Why Auto Stop/Start is Stalled in America

Published: 29-Dec-2009

Just about every hybrid on the road today incorporates some version of a Stop/Start feature, which turns off the engine when the vehicle is stopped and restarts it when the driver steps on the gas -- a feature that adds to overall fuel economy. Why don't we see this fuel-saving trick on non-hybrid cars? According to Mazda, it's because the EPA test mitigates the advantage.

"In Japan, we're seeing anywhere from 7 to 9 percent fuel economy gains from it," Mazda's head of product development in the U.S., Robert Davis, told Automotive News. "That's a jump from 33 to 37 miles per gallon in a metro environment."

So why don't we get it? According to Davis, the EPA's city-mode test cycle includes only one complete stop. Because the car stops only once, the Stop/Start feature is only active for a few moments and as a result, it only improves fuel-economy on the test cycle by 0.1 to 0.2 mpg, rather than the nearly double-digit percentage gains that can be had in normal city driving when the engine would spend more time stopped.

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