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Combination Vehicle Air Brakes

Combination Vehicle Air Brakes is tested under the general operating-practices knowledge area, 49 CFR 383.111(c)(3)(ii), covering how a tractor and trailer's air brake systems interact.

Practice Combination Vehicle Air Brakes

4 Questions

  1. Why is the trailer hand valve (trolley valve) reserved for testing trailer brakes instead of being used as a driving control?
  2. What does the tractor protection valve do at the moment it closes because air pressure has dropped too low?
  3. A driver mistakenly connects the tractor's air-lines to the wrong glad hands, crossing the service and emergency lines, when coupling to a trailer. What is the practical danger of this mistake?
  4. A combination vehicle is towing two trailers. According to the manual, how should the air-line shut-off valves (cut-out cocks) at the back of each trailer be set?