Taking a page out of Mercedes-Benz's playbook, Audi has announced that it is unveiling a new stop-start system for its cars in Europe over the next few months, and is projecting that by 2012 the company's entire lineup will be 20 percent more fuel efficient, with a corresponding reduction in CO2 emissions.

Audi is actually going for two different approaches here--the stop-start system, which will cut the engine while idling and then kick it back in the moment the driver begins to depress the clutch pedal to shift the car back into gear. Audi's system will be inactive while the car is warning up, and it's also defeatable with a switch on the dashboard in case the driver doesn't like it. First up to get it is the Audi A3 1.4 TFSI with manual transmission, along with the Audi A4 and A5 with two-liter engines and manual--with others to follow soon after.

Audi's other tack is a new Efficiency Program for its on-board computer, which will display real-time info about fuel consumption and offer the driver tips on how to conserve fuel based on his or her current driving style.