What happens automatically if the red supply line of a dual-line pneumatic trailer breaks or tears off while driving?

1. The sudden pressure drop in the red line triggers the trailer's emergency valve, applying the trailer brakes automatically at full force
2. The trailer keeps braking normally from the air already stored in its reservoir
3. The trailer brakes release completely and the trailer rolls on freely
4. Only the tractor's own braking is affected; the trailer is unaffected until the yellow line also fails