Tips for Motorists: Be alert and slow down when driving in neighborhoods with school zones. For those school districts returning to campuses, obey the "flashing signal light system" used for school buses. Yellow flashing lights indicate the bus is preparing to stop to load or unload children. Motorists should slow down and prepare to stop their vehicles.
Red flashing lights and extended stop arms indicate the bus has stopped and children are getting on or off. Motorists must stop their cars and wait until the red lights stop flashing, the extended stop-arm is withdrawn, and the bus begins moving before they can start driving again.
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School Bus Safety - NHTSA