Looks like the proliferation of hybrid and electric vehicles is having a consequence that the automakers didn't expect to be a problem: these vehicles can be so quiet that pedestrians, especially those who are sight-impaired or too occupied with their iPods or cell phones don't hear them coming and consequently, may get hit.
Well, here's another problem begging for a mandated solution. Apparently, California is considering legislation that would require set minimum sound-level standards for vehicles. Talk about no good deed going unpunished!
And then there are these questions: would the sound level be a function of speed? How much time would it take to design and test in the development stage, both in up-front simulation and the prototype wind-tunnel test?
And how would it be implemented? With a loudspeaker controlled by the car's ECU (engine control unit)? By a mechanical "whistler" on the car (another thing to be damaged)? Via noisier tires (likely bad for mileage, due to higher rolling resistance)?
Here's my solution: for California cars: issue each owner a stack of playing cards or baseball cards, plus a few heavy-duty clips. Then they can fasten these to the car's frame in various ways, per suggestions in the owner's manual, to make whistling or rushing noises as the wind passes through them. Or perhaps owners can attach them so the cards rub against a tire or wheel, just like kids in the old days used to use a clothespin (what's that?) to attach a card to the bike's fork and then make a rat-a-tat-tat noise as the spokes hit the card?
You never know how these things turn out--it's a corollary of the law of unintended consequences! How do you suggest the automakers implement the noise standard?