A high-mounted trailer kingpin is dangerous because:
Correct. If the trailer is too high, the fifth wheel slides under without the kingpin engaging the locking jaws. The trailer is not coupled and can drop when you pull away.
CDL Practice Question #182
Category: Combination Vehicles
Why this question matters
This question is one of 55 in our Combination Vehicles bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.