The Juice

Vroom for Improvement

“Start-stop” technology shuts down car engines at stoplights to save gas. It’s coming to America.

New Chevy Malibu 2015
Gentlemen, start and stop your engines. Above, Chevrolet introduces its new Malibu and Hybrid Malibu models at the New York International Auto Show on April 1, 2015.

Photo by Kevin Hagen/Getty Images

When you drive a manual-shift car after a long period of driving only automatics, stalling is part of the territory. But the last few times I’ve done so, while renting cars in Europe, it seems that virtually every time I stopped for a light, the engine shut down, only to chug back to life when I re-engaged the gears. After enduring a series of withering looks from my passengers, I finally spoke up in my defense. Yes, some of the stalls could be chalked up to my incompetence. But most were due to the vehicle’s “start-stop” feature—a quietly revolutionary step toward energy efficiency that is becoming standard in Europe, and may come soon to a new American car near you.

Pessimists tend to lament that making significant improvements in energy efficiency and emissions will require unrealistic, impossibly expensive leaps in technology that will take decades to materialize. (Teslas for everyone!) But as readers of this column should know by now, affordable materials and incremental technological improvements can make environmental and economic sense right now—like Ford using lightweight aluminum instead of steel on its pickup trucks. (Thanks in large measure to such improvements, the typical U.S. car sold in July 2015 got 25.4 miles per gallon, 26 percent better than the October 2007 figure, according to Michael Sivak and Brandon Schoettle at the University of Michigan Transportation Research Institute.)

We can start adding start-stop technology to the mix. Modern start-stop was pioneered by German automakers several years ago, and was generally limited to manual-shift vehicles. But it has become standard in, for example, all BMW 1 and 3 Series models that have manual transmissions and four-cylinder engines, as well as in many other vehicles that ply the Autobahn. Today, about 60 percent of the new cars sold in Europe each year have start-stop. Now it’s coming to the U.S., and to automatic-transmission vehicles. And it could improve the typical car’s efficiency by about 5 percent, according to Craig Rigby, who holds the (somewhat unwieldy) title of advanced market and technology strategist for power solutions at Johnson Controls Power Solutions, a unit of Johnson Controls.

How? When they go into neutral, or brake to a full stop, the engines of cars equipped with start-stop switch off—only to start up again automatically when you step on the gas or release the clutch. Programming engines not to idle—and saving fuel in the process—may seem simple. But it’s not a no-brainer. “When that engine shuts off, all the electrical content—the radio, the blowers, the lights, whatever is consuming electricity—no longer has the alternator,” Rigby said. “So you need a battery that is different than the traditional starting battery.” Johnson Controls, one of the world’s leading providers of auto batteries, has been developing “absorbent glass mat,” or AGM, technology, a wrinkle that provides more rapid and consistent charging and discharging cycles.

Of course, a better battery isn’t the only challenge in making start-stop work. The power trains need to be tweaked. (Here’s a video showing how.) And there’s a consumer-experience barrier to overcome. Generations of drivers have become accustomed to the reassuring hum of idling engines, and must grow comfortable with the idea of the engine constantly switching on and off. But the logic of start-stop is inescapable, from both an engineering and a financial perspective.

The discomfort can be eased with cash. Johnson Controls estimates that drivers recoup the additional cost associated with the start-stop technology—about $250 to $300—within three years in the form of less money spent on gas. The investment then continues to pay an annual dividend of $100 in gas savings for the rest of the vehicle’s life (assuming gas prices stay constant). That’s an excellent return by any measure.

As is the case with many European trends (men wearing capri pants, mindless austerity), the domestic uptake of stop-start has been slow. Johnson Controls started U.S. production at a plant in Toledo, Ohio, in 2012. Johnson Controls has inked deals to supply start-stop to popular models like the Chevy Malibu and the Ford Fusion, as well as to the lower-testosterone version of the best-selling Ford F-150 pickup truck. Rigby estimates that market penetration is low, at about 5 percent. But with popular vehicles jumping on the bandwagon, he predicts substantial growth. “We see the market share of new vehicles going to about 40 percent by the end of the decade,” he said. In Europe we could see a day when 80 percent of new vehicles are equipped with start-stop. In anticipation of the domestic growth, Johnson Controls last week announced it is investing to expand the capacity of the Toledo plant that makes start-stop devices.

A 5 percent improvement in fuel efficiency may not sound like much. But it’s nothing to sneeze at, especially for automakers who are laboring to meet the Environmental Protection Agency’s tough fuel efficiency standards. And when money-saving technologies effectively pay for themselves, they gain scale very quickly—thus lowering the manufacturing costs and further boosting the return on investment. The logic of start-stop will become only more compelling as it becomes more popular.

There are a few other points to keep in mind about start-stop. First, these efforts represent important incremental advances in traditional lead-acid batteries at a time when moonshot efforts to supercharge the effectiveness of lithium-ion batteries have run up against the limits of chemistry and physics, as Steven LeVine documented in his fine book The Powerhouse. Second, while government funds have controversially been deployed to help startups and incumbents develop power supplies for new vehicles (Johnson Controls got a $299 million Department of Energy grant to work on lithium-ion batteries, and A123 Systems went down in flames after receiving government aid), start-stop is a market-driven, private-sector effort.

While the flurry of public- and private-sector efforts in recent years hasn’t led to a cheap, highly popular all-electric car, it has spurred a great deal of innovation that makes greater use of electricity in driving. Start-stop—and the hybrid, hybrid-lite, and plug-in hybrid systems that are being developed in parallel—won’t replace gasoline as a transportation fuel. But they will displace gasoline as a transportation fuel.

Finally, as Rigby argues, start-stop can be a starting point, not a stopping point. “We think there’s more you can do, even with 12-volt standard batteries,” he said. By pairing a small lithium-ion with the more powerful batteries that enable start-stop, vehicle-makers could roll out a series of fuel-saving features, like regenerative braking (which captures the energy from braking to recharge batteries), as well as engines that turn off when cars are rolling at very low speeds and stay off for slightly longer when cars start up again. Such efforts “could bump 5 percent savings up to 8 percent,” he said. “We think there’s room to extend the existing start-stop paradigm and get more.” In automotive efficiency, as in so many areas, evolution is the real revolution.