CDL General Knowledge TestCombination Vehicles (if applicable)Medium
What is the primary danger of driving a combination vehicle with an improperly secured or absent kingpin locking pin (safety latch)?
- AThe trailer lights may intermittently fail due to electrical disconnection.
- BIncreased wear on the fifth wheel plate due to excessive movement.
- CThe air brake system could lose pressure, causing brake failure.
- DThe trailer could unexpectedly detach from the tractor during operation.
Show answer & explanationAnswer & explanation
Correct answer: D. The trailer could unexpectedly detach from the tractor during operation.
The kingpin locking pin (safety latch) prevents the fifth wheel operating handle from inadvertently opening, which would release the locking jaws and allow the trailer to detach. Its absence or improper securing is a direct risk of uncoupling.
Why the other options are wrong
- A. Electrical connection issues are separate from the mechanical security of the kingpin.
- B. While some movement might occur, the primary danger is detachment, not just wear.
- C. Air lines are separate connections; their integrity is not directly dependent on the kingpin locking pin.
Kingpin Safety Latch
A mechanism that locks the fifth wheel operating handle in the closed position, preventing accidental release of the kingpin and trailer detachment.
- Prevents accidental uncoupling.
- Must be engaged after coupling.
- A critical safety feature for combination vehicles.
Memory trick: No pin, no win, just the trailer spinning.