I support this. Looking is fine, but every warning helps. It doesn't have to be terrifically noisy at normal speeds; I'm sure the broadcast can be proportional to the car's speed.

Last year I crossed the street in front of an idling DEP electric, and even though I knew it wasn't moving, my sense of alert spiked as I entered the road. I couldn't figure out why for a second, until I realized I knew the car was on and could move but it wasn't making any noise. Ever since then, I figured a development like this was inevitable and a good idea. Just a little bit of warning for, say, the vision-impaired, deer, and pedestrians at large.