Before pulling away from a stop, what does the manual say a bus driver should wait for?

49 CFR 383.117(a)(5), proper braking procedures; AAMVA CDL Manual Section 4.3.2, p.4-3

Bus riders usually aren't seat-belted, so an abrupt start can throw a standing or just-seated rider off balance. This is the manual's direct explanation behind the federal "proper braking procedures" knowledge-test topic for the Passenger endorsement.