In 2018 the NHTSA finalized rules that require EVs and hybrid to emit alert sounds to warn pedestrians they are approaching. The deadline was extended to 2020 for full participation from automakers. The rules were first requested from Congress in 2010 and have been a decade coming.

The rules call for automakers to add sounds to quiet vehicles when they are moving at speeds up to 18.6 mph to prevent injuries to pedestrians, cyclists, and the blind who may not hear the vehicles coming.
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https://www.slashgear.com/drivers-will-get-to-choose-their-ev-alert-sounds-17591959/