Sonoma-Marin Area Rail Transit officials Wednesday approved spending $6.6 million on an additional two-car train, improving service and raising the possibility of extending service to Airport Boulevard near Windsor.

With the extra cars, SMART officials said they will have enough trains to run passenger trains at 30-minute intervals to the Guerneville Road station in Santa Rosa, a station that will serve the most riders.

It also makes it possible to extend service farther north, to Airport Boulevard, if efforts to get more funds for track work are successful.

"We will be able to serve a tremendous number of riders, and that is important," said SMART Director Carol Russell, a Cloverdale councilwoman. "And it moves us a little bit farther north."

SMART is now rebuilding track and preparing to start service between Guerneville Road in Santa Rosa and downtown San Rafael in late 2015 or early 2016.

The commute rail agency is also constructing a maintenance and operations facility at Airport Boulevard near Windsor, which now will be accessed over the existing freight line.

There is a request before the Metropolitan Transportation Commission by state Sen. Noreen Evans, D-Santa Rosa, for $10 million to $15 million to rebuild the tracks from Guerneville Road to Airport Boulevard. MTC is expected to act on the request next month.

A station at Airport Boulevard would be a possibility if Evans' funding request is granted. It would provide service to the Charles M. Schulz-Sonoma County Airport and 6,000 workers who are employed in business parks in that area.

The $6.6 million will be drawn from federal funds earmarked for projects to reduce congestion and improve air quality in Sonoma County.

The Sonoma County Transportation Authority approved the funds for SMART, even though it consumes two-thirds of the $9.9 million allocated to Sonoma County for such projects.

Those funds would otherwise have been spent on pedestrian and bicycle safety projects, such as bike and pedestrian paths, bike lanes, and Safe Routes to Schools programs.

SMART needed to submit its order for the additional cars this month to Nippon Sharyo USA to ensure they will be constructed alongside the initial order. Otherwise, the agency could face a higher price and see delivery delayed until 2018.

SMART has a contract to build six two-car trains at a total cost of $40 million, with a delivery date for the prototype in October or November.

Kevin Koyasu, chief executive officer and president of Nippon Sharyo USA, said Wednesday it takes time to get the raw materials and components for the cars.

"They want those two cars together with the existing order," Koyasu said. "In that sense, we need the order as soon as possible. There are many, many long-lead items for those cars."

A prototype two-car train is now being built at the company's plant near Tokyo. Once completed, it will be tested, disassembled and shipped to the company's new production facility in Rochelle, Ill., for reassembly.