Ride-sharing service Uber is taking on the challenges of operating driverless cars in San Francisco.

The service has added sensors to a few of its Volvo SUVs, enabling the vehicles to steer, accelerate, brake, and change lanes independently. As with Uber’s current test in Pittsburgh, Penn., each car is also equipped with an Uber employee as a fail-safe mechanism.

Uber car in San Francisco. Credit: Wikimedia CommonsUber car in San Francisco. Credit: Wikimedia CommonsSan Francisco streets have steep hills, bicyclists, iconic cable cars, and fog. Road repaving projects and lane changes add to the challenges facing human drivers. On a test drive given to an Associated Press reporter, Uber’s Volvo appeared to drive with more than necessary caution. The car idled in a traffic jam when an adjacent lane was clear and stopped in the middle of the street when it arrived at a restaurant.

A more significant challenge may come from California regulators. State law requires a test permit for self-driving prototype vehicles. The California Department of Motor Vehicles states that 20 companies have permits to test autonomous vehicles. The law defines autonomous as "without the active physical control or monitoring of a natural person."

Uber says that the test permit stipulation does not apply in its case bedcause the cars have a backup human driver. According to Anthony Levandowski, the leader of Uber's self-driving program, Uber's cars simply aren't advanced enough to drive themselves without human monitoring. "We're just not capable of doing that yet," he says.

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