Combination
All applicants who are applying for a Class A CDL should be prepared to take the Combination test. This test covers information found in Section 6 of the Commercial Driver License Manual. Section 6 provides the information needed to safely operate tractor-trailers, doubles, triples, and straight trucks with trailers. The test is made up of 20 multiple-choice questions, and applicants will need to correctly answer a minimum of 16 questions to pass. The Combination test is not a replacement for the Double/Triple endorsement test.
1. The trailer hand valve should be used:
The trailer hand valve (also referred to as the "trolley valve" or "Johnson bar") works the trailer brakes and should be used only when testing them. Using the trailer hand valve while driving could result in a skid.
2. If a parked trailer does not have spring brakes, you should keep the trailer from moving by:
If a parked trailer does not have spring brakes, wheel chocks should be used to prevent it from moving. Air brakes can only hold a parked trailer for as long as there is air pressure remaining in the air tanks, so wheel chocks will ensure safety.
3. A combination vehicle has:
Combination vehicles have two air lines: a service line and an emergency line.
4. Combination vehicles need extra space on the road because they:
Combination vehicles need more space on the road than other commercial vehicles because they are longer and need more space to turn and stop. It is especially important to properly manage space when you are operating a combination vehicle.
5. What can the “crack-the-whip” effect do?
The "crack-the-whip" effect can cause a trailer to turn over during a lane change. To avoid this phenomenon, drivers should make lane changes at slow, safe speeds.
6. Rollovers happen when:
Rollovers occur when drivers turn or change lanes too quickly.
7. What does the trailer air supply control look like?
On newer vehicles, the trailer air supply control is an eight-sided red knob. It's used to control the tractor protection valve.
See the exact questions that will be on the 2025 Mississippi DMV exam.
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