The 1995 report of the RTCA Board of Directors' Select Committee on Free Flight states that 'insufficient capacity, limited access, and excessive operating restrictions have escalated operating costs, increase delays, and decreased efficiency for all users' of the national airspace system. The Air Transport Association estimates the annual loss to be 3.5 billion dollars. The goal of the user preferred routing research is to develop integrated airborne and ground technologies that enable the highest possible level of unconstrained, user-preferred routing in enroute airspace.
B. David McNally,
"Technologies for user-preferred routing", Proc. SPIE 2737, Air Traffic Control Technologies II, (27 May 1996); doi: 10.1117/12.241063; https://doi.org/10.1117/12.241063