Four prototypes of the Re 6/6 were initially built, of which two were equipped with divided locomotive bodies that move vertically thus adapting to conditions in an optimal manner. Test runs showed that this was not necessary for the regular production locomotive and all 85 regular units built from 1975 to 1980 were equipped with a one piece locomotive body. The engineer's cabs on the Re 6/6 borrowed heavily from the design for the Re 4/4 II as did the electrical equipment for the transformers, of which the Re 6/6 has two. These locomotives are 19,310 mm / 63 feet 4-3/16 inches long, weigh 120 metric tons, and have a maximum speed of 140 km/h / 87 mph; their performance is 7,850 kilowatts / 10,527 horsepower. One particular technical feature is the locomotives' acceleration under optimal conditions: From 0 to 100 km/h / 63 mph in 5.8 seconds. The Re 6/6 locomotives have had to undergo several paint variations and overhauls. Thirty locomotives were equipped with remote radio control starting in 2000; these units are used with the designation Re 6/6 f. The UIC designation for the class Re 6/6 is the class 620, which can be seen with increasing frequency on the locomotives. The 88 units still in service all belong to the SBB Cargo business area and haul heavy freight trains to all corners of Switzerland, also over the Gotthard route with a Re 4/4 II or Re 4/4 III in tandem motive power consists. The class Re 6/6 locomotives were even an alternative to a Re 4/4 II double motive power combination in heavy passenger service. After the modern class 460 was mainly assigned to passenger service, the impressive Re 6/6 with its three trucks once again dominates freight service on the Gotthard.