The Caltrain downtown extension (DTX) is going to cost $10 billion (or more) because the planners have no real incentive to control costs, not because it has to

The Caltrain downtown extension (DTX) is going to cost $10 billion (or more) because the planners have no real incentive to control costs, not because it has to. First, note that the "Pennsylvania alignment" has little to do with bringing Caltrain from 4th and Townsend (where it currently ends) to the Transbay Terminal. Pennsylvania Avenue is not between those two points! No, the city wants to redo the entire line between 22nd St. station and 4th and Townsend, to increase grade separation for Mission Bay. Which is probably a good thing to do in its own right, but it doesn't have to mean "let's just bore a huge tunnel through the whole thing", which is the most expensive option. See here for a much cheaper alternative that was summarily dismissed: https://caltrain-hsr.blogspot.com/2014/01/focus-on-mission-bay-grade-separations.html https://caltrain-hsr.blogspot.com/2014/01/focus-on-mission-b...