The human factor of Google's driverless cars

Google's futuristic autonomous cars have required stand-by drivers to take over the controls in 11 instances to avoid crashes, the US company has said. Nevertheless, it spoke of encouraging results given that the firm's test fleet was logging tens of thousands of miles each month.

Google's conceded that self-driving technology had yet to reach the goal of not needing someone behind the wheel.

The company said there were another 272 cases in which failures of the cars' software or onboard sensors forced the stand-by driver to grab the wheel.

Detected problems included issues with the autonomous cars seeing traffic lights, yielding to pedestrians or committing traffic violations. In a number of cases, human intervention was required because other drivers were reckless.

Not quite there

In the current phase of testing, Google cars usually stay below 35 mph (56 kmh), although they are also tested on highways.

"We're seeing a lot of improvement," said Chris Urmson, head of Google's self-driving car project. "But it's not quite ready yet and that's exactly why we test our vehicles with a steering wheel and pedals."

Autonomous driving expert Bryant Walker Smith from the University of South Carolina said the rate of potential collisions was "not terribly high, but certainly not trivial."

There'll be new challenges ahead when the company starts testing the cars in more demanding environments, also allowing them to move at a much faster pace and in adverse weather conditions.

hg/cjc (AP, dpa)