Traffic lights for sure. If we took a small portion of our energy subsidies and put them into upgrading traffic systems I bet it would save 2% in fuel and increase productivity. How many times do you sit at a light idling for 3 minutes with no cross traffic. Even an electric car or hybrid expends energy running the heater or air conditioning at a stoplight.

With all our network traffic shaping experience it should be relatively simple to extend those same rules out to traffic queues.