Many of the people I work with are under the impression that NRS (Navigation Reference System) waypoints are only available above FL390 under the NRR (Non-Restrictive Routing) program. NRS waypoints are the 5 character waypoints starting with K (i.e. KP06K) that are spaced out in a grid across the U.S. As far as I know, these waypoints are usable at any normal cruising altitude as part of a route string. The waypoints were initially introduced in the early 2000s as part of the NRR program, which specified that aircraft flying above FL390 could use these waypoints. However, as far as I know, they are currently just part of the overall waypoint structure (VORs, airway intersections, RNAV waypoints, etc) available for direct routes. I see a lot of 121 carriers filing these waypoints and they are even included in some FAA preferred routes. Given that using them can make for a more efficient route, I'm curious if anyone actually uses these waypoints on a regular basis and if the NRR program is actually obsolete. The FAA is really good at vaguely documenting programs and initiatives in various stages of use.