BMW has reported great success in improving traffic flow by adjusting the timing of traffic lights, and Audi is working on a concept they call "travolution."
From Audi's press release: The "travolution project is a concept for a dialogue between cars and traffic signals. It reduces the amount of time spent at a standstill or accelerating, and in this way cuts the vehicles' fuel consumption."
Bengt Halvorson at The Car Connection reports on BMW's activities:
"Through a test course in Munich, vehicles were able to post phenomenal fuel-efficiency gains simply by adjusting the timing of traffic lights depending on traffic volume-to whatever speed provides a so-called 'green wave' of four or more synchronized signals."