On Right-of-Way and Drainage

 There is very little 'flat' about the details along railroad tracks.  Even in some of the most flat and level territory, tracks are installed to facilitate drainage, which means some elevation changes are present even if they must be added by the construction.  

One reason most larger model railroads are built with subroadbed cut to fit the track areas and then mounted on support piers is that the terrain around the roadbed then can easily be built to be above and, more importantly, below the track level.  Water flows down, and adding simulated ditches where that would happen adds a lot of plausibility to your model.  

Here is a scene on the OC where the terrain is both above and below the right of way.  The bridge is up on abutments with slopes down and away from the road, but those slopes keep right on going down past the tracks, suggesting a spot where the railroad is on an embankment.  This is a key to a scene's plausibility and adds a to the overall feel of an area.  Real railroads provide a spot for water to run off too, and modelers should, too.