Get a copy of the Manual for Railway Engineering from the American Railway Engineering and Maintenance-of-way Association (AREMA).

Thanks for the reply, unfortunatley I am based in the UK and the reference is not something I can come across easily, and a google search is no help!

I would treat the load as a surface pressue nine feet in width perpendicular to the slope.  The magnitude of the pressure can be figured by taking the geometry of the train cars and averaging the load.  I have done this, but unfortunately do not have access to the figures at this time.

Also, since you are in the UK, the width of the railroad ties may not be nine feet.  I have not done any analysis assuming that the trains create a dynamic loading for the slope, only static loads.

Try this:

http://www.dot.ca.gov/hq/esc/construction/Manuals/Trenc...

Go to Thread255-55069 for a good dicussion of this issue.

Thanks for all the responses, I find it amazing that responses were so quick and helpful!  

I have found a document, Design of Earthworks and Earthwork Remediations (RT/CE/S/071), which states that design should take into account a nominal 50kN/m2 surcharge loading 2600mm wide and unlimited width applied for each track with an additional nominal 10kN/m2 surcharge loading should be applied to the cess.

Recently I have been reviewing the analysis of an mse retaining wall for a rail road.  The train load was treated as a uniformly distributed load.  The magnitude of the distributed load was obtained by dividing the train load by 5 x the tie length.  I think the reference was from AREMA. Hope that helps.