Most major cities are decades, if not centuries, old. Their infrastructure was based on a small population and estimates of where it could grow to. Some have already outgrown those estimates while others are coming in to their own. What cities prepared the best for a hugely populous future?
Top Gear showed that Burma might have the right with Naypyidaw, their new seat of government. It isn't crowded at all yet, so the wide and empty roads look ridiculous. But as the population explodes, they won't look so silly.
What other cities have infrastructure that was forward thinking and ready for the next billion people on the planet?