PETALUMA — The Federal Transit Administration has awarded $2.5 million to the Sonoma Marin Area Rail Transit Authority to fund planning work for an extension of the North Bay’s upcoming passenger rail line from downtown San Rafael to Larkspur, the rail agency announced.

The project was one of 41 awards nationally through the FTA’s competitive “Small Starts” and “New Starts” funding programs, and will allow SMART to complete environmental review and final engineering for the so-called Larkspur extension, said SMART General Manager Farhad Mansourian.

Though final costs will be more narrowly determined after the expected completion of the project development phase in late 2014, the agency currently estimates the Larkspur segment to cost around $35 million, Mr. Mansourian said.

“It’s a great start,” he said. “The FTA will review our work and consider providing funding for construction, as long as we have a 20 percent match,” he said.

The FTA evaluates projects applying for funding through the Small Starts program based on factors like cost effectiveness, land use and economic development. Local match funding is also a factor, though Mr. Mansourian said that the recent grant does not include a local match.

The San Rafael-to-Larkspur segment is considered a priority in completing the full length of the SMART passenger rail corridor, which is ultimately envisioned to stretch 70 miles from the Larkspur ferry to the city of Cloverdale in northern Sonoma County.

A diminished funding outlook following the recession spurred the decision to open the system with an initial, 38.5 mile operating segment between Santa Rosa in Sonoma County and San Rafael in Marin County. That segment is estimated to cost around $360 million, and to be operational in late 2014 or early 2015.

Recent work has include the installation of  mainline track for a 16.8-mile stretch between Guerneville Road in Santa Rosa and D Street in Petaluma, with 25 crossings rebuilt in that stretch, according to the most recent general manager report presented to the SMART board of directors. Four bridges have also been repaired, and construction will commence south of Petaluma in the coming months.

Construction is also under way for SMART's fleet of rail cars, which are being assembled in Rochelle, Illinois by Sumitomo Corp. of America/Nippon Sharyo. The Sonoma County Transportation Authority voted late last year to awards smart $6.6 million from a pool of federal allocated for congestion mitigation, allowing the agency to purchase a total of eight of the 158-seat vehicles. The first two-car set is expected for delivery in early 2014.

Current construction stems from the rail agency's first $103 million contract, and will stop just short of downtown San Rafael. A separate yet-to-be-awarded contract, anticipated at around $60 million to $80 million, will concern elements that include the final stretch into San Rafael.

While planners are expecting the majority of passenger trips to be between those two city centers, the authority’s board of directors has been searching for revenue to support the full system.

“When we started this process some said it couldn’t be done,” said SMART board chair Judy Arnold, in the announcement. “But here we are, and it’s because every board member representing every community is determined to complete the entire project to both the north and to the south in the shortest time possible. We’re set to work with our other regional partners to get this done.”