Back when we were kids, we’d attach bits of cardboard to the forks on our bicycles, so that they stuck into the spokes of the wheels. Then, when we rode around, the noise they made as the spokes hit them sounded almost but not entirely unlike a motorbike.
We’re going to have to something almost but not entirely unlike that with electric vehicles: they’re silent … so, if we don’t, a lot of blind people are going to be even more disadvantaged when crossing the road than they already are — not to mention their guide-/seeing-eye dogs. 
 Especially if the latter are deaf. 
 I’ll just let that one sink in. ;)