What should you do if the trailer's air supply line breaks while driving?

If the trailer air supply line breaks (commonly called a 'glad hand' separation), air pressure in the trailer brake system drops rapidly and the trailer's emergency (spring) brakes apply automatically. This is the fail-safe design: a broken line cannot allow a runaway trailer. The driver should expect a sudden, strong pull and possibly a jackknife if the failure happens during braking. Get off the road as safely as possible — do not try to drive with the trailer emergency brakes applied; this can damage the brakes and may not allow normal driving anyway. After stopping, inspect the air line; commonly a glad hand has popped off the trailer connector, which can be reconnected, but a torn or cut line requires repair before continuing.