What interests me more, is how does the rest of the car behave once the engine is off?
Some of the systems, like cooling, are usually driven by the serpentine belt that in turn is driven by the engine. Once the engine is stopped, the belt stops, which means that those critical systems need to be driven by something else, other than the engine. First thing that comes to mind is an electric motor of some sort, most likely powered by the battery.
What happens if the engine is stopped, the car thinks you're waiting for the green light, but you actually just stepped outside to get some bagels for your family that waits in the car. Unfortunately it's a busy day at the bagel place and it takes you longer to get back to the car than expected. All this time your car is running the AC, engine cooling and whatnots, draining the batteries. Does the car shut down completely before the battery drains to the point where it doesn't have enough energy to restart the car, or does it restart the car to recharge the battery?