The 2010 BMW M3 was rated at 14 mpg in the city and 20 on highway. The 2011 model gets exactly the same numbers, despite the introduction of idle-stop.
Though idle-stop technology has been available on European cars for years and is projected by the EPA and NHTSA to be included on a whopping 42 percent of vehicles by 2016, there are currently only three non-hybrids offering the feature in the United States: the BMW M3, and the Porsche Cayenne and Panamera models. Unfortunately, these 2011 models using idle-stop get absolutely no boost in MPG on window stickers, or for CAFE standards, compared to 2010 models without idle-stop. This is despite the technology’s great promise to improve efficiency at a modest cost.
Idle-stop, or stop-start as it’s often called, shuts down a car’s engine completely when it isn’t needed. The engine restarts when the driver accelerates. The feature can provide fuel savings of 5-10 percent at an added cost of as little as $300.
With gas prices threatening to surpass record highs this summer, mainstream American consumers who could take advantage of the system’s cheap mileage boost are out of luck. The only vehicles offering stop-start are hybrids and luxury models priced beyond the range of the people hardest hit by rising fuel costs.
So why is one of the most inexpensive yet powerful fuel-saving technologies in existence not available on mainstream vehicles? Partly because the EPA and the National Highway Traffic Safety Administration don’t count it towards the official fuel economy rating of a vehicle—meaning that carmakers get no credit for the boost in their CAFE ratings or on EPA window stickers. In other words, automakers have no incentive to add idle-stop.