A Skybridge or a Tunnel?

There are other things that don't quite look exactly like a sky bridge, but they clearly serve the same function. Though to some degree, i think what we're thinking of as a skybridge really has more to do with external appearance and how high is itd than function. For instance, we mentioned cold cities, or of cities that have cold winters. A the chicago ped way is a strong example of a system like this. Parts of it are elevated, but then also parts of it completely underground.