In Europe, the performance of electrical and electronic equipment in railway applications is governed by two international standards. The one most frequently cited in design specifications is the document IEC571, “Electronic Equipment on Rail Vehicles,” also known as European Norm EN50155, “Electronic Equipment Used on Rolling Stock Equipment.” In the U.K. the standard that applies is RIA12, “General Specification for Protection of Traction and Rolling Stock Equipment from Transients and Surges in DC Control Systems,” developed by the Railway Industries Association (RIA). While these two standards are similar in most respects, the RIA12 standard also requires a specific surge withstanding capability. 

This below Vicor application notes shows how to comply with these standards using modular DC-DC converters to facilitate the design of complex power supplies.

http://www.vicorpower.com/documents/application_notes/AN201_RailwayApplications.pdf