Double

This endorsement is required if the driver will pull two or three trailers. To receive this endorsement, applicants must pass a test. The test consists of 20 multiple choice.. Read More

This endorsement is required if the driver will pull two or three trailers. To receive this endorsement, applicants must pass a test. The test consists of 20 multiple choice questions. To pass, the applicant must answer at least 16 questions correctly. Each question has three or four possible answer choices. Test questions come from the Maryland Commercial Driver Guide. Questions come from chapters covering: Driving Safely, Air Brakes (if applicable), Combination Vehicles and Doubles and Triples. The Double/Triple endorsement can be used with the Class A CDL.

Number of Question
Passing Score

1. The trailer hand valve should 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.

2. Which of the following is not a type of retarder?

Explanation
Retarders are mechanisms in some vehicles that help slow a vehicle and reduce the need for braking. The four basic types of retarders are exhaust, engine, hydraulic, and electric.

3. If a vehicle is found to be over-length during a pre-trip inspection, the driver should:

Explanation
If a pre-trip inspection reveals a load to be oversize, the driver must confirm that all required signs, flags, lamps, and reflectors are safely and properly mounted, and that and all required permits are in their possession.

4. If a driver has stopped on the road and is placing triangles to warn other motorists:

Explanation
For your own safety, when placing reflective warning triangles, you should carry them between your body and the oncoming traffic.

5. Front brake limiting valves were intended to:

Explanation
Some older vehicles with air brakes have front brake limiting valves. These valves were intended to reduce the risk of front wheels skidding. However, research has shown that such devices are unnecessary, so they should be left in the "normal" position.

6. On trucks and buses, where are ABS malfunction lamps located?

Explanation
Tractors, trucks, and buses with Anti-Lock Braking Systems (ABS) have yellow malfunction lamps located on their instrument panels. Trailers have yellow ABS malfunction lamps on their left side, either on the front or rear corner.

7. The "crack-the-whip" effect is caused by:

Explanation
Vehicles with trailers are vulnerable to rollover due to the "crack-the-whip" effect, which is caused by rearward amplification. Rearward amplification varies from vehicle to vehicle, so it is important that drivers are aware of the rearward amplification of their specific vehicles.
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