What are the two functions of a combination vehicle’s emergency air line?
Correct answer: C – It performs both functions
The emergency or supply line carries air to the trailer’s air tanks and controls the trailer emergency brakes. If pressure is lost through this line, the trailer emergency brakes apply. Pressure loss may result from a broken hose, damaged tubing, or a trailer separating from the power unit.
Source: Vermont Commercial Driver’s Manual — § 6.2.4, “Trailer Air-lines”


