CDL Combination Vehicles Practice Test

Correct answer: Truck rollovers

Rollovers cause more than half of truck-driver crash deaths. The two biggest defenses are keeping the load low and slowing down for turns.

Correct answer: Keeping the cargo low and driving slowly around turns

A high center of gravity makes a rig easy to tip, and rollovers happen when you turn too fast. Keep cargo as low as possible and take corners, on-ramps, and off-ramps slowly.

Correct answer: Ten times more likely

Piling cargo up raises the center of gravity, so a fully loaded rig is roughly ten times more likely to roll over in a crash than an empty one. Keeping cargo low matters even more in combinations.

Correct answer: Centered and spread out as much as possible

A load pushed to one side makes the trailer lean and roll more easily. Keep cargo centered and spread out so weight is balanced side to side.

Correct answer: Rearward amplification

Rearward amplification makes a quick steering move at the tractor grow into a much larger, faster swing at the back — the crack-the-whip effect that overturns trailers.

Correct answer: The last (rearmost) trailer

Rearward amplification is strongest at the back, so the last trailer rolls most easily — you can roll the rear trailer of a set of triples several times as easily as the tractor.

Correct answer: Steer gently and smoothly and avoid quick lane changes

A sudden steering move can tip the trailer. Steer gently, look far ahead so you are not surprised into a quick lane change, and slow to a safe speed before turns.

Correct answer: Empty than when it is fully loaded

Empty rigs stop worse: the stiff suspension and strong brakes give poor traction, so the wheels lock up easily. That makes an empty combination take longer to stop than a loaded one.

Correct answer: Give poor traction and make it easy to lock the wheels

With little weight over the wheels, the springs stay stiff and the brakes can easily lock the wheels. That can swing the trailer out or jackknife the tractor very quickly.

Correct answer: Can be very hard to stop and may take longer to stop than a loaded tractor-semitrailer

It is a common myth that a bobtail stops quickly. In fact bobtails can be very hard to stop smoothly and may take longer to stop than a tractor-semitrailer loaded to maximum weight.

Correct answer: Brake early and avoid having to make a panic stop

Looking far ahead and keeping plenty of space lets you slow down gradually. Braking early keeps you from being surprised into a hard panic stop that could jackknife the rig.

Correct answer: Swing around, which is often called a trailer jackknife

Locked trailer wheels lose grip and the trailer swings out of line — a trailer jackknife. It is most likely when the trailer is empty or lightly loaded.

Correct answer: See it in your mirrors

Any time you brake hard, check your mirrors. Spotting the trailer swinging early gives you a chance to react — once it is out of your lane a jackknife is very hard to prevent.

Correct answer: Release the brakes to get traction back

The locked trailer wheels caused the skid, so release the brakes to let them roll and grip again. Once they have traction the trailer follows the tractor and straightens out.

Correct answer: The wrong thing to do, because the trailer brakes caused the skid in the first place

Applying the trailer hand valve puts more braking on the very wheels that are skidding. Release the brakes instead so the trailer wheels can grip and the rig can straighten.