I've never perceived the problem of getting vehicles to turn off engines at traffic lights as being a technical issue. Rather, the problem is much more one of regulation, and forcing everyone to adopt a standard. To make the strategy work, you need to:
(a) get every state in the union, and perhaps every municipality in every state, to modify their traffic lights in the same way, and (b) get every automaker to make cars that with electronic modules that work with the *SAME* standard as the traffic lights, and (c) get every class action litigator to agree to not sue anyone.
Business text books clearly say to "run away" from any system that requires broad corporate/public/governmental agreement, particularly if the system involves long-term governmental and corporate cooperation.
Let me add a monkey wrench into your list bud...
I have a 1990 Ford Van... how are you going to get MY old beast to conform to this new toy?
Life is a whim of several billion cells to be you for a while.