EMD SD70M

The EMD SD70M entered production in 1992 as part of Electro-Motive Division's broader SD70 family, itself a development of the earlier SD60 series. The model distinguished itself from the base SD70 variant primarily through its adoption of the wide-nose North American Safety Cab, a comfort-oriented design that provided crews with significantly improved working conditions compared to the older spartan cab configuration. The cab appeared in two distinct phases during the model's production run: the Phase 1 cab, which had been introduced earlier on the SD60M, and the later Phase 2 cab, recognizable by its boxier profile and taller midsection designed to increase headroom. Union Pacific became the dominant customer for the SD70M by a considerable margin, and in 2000 the railroad placed a landmark order for 1,000 units numbered from 4000 through 4999, one of the largest single locomotive orders in American railroad history. The order was subsequently extended by nearly 500 additional units, cementing the SD70M as a defining piece of motive power on Union Pacific's system. Other North American purchasers included Norfolk Southern, Southern Pacific, and the New York, Susquehanna and Western. Export customers included CVG Ferrominera Orinoco in Venezuela and Companhia Vale do Rio Doce in Brazil, the latter acquiring approximately 55 units for heavy iron ore service on the broad-gauge Carajás Railroad. Production of the SD70M wound down in late 2004, at which point the incoming EPA Tier 2 emissions standards that took effect on January 1, 2005, necessitated a transition to the updated SD70M-2 model. Approximately 1,609 SD70Ms were built during the model's production run, though some sources associated with the broader SD70M designation record figures approaching 1,858 units depending on how certain variants and export orders are counted. The model left a substantial legacy on American railroading, particularly on Union Pacific, where the type remained a common sight on mainline freight assignments for decades after its introduction.

The SD70M is powered by the EMD 710G3B prime mover, a turbocharged 16-cylinder two-stroke diesel engine rated at 4,000 horsepower. Traction is transmitted through D90TR direct current traction motors, and the locomotive produces a continuous tractive effort of approximately 109,000 pounds-force. The DC electrical system, while less sophisticated than the AC arrangements used in the concurrent SD70MAC, simplified the overall design by eliminating the need for computer-controlled inverters. The locomotive rides on C-C trucks, originally the bolsterless radial HTCR design introduced across the SD70 family, which provided improved tracking through curves compared to the older HTC truck used on preceding models. Beginning in late 2001, SD70Ms were built with flared radiators derived from the SD45 design, a modification required to accommodate the larger radiator cores associated with split-cooling, a system that separates the coolant circuit of the prime mover from that serving the turbocharger and air pumps. This change was made in direct response to EPA Tier 1 emissions requirements. The Brazilian units built for Companhia Vale do Rio Doce required a specially developed wider bogie designated the HTSC2, owing to the 1,600-millimeter track gauge used on that railroad's infrastructure.

Models by: Athearn · Kato · Walthers