you write "electrification of Caltrain has been largely a function of the desire for an interoperable HSR/Caltrain corridor," Nonsense,the plans to electrify and extend Caltrain closer to the main rider catchment area dates to the 80s--not much HSR noise then. As to electric v diesel, that debate was settled decades ago. The acceleration/deceleration rates are better for EMUs that for diesel hauled trains, which enables tighter headways, faster trains, and more total throughput. They also need a real 4 track mainline in order to offer serious transit on the peninsula; the best example of what could be done was the Illinois Central electric the 50s when trains ran fast and frequently all day and nearly like subways in rush hour.and, of course, no direct pollution.