Replying to a message of Richard Webb to Bob Ackley:

 BA>> I don't know how they did it in San Francisco.  In downtown SF, some
 BA>> of the  city's trolleys were already subways and BART was put in
 BA>> below them. 

 RW> That's one good way to do it.  WHat really sorta makes me
 RW> shake my head is different proposals I've heard over the
 RW> years for a subway system in L.A.  Yah just what you need so close to
 RW> a major fault line >

The tube that BART trains run under the bay in crosses the San Andreas fault.
So, FTM, do the Dumbarton, San Mateo and Oakland-San Francisco bridges.

The Dumbarton is (or was, I haven't been on it in half a century) basically a
causeway built on pilings with a steel drawbridge over a ship channel in the middle.

The San Mateo was similar construction until many years ago when the state replaced
it with what is essentially an elevated freeway, with a nice overpass over that ship
channel (for years the steel drawbridge section remained isolated - the road on both
sides had been removed - right next to that overpass - it was too expensive to
dismantle), all concrete (which doesn't do well in salt water or under
lateral stress).
Of some interest is that the last time I crossed the San Mateo Bridge (30 or so years
ago) I noted that the roadway was about ten feet above the rooftops of Foster City (a
development built entirely on crud dredged up from the bottom of the bay and piled on
top of what had been mud flats - that sort of fill turns to mud and jelly during
earthquakes, not the sort of thing one wants to build anything on).

--- FleetStreet 1.19+