To cross the Moffat Tunnel over the Rollins Pass between Denver, CO and Salt Lake City, Utah, the D&RGW purchased machines from EMD in the mid-1970s that were specially designed for tunnel routes. These had a much larger cooling fan at the end of the machines. The Moffat Tunnel, which was over 7 miles long, pushed machines (SD40, SD45) that were regularly cooled with circulating air to their performance limits, as the cooling in the long tube often failed due to the hot exhaust gases they themselves emitted. These models are clearly recognizable by the large air supply grids at the rear of the machines. The SD40T-2 ("T" for tunnel) models have two inspection hatches, the SD45T-2 machines have three inspection hatches at the rear. After the takeover by the Union Pacific, many machines were.
