[1] The BL2 was not very successful, as it was unreliable and occupied a gap between carbody and hood units, which resulted in it suffering from the drawbacks of both designs.

EMD developed the BL1, basing it on the F3 and using the same bridge-truss carbody construction as the F-unit (as opposed to the weight-bearing frame of a true road switcher locomotive like the Alco RS-1) with the body cut away behind the cab to provide visibility to the rear.

The BL in the model name stood for "Branch Line", indicating that EMD felt the locomotive was best suited for light traffic and frequent switching chores.

The BL2 could be equipped with a train-heating steam generator for passenger service, identified by an exhaust stack between the panes of the front windshield.

[3] The mechanical components in the engine compartment were difficult to access and maintain, reducing its appeal among railroad shop crews.