11/11 more by luck than judgement.
Tim route from San Francisco Airport to Market Street is easy it's the little spur on the Western line. OAP's can buy cheap tickets on Bart. Also you can buy multi day tickets on Muni which covers you on the trams, trolley buses buses and the cable cars.
www.citypass.com/SanFranciscoMuni San Francisco is a public transport enthusiasts paradise.
Don't forget the ferries across the Bay and Caltran (big diesels on commuter trains) at their station at 700 4th St., San Francisco 94107.
Thanks. I'd spotted the tiny spur to the airport.