The value of intercity rail, as several commenters have noted, is in relatively short routes with intermediate stations that are serious origin or destinations. Boston – New Haven – New York – Philadelphia – Baltimore – Washington – Richmond qualifies, as does Minneapolis – Madison – Milwaukee – Chicago – Indianapolis – Cincinnati or St. Louis – Springfield – Chicago – Toledo – Cleveland and a few other candidates that commenters have offered. (Denver, unfortunately, is somewhat remote from other cities in such a way as to make possible a corridor network centered there.)
But going longer distances by rail is iffy. There was a plan, early in the twentieth century, to build an electric railroad permitting ten hour timings Chicago to New York. There’s history here: http://www.marymaclane.com/airline/, and my comments here: http://coldspringshops.blogspot.com/2008_06_01_archive.html#8709269772789142305 (a reaction to Megan McArdle’s thoughts.) The problem with running the most direct line Chicago to New York is that you miss other population centers that could provide short-haul traffic. Although the Germans may lay on some all-day fast trains, much of their traffic is on and off at the intermediate cities. To apply the Air Line concept to Denver-Chicago, one would really have to think carefully about intermediate traffic in or out of Omaha or the Iowa cities or the cities of western Illinois.
More on these things here: http://coldspringshops.blogspot.com/2008_06_01_archive.html#1042365847404025841
