Home › Practice › Combination Vehicles › Question 47

Combination Vehicles Practice Question 47

Required for Class ACombination Vehicles · Question 47

When driving across railroad tracks with a low-clearance trailer (lowboy), you should:

• AApproach slowly to avoid hanging up the trailer on the rails
• BMaintain highway speed
• CStop on the tracks
• DCross diagonally

Correct answer: A. Approach slowly to avoid hanging up the trailer on the rails

Why: Low-clearance trailers can hang up on humped crossings. Approach slowly to evaluate clearance, and if any doubt exists do not cross.

How this question fits the Combination test

Articulated vehicles fail in unique ways: trailer swing under braking, rearward amplification under steering, and jackknife under loss of traction. Combination Vehicle knowledge is required for any Class A applicant under 49 CFR 383.111.

Study technique for this topic

Walk through the coupling sequence verbally until it's second nature. Know the safe-rolling rearward amplification factor, the difference between trailer service brakes and parking brakes, and what creates the conditions for a tractor jackknife.

Related Combination practice questions

• Q16. A loaded trailer with a high center of gravity is most prone to roll over:
• Q29. A leaky air line between tractor and trailer will most likely cause:
• Q42. Trailer length affects:
• Q56. When sliding the fifth wheel forward, the load on the steering axle:
• Q5. After backing under the trailer, you should:

Continue your CDL preparation

The Combination Vehicles portion of the CDL knowledge exam covers more than this single question. Use this site's full Combination Vehicles bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.

If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.