An MIT Technology Review report released last week said that the cars rely so much on maps and detailed data that they can't drive themselves around 99% of the USA. It's not a promising outlook for Google's new project.

Although the vehicles have already driven 700,000 miles safely, there is clearly still a lot of testing still to do. The cars have yet to drive in snowy conditions and it's not yet safe to drive in heavy rain either. Many of the problems arise from how good the detection technology is on the car and how well it is able to discriminate between different objects in view and between different weather conditions.

The vehicle's video cameras can detect the blink of a traffic light, but Google is still working on trying make sure the cameras aren't blinded by sunlight. There are also countless other unexpected obstacles the cars may face ? potholes, pedestrians running on roads, and parking.

Chris Urmson, director of the Google car team, acknowledges that the cars still had a lot of navigation problems. Illustrating the point, he told MIT Technology: "I could contruct a construction zone that could befuddle the car." The cars detect pedestrians as moving, column-shaped pixels. Urmson recognizes this could cause problems. For example, the cars wouldn't be able to spot a police officer by the side of the road waving for traffic to stop.