What happens to the spring-loaded parking brake (Federspeicher) if a parked bus loses all pneumatic air pressure over several days?

1. The brakes remain securely locked on mechanically by the internal springs, preventing the bus from rolling away
2. The brakes release completely and the bus begins to roll freely
3. The brake pads rapidly pulse on and off until the battery discharges
4. The front steering locks to the maximum left angle