From a brief scan of SkyTran on Wikipedia...neat idea, completely unworkable. (At least not in any significant US metro area).
How is that system going to handle several hundred (possibly several thousand) people waiting in line to hop on for their morning/evening commute home? How long are people going to be stuck waiting in line for their turn during these rushes? Add to this the fact that large metro areas that two of our largest metro areas (New York and Chicago) have some real nasty winters. So factor in the cost of very large enclosed & heated areas for people to stand around and wait their turn to hop into one of these things (and the cost of acquiring the real estate to build said areas).
The US has a larrrrge amount of real estate. A whole lot of people commute in from suburbs to the major metro areas. Thus, for this to even make a dent in traffic, you'd have to have just an absurd amount of connection points throughout every suburb and into the city, which would also create several very backed up 'exit points' when you have a small army of corporate types heading to the office.
Now, if we're talking about just doing it within a large city itself, okay. You still need to address the sheer mass of people trying to get on and off at a single point (can you imagine how long it would take to board this thing after, say, a sporting event?), and how one can cram this thing into densely built cities. Much easier said than done.
Unless I'm just not seeing it, this would NEVER be efficient in a densely populated area, especially during rush hour times. A combo of high speed mass transit and self driving cars is really the only feasible Solution To Transit In The Future (tm)....unless/until we get our Star Trek Transporters.