Bob, they are different types of track by Bloodnok.
60850:38004 = Standard rail spline, grey ballast, wooden sleepers, oil stain, 2m repeat distance, to match the SR and LU track spline sets.
60850:38144 = Standard rail spline, overgrown trackbed, rusty rails, 2m repeat distance, to match the SR and LU track spline sets.
They're built-in assets in TRS2006 maybe 04 as well.
Many thanks for the prompt reply, they show as missing items in 04 so I assume they are not built in, at least now I know what I’m looking to replace Bob V