EMD SD70MAC

The EMD SD70MAC entered production in 1993 as Electro-Motive Division's answer to the growing demand for high-horsepower AC traction locomotives in North American freight service. It represented EMD's direct competitive response to General Electric's AC4400CW, which had begun attracting orders from major railroads eager to exploit the superior pulling characteristics of alternating current traction technology, particularly on heavy-grade mountain operations. Burlington Northern was among the earliest and largest customers, acquiring substantial numbers of SD70MACs for service across its extensive western network, where the locomotives proved well suited to coal train operations in the Powder River Basin and demanding mountain territory. Conrail, CSX, and Transportación Ferroviaria Mexicana also placed orders for the SD70MAC, though Burlington Northern and its successor BNSF Railway accounted for the majority of units built. The Alaska Railroad ordered a distinctive variant equipped with head-end power capability, making those units suitable for combined freight and passenger service. So satisfied was the Alaska Railroad with the model's performance that it continued placing special orders even after EMD had transitioned its standard production to the successor SD70ACe in 2004. The final delivery of Alaska Railroad SD70MACs took place in late 2007, extending the model's production run well beyond its nominal end date. In total, approximately 1,109 SD70MACs were constructed across the model's production life, which formally spanned 1993 to 2007. The SD70MAC's legacy rests substantially on its role in demonstrating that EMD could compete effectively in the AC traction market, a segment that GE had moved into aggressively during the early 1990s. Although the SD70MAC was ultimately succeeded by the SD70ACe, which incorporated design revisions to meet tightening EPA emissions standards, the earlier model established AC technology firmly within EMD's product line and provided railroads with a capable and reliable heavy freight locomotive that many operators continued to run in revenue service decades after delivery.

The SD70MAC is powered by the EMD 710G3B prime mover, a turbocharged 16-cylinder two-stroke diesel engine producing 4,000 horsepower, though later production units were uprated to approximately 4,300 horsepower and fitted with flared radiators similar in style to those used on the earlier SD45, which provided increased cooling capacity. The locomotive rides on C-C trucks using the bolsterless radial HTCR design, which was standard across the SD70 family during its early production years before being updated to the HTCR-4 configuration on later units. The defining characteristic distinguishing the SD70MAC from its DC-motored counterparts in the SD70 family is its three-phase AC traction motor system, which requires computer-controlled inverters to convert the generator's output into the variable-frequency alternating current needed to drive the motors. This arrangement delivers significantly higher continuous tractive effort than a comparable DC-motored locomotive, an advantage particularly pronounced at low speeds under heavy load conditions. The use of AC traction motors gave the SD70MAC exceptional adhesion characteristics, allowing it to haul heavier trains on steep grades with reduced wheel slip compared to earlier DC locomotives of similar horsepower ratings. The locomotive follows the standard C-C wheel arrangement common to the broader SD70 series and is classified as a road switcher type, reflecting its intended primary role in long-haul freight service rather than terminal switching operations. The Alaska Railroad's head-end power variant added electrical generating capacity to supply passenger car heating, lighting, and climate control systems, a relatively uncommon configuration for what was otherwise a dedicated freight locomotive platform.

Models by: Athearn · Bachmann · Kato · Walthers