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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 Iowa doubles triples test consists of 20 questions. To pass, you must correctly answer at least 16 questions (80%). The IA CDL doubles triples test covers the following sections of the Iowa CDL Manual: Driving Safely, Air Brakes (if you plan to operate vehicles equipped with air brakes), Combination Vehicles, Doubles and Triples. Take this IA CDL practice test now to prepare for the actual test!
1. Which of the following statements about retarders is NOT correct?
You should turn the retarder off whenever the road is wet, icy, or snow covered.
Retarders help slow a vehicle, reducing the need for using brakes.
RetardersĀ help you avoid skids.
2. When driving on slippery roads, you should NOT:
go slowly.
try to anticipate stops early.
use the engine brake.
3. A bridge formula permits:
more maximum axle weight for axles that are closer together.
less maximum axle weight for axles that are close together.
less maximum axle weight for axles that are far apart.
4. The safety valve installed in the first tank the air compressor pumps air is set to open:
if there is too much pressure.
if there is too little pressure.
at 30 psi.
5. Excessive use of the service brakes results in overheating. Too much heat can:
cause the brakes to grab.
cause the brakes apply unevenly.
make the brakes stop working.
6. How should you apply the brakes when going down a steep 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.
Apply the brakes when you reach the bottom of the downgrade.
7. ABS:
helps you stop faster.
improves your visibility at night.
helps you avoid skids caused by over braking.
8. If the engine catches fire, you should:
avoid shooting foam from the vehicle's underside.
turn off the engine as soon as you can.
open the hood as soon as you can.
9. When going down a steep downgrade, you should primarily brake using:
the parking brake.
the service brakes.
the braking effect of the engine.
10. Which of the following is not a type of retarder?
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IA Doubles Triples Test

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