In Surveyor try to use ANY spline "delete tools" (with the X in it) to remove them, even object remove tools (where you find buildings etc.) might work. Like in the "tracks", "roads" and other splines menues, even the industry tracks splines one can find in the "object" menu one has to remove with the corresponding "delete" tool. One of these should work.
If that does not work, use TrainzObjectZ in TRS 04 or CMP in TRS 06 to remove these. But with these you gotta know what you are doing or leave this alone.
Cheers
VinnyBarb