Well, to be honest with you this is the first time that I have ever seen anything like this... Usually I would check the roadname on certain sites, but it appears that ROCO did not use prototypical numbering... A Google search did not turn up much, but I did find one person who said that they were used for hauling propane tanks... It makes sense at least :dunno:
EDIT: Make that Calcium Carbide :laugh: