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Combination Vehicles CDL Practice Test

The Combination Vehicles test covers driving tractor-trailers and other combinations with a Gross Vehicle Weight Rating over 26,001 pounds where the towed unit exceeds 10,000 pounds. Topics include coupling and uncoupling, fifth wheel inspection, off-tracking, rearward amplification, jackknife prevention, rollover, antilock brake systems, and emergency procedures specific to articulated vehicles.

Why this test exists

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.

How to study this section

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.

64 practice questions

• Q1. A combination vehicle is generally defined as:
• Q2. The 'fifth wheel' on a tractor is:
• Q3. The kingpin is part of the:
• Q4. When coupling, you should approach the trailer:
• Q5. After backing under the trailer, you should:
• Q6. Visual inspection of the fifth wheel coupling must confirm:
• Q7. The trailer's landing gear should be:
• Q8. When uncoupling, after lowering the landing gear and disconnecting glad hands you should:
• Q9. The coupling height check before backing under the trailer is critical because:
• Q10. A high-coupled trailer (kingpin riding above the jaws) can result in:
• Q11. Off-tracking by the trailer means:
• Q12. Rearward amplification means:
• Q13. A trailer jackknife is:
• Q14. The first sign of a tractor drive-wheel skid is often:
• Q15. To prevent rollover with a high center of gravity, you should:
• Q16. A loaded trailer with a high center of gravity is most prone to roll over:
• Q17. Cargo loaded too far to one side will:
• Q18. Cargo loaded too far forward can:
• Q19. Cargo loaded too far rearward can:
• Q20. When checking trailer brakes via the hand valve, you should:
• Q21. The fifth wheel should be greased:
• Q22. Air lines and electrical cables between tractor and trailer must be:
• Q23. When backing a trailer, the trailer initially turns:
• Q24. When backing into a tight spot, you should:
• Q25. The 'safety latch' on the fifth wheel locking lever:
• Q26. The legal maximum trailer length on the National Network is generally:
• Q27. A converter dolly is used to:
• Q28. When uncoupling a trailer, the order generally includes:
• Q29. A leaky air line between tractor and trailer will most likely cause:
• Q30. Stopping distance for a fully loaded combination vehicle is:
• Q31. Trailer ABS sensors are typically located at:
• Q32. When climbing a long uphill grade with a heavy load, you should:
• Q33. When the trailer wheels lock during heavy braking, you should:
• Q34. Tracks of the tractor and trailer in a tight right turn should be:
• Q35. Antilock brakes on a tractor without ABS on the trailer:
• Q36. When pulling a trailer through a sharp curve, the load can shift if it is not:
• Q37. The trailer hand valve is sometimes called:
• Q38. A heavy trailer pushing on the tractor going downhill is called:
• Q39. The forward thrust between trailer and tractor on a hard stop is absorbed by:
• Q40. When approaching an intersection in a combination vehicle, you should:
• Q41. The most common cause of trailer wheel lockup in non-ABS trailers is:
• Q42. Trailer length affects:
• Q43. When parking a combination vehicle, you should:
• Q44. Glad hand color coding is required because:
• Q45. Cargo securement requirements depend on:
• Q46. Inspecting the rear of a trailer at a stop should include:
• Q47. When driving across railroad tracks with a low-clearance trailer (lowboy), you should:
• Q48. The trailer brake valve (hand valve) is intended for use:
• Q49. A coupled tractor-trailer with the trailer brakes locked and the tractor moving forward will cause:
• Q50. The risk of rollover is greatest when:
• Q51. When you must back into a busy area, you should:
• Q52. A tractor-trailer encountering a steep downgrade should choose a gear:
• Q53. The blind spots of a tractor-trailer include:
• Q54. When a passenger car cuts in front of you, you should:
• Q55. A trailer with sliding tandems lets you:
• Q56. When sliding the fifth wheel forward, the load on the steering axle:
• Q57. A pressure test of trailer air lines should include:
• Q58. When making a long left turn at an intersection, you should:
• Q59. A combination vehicle's empty trailer:
• Q60. When making a tight backing maneuver, looking ahead in your mirrors to predict trailer movement is b…
• Q61. Failing to set the trailer parking brake before uncoupling can cause:
• Q62. When the trailer landing gear sticks during raising or lowering, you should:
• Q63. When you cannot see the spotter in the mirror while backing, you should:
• Q64. The forward visibility of a tractor's hood and mirrors creates a blind area in front of the cab of a…

State-specific resources

Each U.S. state administers the CDL knowledge test through its own DMV. The federal questions are the same; the test scheduling, fees, and identification requirements vary. Start with your state's overview:

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