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You may be thinking of something very much like Personal Rapid Transit: http://en.wikipedia.org/wiki/Personal_rapid_transit

My favorite design of PRT was always SkyTran, featured in a Popular Science or Popular Mechanics magazine years ago: http://www.skytran.net/phpsite/home/Home%20Intro.php

Real world engineering issues aside, my gut feeling was that a suspended/hanging pod would offer more stability and ability to accelerate than a traditional pod resting on top of tracks. If the pod could swing back and forth, acceleration and deceleration would push riders down into their seats rather than back or forward toward the windshield.

The Big Bad Wolf and Batman roller coasters come to mind. :)