The Sonoma-Marin passenger rail agency is planning to build a future station at Airport Boulevard, where riders would be just a shuttle ride away from the Sonoma County airport.

The station would become part of the Sonoma-Marin Area Rail Transit District's construction of an operations and maintenance facility on 6.6 acres that SMART is buying from the Sonoma County Water Agency.

SMART officials said the airport station would be in addition to the 14 that are already promised.

"It is set up for the future, but I suggest it won't happen before the Windsor station is built and some other things in the 72-mile plan," said SMART Chairwoman Valerie Brown. "It will be a board decision. There are a lot of components that will not make it the speediest process, but it is there, it is recognized."

County Supervisor Mike McGuire, whose district encompasses the airport, said it will be an important transportation link to the Charles M. Schultz-Sonoma County Airport.

An Airport Boulevard station was not in SMART's initial plans, which were put together before the Sonoma County airport had Alaska Air passenger service.

"SMART is absolutely right to ensure the train will serve Windsor first, that has always been the plan," McGuire said. "But it is clear via the designation of a new station that this is vitally important to SMART and the county of Sonoma and the North Bay in general."

The district is buying the site on the southwest corner of Airport Boulevard and the railroad tracks from the Water Agency for $2.7 million.

The facility is expected to cost $15 million and is part of the overall $360 million budget for the Santa Rosa-San Rafael service.

It will be where cars are inspected daily, repaired and cleaned and where dispatchers will manage both SMART's passenger trains and the Northwestern Pacific Railroad Co. freight trains.

When service begins in late 2015 or early 2016, there would be about 100 workers at the facility.

"When the board wishes to activate that plan, we will work with the county for a shuttle service," said SMART General Manager Farhad Mansourian. "This makes a lot of sense."

The purchase was announced Thursday, a week before work is scheduled to begin on SMART's initial line, from Guerneville Road in Santa Rosa to the Marin County Civic Center, at a cost of $103 million.

An additional contract will provide for an extension from the Civic Center to downtown San Rafael.

The initial operating line would be 38.5 miles, extended to Cloverdale and to Larkspur as future funding becomes available.

The maintenance facility would be 4.5 miles north of Guerneville Road, the northern end of the initial line and 3 miles from where a station would be located in Windsor.

The track between Guerneville Road and Airport Boulevard is sufficient to run the trains at slow speeds, Mansourian said. Rebuilding it would cost $10 million and is not in the current construction budget.