Would it be possible? -- A fifth mode of transport... There has been a lot of talk about developing a fifth mode of transport, and most of these involve some sort of tube such as the hyperloop idea from Elon Musk. Now I don't know why but I have the idea stuck in my head that the fifth mode of transport should not be close to the ground, but should be around 400-500m above ground, underneath airplanes but above everything else. From here I began thinking of a method of doing this, for instance would it be possible/viable to have some sort of transport similar to a harrier jumpjet that could "hover" as such and be boarded that high up? I then began to consider the fact that the cost efficiency of this would not be worth even considering, which is when ion drives came to mind. Now i'm no expert on this sort of thing whatsoever and i'm sure a lot of corrections/flaws will be pointed out in my idea, but the cheapness of using an ion drive (after the initial investment) appears to be relatively good. Again i'm not even sure if the use of ion drives in anywhere other than space is possible. To actually operate this mode of transport I was picturing that you could take the current gps systems and (once improved) simply raise it up 400-500m and create a new virtual transport grid. So yes they would be automatic. Essentially, in a nut shell, it would be a taxi service. This may well be laughed at and just remain a fantasy inside my own head, but I thought it might be worth to get a few opinions on the matter before I carried on thinking about it any further. In addition to this I am aware I have not thought about every single aspect of this, nor am I giving any validity to this idea.