[JumpCrisscross]

> wider gauge solved(?) the stability problem, but at the cost of always needing custom rolling stock

Why not use Indian rolling stock? Modern Indian metro trains are quieter and more comfortable than BART.

[rsynnott]

Indian _metros_ generally use standard gauge. The BART _may_ be the only metro using this gauge in the world.

[smcin]

For rapid transits, 5'6" (broad gauge) is pretty eccentric [0] and was so back in 1964 when it was chosen; almost all other US rapid transits use 1,435mm/4'8.5". 5'6" is also doubly weird choice since tunnel diameter was one factor/excuse nominally used to object to tunnelling north to Marin County. Also it means the maintenance and carriage work can't easily be moved elsewhere.

(It is the widest gauge in use of heavy-duty mainline railways in the world, but that's a separate thing).

For comparison to other US rapid transit systems (almost all others use 1,435mm/4'8.5"), see table in https://en.wikipedia.org/wiki/Rapid_transit_track_gauge and scroll down to "United States". Or else https://en.wikipedia.org/wiki/List_of_United_States_rapid_tr... which does not list gauges.

[0]: https://en.wikipedia.org/wiki/Track_gauge_in_the_United_Stat...