The only public bus route between Napa and Sonoma will no longer operate starting Saturday, following a decision made three months ago by Napa Valley transit officials to cancel the service because of low ridership.

Vine Transit’s Route 25 bus, which links the Soscal Gateway Transit Center in Napa to Sonoma Plaza, will cease service after Friday, the Napa Valley Transportation Authority said in a news release. The Napa transit agency’s Board of Directors decided Sept. 20 to discontinue the route, which often served less than 1,000 riders a month in recent years, according to an authority staff report.

In its statement Friday reminding the public of the route’s impending closure, the authority said it “continues to explore” transit options among Napa, Marin and Sonoma counties.

“The agency is committed to working with the Metropolitan Transportation Commission and the other three North Bay Counties in order to craft a sustainable transit plan in the North Bay’s most congested corridors,” the statement said.

Route 25 is the North Bay’s sole east-west bus connection, according to a September report from authority staff who said they don’t plan to entirely abandon the idea of linking the three counties via public transit.

The route cost nearly $240,000 to operate annually, more than half of which has been subsidized through federal funds provided by Caltrans. Just 3.4 percent of the route’s costs were recovered from passenger fares, far below every other bus line in the Vine system.

Transportation authority staff have said Route 25’s ridership “has always been the lowest of the Vine’s routes.”

“Transit service between two suburban communities, in rural counties, with small populations is difficult to make operationally efficient,” staff said in September.

The authority’s board previously considered dropping the bus service at a meeting in May, which would have eliminated the route starting at the end of June. But directors instead asked staff to attempt to boost ridership through enhanced marketing efforts, investigate methods of improving its efficiency and seek financial assistance from Napa and Sonoma county stakeholders.

Staff members reported in September their efforts “did not make a material difference” in the number of riders on Route 25 and all funding requests were rejected.

“Additional options for deploying service were considered and while some of the options might have nominally increased ridership, costs incurred to deploy alternatives would have exceeded the benefits derived,” staff said in the September report.

You can reach Staff Writer J.D. Morris at 707-521-5337 or jd.morris@pressdemocrat.com. On Twitter @thejdmorris.