Google says its self-driving cars already can navigate freeways comfortably, albeit with a driver ready to take control. But city driving has been a far greater challenge for the cars' computers.
In a blog entry posted Monday, the project's leader said test cars now can handle thousands of urban situations that would have stumped them a year or two ago.
"We're growing more optimistic that we're heading toward an achievable goal - a vehicle that operates fully without human intervention," project director Chris Urmson wrote.
"We've improved our software so it can detect hundreds of distinct objects simultaneously - pedestrians, buses, a stop sign held up by a crossing guard, or a cyclist making gestures that indicate a possible turn. A self-driving vehicle can pay attention to all of these things in a way that a human physically can't - and it never gets tired or distracted."
Urmson says that as it turns out, what looks chaotic and random on a city street to the human eye is actually fairly predictable to a computer. Google has built software models of what to expect, from the likely (a car stopping at a red light) to the unlikely (blowing through it). However, Google's engineers still have lots of problems to solve, including teaching the car to drive more streets in Mountain View before we tackle another town.
Google says its vehicles have now logged nearly 700,000 autonomous miles.
The company has said its goal is to get the technology to the public by 2017. In initial iterations, human drivers would be expected to take control if the computer fails. The promise is that, eventually, there would be no need for a driver. Passengers could read, daydream, even sleep - or work - while the car drives.
Traditional automakers also are developing driverless cars. Renault-Nissan CEO Carlos Ghosn said he hopes to deliver a model to the public by 2020.