If you are using O31, then I can tell you that if you want to use it with "new equipment" that MTH Realtrax has adapter to get you from tube to it, after that, all Realtrax (straights/curves/switches/ucs/crossovers) will mate up to the adapter. I have used the adapters to go from RT to 031 sections for running older Lionel accessories like the cow loader, coal loader and milk cars.
Perhaps someone else can chime in for you on adaptability of Lionel Fasttrack and other brands. I would think they have adapters. I also think I read that Mennards is making an O31 compatible track, but have no personal knowledge of that.
Good luck, there are plenty of people on here who can help you better than I can. Greg