Trainz aka Trainz Railroad Simulator is a pc game. This game feuters Route Building,Becoming a Locomotive Engineer and create your own consists of trains with active industries and Stations. All this you can create with amazing detail plus you can register on the auran games website and go to the trainz download station and download oodles of trainz industries freight cars, passenger cars, people, and many other things. Here is a video explaning it in better terms.
I have found that Trainz is really helpful not only as a PC game for passing time and having fun, but it allows a kind of design out for my IRL model train railroad layout. It's not completely a perfect simulator, but for people new to model train building, it could be a leg up. If you're really interested in building model trains, there is a really good resource and review of popular beginners guides at http://johnsreviews-modeltrainbuildingguides.blogspot.com/