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Safely pulling double and triple trailers requires knowledge and skill. If you want to pull double or triple trailers, you must add the Doubles/Triples (T) endorsement to your Class A CDL. The Maryland doubles triples test consists of 20 questions. To pass, you must correctly answer at least 16 questions (80%). The MD CDL doubles triples test covers the following sections of the Maryland CDL Manual: Driving Safely, Air Brakes (if you plan to operate vehicles equipped with air brakes), Combination Vehicles, Doubles and Triples. Take this MD CDL practice test now to prepare for the actual test!
1. As part of your vehicle inspection, you are checking that air flows to all trailers. After using the trailer handbrake to provide air to the service line, you go to the rear of the rig. When you open the emergency line shut-off valve at the rear of the last trailer, you should hear:
a thumping sound.
the service line valve close.
a mechanical vibration.
air escaping from the open valve.
2. When driving with more than one trailer, the _______ trailer should be the first one behind the tractor.
3. You can determine if your vehicle is equipped with ABS (anti-lock braking system) by:
checking for a yellow ABS malfunction lamp on the instrument panel.
looking for wheel speed sensor wires coming from the rear of your brakes.
checking if your vehicle was manufactured after March 1, 1998.
All of the above.
4. Foundation brakes are used:
only with the front wheels.
only with the rear wheels.
only with the right wheels.
at each wheel.
5. To prevent rollover, you should:
drive in the left lane whenever possible.
drive faster on ramps and off ramps.
drive slower around corners.
All of the above.
6. When backing, it is best to:
back toward the passenger's side when possible.
try to back in the direction of the drift.
use a helper whenever possible.
use only the passenger's side mirror.
7. ABS helps you:
keep the wheels from locking up.
lock your wheels.
decrease your overall stopping distance.
decrease your average speed.
8. How should you apply the brakes when going down a steep downgrade?
Apply the brakes when you reach the bottom of the downgrade.
Apply the brakes whenever you reach your safe speed, until your speed has been reduced to 5 mph below your safe speed.
Apply the brakes as hard as you can without locking the wheels.
You should not brake, and only use engine braking to prevent brake failure.
9. In a dual air brake system, if one air system is very low on pressure:
the effect won't be noticeable for the first 50 miles.
you should pump the brakes to restore pressure.
you should drive and brake as you always have.
either the front or rear brakes will not be operating fully.
10. When you turn suddenly, which trailer is most likely to turn over?
The last trailer of triples
The rear trailer of doubles
The front trailer
None of the above.
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MD Doubles Triples Test

Number of questions: 20
Correct answers to pass:16
Passing score:80%
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