25 realistic Doubles and Triples practice questions for Idaho CDL applicants. Required for: Drivers pulling more than one trailer. Official test: 20 questions, 16 correct to pass.
Question 1 of 25 · Mountain Driving
What's the recommended speed when descending a steep grade with doubles?
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A.
Slow speed using lower gears and engine braking
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B.
Posted speed limit
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C.
Faster than single trailers
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D.
Use service brakes only
Correct answer: A.
Use lower gears and engine braking. Service brakes only intermittently.
Question 2 of 25 · Vehicle Dynamics
How do you reduce off-tracking in doubles?
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A.
Make wider turns
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B.
Slow down
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C.
Use mirrors carefully
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D.
All of the above
Correct answer: D.
Wider turns, slower speed, and careful mirror use minimize off-tracking impact.
Question 3 of 25 · Speed Management
What's the safe speed for taking corners with doubles or triples?
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A.
Posted speed limit
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B.
Slower than single trailers
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C.
Higher than single trailers
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D.
No different from single trailers
Correct answer: B.
Take corners more slowly than single trailers due to greater rollover risk.
Question 4 of 25 · Cargo
Doubles and triples are most stable when:
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A.
All trailers are properly loaded
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B.
Trailers are empty
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C.
The lead trailer is empty
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D.
The rear trailer is heaviest
Correct answer: A.
Proper loading on every trailer is key to stability.
Question 5 of 25 · Coupling
What's the proper procedure for coupling a second trailer?
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A.
Position the dolly under the second trailer, then back the lead trailer to the dolly
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B.
Drive the lead trailer over the dolly
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C.
Connect electrical first
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D.
Lower the landing gear
Correct answer: A.
Position the dolly first, then back the lead trailer to it for proper coupling.
Question 6 of 25 · Inspection
Why must drivers inspect the dolly before connecting?
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A.
To check for damage and proper operation
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B.
To verify the brakes work
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C.
To inspect the pintle hook
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D.
All of the above
Correct answer: D.
Dolly inspection includes structure, brakes, and pintle hook condition.
Question 7 of 25 · Emergency Maneuvers
How should doubles drivers handle emergency braking?
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A.
Apply brakes firmly but smoothly
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B.
Use only the trailer hand valve
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C.
Pump the brakes
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D.
Use only the engine retarder
Correct answer: A.
Smooth, firm braking is best — let ABS work if equipped.
Question 8 of 25 · Communication
How can drivers communicate effectively when driving doubles?
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A.
Use turn signals well in advance
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B.
Use mirrors continuously
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C.
Use the horn when needed
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D.
All of the above
Correct answer: D.
Clear, early signals, mirrors, and horn use all improve safety.
Question 9 of 25 · Cargo
What's the impact of overloading a trailer in a doubles set?
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A.
Increased rollover risk
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B.
Poor handling
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C.
Brake problems
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D.
All of the above
Correct answer: D.
Overloading creates a chain of safety problems for the whole combination.
Question 10 of 25 · Lane Changes
What's the major risk when changing lanes with doubles or triples?
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A.
The rear trailer may not follow exactly
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B.
Other vehicles may not see the long combination
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C.
The trailer may swing out
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D.
All of the above
Correct answer: D.
Visibility and rear-trailer tracking are both major lane-change risks.
Question 11 of 25 · Inspection
When inspecting doubles and triples, what should you check?
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A.
Each trailer's lights and brakes
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B.
Each converter dolly
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C.
Each fifth wheel and pintle hook
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D.
All of the above
Correct answer: D.
Inspect every trailer, dolly, fifth wheel, and pintle hook before driving.
Question 12 of 25 · CDL Rules
Triples are illegal in many states because:
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A.
They are too long and cause traffic disruption
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B.
They have higher rollover risk
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C.
They require special permits
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D.
All of the above
Correct answer: D.
Many states prohibit triples due to length, rollover risk, and special permitting needs.
Question 13 of 25 · Coupling
What is the pintle hook?
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A.
A coupling device on the dolly that connects to the lead trailer's pintle plate
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B.
A type of tire
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C.
A safety chain
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D.
A brake component
Correct answer: A.
The pintle hook on the dolly connects to the lead trailer for towing.
Question 14 of 25 · Skids
What should you do if a trailer starts to skid?
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A.
Release the brakes to allow trailer wheels to roll
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B.
Apply more brake
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C.
Steer hard right
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D.
Accelerate
Correct answer: A.
Release brakes to let trailer wheels roll; steer to recover.
Question 15 of 25 · Combination Air
What's the role of glad hands in doubles and triples?
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A.
They connect air lines between each unit
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B.
They are coupling devices
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C.
They are safety chains
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D.
They are landing gear
Correct answer: A.
Glad hands connect service and emergency air lines between every unit.
Question 16 of 25 · Vehicle Dynamics
Doubles and triples have ____ rollover risk than single trailers.
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A.
Lower
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B.
Higher
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C.
The same
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D.
No rollover risk
Correct answer: B.
Multiple trailers have higher rollover risk because of greater articulation and "crack-the-whip" effect.
Question 17 of 25 · Cargo
What's the consequence of bad weight distribution in doubles?
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A.
Increased rollover risk
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B.
Poor handling
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C.
Tire wear
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D.
All of the above
Correct answer: D.
Bad distribution increases rollover, handling problems, and tire wear.
Question 18 of 25 · Vehicle Dynamics
What is "crack-the-whip"?
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A.
A driver discipline rule
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B.
When the rear trailer swings out due to sudden steering inputs
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C.
A type of weight distribution
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D.
A coupling procedure
Correct answer: B.
The rear trailer can swing far wider than the tractor, magnifying steering inputs.
Question 19 of 25 · Vehicle Dynamics
What's the importance of "leverage" in doubles and triples?
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A.
Each trailer affects the others; the rear can amplify or reduce stability
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B.
It only affects fuel efficiency
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C.
It doesn't matter
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D.
It only affects loading
Correct answer: A.
Forces transfer between trailers; each one affects the stability of the combination.
Question 20 of 25 · Vehicle Dynamics
When making a turn, the front trailer of a doubles set:
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A.
Tracks like a single trailer
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B.
Off-tracks more than the tractor
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C.
Stays in line with the tractor
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D.
Off-tracks less than the rear trailer
Correct answer: D.
The rear trailer off-tracks more than the front, so the rear is more likely to hit obstacles.
Question 21 of 25 · Hazard Awareness
What is "blind spot" risk for doubles and triples?
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A.
It's minimal due to long mirrors
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B.
It's significant especially behind and to the right
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C.
It's only at night
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D.
It only affects single trailers
Correct answer: B.
Long combinations have large blind spots — especially behind and to the right.
Question 22 of 25 · CDL Rules
Why are doubles and triples drivers required to have additional training?
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A.
They handle differently and require more skill
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B.
Federal regulations require training
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C.
They have higher rollover risk
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D.
All of the above
Correct answer: D.
Skill, regulation, and rollover risk all justify extra training.
Question 23 of 25 · Coupling
What's the role of safety chains on a converter dolly?
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A.
To support the dolly when uncoupled
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B.
To prevent the trailer from coming loose if the pintle hook fails
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C.
To improve traction
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D.
To act as a brake
Correct answer: B.
Safety chains keep the trailer attached if the pintle hook fails.
Question 24 of 25 · Coupling
What's a "spider" or "dolly converter"?
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A.
A type of trailer
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B.
A coupling device with a fifth wheel mounted on a single axle
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C.
A type of brake
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D.
A safety chain
Correct answer: B.
Converter dollies have a fifth wheel and an axle to allow connecting trailers.
Question 25 of 25 · Following Distance
What's the safe way to handle a doubles in heavy traffic?
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A.
Maintain extra following distance and signal early
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B.
Speed up to keep with traffic
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C.
Use the shoulder
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D.
Drive aggressively
Correct answer: A.
Extra space and early signals are critical in heavy traffic with combinations.
About the Doubles and Triples Test
The Doubles and Triples test covers pulling double and triple trailers, coupling and uncoupling, inspecting doubles and triples, antilock brake systems, and safe driving with multiple trailers. Doubles and triples are more likely to roll over than single trailers and are extremely sensitive to steering inputs at the rear trailer.
The Idaho Transportation Department — Driver Services administers this knowledge test as part of its commercial driver license program. To earn the Doubles/Triples (T) on your Idaho CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Vehicle Dynamics: 5 questions
- Coupling: 4 questions
- Cargo: 3 questions
- Inspection: 2 questions
- CDL Rules: 2 questions
- Mountain Driving: 1 question
- Speed Management: 1 question
- Emergency Maneuvers: 1 question
- Communication: 1 question
- Lane Changes: 1 question
- Skids: 1 question
- Combination Air: 1 question
- Hazard Awareness: 1 question
- Following Distance: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for Idaho until you're ready for the official exam.
Tips specific to the Doubles and Triples test
Doubles and Triples questions emphasize the "crack-the-whip" effect, converter dolly inspection and use, pintle hooks, safety chains, the heaviest-trailer-first loading rule, and the higher rollover risk of multi-trailer combinations. Many states prohibit triples; check local rules.