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Question 1

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When coupling a tractor to the first semi-trailer in a double combination, at what height should the trailer be positioned?

Higher than the tractor fifth wheel

Slightly lower than the tractor fifth wheel

At the same height as the tractor fifth wheel

Height does not matter as long as the kingpin engages

to track

2026 Statistics

Key Facts: CDL Doubles/Triples Exam

Exam Questions

State DMV

80%

Passing Score

16/20 correct

$5-30

Endorsement Fee

Varies by state

35%

Coupling/Uncoupling

Largest topic

Skills Test Required

Written only

1-2 wks

Study Time

Recommended

The CDL Doubles/Triples endorsement exam has 20 questions with an 80% passing score (16 correct). Key topics: Coupling/Uncoupling (35%), Inspection (25%), Rearward Amplification (20%), Safe Driving (15%), and Air Brakes (5%). Requires a valid CDL with no separate skills test — written knowledge test only. Exam fee is $5-30 depending on state.

Sample CDL Doubles/Triples Practice Questions

Try these sample questions to test your CDL Doubles/Triples exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 200+ question experience with AI tutoring.

1When coupling a tractor to the first semi-trailer in a double combination, at what height should the trailer be positioned?

A.Higher than the tractor fifth wheel

B.Slightly lower than the tractor fifth wheel

C.At the same height as the tractor fifth wheel

D.Height does not matter as long as the kingpin engages

Explanation: The trailer should be positioned slightly lower than the tractor fifth wheel so that the tractor can roll under the trailer and lift it slightly during coupling. This ensures proper engagement of the kingpin with the fifth wheel locking mechanism. If the trailer is too high, the kingpin may not seat properly, creating a dangerous situation where the trailer could detach.

2What is the correct procedure for connecting the air lines when coupling a trailer?

A.Connect the emergency line first, then the service line

B.Connect the service line first, then the emergency line

C.Connect both lines simultaneously

D.Connect only the service line; the emergency line is optional

Explanation: When coupling air lines, always connect the emergency (supply) line first, then the service (control) line. Connecting the emergency line first charges the trailer air tanks, which prevents the trailer spring brakes from applying. If you connect the service line first without air pressure in the trailer tanks, the spring brakes will engage automatically, potentially causing damage or injury.

3Before backing under a trailer to couple, what should you verify about the trailer brakes?

A.That they are released

B.That they are locked and/or wheels are chocked

C.That they have been tested within the last hour

D.That the brake shoes are new

Explanation: Before backing under a trailer to couple, always ensure the trailer brakes are locked and/or the wheels are chocked. This prevents the trailer from rolling while you are positioning the tractor underneath. Once coupled and air lines are connected, you can release the trailer brakes to move the combination.

4What should you check after coupling but before moving the vehicle?

A.Only that the trailer lights work

B.That the fifth wheel jaws have closed around the kingpin and the locking lever is in the lock position

C.Only that the air lines are connected

D.That the cargo is properly loaded

Explanation: After coupling, you must visually check that the fifth wheel jaws have completely closed around the kingpin and that the locking lever is in the lock position. Many drivers also perform a "tug test" by pulling forward gently against the locked brakes to verify the connection is secure. This verification is critical because an improperly coupled trailer can detach while moving, causing a catastrophic accident.

5When coupling the second trailer in a set of doubles, where should the converter dolly be positioned?

A.At the front of the first semi-trailer

B.At the rear of the first semi-trailer

C.In the middle of the first semi-trailer

D.Anywhere along the side of the first semi-trailer

Explanation: The converter dolly should be positioned at the rear of the first semi-trailer when coupling the second trailer. The dolly is then coupled to the rear trailer, which completes the double combination. Proper positioning ensures the dolly fifth wheel is correctly aligned with the second trailer's kingpin.

6What is the purpose of the pintle hook on a converter dolly?

A.To connect the air lines between trailers

B.To connect the dolly to the front trailer

C.To secure the dolly wheels during transport

D.To hold the spare tire

Explanation: The pintle hook on a converter dolly is used to connect the dolly to the front trailer (or tractor, depending on configuration). It engages with the drawbar eye of the trailer being towed, creating a secure mechanical connection that allows the dolly to pivot and follow the lead trailer through turns.

7How can you release the converter dolly brakes when positioning the dolly for coupling?

A.By using the tractor air system only

B.By using the petcock or parking brake control on the dolly

C.Converter dolly brakes cannot be released manually

D.By disconnecting the air lines

Explanation: Converter dollies are equipped with a petcock or parking brake control that allows you to release the dolly brakes manually when positioning it for coupling. This is necessary because the dolly is not yet connected to the tractor's air system. Once coupled and air lines are connected, the tractor's air system controls the dolly brakes.

8What should you do with the converter dolly support legs after coupling?

A.Leave them down for extra stability

B.Raise them completely and secure them in the raised position

C.Lower them halfway to absorb shocks

D.Remove them entirely

Explanation: After coupling the converter dolly to the trailer, you must raise the dolly support legs completely and secure them in the raised position. Leaving them down can cause them to drag on the ground, potentially damaging the dolly or causing loss of control. The support legs are only used when the dolly is uncoupled and standing alone.

9When coupling a set of doubles, in what order should the air lines be connected to the rear trailer?

A.Service line first, then emergency line

B.Emergency line first, then service line

C.Both lines at the same time

D.It does not matter which line is connected first

Explanation: Just as with the first trailer, connect the emergency (supply) line first when coupling the rear trailer in a set of doubles. This charges the trailer's air tanks before connecting the service line, preventing the automatic application of spring brakes. Consistent procedure for both trailers ensures safe coupling and prevents brake system damage.

10What is a "glad hand" in the context of doubles/triples operations?

A.A type of wrench used for coupling

B.The coupling device used to connect air lines between vehicles

C.A safety glove worn during coupling

D.The handle on the trailer landing gear

Explanation: A glad hand is the coupling device used to connect air lines between the tractor, converter dolly, and trailers. The name comes from its resemblance to a handshake. Glad hands have seals that must be clean and undamaged to prevent air leaks. They are typically color-coded: blue for service lines and red for emergency lines.

About the CDL Doubles/Triples Exam

The CDL Doubles/Triples (T) endorsement exam tests knowledge of safely operating vehicles pulling double or triple trailers. It covers coupling/uncoupling converter dollies, rearward amplification (crack-the-whip effect), inspection procedures, safe driving techniques, and air brake connections for multiple trailers.

Questions

20 scored questions

Time Limit

Varies by state

Passing Score

80%

Exam Fee

$5-30 (State DMV / FMCSA)

CDL Doubles/Triples Exam Content Outline

35%

Coupling/Uncoupling

Converter dolly operation, fifth wheel connections, pintle hooks, and proper coupling sequence

25%

Inspection

Pre-trip and post-trip inspections for doubles/triples including air lines, glad hands, and safety equipment

20%

Rearward Amplification

Crack-the-whip effect, rollover risks, and handling characteristics of multiple trailers

15%

Safe Driving

Following distances, lane changes, turning, and special driving techniques for doubles/triples

Air Brakes

Air line connections, service/emergency lines, and brake system operation

How to Pass the CDL Doubles/Triples Exam

What You Need to Know

Passing score: 80%
Exam length: 20 questions
Time limit: Varies by state
Exam fee: $5-30

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

CDL Doubles/Triples Study Tips from Top Performers

1Master coupling/uncoupling procedures (35%) — know the step-by-step sequence for converter dollies and pintle hooks

2Understand rearward amplification (crack-the-whip effect) and how it increases rollover risk in the last trailer

3Know inspection requirements — air lines, glad hands, fifth wheel, kingpin, and safety chains

4Study following distance rules for doubles/triples — they require more following distance than single trailers

5Know the air brake connections: service line (blue), emergency line (red), and electrical cord

6Review the CDL Manual Section 7 — it covers all testable content for this endorsement

Frequently Asked Questions

How many questions are on the CDL Doubles/Triples test?

The CDL Doubles/Triples endorsement test has 20 multiple-choice questions. You need to score 80% (16 correct answers) to pass. It is a written knowledge test only — no skills test is required for this endorsement.

What is rearward amplification in doubles/triples?

Rearward amplification, also called the "crack-the-whip" effect, is the tendency of the last trailer in a doubles/triples combination to amplify any turning movement. A small lane change can cause the last trailer to swing much wider, increasing rollover risk. The last trailer can turn over even when the tractor stays upright.

Do I need a skills test for the Doubles/Triples endorsement?

No. The CDL Doubles/Triples (T) endorsement only requires passing a written knowledge test at your state DMV. No separate skills test is needed. You must already hold a valid CDL.

What is the proper coupling sequence for doubles/triples?

The general coupling sequence involves: 1) Secure the rear trailer to the converter dolly, 2) Couple the converter dolly to the front trailer, 3) Connect air lines and electrical cord, 4) Test the connection by pulling forward gently, 5) Verify all connections and check for proper height alignment.

How should I prepare for the Doubles/Triples endorsement test?

Plan for 10-20 hours of study over 1-2 weeks. Focus on coupling/uncoupling procedures (35%), inspection requirements (25%), and rearward amplification concepts (20%). Study the CDL Manual Section 7 and complete practice questions. The test is straightforward with proper preparation.