MARTA inched closer to a history-making expansion on Tuesday, but not to the extent many had hoped.

Clayton County commissioners, in a 3-2 vote, opted to let voters decide in a Nov. 4 referendum whether to fund MARTA service within the county by paying a half-penny sales tax. The half-penny sales tax is expected to generate about $25 million.

MARTA officials have said that’s not enough to fund a rail expansion. But it could revive robust bus service as early as next year in a county that has been lacking local public transportation since 2010.

It’s unclear if the MARTA board will approve the Clayton’s participation in the transit system without the same level of sales tax support that Fulton, DeKalb and the city of Atlanta contribute.

MARTA Board Chairman Robbie Ashe told commissioners Tuesday he could provide no guarantees.

“I do not believe majority support for such approach exists on our board or among our existing jurisdictions,” Ashe said.

A full penny would have generated about $49 million, which could bankroll a rail expansion as well as buses.