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.