[CharlesCO]

My understanding was that the original BART plan called for express trains, but that the bores that were reserved for them were later given to the nascent Muni Metro (and one bore each in the downtown Oakland stations weren't dug out). Building the infrastructure for express trains or skip stop service at high frequency would likely require a lot of passing track, and if the entire BART system is above or below grade, that's by no means an inexpensive project.

And we don't have to go to Japan to see the effects of express trains or skip stop. We have that on Caltrain already, and the reason that was an easier switch was that Caltrain runs at grade.