Recreating a railway line is much harder than you think!
As a Trainz and Railworks route designer I can testify that making routes is an incredibly long, difficult and tiresome process. Making a fictional route is a bit easier, but for real routes, you're talking days, weeks and months of work.
The serious developers have to go out and catalogue the entire route they want to build, bit by bit. That means every bridge, every signal, every house, every lake, every little thing has to be recorded and photographed in the route you want to build.
When you're finished with that, you have to put it into the simulation. I use the Railworks route building engine, which is by far the most comprehensive and powerful building tool out there. But even on that, it can take a professional, experienced designer hours and hours of work just to complete one town.
Sticking with your project takes a lot of commitment.
If I was to build the entire UK Network using Railworks/Trainz, I'm looking at a year long project. Longer in fact, because I have to go to school, I can't get an education sitting behind a PC all day. Unfortunately!!!
Falcon