What happens to the trailer brakes if a trailer breaks away from the tractor?

• A.The trailer brakes release completely and the trailer rolls freely
• B.Only the trailer's lights keep working
• C.The trailer service brakes keep operating from the tractor tanks
• D.The tractor protection valve closes to save tractor air, trailer supply pressure is lost, and the trailer's emergency (spring) brakes apply automatically

Why

Breakaway protection works from both ends of the separation: the tractor seals its supply and the trailer applies its own spring brakes. That automatic trailer stop is why the supply and protection system must be tested, not assumed.

Manual topic: Air Brakes - Tractor Protection Valve · From the Air Brakes practice bank (AB-237).

Practice this subject as a full test

More Tractor Protection Valve, Trailer Brakes & Stab Braking questions

• A trailer breaks away from the tractor and tears both air lines loose. What happens on the tractor side in the first moments?
• What does the trailer air supply control (the red control in the cab) do in normal operation?
• At about what pressure will the trailer air supply control pop out (or the tractor protection valve close) as system pressure falls?
• How do you test the tractor protection valve during an inspection?
• What is the difference between the trailer's emergency (supply) air line and its service air line?