Something nobody ever considers is the group impact of lots of people doing this.
Right now, with cars which don’t shut off at idle, we waste about 50% of each stoplight cycle because of people being slow to get moving. The light turns … Driver 1 wakes up & slowly pushes on the gas … finally gets moving … driver two notices driver 1 has moved … he wakes up … he slowly presses on the gas …
It’s not uncommon to have 3 car-lengths between cars by the time they get to the far side of the intersection. So a light cycle that could pass 15 cars if everybody paid attention & accelerated smartly only passes 10 with the typical inattentive unthinking drivers we have today.
Now fast forward to the near future where many people are trying to be gas-conscious, many cars have an auto-shut-off-at-idle feature, and many drivers without the auto feature are doing it themsleves.
Each car saves gas, yet now the light cycle only passes 5 cars. So traffic is much worse, and everybody ends up wasting more gas because of the extra waiting for others than they save by their own “good” habits. And for most of us, the cost in time is far higher than the cost in gas.
Bottom line: Collective advice needs to be designed with collective behavior in mind. Advice which amounts to: “you should do this while everybody else is still doing that” fails as soon as very many people know about it, usually with side effects worse than the status quo ante.