CDL · Doubles and triples
During normal driving, which control applies the trailer brakes on a double or triple combination?
Correct answer: The foot brake pedal.
Answer options
- AThe red trailer air supply knob.
- BThe trailer hand valve, also called the Johnson bar.
- CThe foot brake pedal. Correct
Why
Pressing the brake pedal sends air to the service brakes on the tractor and all trailers simultaneously. The trailer hand valve exists solely to test the trailer brakes, while the red knob supplies or shuts off air to the trailers; neither is for ordinary stops.
About this question
Topic: Doubles and triples License: CDL
Part of these practice sets:
Where it applies: Asked in every state.
Practice the whole set
This question is part of Pulling Doubles and Triples (24 questions). Take the full set and check your score.
Practice Pulling Doubles and TriplesMore questions from Pulling Doubles and Triples
- In a set of triples, which position is safest for the lightest trailer?
- Which statement about making sudden steering moves with a double or triple trailer combination is accurate?
- Which of these best describes safe driving with doubles or triples?
- In a B-train (B-double), at how many points can the combination pivot?
- To begin training as a triple-trailer driver, federal rules say you must first have:
- Compared with driving a smaller vehicle, what does pulling doubles or triples require of you?
- Your 100-foot double-trailer rig is traveling 50 mph on a dry road and visibility is good. What is the smallest following gap, in seconds, you should leave behind the vehicle ahead?
- Counting every joint where connected units can pivot, how many articulation points does a standard double-trailer combination have?
Practice on your phone.
Practice here in your browser, or use the app with the same questions and explanations. It's free on the App Store.