Sonoma County transportation planners Monday approved an additional $3 million for the Sonoma-Marin Area Rail Transit district, part of a regional plan meant to bridge the commute rail line's last financial gap.

"Public transportation like this is long overdue," said Healdsburg Councilman Tom Chambers, a member of the Sonoma County Transportation Authority.

SMART estimates that it is $21 million short of what is needed to open its initial operating line from Railroad Square in Santa Rosa to downtown San Rafael in the fall of 2014. Ultimately, service is to run from Larkspur to Cloverdale.

The proposal passed the SCTA on a 11-0 vote.

It requires that SCTA contribute $3 million; the Transportation Authority of Marin, $8 million; and the Metropolitan Transportation Commission, $10 million.

The plan was drafted by the three agencies but Marin and MTC have not given final approval.

Marin would put in the largest share of the North Bay funding because SCTA already is giving SMART $11 million from its quarter-cent sales tax and Sonoma is bearing the brunt of the cuts that SMART has made to get an initial project going.

"In transportation we try to leverage funding and the big one here is the $10 million from MTC," said Windsor Councilman Sam Salmon, also an SCTA member.

SCTA Executive Director Suzanne Smith said the $3 million is expected to come the 2012 allocation of federal transportation enhancement funds, which are restricted to such projects as bike and pedestrian paths, but can't be used to run trains or for highway projects.

SMART would be restricted to spending the money on its pedestrian-bicycle multiuse path, but not on administration or train operating expenses, Smith said.

Under the proposal total contributions are be capped at $21 million. If bids coming in under estimates or SMART can sell more construction bonds than anticipated, the savings will be returned to the three agencies.

The construction of the Santa Rosa-San Rafael line is estimated to cost $470 million.

SMART directors have made $88 million in cost-saving measures, but remain $21 million short. They are expected on June 15, to seek bids for reconstruction of segment of line between Santa Rosa and San Rafael.

The bids are expected to be returned in mid July, when SMART is also expected to have a clearer idea of how much money it can raise by selling construction bonds.

SMART intends to eventually extend service south to Larkspur and north to Cloverdale, as originally planned.

The initial segment has stations at Railroad Square in Santa Rosa, and in Rohnert Park, Cotati and downtown Petaluma in Sonoma County. In Marin County, stations would be at Novato, Marin Civic Center and downtown San Rafael.

"SMART is the largest infrastructure project in 50 years. It is an exciting project. It will happen. It will create a ton of jobs," said Sonoma County Supervisor Shirlee Zane, who also sits on the SCTA and SMART boards. "This is a great opportunity for us to move ahead."