SAN FRANCISCO Mon Apr 28, 2014 1:45pm EDT 

(Reuters) - Google Inc said it has begun testing its self-driving cars on city streets, a crucial new phase in its quest to eventually make the technology a standard feature in automobiles.

After several years of testing self-driving cars on freeways, where driving conditions are more predictable, Google in the past year shifted its focus to city street driving, the company said in a post on its official blog on Monday.

Google said it has driven thousands of miles on the streets of Mountain View, California, a small suburban community where the company maintains its headquarters roughly 35 miles South of San Francisco. Google's driverless cars rely on video cameras, radar sensors, lasers and a database of information collected from manually driven cars to help navigation, according to the company.

"A mile of city driving is much more complex than a mile of freeway driving, with hundreds of different objects moving according to different rules of the road in a small area," wrote Chris Urmson, the director of Google's self-driving car project in the blog post on Monday.

"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," Urmson said.

Google is one of several companies, including automakers Nissan Motor Co, Volkswagen AG's Audi and Toyota Motor Corp, testing self-driving car technology. Both Nissan and Mercedes-Benz parent Daimler AG say they plan to start selling self-driving cars by 2020.

It is unclear whether Google, the world's No.1 Internet search engine, intends to partner with other companies or develop its own self-driving vehicles.

The company posted a video that depicted how a self-driving car views the world as it navigates. here

Google's test cars have logged more than 700,000 miles in self-driving mode since 2009. Google said its cars have not caused any accidents while operating in self-drive mode.

Google said it still has many "problems to solve," including teaching the car to drive more streets in Mountain View, before testing on the streets of another town.

(Reporting by Alexei Oreskovic; editing by Andrew Hay)