Commuters making the daily slog from homes in Sonoma County to jobs in downtown San Francisco will soon endure one fewer transfer.

Sonoma-Marin Area Rail Transit — the charming but money-losing SMART train that serves two North Bay counties — will open its long-awaited Larkspur Station on Dec. 14, providing a crucial link to the ferry terminal.

“We’ve been talking about connecting Sonoma and Marin to San Francisco since the 1980s,” SMART General Manager Farhad Mansourian said in a phone interview Thursday, as he stood on a wind-lashed stretch of Sir Francis Drake Boulevard, admiring the new station.

Though it was part of the original plan that voters approved in 2008, the Larkspur stop got waylaid by SMART’s economic troubles. The $600 million rail line is struggling with mounting costs and a dearth of sales tax revenue. Its fare box recovery rate — the amount of fare revenue divided by the operating costs — is 10%, far lower than BART’s rate of 73%.

Last month the Board of Directors approved a quarter-cent sales tax extension for the March 2020 ballot in Marin and Sonoma counties. If voters don’t approve the measure, SMART could deplete its funding reserves by 2024.

But on Thursday, Mansourian seemed optimistic. The rail-to-ferry connection isn’t perfect — the new train station is a seven- or eight-minute walk from the ferry, across a busy street. Still, it’s an improvement for commuters who currently get off the train in San Rafael to catch a bus across the Golden Gate Bridge.

SMART will celebrate the opening with a ceremony on Dec. 13.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan