The whole world has weighed in and explained why more starts and stops lead to excessive wear, but I’d like to take a moment and bring a little attention to the environmental damage that having to do a bunch of work to your car because you turn it off at every opportunity does.
Let’s say you need a new starter motor early. That’s copper, aluminum, iron, steel and a handful of rare earths for the solenoid. Melt em, smelt em, form and mold em, that’s more carbon from building the replacement part than you’d have kept out of the atmosphere by shutting off the car at stoplights.
The greenest car parts are the ones already in it.