Combination Vehicles Practice Test Flashcards
6 cards from real CDL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Combination Vehicles Practice Test flashcards as text
When coupling a tractor to a semi-trailer, what is the correct order for connecting the air lines?
Answer: Connect the emergency (red) line first, then the service (blue) line
The emergency (red) line must be connected first so the trailer brakes stay applied while the service line is connected. Reversing this order could release trailer brakes unexpectedly.
What is the purpose of a converter dolly in a double or triple combination?
Answer: It converts the lead trailer's kingpin into a fifth-wheel coupling for connecting an additional trailer
A converter dolly has a fifth wheel on top that accepts the next trailer's kingpin, converting a standard trailer into a lead unit for a double or triple combination. It does not provide independent power or extra braking beyond what is already in the air system.
What should you do if a trailer's air supply valve is in the 'emergency' position during a pre-trip inspection?
Answer: Push it in to restore air supply before moving the vehicle
When the trailer air supply valve (sometimes called the tractor protection valve) is in the emergency position, air is cut off to the trailer and the trailer spring brakes are applied. You must push it to the normal position to supply air and release the brakes before driving.
When uncoupling a combination vehicle, which action must you take BEFORE lowering the landing gear?
Answer: Apply the tractor parking brakes and chock the trailer wheels
You must apply the tractor parking brakes and chock the trailer wheels before lowering the landing gear or disconnecting anything, to prevent the trailer from rolling during the uncoupling process.
When inspecting the pintle hook connection between a converter dolly and a trailing unit, you should verify that:
Answer: The latch is fully closed and the safety latch or lock is engaged
The pintle hook latch must be completely closed and the safety lock engaged. Grease is not required for every trip, and free play indicates wear, not proper function. The draw bar is not designed as a sacrificial breakaway part.
What is 'crack-the-whip' effect in a double or triple combination, and how do you reduce the risk?
Answer: Rearward amplification of sway that can flip rear trailers; reduce speed before curves and avoid abrupt steering
Rearward amplification means that a small swerve at the tractor is magnified at each successive trailer. The rear trailer of a triple can flip even when the tractor barely moves. Reducing speed before curves and avoiding sudden steering inputs are the primary countermeasures.