Random thoughts on all this:
Rail transit has many advantages over automobiles, however the advantages are all hidden benefits and one offs (reduced pollution, reduced traffic congestion, reduced dependence on foreign oil, increased tax revenue from lower land use, etc), while the disadvantages are all obvious and up front (not as convenient as cars, can’t sustain themselves through user fees alone, unsuitable for lower population density areas). It’s a Prisoner’s Dilemma situation, with cars and planes being cheaper and more convenient for individual travelers, and trains and rail being better for society as a whole. Do you think that European governments would keep pumping billions of dollars a year into their rail systems decade after decade unless they though it was worth it?
Population density issues with regards to trains can be a chicken and egg issue. Urban sprawl has led to large areas around cities being unsuitable for rail travel, when it really should be. If there are no train lines going to a geographic area, then the “One house, two car” residential model makes sense. Once the houses are built, then there is no reason to build a rail line there as the population density is not high enough. And of course, tearing down existing housing to build apartment buildings so you can build a train there is a non-starter. When a suburban community passes a zoning ordinance that “No residential building can be more then three stories tall”, they are also saying “No train stations shall be built in our town for the next quarter century”, even if they don’t realize that.
Looks like some of the cost problems with California’s HSR are going to be in setting up the right-of-way. Elevated HSR track across Silicon Valley? Seriously? You could buy every house in the way at market rates and bulldoze them cheaper, but that would mean depriving wealthy people of their land. Creating the routes for rail lines has always been awkward, with optimum train lines frequently going through property owned by wealthy groups and hardcore NIMBY territory. This leads to people trying to reroute train lines around wealthy neighborhoods or creating expensive elevated or submerged rail lines, leading to something that should be a straightforward engineering problem into a political battle.