[2] As of July 2021 just two EF66-0 examples remain in service, those being EF66-27 & EF66-30 With the opening of the Meishin Expressway between Nagoya and Kobe in 1965 and the Tomei Expressway between Tokyo and Nagoya in 1968, JNR faced increasing competition for freight transport from road hauliers.

These locomotives were designed to be used in pairs hauling 1,000-tonne freight trains, but as pairs of locomotives drew excessive current from the overhead wires, 1,000-tonne freight trains had to be split into 600-tonne and 400-tonne sections when operating on the Sanyo Main Line.

[5] Some of the first-batch locomotives (EF66 1 to 20) were also subsequently modified with the "sun visor" style cab end roofs.

[5] Following the privatisation of JNR on 1 April 1987, JR Freight received the prototype (EF66 901) and 39 of the original series (EF66 1 to EF66 39) as well as the Class EF66-100 machines.

Shortly after privatization, JR Freight tried out a number of new experimental liveries on its various locomotives, and one Class EF66, locomotive number EF66 20, received an experimental cream and blue livery with large "JR" logos in August 1987.

No other members of the class were reliveried, however, and EF66 20 received the new JR Freight two-tone blue livery when it underwent refurbishment in October 1993.

Refurbishment included rewinding of the traction motor coils, removal of the former JNR decorations on the front-end number plates, and repainting into a two-tone blue livery similar to that carried by the EF66-100s.