[masraum]

Originally Posted by biosurfer1

A single car? Doesn't save much, but if hundreds of thousands of cars all had it, it would add up to something I'd guess.

4-9% savings over cars without it.

So, if everyone drove vehicles 15,000 miles a year and they all got 30 mpg over the course of that 15k miles, they'd use 500 gallons of gas. If they had a car with start stop, then they'd use 455-480 gallons of gas instead (depending upon whether they were in light or heavy traffic).That's probably 1.5-3.5 tanks of gas a year, which is not completely inconsequential. And that's assuming the average fuel economy is 30 which I suspect is way off.