As part of the D&H South electrification scheme the Portland Shops designed an express motor to run freight at 110+ MPH (class 6 trackage for 110mph/177kph, and some Canadian trackage that was temporarily waivered for 150mph/250kph.)

The solitary class L – #799 – is what came out of it; a motor that drew on 5 years of testing of regeared class E & K motors, actually capable of pulling (short) freights at 150mph without catastrophe.

The big change from the class K design that was giving it a pilot truck to cut down on an alarming leading truck shimmy at speeds over 130mph; that plus the appropriately huge AC transformer it needed for operation on D&H South stretched the carbody out to an unheard of 75' – long enough so that the rear end needed to be tapered so it could remain within the clearance envelope of the Green Mountain subdivision.

Alas, Amtrak balked at the idea of running super-fast freights on the NE Corridor, so 799 was the only unit of this class built.

It has been regeared for 120mph, and remains in service as a freight motor.