Across CDL practice, the same questions come back wrong again and again. They are not the most technical ones. They are the ones where the correct answer contradicts what feels right.
Worth knowing in advance, because recognising the pattern is most of the defence.
Skid recovery
The trailer wheels lock, the trailer starts to swing, and every instinct says brake harder.
The correct response is to release the brakes. Locked wheels cannot steer or track; letting them roll again is what restores control. Braking harder deepens the skid.
This is the single most-missed category on the written tests, and the reason is that instinct is emphatically wrong.
Following distance
The rule is counted in seconds, scaled to vehicle length, and adjusted upward above a threshold speed. People remember roughly one second per unit of length, then forget the additional second at higher speeds, or apply it the wrong way round.
It is worth learning precisely rather than approximately, because the wrong answers on these questions are deliberately near misses.
Blind spots
Asked where the worst blind spot is, most people say directly behind. The answer that questions target is the right side — a long, deep area running back along the trailer that mirrors cover poorly and that drivers check less often because turning right feels safer than turning left.
The pattern behind the traps
Most missed questions punish the intuitive answer. When a question feels obvious, that is the moment to slow down and ask which rule actually applies. The obviousness is often the trap.
What happens at low air pressure
Two separate events at two different pressures, routinely conflated.
The low air warning activates first, before pressure falls below 60 psi. The spring brakes apply automatically later, typically somewhere in the 20 to 45 psi range.
Questions ask about one and offer the other as a distractor. Learn them as two distinct stages.
Railroad crossings
Several traps here. Whether you must stop depends on the vehicle and the load, not on whether there are signals. Certain vehicles stop at every crossing regardless.
And the rule people forget entirely: never change gears while crossing the tracks. Stalling on a crossing is the scenario the rule exists to prevent.
Braking on a downgrade
The intuitive approach is to ride the brakes to hold a steady speed. That overheats them and causes brake fade, which is how you end up with no brakes at the bottom.
The correct method is to select the right gear before starting down and use brief firm applications to bring the speed down, then release to let the brakes cool. Which gear is decided at the top; by halfway down the option has gone.
Vehicle weight and stopping
A counter-intuitive one: an empty truck can take longer to stop than a loaded one. With less weight pressing the tyres onto the road there is less traction, and the brakes and suspension are designed for a load.
Empty does not mean easier to stop, and questions test exactly that assumption.
Cargo weight and securement
Weight questions catch people because there are several limits operating at once and they are easy to conflate.
Gross vehicle weight, gross combination weight, and individual axle weights are separate limits, and you must satisfy all of them. A load can be under the gross limit and still illegal because too much of it sits over one axle. Sliding the tandems changes axle distribution without changing the total, which is exactly why the question is asked.
Securement questions turn on the number of tiedowns required, which depends on the length and weight of the article rather than on judgement. Cargo that could shift needs blocking or bracing regardless of how many straps are on it.
Speed, distance and the arithmetic
A cluster of questions involves multiplying or adding, and pressure makes arithmetic unreliable.
Total stopping distance is not just braking distance. It is perception distance plus reaction distance plus braking distance, and questions frequently offer braking distance alone as a plausible wrong answer.
Stopping distance grows faster than speed does. Doubling the speed does not double the distance; it increases it considerably more. And a wet or icy surface multiplies it again.
Learn the components as a named list. If you can say what the three parts are, you can avoid the distractor even when the numbers are unfamiliar.
Hazard perception
The hazard questions describe a scene and ask what you should be watching. The answer is nearly always the thing that could enter your path rather than the thing already in it.
A parked car with someone in the driver's seat. A ball rolling into the road. A vehicle drifting within its lane. A truck ahead with its brake lights flickering. These are all situations where nothing has happened yet, and the correct answer treats them as though something is about to.
Drivers who miss these are usually answering about what is happening rather than what might. Once you notice that pattern, the whole category becomes straightforward.
Why the wrong answers look right
CDL questions are not written to trick you, but the distractors are constructed carefully. The usual pattern is a correct-sounding statement with one element changed: the right procedure at the wrong pressure, the right list in the wrong order, or the right action for a different failure.
This is why recognition fails and recall works. If you can state the answer before reading the options, a near-miss distractor has no power. If you are choosing the most familiar-looking option, it has a great deal.
Quick answers
Why is the right side the worst blind spot?
It is long, deep and poorly covered by mirrors, and drivers check it less because right turns feel lower risk. It is where a vehicle can sit unseen for a long time.
What do I do in a trailer skid?
Release the brakes so the wheels can roll and you regain steering. Do not brake harder, and do not use the trailer hand valve.
At what pressure do the spring brakes apply?
Typically somewhere between 20 and 45 psi, depending on the vehicle. The low air warning comes earlier, before 60 psi.
Is an empty truck easier to stop?
Not necessarily. Less weight means less traction, and an empty vehicle can require a longer stopping distance than a loaded one.
Where to get it
CDL Prep Exam 2026: Permit brings your wrong answers back more often, which is exactly where the value is. Offline, free to start.
When an answer feels obvious, check which rule applies. That habit alone is worth several marks.