What is the maximum statutory speed limit for a bus inside a designated 30 km/h residential zone (30er-Zone)?

1. Max 30 km/h under StVO § 20
2. 50 km/h because scheduled buses are exempt from local zone limits
3. 40 km/h if the bus has emergency hazard lights flashing
4. 35 km/h if the bus is running behind its official timetable