I should add that driving in dense urban areas means fewer miles, lower speed, and more frequent stopping and starting, so the savings in a smaller city would be smaller.
More frequent stopping and starting would actually be an advantage here. If you're driving a long route between bus stops and don't brake frequently, you're only taking energy out of the flywheel when you initially get up to speed, and you're only putting it back in when you stop at the end. Regenerative braking is a lot more valuable in stop and go traffic. Every time you accelerate out of a stop light you're burning less fuel.
Right, that's why I said in a smaller city (less dense, more long stretches of roads) there would be fewer savings from a flywheel or hybrid.
So you did, I must have misread your comment before.
Smaller city means less dense. I missed that at first.