If we were talking about a car from the 1970s with a carburetor, there would be no fuel savings from shutting it off for 120 seconds. However, with today’s fuel injected cars, if you are going to leave it on for more than 60 seconds, you can save fuel by shutting it off. However, saving fuel shouldn’t be your only concern.
How much fuel will you save? I don’t know. Is it worth the extra wear and tear on your starter? Not in my opinion.
Think about carjacking. If you are first in line, and your car is approached by a carjacker, you have the option of running the red light, but only if your car is already running. Even if you are not first in line, having the car running might allow you to escape faster.
At truck driving school and the Motorcycle Safety Foundation’s Basic Rider’s Course, we were taught there is a remote chance that being in gear ready to go can give you a safety advantage. Even if the chances of you reaping any benefit are remote, I think it is still a good idea to leave it running.
If you are so obsessed about saving fuel, buy a moped.