The SMART train has a station which appears to be about a mile from the airport. It is currently the "north end" of the line, but you can ride down as far as Larkspur, right by the ferry terminal to SF. I'm not suggesting this as an efficient way to get between STS and SF Just explaining the transit options should one not want to get a car, and also, for those who have 101 corridor travels. https://sonomamarintrain.org/stations