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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 Missouri doubles triples test consists of 20 questions. To pass, you must correctly answer at least 16 questions (80%). The MO CDL doubles triples test covers the following sections of the Missouri CDL Manual: Driving Safely, Air Brakes (if you plan to operate vehicles equipped with air brakes), Combination Vehicles, Doubles and Triples. Take this MO CDL practice test now to prepare for the actual test!
1. If your vehicle has air brakes, to check that air flows to all trailers:
watch each trailer’s air gauge for a drop of 25 psi.
pull gently on the trailer with the tractor.
go to the rear of the second trailer and open the emergency line shut-off.
2. When driving, you should check mirrors regularly to know where other vehicles are around you. Remember that:
convex mirrors make things look larger and closer than they really are.
you should check your after the start of any trip to make sure they are properly adjusted.
there are blind spots that your mirrors cannot show you.
3. When driving trucks with trailers, drivers should:
make quick lane changes.
avoid making sudden movements with the steering wheel.
push the brake pedal to the floor when braking.
4. When driving in extremely hot weather, if the air pressure in the tires is too high, you should:
let air out of the tires to decrease pressure.
continue driving.
stop and remain stopped until the tires cool off.
5. If an aggressive driver is involved in an accident down the road, you should:
stop a safe distance from the accident scene, wait for the police and report the behavior you witnessed.
confront the aggressive driver.
try to get their vehicle to the side of the road.
6. Glad hands are:
coupling devices.
securement devices.
warning devices.
7. In vehicles with air brakes, the two markings on a front brake limiting valve are:
left and right.
normal and slippery.
high and low.
8. What should you do if you doubt you have safe space to pass under a low bridge?
Go slowly, and take another route if you are not sure you can make it.
Increase the weight of your vehicle to clearing under the bridge.
If no warnings are posted, assume there is enough clearance under the bridge and proceed slowly.
9. Empty trucks:
require a shorter stopping distance than full trucks.
require a greater stopping distance than full trucks.
require the same stopping distance than full trucks.
10. You should NOT use the parking brakes if:
the brakes are cold.
the brakes are too dry.
the brakes are very hot.
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MO CDL Doubles Triples Test

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