What is the purpose of the 'Emergency Line' (Red) in a combination vehicle?

It supplies air to the trailer air tanks and controls the emergency brakes.. Section 6.2: The emergency line supplies air to the trailer

What is the purpose of the 'Emergency Line' (Red) in a combination vehicle?

ANSWER BREAKDOWN
  • A. Correct. The emergency line supplies air to the trailer air tanks and controls the emergency brakes.
  • B. Incorrect. "It controls the service brakes." is not correct. The emergency line supplies air to the trailer air tanks and controls the emergency brakes.
  • C. Incorrect. "It is for lights." is not correct. The emergency line supplies air to the trailer air tanks and controls the emergency brakes.
  • D. Incorrect. "It is for the radio." is not correct. The emergency line supplies air to the trailer air tanks and controls the emergency brakes.