Re: Transit and energy intensity
I had the PRT fantasy even before I knew what it was called. It's main problem is the chicken-and-egg 'needs to have world domination before it's successful' issue. It can't build up the way something like EZ-pass did, which needed MUCH less infrastructure.
My favorite theory on how mass-transit will evolve is basically that self-navigating/crash-avoiding technologies will evolve and mature at the same time as Japan-like minicar options will become more available near American cities (e.g. Vespas with 4 wheels). Self-navigation will eventually become good enough to navigate huge traffic flows (From a tech perspective, if 802.11s can do it at gigabyte speeds, it can definitely be done at >1millisecond speeds for cars) and most cars by then will be powered by electricity.
Then hopefully, all it will take is a couple cities to pay for specialized car/rail connections for continuous power. Then the connections may become available to the population (maybe!).