Video of Caltrain on the bridge. Although you can't see it in this video, the footing of the south end of the bridge is much wider than the bridge. In fact this is a second footing. I believe it was built at the time of the bridge's construction to accomodate a second span in the event the SP decided to add an additional 2 tracks to the Bayshore Line, which was under consideration at the time. Another remnant of this four track plan--which would probably have been two main lines and drill tracks for switching--is the double bore tunnel 2 and the cut south of tunnel 1. This was made wide enough for four tracks and the two bores put in at tunnel 2 where the cut was filled in.

[www.youtube.com]