SamTrans riders will soon have the luxury of knowing exactly when their bus will arrive without having to leave their computer or telephone, the agency said Thursday.

The San Mateo County Transit District, which operates SamTrans buses, has hired a private company to install global positioning system trackers inside its vehicles.

The GPS system will track the location of a bus as it travels along its route and give riders expected arrival and departure times on the Web, by phone and at major transportation hubs.

SamTrans spokeswoman Tasha Bartholomew said the $1.2 million project has already begun and should be completed by March 2010.

The arrival and departure times will be displayed on digital signs at several transit centers where SamTrans buses stop. They include the Daly City and Colma BART stations, the Millbrae BART-Caltrain center, plus the Redwood City and Palo Alto Caltrain hubs.

Riders can also access the information at 511.org and by calling 511.

With the information, passengers "won't have to wonder what time their bus will arrive anymore," Bartholomew said.

Riders can currently pick up paper schedules on SamTrans' Web site or at bus shelters and on board buses. Bus routes are on time at a rate of 85 percent.

Bartholomew said the agency has not necessarily received an outpouring of complaints from riders about a lack of real-time information, but past surveys of passengers indicated a desire for the service.

The company SamTrans hired to install the system, Dallas-based Affiliated Computer Services, said they will also equip some signs with audio components that will be compliant with the Americans with Disabilities Act.

Passengers of SamTrans' sister agency, Caltrain, have long yearned for real-time arrival information. Riders recently created a Twitter account that posts delays, and it now has 2,700 followers.

Bartholomew said Caltrain has plans to adopt a similar system to provide real-time arrival information to its passengers but is still working out the specifics. She said they hope to hire a vendor next year.

Several other Bay Area transit providers, such as San Francisco MUNI, AC Transit and the Genentech shuttle service, use a similar GPS system called NextBus, which also sends expected arrival times to the Web, cell phones and station display signs.

BART uses digital display signs that show expected arrival times at its stations.

Staff writer Mike Rosenberg covers San Mateo, Burlingame, Belmont and transportation issues. Reach him at 650-348-4324.