The ongoing debate over high-speed rail generates heated passions on all sides. Those opposed see high-speed rail as too costly and the U.S. as lacking the density to make the numbers work. Those in favor argue that high-speed rail is a way to move the U.S. to smarter, more energy-efficient transportation alternatives. My own take is that high-speed rail offers a mechanism to both expand and intensify the use of urban space leading to what geographers call a new "spatial fix" - required, I would add, to spur long-run economic recovery.
Here's some useful analysis by America 2050 which can help advance the dialogue. Its new report uses six factors - population, economic output, distance between cities, quality of local transit networks, highway congestion, and mega-region designation - to rank the top 50 routes across the U.S. (via Planetizen and Infrastructurist).