The Sonoma-Marin Area Rail Transit line cleared a major funding hurdle Wednesday, earning the approval of $20 million in regional transportation money — half the funds needed to extend commuter service to Larkspur.

The financial support, unanimously authorized by Metropolitan Transportation Commission, will go toward a 2.2-mile extension of SMART, from downtown San Rafael to the ferry terminal at Larkspur.

The other $20 million needed for the extension could come from a federal transportation grant that will be decided on later this year. That funding, tied to the federal stimulus, requires local matching funds, which the project now has with Wednesday’s MTC action.

“We’re all anxious to hear about the TIGER grant,” said Rohnert Park Councilman Jake Mackenzie, a SMART and MTC board member, referring to the federal Transportation Investment Generating Economic Recovery grant.

The MTC board approved moving $20 million in bridge toll money to SMART from a now-abandoned Greenbrae interchange project. The action affirmed a funding move endorsed by the agency’s Programming and Allocations Committee two weeks ago.

SMART officials applauded the final decision.

“They picked the right project,” said Farhad Mansourian, SMART general manager.

SMART officials have been working for three years to secure funding to extend the commuter line to its original southern terminus at Larkspur. The initial commuter line was scaled back to stop in downtown San Rafael in 2011 after agency officials said lagging sale tax revenue forced them to curtail the project.

Since then, amid a rebound in sales tax income, agency officials have sought out regional, state and federal sources to help fill their funding gap.

Mansourian said that he was in Washington, D.C. last week meeting with congressional representatives to gather support for SMART’s TIGER grant.

The Larkspur extension will give the commuter rail line bookends at major North Bay transportation hubs when the service launches. SMART officials have said the first trains will roll in late 2016. They are building the line in stages due to the funding shortfall.

The north end of the line was extended from Santa Rosa to Airport Boulevard after SMART received MTC funding in December. The Airport Boulevard area includes an expanding Charles M. Schulz-Sonoma County Airport, a widened Highway 101 and new interchange, and a business park with 5,000 jobs.

Voters in Sonoma and Marin counties approved the 70-mile Cloverdale-to-Larkspur rail and bike path system in 2008. The rail authority still lacks the funding to extend the line north of Airport Boulevard and to build much of the bike path.