One crazy thing about Japan, specifically Tokyo, is you never know what is below your feet. Take this passageway for example that runs underneath a busy street above it. I would venture a majority of roads around stations actually sit on to of passage ways and parking lots like this one. You never really know until you go downstairs.
I once had to park in an underground below a major artery that also had the elevated expressway on top of it. That was pretty interesting. When there is little space you build up and down I guess.