San Mateo County opted out of the initial BART system in 1961 though, and is still not a member of the BART district, which is why trips to/from San Mateo county are charged more. http://www.flickr.com/photos/walkingsf/5427069831/in/photost... has plans around that include a line going down what is approximately the current Caltrain route to Palo Alto. (along with an unbuilt line to the Richmond District and Marin county, since Marin County also opted out)