Why is checking the tractor protection valve's automatic activation part of a thorough air brake inspection?

Pick an answer

1. It tests whether the trailer brakes release properly once air pressure is restored, which some drivers pick up wrong about inspection
2. This check is purely optional and rarely performed by any driver
3. It only matters for trailers that are more than ten years old
4. It confirms the tractor will still be able to brake even if the trailer's air supply is completely lost

Correct!

Not quite. The correct answer is highlighted.