. Space is the only protection that works against a vehicle that may drift without warning.

Believing that passing quickly removes the exposure. The pass is the highest-risk moment precisely because you are alongside a driver who has not registered your presence and may drift into the space you occupy.

Not quiteCorrect answer: B — Much more room, since it takes longer to reach traffic speed and covers more pavement

A heavy vehicle spends far longer getting up to traffic speed and occupies much more of the roadway while doing it, so a gap that would work in a car leaves approaching traffic closing on you.

The belief that a gap can be judged by the same feel a driver developed in a car, when acceleration and length have both changed dramatically.

Not quiteCorrect answer: C — How much of the vehicle's total load one axle, or one set of axles, presses onto the pavement

Axle weight describes how much of the vehicle's total load that axle pushes down onto the pavement, which is exactly what a scale platform under those wheels reads. It is a load, not a piece of hardware and not a tire rating.

Confusing the load an axle carries with either the mass of the axle hardware or the load rating stamped on the tire sidewall.

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 — Ideal ones: a driver who is alert, dry pavement, and brakes in good condition

Every one of the three segments is quoted for ideal conditions, so the total is a floor, not a typical outcome. A tired driver, a wet surface, worn linings or a heavy load each push the real distance beyond it, and they stack. Treating the published number as your worst case is how drivers run out of road.

Reading textbook stopping distances as a safety margin already padded for bad conditions. They are the best the vehicle can do on its best day, which means real-world distance is always longer than the number you memorized.

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.