Why you won't be flying in a taxi anytime soon

THE idea is certainly audacious: Thwart traffic in congested cities by flying over it. Quick, quiet, clean, cheap.

This concept - which requires a new type of battery-powered vertical takeoff and landing vehicle (VTOL) - is Silicon Valley to its core in terms of self-liberation and greater efficiency. These electric vehicles would operate from "vertiports" situated around urban areas, predominantly atop buildings. And, at some point in the future, they would be unmanned.

"In the nerd hierarchy of needs, the flying car is up there with downloadable bra…