EMD SD70MAC

EMD SD70MAC
Name	EMD SD70MAC
Powertype	Diesel-electric
Builder	Electro-Motive Division
Builddate	1993–2004
Buildmodel	SD70MAC
Totalproduction	300
Aarwheels	C-C
Prime mover	EMD 16-710G3B
Poweroutput	4000 hp
Tractiveeffort	92,000 lbf

EMD SD70MAC is a six-axle, diesel-electric freight locomotive built by the Electro-Motive Division of General Motors and later Electro-Motive Diesel. It combined an EMD 16-cylinder 710 series diesel engine with an AC traction alternator and individual axle converters for heavy-haul service across North America. The design aimed to improve adhesion, tractive effort, and reliability for Class I railroads such as Union Pacific Railroad, BNSF Railway, and Canadian Pacific Railway.

Design and Development

Development began as a response to advances by General Electric Company and the market shift toward AC traction exemplified by the GE AC4400CW. EMD engineers in La Grange, Illinois evaluated AC traction motors developed with partners including Hitachi and Siemens. The SD70MAC introduced an AC alternator and three-phase inverters derived from research programs involving National Railway Equipment Company and testing at Transportation Technology Center, Pueblo. Project milestones included wind-tunnel testing at Argonne National Laboratory and noise attenuation studies with the Federal Railroad Administration. The platform incorporated microprocessor controls influenced by standards from Association of American Railroads and diagnostic systems similar to those in locomotives ordered by Conrail and Norfolk Southern Railway.

Technical Specifications

The locomotive used an EMD 16-710G3B two-stroke diesel producing 4,000 horsepower, feeding an AR11 alternator paired with AC traction motors supplied through inverters from vendors such as Katz and Siemens. The C-C wheel arrangement rode on HTCR radial trucks derived from research with Canadian National Railway and featured dynamic braking capacity used in mountain territories like the Rocky Mountains and Sierra Nevada. Onboard systems included electronic fuel injection, modular cooling derived from EMD SD60 lineage, and a computerized locomotive control unit compatible with Positive Train Control initiatives. Safety systems and signaling interfaces included compatibility with cab signaling practices in New York State and the California Department of Transportation corridors.

Variants and Submodels

Multiple orders produced submodels and customizations for Union Pacific Railroad, Burlington Northern Santa Fe, and CSX Transportation. Variants included factory-ordered modifications such as extended-range fuel tanks popular with Santa Fe predecessor fleets and options for dual-mode auxiliary power requested by Amtrak-affiliated projects. Units built for Canadian Pacific Railway often had cold-weather adaptations referencing standards used in Canadian National Railway operations. Aftermarket conversions by shops like Versatile Railroad Services and rebuild programs at Illinois Terminal produced updated electronics and traction-control algorithms similar to retrofit work on EMD SD70M units.

Production and Manufacturing

Production took place at EMD facilities in La Grange, Illinois and later at plants managed under Electro-Motive Diesel ownership. Major contracts were awarded through competitive procurements with bidding by Union Pacific Railroad and BNSF Railway procurement groups in the 1990s and early 2000s. Supply chains included suppliers such as Cummins for ancillary generators, Wabtec for braking systems, and Rockwell International-derived components for control hardware. Manufacturing followed quality assurance practices aligned with American Railway Engineering and Maintenance-of-Way Association guidelines and was audited by independent firms in Chicago and Cleveland.

Operational History

The SD70MAC entered service hauling unit coal, intermodal, and manifest freight trains over routes operated by Union Pacific Railroad, BNSF Railway, Canadian Pacific Railway, and CSX Transportation. In western corridors, the locomotives frequently operated in lashups with GE Transportation units and older EMD SD40-2 locomotives on freights crossing the Wasatch Range and the Cascade Range. Crews reported improved adhesion on grades compared with earlier AC experiments such as those involving AMTK prototypes. The type also appeared in high-profile excursions and joint testing with Federal Railroad Administration research programs monitoring emissions and fuel consumption relative to Tier 1 standards.

Notable Incidents and Modifications

Several units were involved in derailments and collisions that prompted investigations by the National Transportation Safety Board and resulted in retrofits like strengthened fuel tanks and upgraded crashworthiness features recommended by Association of American Railroads committees. Some SD70MACs received cab upgrades influenced by ergonomic studies from University of Illinois at Urbana–Champaign researchers and installation of PTC hardware to meet mandates shaped by the Rail Safety Improvement Act of 2008. Rebuild programs converted older SD70MACs into SD70ACe-equivalent control systems in shops including facilities in Waycross, Georgia and Beaumont, Texas.

Preserved Units and Museums

A small number of SD70MACs entered preservation or display at museums and heritage organizations such as the Lake Shore Railway Museum and regional collections in Oregon and Colorado. Preservation efforts were coordinated with railroad historical societies including the Railroaders Memorial Museum and volunteers from the Railroad Historical Society network. Exhibits emphasize the locomotive’s role in the transition to AC traction technology seen alongside preserved EMD SD45 and GE Dash 9 examples in national and regional railway collections.

Category:Diesel-electric locomotives Category:Electro-Motive Division locomotives Category:Freight locomotives