An urban transit coach's rear door is open and the brake-door interlock has applied the service brakes and held the throttle idle. What is the correct driver understanding?

1. The interlock is a safety feature and must not be used in place of the parking brake
2. The rear door must be open to apply the parking brake
3. The interlock means the driver can leave the seat without securing the bus
4. The interlock replaces all normal braking systems