A quarter of all miles driven in the U.S. could be in shared, self-driving electric cars by the end of the next decade, setting off a seismic shift that will upend the auto industry, according to a study on the rise of the autonomous age. A convergence of three trends -- ride sharing, autonomous driving and vehicle electrification -- will drive the shift, the Boston Consulting Group said in a study released Monday. The change will be most profound in cities with more than 1 million people, where consumers will find it more economically advantageous to exit their personal vehicles and start hailing robot taxis.