There is a picture of one at http://www.otif.org/otif/_dpdf/dir_rid_2006/08_2006-3_D.pdf
and in http://www.freepatentsonline.com/EP0281827.html they talk about "support bars" in the context of rail tankers but treat slightly with a pinch of salt because it looks a bit translated... As I look up justification for the above I think I have found it - see the http://www.otif.org/otif/_epdf/dir_rid_2006/08_2006-A_E.pdf and its German equivalent http://www.otif.org/otif/_dpdf/dir_rid_2006/08_2006-A_D.pdf where they use "supports [for tank wagons]" to refer to Tragleisten. Probably right because the OTIF is the Intergovernmental Organisation for International Carriage by Rail - so they should know!!