Its been said many times, but maybe not enough, that its not just what you drive but how you drive that effects your fuel economy. This point was comically illustrated by the boys at TOP GEAR by pitting a Prius against a M3, with the M3 coming out on top. Of course this was done tongue in cheek, but that point is driving style has a very large impact on efficiency. Driving style also can impact the were and tear to your vehicle and therefore maintenance costs.

When I was just learning to drive, my grandfather showed me that one of the main highways could be driven at 2-3 mph below the speed limit and you would never stop at a red light for 20 miles (thanks to the co-ordinated timing of the lights every 2-3 miles). Even with heavier traffic the worst that would happen is you would have to coast a little at the light where stopped traffic had built up. Of course this was more efficient, less wear and tear and would take the same time to do the trip at the speed limit or above it. This worked because of the timing of the lights and unfortunately is more the exception than the rule when it comes to engineering traffic. This system by Audi could allow you to do the same type of thing even without knowing the history of a particular road and how to drive it efficiently. Lots of technology involved but certainly an interesting concept.