If I recall correctly, MS TrainSim 2 (see also Wikipedia) had resolution down to the centimeters level, as you needed that to prevent problems with malformed vector tracks (tracks needed to be “smooth” both vertically & horizontally). You don’t need that everywhere, just a few meters either side of the centerline of each track. They also had a higher LOD around the track areas with custom terrain textures, as the user would obviously only be meters above the ground and so needed more detailed ground textures than a flightsim user. These textures were blended out to lower LOD levels as distance from the track increased.
Jon
