I love that Jetsons sound, but only as an amusement, mind you!
That would get very old, very fast, even in a single car. Can you imagine a traffic jam (or even just a couple of blocks of not-jammed urban traffic) where they all made this sound?!
It seems that versions of white noise at a low level (which is not all that much different than what an ICE makes) is coming into the design picture with relative frequency.