AAA: Stop-start engines save gas, cut emissions

Automatic stop-start systems in automobiles provide a 5% to 7% improvement in fuel economy and a similar reduction in carbon-dioxide emissions, according to new research from auto club AAA.

Based on AAA's research, which was conducted with the Auto Club of Southern California's Automotive Research Center, motorists could save up to $179 in annual fuel costs. That's based on driving 15,000 miles a year in a vehicle that averages 20 miles per gallon with fuel prices at $3.65 a gallon.

"It's not too intrusive," John Nielsen, AAA's managing director of engineering, says of the technology, which shuts the engine off when drivers come to a complete stop, such as at traffic lights or stop signs. While the engine is shut off, systems and gadgets run on battery power. The engine starts again when the driver releases the brake or clutch.

"The biggest thing is adjusting to having the car turn off," Nielsen says. "When you pull up and the car quits running, you're like, wow, that's unusual. But it's pretty much seamless."

Many drivers of gasoline and diesel vehicles are probably unfamiliar with the technology. Automatic stop-start systems were available on only about 500,000 of the vehicles sold in the USA in 2013, AAA says, citing Navigant Research.

But that number could surpass 7 million by 2022 as automakers look for new fuel-saving technologies to help them meet federal Corporate Average Fuel Economy (CAFE) standards of 54.5 miles per gallon by 2025. For the month of June, the window-sticker value of average fuel economy for new vehicles sold in the USA was 25.5 mpg, according to researchers at the University of Michigan's Transportation Research Institute.

"You're going to see a lot more of it," Nielsen says. "This is one of the cheapest ways to increase your CAFE (efficiency)."

Some consumers already are embracing the technology. According to General Motors, 97% of consumers who bought a 2014 or 2015 Chevrolet Malibuopted for the 2.5-liter, 4-cylinder base engine equipped with standard stop-start technology.

Ford announced this week the debut of an engine with stop-start technology in its 2015 model F-150 pickup trucks. The system disengages when the vehicle is towing or in four-wheel drive mode, Ford says.

Greg Brannon, AAA's director of engineering, says it costs consumers around $300 to buy automobiles equipped with stop-start systems. "This is an excellent way for a consumer who isn't ready to switch to an electric vehicle or hybrid to go green," he says. "With very little adjustment, consumers can go green."

AAA tested a 2013 Ford Fusion, a 2014 Mercedes Benz CLS 550 and a 2013 Chevrolet Malibu. The vehicles were put through the Environmental Protection Agency's "urban" cycle, which simulates a commuting trip of 11.04 miles at an average speed of 21.2 miles per hour. They were "driven" on a dynamometer in a climate-controlled room, with the stop-start system engaged and with it disengaged.

The stop-start systems also reduced greenhouse-gas emissions by 5% to 7%, AAA says.

The fuel economy and emissions reductions apply only to urban driving, Nielsen says. "This really helps you around town, but it doesn't do much for you on the highway," he says.

The research is part of AAA's ongoing "Driving Fuel Efficiency" series, which included an electric vehicle climate study that found the range of electric vehicles can be reduced by up to 57% in extreme temperatures.