Common DLC requirements for all Route downloads:
The routes all require the 'Train Simulator Classic' game and 5 routes all by Dovetail Games and available from Steam.com:
Riviera 50's
Falmouth
Isle of Wight
Woodhead Route
West Somerset
After downloading the routes below use 7-Zip to extract the package. 7-Zip is free download from here: 7-Zip for 64-bit Windows x64
Then use Steam\SteamApps\common\RailWorks\Utilities.exe, 'Package Manager' page, to install the .RWP file.
The Route Downloads below are free and require no further assets to be found. Scenarios may require additional payware.