Cars of the future, especially the all electric ones, will be stealthy, especially at speeds under 20 mph, where road friction and aerodynamic drag don't really come into play.
Quiet cars is a good thing, right? (Boats, too--electric boats are coming!) Well, yes, unless you're blind, or you're the type of pedestrian (child, elderly) whose attention to his/her surroundings is less than it should be.
One solution, being batted around in industry circles and safety regulatory agencies these days, is to require electric cars to emit some kind of sound, at least at low speeds. Of course, that sound needn't necessarily be that of engine noise.
Indeed, cars of the future may emit unique "drive tones" (the term is already copyrighted) like your cell phone's ring tone. An interesting proposition. Will our little Prius's successor be rolling down the highway emitting the guttural guitar sounds of Jimi Hendrix, or bouncing to the rap tunes the kids favor?
And how will that sound when it's all mixed together?
The next generation of autos will be interesting. Along with drive tones, expect all kinds of light variations as manufacturers begin to embed colorful LED lights both inside and out. Car shapes may change radically as well, as an electric engine is a lot smaller than today's gas powered models, eliminating the need for a lot of the gear under the hood. Eventually, these cars will drive themselves, as well.
What will we do, while the car's driving itself? Why, we'll blog, download new drivetunes, Facebook, etc. The same things we do at home now!