EMD SD45T-2

The EMD SD45T-2 was a diesel-electric locomotive built by Electro-Motive Division between February 1972 and June 1975, with a total production run of 247 units. The model was developed primarily for the Southern Pacific Railroad, which had experienced persistent overheating problems with its earlier SD45 fleet when operating through the long tunnels and high mountain grades of the western United States. The solution was a redesigned cooling system that gave the locomotive its widely used nickname, the tunnel motor. Of the 247 units produced, 84 were delivered to the St. Louis Southwestern Railway, commonly known as the Cotton Belt Route, which operated as a Southern Pacific subsidiary. The SD45T-2 proved to be a capable and durable machine in mountain service, and Southern Pacific relied on the type heavily across its challenging western routes. Beginning in April 1986, the Southern Pacific Transportation Company and the Cotton Belt undertook a substantial rebuilding program, converting 126 of the SD45T-2 locomotives into an upgraded variant redesignated the SD45T-2R. This program ran through December 1989 and included 24 Cotton Belt units, leaving 121 locomotives unrebuilt. Following Union Pacific's absorption of Southern Pacific in 1996, the surviving tunnel motors were dispersed more widely, with examples eventually operated by railroads including Kansas City Southern, the Bessemer and Lake Erie, and the Duluth, Missabe and Iron Range. At least one unit, Cotton Belt 9385, was exported to Brazil for service with America Latina Logistica. The legacy of the SD45T-2 endures in both preservation and continued study of railroad engineering solutions for mountain operations. A rebuilt SD45T-2R, originally Southern Pacific 9193 and later renumbered 6819, was donated by Union Pacific in December 2001 and is preserved at the California State Railroad Museum in Sacramento, California. The tunnel motor concept pioneered in the SD45T-2 was subsequently applied to the related SD40T-2, which became an equally significant locomotive for Southern Pacific's mountain operations.

The SD45T-2 was powered by the EMD 645E3 prime mover, a 20-cylinder V-configuration two-stroke diesel engine producing 3,600 horsepower. The locomotive rode on a C-C wheel arrangement, with two three-axle trucks providing six powered axles, and used direct current traction. As a member of EMD's Dash 2 family, the SD45T-2 incorporated improved electrical components and high-adhesion trucks compared to earlier SD45 variants. The defining engineering feature of the design was its modified cooling arrangement: rather than drawing radiator cooling air from the top of the long hood as was conventional, the intakes were relocated to walkway level along the sides of the carbody, and the cooling fans were repositioned below the radiator cores rather than above them. This configuration allowed the locomotive to draw cooler, denser air from lower in a tunnel environment rather than the hot, exhaust-laden air that would accumulate near the ceiling, directly addressing the overheating failures that had plagued the earlier SD45 fleet in tunnel operations. Visually, the SD45T-2 can be distinguished from the closely related SD40T-2 by several external details. The longer hood of the SD45T-2 reflects the greater length of its 20-cylinder prime mover compared to the 16-cylinder engine used in the SD40T-2. Additionally, the SD45T-2's cab sits further forward on the frame, reducing the length of the front platform, and each side of the locomotive features three fan access doors above the cooling air intake, whereas the SD40T-2 has only two on each side.

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