An excellent article Martin Buchert turned me on to: http://www.economist.com/node/21528294
To some extent, HSR is a 'solution looking for a problem'. Like the advantage of LRT over bus, some of the speed gains are created purely by bypassing stops* and concentrating activity into highly networked hubs.
Which makes me wonder about the new UTA bus system. UTA has unveiled a series of 'flex' buses that are demand-response (dial-a-ride**) rather than fixed route buses. It seems to be positively received, and will (hopefully) lead to fewer empty buses meandering through suburban neighborhoods in an effort to fulfill federally mandated coverage standards.
Perhaps the long-term evolution of transit network will be a 2-tier system--Flex shuttles ferrying people in and out, and long-straight high speed BRT and TRAX lines moving people from location to location. The key issue becomes 'peak hour' transportation, when everyone is trying to use the system at once. Make the 'Flex' shuttles larger, unto 40' buses? Or run two shuttles?
*God knows Amtrak could use some of that.
**How is that not a private taxi? -- Because it only drops you within its service area, or at the nearest transfer point.