Practice question

For the Washington CDL Air Brakes knowledge test, what happens if the emergency (supply) air line to the trailer is broken or disconnected during driving?

  1. The trailer keeps rolling freely
  2. The trailer's emergency brakes (spring brakes) apply automatically because supply line pressure drops
  3. The tractor brakes lock up
  4. The engine stops

Answer: B — The trailer's emergency brakes (spring brakes) apply automatically because supply line pressure drops

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