Driving the micro-hybrid Porsche Cayenne with Stop-Start technology

As the name suggests, Stop-Start technology is a system that stops the engine to save fuel while you're idling, then restarts it the moment you let your foot off the brake. In Europe, "S-S" technology has been used on some Volkswagen models since the mid-1980s, and it has since become a key gas-saving system on modern hybrids. In fact, some companies refer to this as a "micro-hybrid," but really, a "hybrid" combines two different things, such as an electric motor and gasoline engine.

I have been experiencing S-S in action with our 2011 Porsche Cayenne V6, a vehicle that capably combines both sport and utility. The other day while driving my son to school, the Cayenne's engine stopped repeatedly while we crawled through the drop-off line. Jordan said, "Hey, is this a hybrid?" I explained it wasn't, but his question got me thinking.

I've gotten so used to auto-shut off with hybrids, that I just didn't consider it as being usual anymore. But in the Cayenne, the engine crank-up is indeed pretty noticeable. It's also a little unpredictable. Sometimes when I pull up to a stop sign, the engine shuts down promptly, while other times it lingers at idle awhile before deciding to take a break. And, if you're in a hurry for a quick take off, you lose a precious half a second for the crank-up. Around the water-cooler at the test track, some of the engineers are joking about, "Did you stall the Cayenne, yet?"

Some experts in the field assert that the Stop-Start feature is good for a 5- to 10-percent reduction in fuel consumption, and consequently CO2 emissions, in lab conditions. More real-life assessments peg the benefits as being closer to a 2- to 4-percent reduction. Stop-Start is but one of many measures automakers now have in their toolbox, such as low-rolling-resistance tires and electrically-assisted power steering, that can result in single-digit improvements in fuel economy. Taken alone these gains don't sound like much, but cumulatively, multiplied by millions of cars, the savings can really add up.

Proponents argue that S-S technology is the cheapest way to eke out a few incremental fuel-use reductions on the way to lowering emissions and meeting the stricter new-car fuel-economy requirements of 34 mpg by 2016. This technology works with the regular 12-volt lead-acid battery found in every current car, though it favors advanced lead-acid batteries that were prominent at the battery show I recently attended. And, unlike resorting to a real hybrid, S-S doesn't require expensive lithium-ion batteries or a traditional hybrid powertrain.

So as long as S-S doesn't create some new inconvenience, and keeps the air-conditioning, audio system, and wipers running even when the engine isn't, then I see no problem with it. The Cayenne imposes none of those burdens. All systems are go, even when you're stopped. And if it becomes annoying, the Cayenne has a switch on the center console to turn the system off. But if you hit that switch, you don't get the big green cookie.

See our guide to fuel economy for advice on saving gasoline. Learn about future technologies in our guide to alternative fuels.

 —Gabe Shenhar