A lash-up of four SD45T-2 "tunnel motors", which were only operated by the Southern Pacific and its subsidiary Cotton Belt, are seen on the Donner Pass route in 1987. This variant of the EMD SD45-2 locomotive was necessary because the standard configuration could not get a sufficient amount of cool air into the radiator while working SP's extensive snow shed and tunnel system in the Cascades and over Donner Pass.
The "tunnel motors" had radiator air intakes located at the locomotive carbody's walkway level, rather than EMD's typical radiator setup with fans on the locomotive's long hood roof pulling air through radiators mounted at the top/side of the locomotive's body. Inside tunnels and snow sheds, the hot exhaust gases from lead units would accumulate near the top of the tunnel or snow shed, and be drawn into the radiators of trailing non-tunnel motor locomotives, causing them to shut down as their diesel engines overheated.
A total of 1,260 SD45-2's were produced between December 1965 and December 1971. They were Co-Co type equipped with 20-cylinder EMD 645E3 prime movers with power output of 3,600 hp or 2,680 kW.
The Southern Pacific also operated tunnel motor variants of the EMD SD40-2, as did the Denver and Rio Grande Western Railroad. (Drew Jacksisch pic)
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