Fortunately, younger cities like London and Paris don't have the problem that ancient metropolises like San Francisco have, so they can build subway at a fraction of the cost of $4b/mi that SF needs to ensure that it's built right. There's a lot of history in California. Pretty unique in that regard.

To be honest, I like 280 without there being something on top of it, but if that's what's necessary to get a rail line down there I'd gladly accept it. Just the per-mile cost. Well, I'm not looking forward to paying more than half of every marginal dollar to the government so it can give it to its cronies who just happen to be husbands of famous California politicians.