Dear Tom and Ray:

About once a week, my boyfriend and I drive to a nearby city, about 150 miles round trip. When we go together, he drives my Toyota Yaris. He insists on shutting off the engine at EVERY stoplight, which he says improves gas mileage. I say it's dangerous; it's going to require a new starter sooner rather than later; and it upsets the drivers behind him as they wait for him to start up the car when the light turns green. On the weeks he doesn't drive the car, my mileage is about 41-42 miles per gallon, and on the weeks he does drive my car, the mileage is about 40-41 mpg. So, does shutting off the engine at stoplights improve gas mileage, and is it worth it?

-- Terry

TOM: Yes, and probably not. It certainly does save fuel when you turn off the engine at stoplights. That's why hybrids and newer cars are coming equipped with automatic "stop/start" features.

RAY: What does stop/start do? It turns off the engine when you stop at a light and turns it back on for you the moment you take your foot off the brake -- to save fuel.

TOM: So why isn't your mileage better when your boyfriend drives, then? Probably because he's got a lead foot the rest of the time. He likely accelerates harder than you do, and drives faster. And that's costing you more in mileage than he's saving by shutting down the engine at stoplights.

RAY: But there's no question that running the engine less uses less fuel. We used to hear people cite the myth that it takes more fuel to restart the car than it does to keep it running while you're waiting at a light. That's nonsense.

TOM: Engineers say stop/start technology can add about 5 percent to fuel economy, give or take, depending on how much stop-and-go driving is done.

RAY: But the cars that come equipped with stop/start features have something your Yaris doesn't have: heavy-duty starters that are designed to make hundreds of starts a day rather than the five or 10 starts your starter typically handles.

TOM: So I suspect, in your case, any money El Boyfriend saves on your fuel bill will eventually be eaten up by the cost of a new starter.

RAY: So here's our advice: When you're stopping for, say, two minutes or more, turn off the engine. That means you won't turn it off at every traffic light. But you will turn it off if one of you runs into a store, or when you get stuck while one of those six-mile-long freight trains full of bulgur wheat crosses the road in front of you.

TOM: And suggest to your boyfriend that he go a little lighter on the pedal. Going 65 instead of 70 or 75 will save quite a bit of fuel, as will accelerating gently away from stoplights.

RAY: Because if his real goal were to save fuel rather than annoy you and the people in cars behind him, the proof would be in the mileage numbers. And he's not making his case.