Of course, anyone can turn the engine off at a stop light. Lead acid car batteries aren't ideal for this, because every time you draw a lot of current from them, you create some sediment. Repeated start-stop cycles, a short time apart, means you're running lots of current through the battery often. So it tends to reduce their lifetime. (That's why lead acid batteries meant for use in boats have very deep cases.)
And the auto-start feature is nice to have too, in cars set up for this by design.
Buses don't use the battery for starting, but rather compressed air. At least, most buses.
My bet is that city driving fuel economy goes up by a good margin with this technique. It avoids all those 0 mpg periods while you're waiting for the light to turn green. Of course, in cold winter nights, or worse, hot, muggy summer days, doesn't work too well, eh?
I suspect that the real advantage of a microhybrid is that it turns the engine off and on with no driver intervention so it is likely to happen more often and may be useed for shorter intervals where a human might not think to do it. There's a stop sign in my way to work where there is often a significant wait but I would be reluctant to turn the engine off because of having to get going quickly when its time to go.
Regenitrave braking would be a plus and could be the next step in such a car.
@selinz, that's a great example. (Japanese bus drivers shutting off the engine at every light) I am not sure, either, if how much of an advantage a microhybrid can offer...but it's itneresting to find that out.
The company ran before it could walk steadily because hype-investors over-reacted and gave them lots of money. So a better name would be Z321 to remind themselves of the big mistake they made: not executing in a 1,2,3 fashion.
When i found myself in Japan for repeated and extended periods in the 2004 timeframe, the bus driver that transported us from the train to the company shut off the engine at every light. At the time, it seemed absurd. Now I find myself uncomfortable not doing it (in my wife's non-hybid vehicle). It's unclear to me how much of an advantage a microhybrid is over using the vehicles lead-acid battery and a slightly beefed up starter unless there is some regenerative braking.