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Combination Vehicles Practice Question 13

Required for Class ACombination Vehicles · Question 13

A trailer jackknife is:

• AWhen the tractor swings around in front of the trailer
• BWhen the trailer swings out beyond the tractor and the unit folds at the coupling
• CWhen the trailer tips over
• DWhen the trailer detaches

Correct answer: B. When the trailer swings out beyond the tractor and the unit folds at the coupling

Why: In a trailer jackknife, the trailer brakes lock or lose traction and the trailer swings around the coupling. Drive-wheel jackknife is when tractor drive wheels lose traction.

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

• Q34. Tracks of the tractor and trailer in a tight right turn should be:
• Q47. When driving across railroad tracks with a low-clearance trailer (lowboy), you should:
• Q60. When making a tight backing maneuver, looking ahead in your mirrors to predict trailer mov…
• Q9. The coupling height check before backing under the trailer is critical because:
• Q23. When backing a trailer, the trailer initially turns:

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.