All new EVs, including those from existing lineups, will have to include noisemakers by 2021. Cars already on the streets are likely to get retrofits.

The rules won't please everyone. The charity Guide Dogs and other accessibility advocates have called for electric cars to make sounds at all speeds. It might also irk people hoping that EVs could usher in an era of far quieter streets. Still, this could increase practical safety and help EVs gain acceptance from people worried they could become hazards.