Regarding Folders: This from SVBC...

It used to be that almost no one used folding bikes on Caltrain. I rarely
ever saw more than one other folding bike on the train besides mine, and
never in the luggage car, those times I chose to fold my bike up and board

This evening, going northbound I folded my bike and boarded in the luggage
car, leaving Sunnyvale at about 6 pm. There were 2 other folding bikes
already stashed in the luggage area. By the time I dismounted in San Carlos,
there were a total of five folded bikes included mine stashed in the luggage
area. Including some large suitcases from other travelers, the luggage area
was almost completely full.

I've also had the experience of boarding a VTA bus with a folded bike and
found someone else already boarded with a folded bike.