[Tom_G35C]

I also heard that the break-even for gas savings is that you should shut off the car if you idle for 30 sec or more. I tried it at major traffic lights and my city gas mileage improved by 0.4 mpg (from 16.3 to 16.7mpg).

It was not too hard to shut it off and restart when I saw the traffic light start to change, but I had to keep watching the light. Also, the A/C and turn signals didn't work when I turned it off.

In Europe it is the law to shut off your engine when you are stopped a while at a traffic light. It's the law for pollution control.

So if it improved MPG by 0.4 in city driving, it saved me about 0.5 gal of gas per fillup, or $2. I'm not sure that it's worth the inconvenience except on principle to save gas.