Commercial Driving Combination Vehicles 1 — Questions and Answers
Question 1: What is the primary danger of trailer swing (trailer jackknife)?
- The trailer overheats
- The trailer swings out and may strike other vehicles or cause a rollover (Correct answer)
- The engine stalls
- The landing gear collapses
Correct answer: The trailer swings out and may strike other vehicles or cause a rollover
During a trailer jackknife, the trailer swings outward uncontrollably and can strike adjacent vehicles, barriers, or cause the entire rig to roll over.
Question 2: When coupling a tractor to a semi-trailer, what must you verify about the fifth wheel?
- The fifth wheel is dry and ungreased
- The kingpin is locked in the fifth wheel jaws and the locking lever is secured (Correct answer)
- The fifth wheel plate is exactly level with the trailer floor
- The trailer air lines are connected before coupling
Correct answer: The kingpin is locked in the fifth wheel jaws and the locking lever is secured
After coupling, you must confirm the kingpin is fully locked in the fifth wheel jaws and the locking handle is in the locked position to prevent separation.
Question 3: What is the correct procedure for testing trailer brakes after coupling?
- Apply service brakes at highway speed and note stopping distance
- With tractor and trailer connected, move forward slowly while applying only the trailer hand valve (Correct answer)
- Apply the parking brake only and release it quickly
- Have a passenger watch the trailer wheels while you drive past
Correct answer: With tractor and trailer connected, move forward slowly while applying only the trailer hand valve
Moving slowly forward while applying the trailer hand valve confirms trailer brakes are working; drag from the trailer brakes will indicate they are functional.
Question 4: When uncoupling a semi-trailer, what must you do before cranking the landing gear down?
- Disconnect the air lines first
- Lower the trailer on a firm, level surface and apply the trailer parking brake (Correct answer)
- Remove the kingpin safety lock
- Drain the air tanks completely
Correct answer: Lower the trailer on a firm, level surface and apply the trailer parking brake
Before cranking down the landing gear, the driver must ensure the trailer is on firm, level ground and the trailer parking brake is set so the trailer cannot roll.
Question 5: Which air line on a combination vehicle supplies continuous air to the trailer to charge the emergency brakes?
- Service line (blue)
- Emergency line (red) (Correct answer)
- Auxiliary supply line (green)
- Control line (yellow)
Correct answer: Emergency line (red)
The emergency (red) line, also called the supply line, provides continuous pressurized air to charge the trailer's emergency brakes and keep them released.
Question 6: What is rearward amplification in a doubles or triples combination?
- The tendency of the rear trailer to whip more violently than the front during swerving (Correct answer)
- The increase in engine noise at higher speeds
- The amplified braking force at the rear axle
- The magnified turn radius of a long combination
Correct answer: The tendency of the rear trailer to whip more violently than the front during swerving
Rearward amplification means that each successive trailer behind the tractor sways more violently than the one in front, making the last trailer most prone to rollover.
Commercial Driving Combination Vehicles 1
What is the primary danger of trailer swing (trailer jackknife)?