There was an interesting section in "The Cat Who Walks Through Walls" where Heinlein writes about electric cars, and how the law eventually required them to ins

There was an interesting section in "The Cat Who Walks Through Walls" where Heinlein writes about electric cars, and how the law eventually required them to install speakers which produced fake engine sounds. This was because the cars were so quiet that no one would hear them coming, and they'd step out into the road without looking.