Are you using TRS2004 or 06 please ??
If you are using TRS2006 then archive each route using CMP, then all locomotives, then all rolling stock, etc, etc. Produce some new folders in Your Documents area within your computer, then put all your routes, rolling stock, etc, into separate folders making sure that you have only 700mb of stuff in each folder, then burn them onto a CD or DVD, in England we can only get discs with a 700mb maximum data storage, so you will require quite a few discs, but you can get them in packs of 10 or 20 I'm sure in the US for only a few bucks. It will take a while for you to do this, but once you have all your assets stored you can use them FOREVER.....
Cheerz. ex-railwayman.