>Thanks for clarifying that I thought the engineers and conductors unions had merged a few years ago.

On some properties, one union or the other represents both crafts. On Amtrak, and most freights, there are two separate unions.

>If Caltrain or another commuter operator bought new DMU or EMU trains that had the BART train type of equipment that allowed car doors to be opened by an engineer would the FRA still require them to have conductors and assistant conductors aboard?

If the FRA requires a trainman's presence on passenger trains, the kind of [passenger] equipment making up the trains is irrelevant.

The applicability of state or federal regulations (i.e. CPUC/FRA) to any given operation is dependent on the situation with the trackage, not the equipment run thereon. By this I'm referring to the "general system = FRA yes/non-general system = FRA no" test, which can be accused of being a very simplistic way of putting it. The PCS trackage is part of the gerneral system, so CFR/FRA regs apply to whatever is run thereon.

>Is there any formula...say conductor only for one or two cars and assist. conductor required if the train had a certain number of cars?

This sort of thing is covered by the [trainmen's] union agreement, and the FRA will tell you quite clearly and firmly that they have nothing to do with enforcing any union agreement provisions.