Air Brake Coach
TrailersQuestion 29 of 116

What do the two air lines to the trailer carry?

  1. Oil and air
  2. Only the brake signal
  3. Only the air supply
  4. The air supply and the brake signal
Show answer

Correct answer: The air supply and the brake signal

One line carries the air supply. The other line carries the brake signal.

Source: Air Brake Manual: A Guide for Instructors (Government of Alberta, Alberta Transportation, March/April 2012), Module 6: Tractor and trailer circuits, page 60

Practice trailers

Questions last reviewed: 18 October 2026