Frederic J. Brown/AFP/Getty Images A Chinese city that failed to attract people has become a sandbox for machines. Ordos, a coal-rich northern Chinese city that never took off after prices crashed in 2012, has attracted more than a dozen autonomous vehicle companies seeking risk-free testing environments. Its wide, well-paved roads and minimal traffic provide a real-world laboratory where self-driving vehicles can operate without endangering pedestrians or navigating complex traffic. Ordos’ tran...