90. If your bus or truck has dual parking control valves, you can use pressure from a separate tank to:
Detailed Explanation
The correct answer is "Release the spring emergency/parking brakes to move a short distance.". This question tests passenger safety, vehicle inspection, and the additional responsibilities of a bus driver. For a differently worded version of this question, identify the hazard first and then choose the answer that preserves control, visibility, or legal compliance.
Correct Answer: Release the spring emergency/parking brakes to move a short distance.
Why This Matters on the CDL Test
Use this as part of your Air Brakes review. The real CDL knowledge test rewards drivers who understand the reason behind each rule, not only the answer letter, so read the explanation and then try a few related questions.
How to Remember It
Say the rule in your own words, then explain why the wrong answers are unsafe or incomplete. That habit makes similar Air Brakes questions easier when the exam changes the wording.
Answer Review
Choose "Release the spring emergency/parking brakes to move a short distance." because this answer matches the safe CDL action for air brakes knowledge. On the knowledge test, the safest answer is usually the one that protects space, control, visibility, legal compliance, or inspection accuracy before the vehicle is put at risk.
Why the other answers are weaker
- Balance the service brake system when you are parked."Balance the service brake system when you are parked." does not best answer this air brakes knowledge question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
- Stay parked twice as long without using up service air pressure."Stay parked twice as long without using up service air pressure." does not best answer this air brakes knowledge question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
Test-Day Checklist
- Read the question once for the topic, then read it again for the exact CDL action being tested in Air Brakes.
- Eliminate answers that sound convenient but skip an inspection, warning sign, or safety step.
- Say the correct rule out loud before moving on so you can recognize it when the exam changes the wording.
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Start Practice TestRelated Questions
12. If your truck or bus has dual parking control valves, you can use pressure from a separate tank to:
100. Your bus or truck has a dual air brake system. If a low air pressure warning comes on for only one system, what should you do?
11. Your truck has a dual air system, and one of the systems loses its pressure. What will happen?
13. If your truck has a properly functioning dual air brake system and minimum size air tanks, the air pressure should build from 85 to 100 psi within _ seconds?
62. When is it OK to leave your truck unattended without applying parking brakes or chocking the wheels?
Keep Studying Air Brakes
Question pages help you review one rule at a time. To build test-day speed, move back into the full Air Brakes practice test and answer a mixed set without looking at the explanation first.
State CDL Practice Paths
After you understand this answer, use a state practice path to connect the federal CDL rule with the DMV test pages drivers search for most.