Google has added the nation's biggest public transportation system to its popular mapping service, showing travelers how to navigate New York City's mass transit system.

As of Tuesday, people looking up locations in the city get public transit options alongside driving directions. The feature includes information about subways, buses and commuter railroads.

New York's Metropolitan Transportation Authority and some other organizations already provide transit trip planners, but Google executives note that their version is integrated with other search features, such as street views and restaurant reviews.

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Google, the world's largest search engine, offers transit information in about 70 other cities worldwide, including Chicago and Tokyo.

The Mountain View, Calif.-based company worked for two years to add 40,000 subway stations, bus stops and other points on the New York metropolitan area's mass transportation network, executives said.

"It's just a huge volume of routes and data," co-founder Sergey Brin said.

The MTA provided data but no money for the effort, which comes as the agency projects a $900 million deficit next year.

Transit officials are hoping to plug the gap by raising fares and tolls, but also say they may have to cut service.

More than 8.5 million riders use the MTA's subway, bus and rail lines on an average weekday.