I have just come across this piece of design genius on the interweb. It's the vision of  Shenzen Huashi; a monorail system to make use of the space ABOVE travelling cars. Apparently this is in production already and building will start at the end of the year.

This is unbeatably cool whichever way you look at it and really does mark the start of 3 dimensional travel possibilities - like those that were previously only seen in sic fi.