The "unit train" concept originated, IIRC, in the UK.
Technically, a unit train is made up of identical rolling stock hauling a
single commodity.
In the UK this was originally coal hauled in identical, specially designed,
hopper cars.
Cheers.
Roger T.
Home of the late Great Eastern Railway
http://greateasternrailway.com
More photos of the late GER at: -
http://s94.photobucket.com/albums/l99/rogertra/Great_Eastern/
