As automakers stretch to improve fuel economy, consumers will face all sorts of new technology including one that will take some getting used to because it shuts the engine down at red-lights.

As many as 8 million vehicles sold in the United States will have the so-called "stop-start "technology by 2017, according to a study released by Lux Research, an independent research firm that monitors emerging technologies.

Stop-start systems are common in Europe, which has long been ahead of the U.S. on fuel efficiency, but so far it is in only a few vehicles in the U.S. Is it worth it? Start-stop can improve fuel economy by as much as 12 percent, according to AAA.

Here's how it works: Start-stop technology can power down a car's engine when it's idling or when the brakes are applied, such as at a red-light, and returns power in time for acceleration.

The technology itself is not new - some trucks have used it for two decades. But automakers have advanced it as they search for ways to comply with the 34.1 miles-per-gallon Corporate Average Fuel Economy standard that goes into effect in 2016.

"This technology is only going to gain momentum," said John Nielsen, AAA's Director of Automotive Engineering and Repair.

More than 40 percent of vehicles sold in Europe and Japan already use start-stop technology, according to AAA. In the U.S., hybrid cars offer stop-start, and in 2012, a few luxury automakers began offering it in conventional vehicles, notably the BMW 3-series. Kia has also rolling it into the Soul and Rio at the lower end of the price ladder.

While many automakers, such as BMW and Porsche, offer it as standard equipment, others, like Ford, are offering it as an add-on. The 2013 Ford Fusion, for example, will come with a start-stop option priced at $295.

Consumers can expect to save an average of $167 per year, the study says, based on 12,000 miles driven per year and $3.75 per gallon prices with an average of 20 mpgs.

Whether or not consumers accept the technology may be another matter. In some vehicles, the start-stop system operates so seamlessly, the driver may not notice it at all. In others, the lag between starting and stopping is more pronounced. AOL Autos has tested different systems, and has found, for example, that General Motors system, found on the Chevy Malibu Eco and Buick LaCrosse eAssist works almost invisibly, while the system on the BMW 3 Series was a little more pronounced and even rough.

The automakers, as well as dealers, are challenged to educate buyers about how it works. At first, it can be disconcerting, to feel the car's engine go off and then come back on at a red-light, especially for seniors who have been driving for many decades.

"There is no question that there are drivers and car buyers who are going to have to be walked through it - how it works and what it's on their car," Rebecca Lindland, chief of auto industry analysis at HIS Global Insight, said.