I use 3D studio max.
Creating Locomotives and rolling stock however, is probably the hardest thing you want to start with, its not impossible to do, but don't expect dazzling results after 2 hours, because 3D programs take practice, practice, practice and lots more practice. I've been using 3D studio max for 10 years and you can see the changes I made year after year after year. You also need to learn Adobe's Photoshop as well really, or the GIMP as "textures" as they are called, are another thing you need to learn. The word "poly count" is probably a new buzz phrase for you as well.
Try this, download GMAX, create a box, then use a modifier known as edit mesh and have a play around with it. In fact, have a play around with the program, you won't break it, you'll actually learn a lot from it.