The development of the 16-cylinder EMD 50 and 60 series locomotives in the late 1970s and early 1980s was spurred by the introduction of 16-cylinder GE B36-7 and GE C36-7 locomotives by EMD's main competitor General Electric. EMD previously manufactured the 20-cylinder SD45 and SD45-2 locomotives, but they had a reputation for high fuel consumption. In 1980, the SD50 model was added to the EMD Catalog. However, the SD50's electrical reliability was poor and, similarly, the 16-645F engine had poor mechanical reliability, both believed to be largely due to excessive vibration from the 950 maximum rpm of the 645F prime mover. It was time to develop a replacement for the venerable 645 engine which, in its earlier 16-645E form, had proved to be exceptionally reliable. EMD therefore quickly commenced development of the SD60 series, which would eliminate the weaknesses of the SD50. The lessons learned in developing the 645F crankcase and crankshaft were incorporated in the replacement, the 710G, first employed in the SD60. Although the carbody and frame are nearly indistinguishable from the earlier SD50, the SD60 featured the new 16-cylinder EMD 710G3A prime mover, AR-11 traction alternator, D-87 traction motors and a microprocessor-based control system that governed various electrical systems within the locomotive. The SD60 proved to be more reliable and fuel-efficient than the SD50, but it was not a resounding success in terms of regaining the market share that was lost due to the electrical and mechanical issues that plagued the earlier SD50. The goal was to equal or exceed the reliability of the earlier 645E-powered SD40-2, which was an industry standard benchmark for reliability, in the new 710G-powered SD60. This goal was largely achieved and the later 710G-powered SD70M received what would be the largest single order for new locomotives, a 1,000 unit order from Union Pacific,. Norfolk Southern has now retired nearly all of its original SD60 fleet. As an indication of its sound design, many SD60s were re-manufactured by their owners or by subcontractors; 135 such units were rebuilt by Norfolk Southern alone, some of which were acquired on the secondary market from locomotive lessors. These NS conversions, designated SD60E, are reported to be upgraded to include electronic fuel injection, intercooling, "crash-worthy" fuel tanks and other components and features found in late SD70s. The traditional "spartan" cab will also be replaced with a new "crash-worthy" wide cab built to NS specifications, dubbed the “Crescent cab”. Early units were completed at the original SD60's 3,800 HP rating, but all were later uprated to 4,000 HP, thereby becoming for all intents and purposes the equivalent of a late SD70M, but at a fraction of an SD70M's cost.
Models
Several variants of the SD60 were built, including:
SD60
This was the original model, and had a conventional hood unit configuration with the 40 Series cab first employed on the SD40-2.
SD60F
The SD60F was ordered and was operated byCanadian National and has a full-width cowl body and crashworthy "safety cab" with a four-piece windshield. CN retired the SD60F in 2017, however a handful were sold off and are still working on a shortline in Minnesota.
SD60I
The SD60I model has a full-width short hood and features the so-called "WhisperCab" that was insulated from sound and vibration using a system of rubber gaskets. The same cab was later used on EMD's SD70I, SD75I, SD80MAC and SD90MAC locomotives. Only Conrail ordered this model, and all now belong to the Norfolk Southern Railway and CSX Transportation.
SD60M
The SD60M features a "North American safety cab" design and has a full-width short hood. Early models until 1990 featured a three-piece windshield with vertical windows, identical to the windshields found on EMD's SD40-2F and F59PH models. Later production from 1991 used two windshield panes that were sloped back, and had a somewhat shorter nose tapered on the sides. Purchasers of this model included Conrail, Union Pacific Railroad, Burlington Northern Railroad and the Soo Line Railroad.
SD60MAC
The SD60MAC is similar to the SD60M but is equipped with alternating current traction motors. Although four demonstrator SD60MAC units tested on the Burlington Northern Railroad proved the viability of EMD's AC traction system, all subsequent orders were for the SD70MAC locomotive.
SD60E
The SD60E is a custom rebuilt SD60 for Norfolk Southern created at the Juniata Shops. So far, only standard SD60s have entered this rebuild program, which began in 2010. The SD60E utilizes a new NS-designed "Crescent" cab with a wide short hood, replacing the "spartan" cab. The name Crescent comes from the Norfolk Southern Crescent Corridor which runs from Louisiana to New Jersey. The upgrade also installs new electronics and upgrades the engine to the 710G3B standard rated at 4000 hp. Norfolk Southern bought additional SD60s from HLCX specifically for the SD60E program with the aim to eventually rebuild 240 SD60Es; however, the project was terminated after 135 units had been completed with focus shifting to AC traction rebuilds of EMD SD70 and GE C44-9W locomotives. Norfolk Southern's remaining inventory of unrebuilt SD60, SD60M and SD60I locomotives were subsequently sold or scrapped in 2019. Notable SD60Es include the NS 6920 "Veterans Unit," the NS 6963 "GoRail Unit," and the NS 9-1-1 "Honoring Our First Responders Unit."
