What is the inspection purpose of the school bus stop arm and safety arm in PennDOT's CDL manual?

1. The stop arm warns traffic, and the safety arm forces students to cross about 10 feet in front where the driver can see them
2. Both arms are decorative and not part of the inspection
3. The stop arm holds the bus in place on hills, and the safety arm opens emergency exits
4. The safety arm lets students cross behind the bus