I remember my neighbor (a Bechtel engineer)tell my dad that the BART system was built to be a grade separated high speed train system as such it would have more aerodynamic cars and its own set of standards.

The wide gauge made sense to have a more comfortable car as the seats could be wider and the car handle a higher crush load.

I still do not understand the following decisions:

1) 3rd rail power vs overhead

2) 1000v DC power vs 125kw AC

3) Hydraulic brakes va air brakes

4) No signal system to allow full manual operation if needed only turnout indicators

5) Aircraft based car design (however I think that was then governors Reagan's input)

Also the gauge reference to the SP wanting something different may have also applied to the Sacramento Northern which could have served industries along the Bart line to Concord or the WP along the Fremont line.

I also concur that eBart being built in the Antioch area and the proposed eBart in the Alamador Valley are being built to standard gauge so that they can use off the shelf DMUs and reduce infrastructure and vehicle costs.