What do the amber (yellow) flashing lights on a school bus signal?

The amber flashing lights on a school bus warn other drivers that the bus is about to stop to load or unload students. They are typically activated about 200 feet before the stop. Other drivers should slow down and prepare to stop; in most states it is illegal to pass a school bus showing amber warning lights when it is approaching a stop. The amber lights transition to red flashing lights and an extended stop arm once the bus is actually stopped at the loading/unloading point — at which time stopping is required in both directions on undivided roads in most states. Watch the lights carefully: amber means 'about to stop'; red means 'stop now'.