I see that some well meaning but misguided boffins at Lotus are talking about building systems to add sound effects to electric cars. The justification for this is supposed to be two fold: to allow the driver to judge by ear how fast they are going, and to alert pedestrians to the approach of the vehicle, so that they don't step out in front of it. Now I will admit that it took me a couple of weeks to adjust to my Prius, and not being able to judge speed by sound (which I hadn't fully realised that I did, until it stopped working). But I'm adaptable, and I learned, fortunately before I got a speeding ticket.
But I see absolutely no reason to add to the noise pollution of this planet to alert pedestrians to the approach of cars. If a pedestrian is about to step into the street, they should assume that there may be a car approaching and check. Most of the people I have to dodge in the city have the ear pieces of some electronic device in their ears, anyway, and probably wouldn't hear it if my car made a noise like a jet taking off. Bicycles can be silent, so are we going to add noise makers to them, as well?
The average human being does not pay nearly enough attention to what is going on around them as it is. If we could just reintroduce some large carnivore to our communities - I'm thinking a sabre toothed tiger or similar - people would become a damn sight more alert to their surrounding, and less inclined to wander about in a daze, expecting others to avoid them. This might lead to a general improvement in manners and general standards of behaviour.
I can dream.