The notion of an efficiency gap in the current transportation networks is explored in a Master's thesis by Columbia University graduate student and America 2050 research intern, Yoav Hagler. At short distances, the most efficient mode of intra-megaregion travel is auto, and at long distances, the most efficient mode is air. However there exists an intermediate distance at which the most efficient mode based on these four criteria is high-speed rail. The efficiency gap, which peaks between 200-400 miles can aid future studies in regards to preferred route selection, station, location, and the location of megaregional transportation hubs.
The Master's thesis titled "Back on Track: An Examination of Current Transportation Networks and Potential High-Speed Rail Systems in Three U.S. Megaregions is available for download here. The study analyzed the current transportation networks and proposed high-speed rail networks in the Northeast, Midwest, and the Florida megaregions. This research analyzed, from the consumer prospective the total reach, cost, reliability, and convenience of four modes (Air, Auto, Rail and High-Speed Rail) for travel within these megaregions.