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 30 multiple-choice questions, and applicants will need to correctly answer a minimum of 24 questions to pass. The Combination test is not a replacement for the Double/Triple endorsement test.
Number of Question
Passing Score
9. When lightly loaded, combination vehicles:
Explanation
When a combination vehicle is lightly loaded, it may have poor traction. It is very easy for wheels to lock up on lightly-loaded vehicles when they are being stopped.
10. When a vehicle goes around a corner, the rear wheels:
Explanation
When any vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is called off-tracking. The degree of off-tracking will be greater on long vehicles than on short vehicles.
11. During a trip, the ____ should be open.
Explanation
When starting a trip, be sure that all shut-off valves are in the open position, except for the last valves on the rear trailer. It is important that air reaches the brakes on all trailers and that it is not able to escape from the back of the vehicle.
12. Compared to other commercial motor vehicles, combination vehicles need more space on the road because they are longer and they:
Explanation
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.
13. Failure to keep the fifth wheel plate properly greased could:
Explanation
Failure to keep the fifth wheel plate properly lubricated can create friction between the tractor and trailer, causing steering problems.
14. The service air line is often controlled by the foot brake and is attached to the ____ valves.
Explanation
The service air line carries air and is controlled by either the foot brake or trailer hand brake. The service air line is attached to relay valves, which allow the trailer brakes to be applied quickly.
15. When should the trailer hand valve be used?
Explanation
The trailer hand valve, also called the trolley valve or Johnson bar, is used to work the trailer brakes. It should be used only to test the brakes. Using it while a vehicle is in motion could cause a skid.
16. If unsure if a trailer has an Anti-Lock Braking System (ABS), you can:
Explanation
