EVERY day for two months, Sebastian Thrun drove Stanley, his customised Volkswagen SUV, through the Sonoran desert, Arizona, burning down dusty roads and avoiding boulders and potholes. With every twist and turn, Stanley's on-board computers watched and learned. Then one day Thrun did something most people would find rather scary. He turned over control of the car to the computers. "I learned to trust it, and pretty soon the car was driving me," says Thrun.

Thrun, director of the artificial intelligence lab at Stanford University, California, was preparing Stanley for the ultimate race for robot cars. On 8 October Stanley took part in the Grand Challenge, sponsored by the Pentagon's Defense Advanced Research Projects Agency (DARPA), in which 23 self-guiding vehicles were pitted against one another to navigate a 212-kilometre course over dirt roads, around narrow mountain tracks and through tunnels to the finish line just outside Primm, Nevada.

Stanley ...