I recently got a ride in an autonomous car. Very cool. I want one! Ever since October 2005, when a Stanford autonomous vehicle traversed 132 miles of desert terrain and won the $2 million Grand Challenge prize from the Defense Advanced Research Projects Agency, dreams of self-driving cars have become feverish.

Cars that drop you off at a restaurant and park themselves while you dine, restful commutes, hyperbolic Elon Musk predicting a million Tesla robo-taxis by 2020, 40,000 annual U.S. car crash fatalities dropping to almost...