Human drivers need to take control of Uber's self-driving cars about once per mile

"Human drivers were forced to take control of Uber's self-driving cars about once per mile driven in early March during testing in Arizona, according to an internal performance report obtained by BuzzFeed News. The report reveals for the first time how Uber’s self-driving car program is performing, using a key metric for evaluating progress toward fully autonomous vehicles.
Human drivers take manual control of autonomous vehicles during testing for a number of reasons — for example, to address a technical issue or avoid a traffic violation or collision. The self-driving car industry refers to such events as “disengagements,” though Uber uses the term “intervention” in the performance report reviewed by BuzzFeed News. During a series of autonomous tests the week of March 5, Uber saw disengagement rates greater than those publicly reported by some of its rivals in the self-driving car space.
When regulatory issues in December 2016 forced Uber to suspend a self-driving pilot program in San Francisco, the company sent some of its cars to Arizona. Since then, Uber has been testing its autonomous cars along two routes in the state. The first is a multi-lane street called Scottsdale Road — a straight, 24-mile stretch that runs through the city of the same name. According to Uber's performance report on tests for the week of March 5, the company's self-driving cars were able to travel an average of 0.67 miles on Scottsdale Road without human intervention and an average of 2 miles without a “bad experience" — Uber’s classification for incidents in which a car brakes too hard, jerks forcefully, or behaves in a way that might startle passengers. Uber described the overall passenger experience for this particular week as "not great," but noted improvement compared to the prior week's tests, which included one "harmful" incident — an event that might have caused human injury."

Source - Buzzfeed, 16th March 2017