The EMD SD40T-2 is a type of high-powered, six-axle, 3,000hp diesel locomotive built specially for the Southern Pacific (including the SSW) and Rio Grande (DRGW) US Class 1 railroads from 1974 to 1980.
It is a modified version of the SD40-2 (as stated in an EMD owners manual), and was originally an experimental model, it came to be known as a "tunnel motor", due to it's large air intake vents placed on the sides of the overall body or along the carbody of the actual locomotive, and was used for cooling the engines while traveling through tunnels up steep mountain grades.
Many still exist, but are no longer used or seen on the Union Pacific (the only owner which owned a large fleet as a result of the acquirement of the SP and D&RGW) as of 2009, although the last units were officially retired in 2010 (including the sole-surviving unpatched D&RGW SD40T-2 unit: #5371).
Many currently operate on various shortlines (including rebuilt and non-rebuilt SD45T-2 units; which were rebuilt as a result of engine issues) while one (D&RGW #5371) currently resides at the Utah Railway Museum in Ogden, Utah.
During the 1970's, six-axle diesel locomotives were in high demand on US Class 1 railroads throughout the United States, and the most desperate of them all, were the Southern Pacific (aside from the SSW subsidiary of the SP) and Rio Grande railroads; who began to wear their aging four-axle diesel locomotives and were in desire need of stronger and more powerful six-axle diesel locomotives that wouldn't overheat so easily like the original SD40-2 and subsequent SD45. Hence, EMD's solution to inventing a revolutionary and advanced cooling system equipped on an actual unit known as a "tunnel motor", which was able to be used on SD40-2 units; thus, the creation of the EMD SD40T-2 (the "T" meaning "tunnel motor").
The EMD SD40T-2 was an initial success, and even inspired the development for the SD45T-2, as well as the GP15T and GP15-1 typ
The SD40T-2 survived well past the merger of the UP and SP up until 2009; as well as the remainder of the D&RGW still having SD40T-2 units left in their original paint existing as of today. (Yet, most former SP and D&RGW units are commonly seen in scrap yards and on shortlines; including those repainted into UP paint.)
There is often a confusion between the SD40T-2 and SD45T-2.
The main external differences between the SD40T-2 and SD45T-2 are the number of radiator fan access doors, located above the radiator intakes; 2 for SD40T-2s and 3 for SD45T-2s.
- DFTR #2003 is a former SP SD45T-2 fitted with an EMD SD70MAC cab used for crash test experiments for Operation Lifesaver and various other safety companies.
- SSW #9389; an SD40T-2 from the SSW portion of SP's; roster was painted in an exclusive bicentennial scheme in 1976 to commemorate the 200th Anniversary of the United States.
- The GP15T-1 is often nicknamed the "baby Tunnel Motor" by railfans and train enthusiasts.
- The UP originally intended on ordering a fleet of "Tunnel Motor" units, but received former MP (Missouri Pacific) GP15-1 and GP15T units after the MP's purchase.
- The UP had the smallest fleet of "Tunnel Motor" units (consisting of their former MP GP15-1 units) before the purchase SP and D&RGW; to which their fleet doubled in size, but have all since been retired even before all units were renumbered or repainted (excluding their former MP GP15 units which still serve as designated yard units).
- The Bessemer And Lake Erie shortline railroad (owned by CN as of 2008-2009) owns a fairly large fleet of rebuilt SD40T-3 units which are actually rebuilt from various SD45T and SD40T units once owned by the SP.