Rivermill Studios The Railway Tracks Pack provides a tiled set of railway track pieces.
The curved and straight pieces snap together in any combination, each being surrounded by a seamless countryside environment.
An example scene is included, complete with sky dome and lighting.
Three texture sets at different resolutions are supplied, along with Maya source files.
A realistic steam train smoke particle effect complete with sound effects is also available here: http://u3d.as/y4b