As Sonoma County's transportation landscape undergoes major changes, regional commuter bus operator Golden Gate Transit could be adding service for the first time in a decade.

The agency, which buses nearly half a million passengers a year from Sonoma County to Marin County and San Francisco, launched its first long-term planning process last week since the agency reduced bus service by 22 percent in 2003.

As part of the process, the agency is considering providing new or additional service to growing Sonoma County communities including Windsor and east Santa Rosa, said Ron Downing, Golden Gate Transit director of planning.

Ridership on the North Bay bus network has grown 3 percent each month in the past year. To capitalize on this growth, the transit district board will consider reconfiguring routes in Sonoma County to add more express service and potentially add bus service to Rincon Valley, Downing said.

"We're looking at making better use of what have rather than spending more money," he said. "It would cost a lot to put in a new route. We need to do more survey work."

In 2010, the agency eliminated or reduced four bus routes from Santa Rosa that served San Francisco or San Rafael, citing low ridership. Earlier that decade, Golden Gate Transit eliminated routes or trips several years in a row as the agency grappled with deficits.

The commuter bus network is gaining popularity in Sonoma County, Downing said. The agency has 15 weekday buses on the popular 101 route from Sonoma County to San Francisco's Financial District and Mission District. The buses originate in Santa Rosa with stops in Rohnert Park, Cotati, Petaluma, Novato and San Rafael.

The 57-seat buses run about half full, Downing said.

"Sonoma County is growing, but we have capacity on buses," he said. "We do have some seats available."

The board last week adopted a "strategic vision," and more specific plans are expected by spring, Downing said.

A major short-term project is readying a new bus yard at Fourth and Perry streets in San Francisco, which will deliver commuters to within three blocks of the end of the Caltrain line that serves the San Francisco Peninsula and Silicon Valley.

In the long term, Golden Gate Transit will be monitoring changes in the Sonoma County transportation network to see where commuter bus service fits, Downing said.

This includes working with the Sonoma-Marin Area Rail Transit district to create a "comprehensive transit network" that gets commuters out of their cars.

SMART trains are expected to run from north of Santa Rosa to San Rafael starting in late 2016.

The widening of Highway 101 also could boost the bus service, Downing said.

Buses will be able to take advantage of added high-occupancy vehicle lanes to get passengers past stagnant freeway traffic.

"We're hoping there will be some time savings with HOV lanes," Downing said. "We are hoping that we can see some running speed improvements."

You can reach Staff Writer Matt Brown at 521-5206 or matt.brown@pressdemocrat.com.