It may sound obvious, but the most effective way to cut a car's fuel consumption is to turn the car off. Of course that isn’t very useful if you're trying to get from A to B. But for many trips, particularly for city driving, a car can be idle for a significant amount of time. Such stop-start driving is far from being fuel-efficient, but Audi has turned that around with a new system that shuts down the engine when the car comes to a stop. The start-stop system joins a new on-board computer, as part of Audi’s modular efficiency platform, which is designed to reduce fuel consumption and cut carbon emissions.