The BL2 is one of the most unusual locomotives in the history of the American railroad. It was conceived as an ancillary train locomotive and could therefore be used both for light goods traffic as well for passenger traffic. Its unusual form is due to the attempt to make this train interesting and attractive for passenger traffic.
Although it wasn't really one of the really successful locomotives, it still marks the transition from the older conventional design of the diesel locomotive to the later more modern form of the shunting locomotives.
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(Apologies for the double post)