SAN FRANCISCO -- Google is set to expand a San Francisco carpooling program that could morph into a showdown with its one-time ally, the popular ride-hailing service Uber.

The plans will build upon a test service that Google's navigation app Waze launched three months ago in the San Francisco Bay Area.

The program allows anyone using the Waze app to offer a ride to a limited pool of people trying to get to work or home.

Now, only people working at six companies, including Google, Wal-Mart Stores and Adobe Systems, can request rides. Waze says anyone with its app will be able to request a ride within the next few months.

Riders reimburse the drivers in the program for gas and wear on their vehicles.

Google was an early investor in Uber.