The Altamont Commuter Express or ACE could add another 350,000 commuters from Stanislaus County.
But to do that, voters would need to approve a half-cent sales tax increase for transportation.
About 12 percent of the new revenue would go to ACE and pay to extend rail service into Modesto, Turlock, and Ripon.
Karhla Davies of ACE says federal and state funding would also be in the mix as pollution is cut back.
"What our service is able to do is remove 24.4. million pounds of CO2 emissions. We hope to double the number almost to 50.1 percent by getting to Stanislaus County in 2020."
The Stanislaus Council of Governments is measuring public support for the possibility of placing a tax measure on the ballot this year.
The transportation tax would need two-thirds majority to pass.