EMD "Tunnel Motors" (Locomotives): SD45T-2 and SD40T-2

Last revised: November 6, 2024

The term tunnel motors was a nickname describing the SD45T-2 and later SD40T-2 built during a nearly ten-year period starting in the early 1970s.

The idea began as a test by Electro-Motive and Southern Pacific to solve an overheating issue.

Engineers from both companies tried several different ideas to reduce, and hopefully eliminate locomotives from overheating inside the long tunnels and snowsheds found along the Southern Pacific's main line in the Sierra Nevada Mountains of California and Nevada.

Ultimately, they determined that by merely moving the air-intakes near the bottom of the carbody to draw in cooler air would solve the issue and the idea proved successful. Later, Rio Grande used the same concept on a large order of SD40T-2s, which was also purchased by SP.

Today, many of these units remain in service on various short lines and regionals. Ironically, they no longer operate in the environments (tunnels) which necessitated their development.

However, the six-axle workhorses can still be found lugging heavy freights over stiff grades on operations like RJ Corman, Kyle Railroad, and Indiana & Ohio.

Photos

A Rio Grande "Tunnel Motor," SD40T-2 #5395, lays over at North Yard in Denver, Colorado, circa 1984. Mike Bledsoe photo. American-Rails.com collection.

Purpose

By the early 1960s Southern Pacific was experiencing a growing problem it had once solved concerning operations within its many tunnels and snowsheds located along its main line in the Sierra Nevadas.

During the steam era the railroad was able to correct an asphyxiation issue through the development of its unique Cab Forwards whereby the cab was placed at the front of the locomotive.

However, in the diesel age the problem was not breathing difficulties for crewmen but overheating of the locomotive itself. With delays and operations being affected this headache needed to be solved so the SP began working with Electro-Motive to come up with a solution.

The builder took its SD45 model, a 20-cylinder monster first released in 1965 capable of producing 3,600 horsepower and utilizing the new model 645E3 prime mover, and began testing various ideas to correct the problem.

Development

Engineers tried many different ideas but ultimately came up with a simple but ingenious solution; taking a tunnel's cool air into account found low near the tracks they moved the air-intake grills lower on the carbody and shifted the radiators high on the hood.

In 1972 EMD released the SD45-2, which featured upgraded "Dash 2" components such as improved electronics and high traction trucks.

A variant of the new model was the SD45T-2, with the "T" denoting its design tunnel use. Built from February of that year through June of 1975, the Southern Pacific was the only buyer acquiring a healthy 247 examples that worked very well in solving its overheating problems. The success of this model even saw it covered in the magazine Trains during the September, 1972 issue.

A pair of Rio Grande SD40T-2 "Tunnel Motors," led by #5377 work freight service near Woodside, Utah, circa 1980. American-Rails.com collection.

Legendary railroad photography Richard Steinheimer did a four-page feature on the SD45T-2, mostly via photos showing up-close views of the locomotive, its differences from standard models, and the latest "Dash 2" design features.

The success of these tunnel motors also drew interest from a nearby road, the Rio Grande that was also plagued with overheating problems via several bores along its main lines between Denver and Salt Lake City. During 1972 EMD began cataloging its "Dash 2" variant of the SD40, the SD40-2.

This model was the top locomotive of that decade, continuing through the mid-1980s selling nearly 4,000 units during that time. In 1974 the D&RGW approached Electro-Motive asking for something similar to the SD45T-2 but as an SD40-2.

Applying the same setup EMD released the SD40T-2 in 1974, which closely resembled its cousin in outward appearances except that the '45T-2 sported a longer frame and extra radiator door. Under the hood, however, things were somewhat different.

While both used EMD's model 645E3 prime mover the SD40T-2's used only 16 cylinders and featured 3,000 horsepower.

The Rio Grande went on to purchase 73 "T-2s," as they were also known, rostering them as 5341-5413. Once again, Southern Pacific became the largest buyer acquiring 229 units as well as 10 more lettered for subsidiary St. Louis Southwestern Railway (Cotton Belt).

The reliability of both designs, in particular the SD40T-2, saw tunnel motors operate for many years and in the process became a railfan favorite.

Data Sheet and Specifications

SD40T-2

Entered Production	6/1974 (Southern Pacific #8300)
Years Produced	6/1974 - 3/1980
Engine	645E3
Engine Builder	GM
Horsepower	3000
RPM	904
Cylinders	16
Length	70' 8"
Height (Top Of Rail To Top Of Cab)	15' 7 ½"
Width	10' 3"
Weight	368,000 Lbs
Fuel Capacity	3200 Gallons
Air Compressor	Gardner-Denver
Air Compressor Model	WBO
Air Brake Manufacturer	Westinghouse
Air Brake Schedule	26L
Trucks	C-C
Truck Type	HT-C
Truck Wheelbase	13' 7"
Wheel Size	40"
Traction Motors	D77 (6), GM
Primary Generator	AR10, GM
Auxiliary Generator	Delco (A8102)
Alternator	D14
MU (Multiple-Unit)	Yes
Dynamic Brakes	Yes
Gear Ratio	62:15
Tractive Effort (Starting)	92,000 Lbs at 25%
Tractive Effort (Continuous)	82,100 Lbs at 11 mph
Top Speed	65 mph

SD45T-2

Entered Production	2/1972 (Southern Pacific #9166)
Years Produced	2/1972 - 6/1975
Engine	645E3
Engine Builder	GM
Horsepower	3600
RPM	904
Cylinders	20
Length	70' 8"
Height (Top Of Rail To Top Of Cab)	15' 7 ½"
Width	10' 3"
Weight	368,000 Lbs
Fuel Capacity	3200 Gallons
Air Compressor	Gardner-Denver
Air Compressor Model	WBO
Air Brake Manufacturer	Westinghouse
Air Brake Schedule	26L
Trucks	C-C
Truck Type	Flexicoil
Truck Wheelbase	13' 7"
Wheel Size	40"
Traction Motors	D77 (6), GM
Primary Generator	AR10, GM
Auxiliary Generator	Delco (A8102)
Alternator	D14
MU (Multiple-Unit)	Yes
Dynamic Brakes	Yes
Gear Ratio	62:15
Tractive Effort (Starting)	92,000 Lbs at 25%
Tractive Effort (Continuous)	82,100 Lbs at 11 mph
Top Speed	65 mph

Production Rosters

SD40T-2

Total Built = 312

Owner	Road Number(s)	Serial Number(s)	Completion Date
Southern Pacific	8300-8306	73629-1 thru 73629-7	6/1974-7/1974
Southern Pacific	8350-8356	73685-1 thru 73685-7	6/1974-7/1974
Denver & Rio Grande Western	5341-5355	74636-1 thru 74636-15	10/1974
Denver & Rio Grande Western	5356-5373	756046-1 thru 756046-18	7/1975-8/1975
Denver & Rio Grande Western	5374-5385	766050-1 thru 766050-12	1/1977
Southern Pacific	8489-8498	776068-1 thru 776068-10	1/1978-2/1978
Southern Pacific	8307-8321	776069-1 thru 776069-15	2/1978-4/1978
Southern Pacific	8357-8371	776070-1 thru 776070-15	2/1978-3/1978
St. Louis Southwestern Railway (Cotton Belt)	8322-8326	776075-1 thru 776075-5	1/1978
St. Louis Southwestern Railway (Cotton Belt)	8372-8376	776076-1 thru 776076-5	1/1978-2/1978
Denver & Rio Grande Western	5386-5397	776098-1 thru 776098-12	8/1978
Southern Pacific	8499-8573	786174-1 thru 786174-75	11/1978-2/1979
Southern Pacific	8327-8341	786175-1 thru 786175-15	3/1979-5/1979
Southern Pacific	8377-8391	786201-1 thru 786201-15	5/1979-7/1979
Denver & Rio Grande Western	5398-5413	786264-1 thru 786264-16	3/1980
Southern Pacific	8230-8299	786265-1 thru 786265-70	3/1980-7/1980

SD45T-2

Total Built = 247

Owner	Road Number(s)	Serial Number(s)	Completion Date
Southern Pacific	9166-9208	7336-1 thru 7336-43	2/1972-3/1972
St. Louis Southwestern Railway (Cotton Belt)	9157-9165	7348-1 thru 7348-9	7/1972
Southern Pacific	9209-9260	72601-1 thru 72601-52	04/1972-6/1972
St. Louis Southwestern Railway (Cotton Belt)	9261-9301	72625-1 thru 72625-41	2/1973-3/1973
Southern Pacific	9302-9313	73621-1 thru 73621-12	9/1973
Southern Pacific	9315-9343	73630-1 thru 73630-29	1/1974-2/1974
Southern Pacific	9344-9370	73674-1 thru 73674-27	1/1975-2/1975
St. Louis Southwestern Railway (Cotton Belt)	9371-9404	74696-1 thru 74696-34	3/1975-6/1975

Southern Pacific "Tunnel Motors" (SD45T-2 #9196 and SD40T-2 #8538) at Ennis, Texas, circa 1983. Mike Bledsoe photo. In later years these units tended to roam round the SP system. American-Rails.com collection.

Both examples of the T-2 logged millions of miles on their respective systems, carrying through to new owner Union Pacific when it acquired the SP in 1996 (the Rio Grande had disappeared into the Espee in 1988).

As UP purchased new power in the 2000s it slowly replaced its fleet of tunnel motors and today none remain on its roster.

However, many are still in service on other roads, notably Class I Kansas City Southern which purchased several and rebuilt them as SD40-3s although some still carry their original T-2 design characteristics.

Other places to find tunnel motors, either overhauled or otherwise include the Wheeling & Lake Erie, RJ Corman, Respondek, Susquehanna, various leasing companies, Buffalo & Pittsburgh, Alabama & Tennessee River, and Fort Worth & Western.

A grimy set of Southern Pacific Tunnel Motors, led by SD40T-2 #8358 and SD45T-2R #6886 are on Tennessee Pass at Minturn, Colorado on October 24, 1994. Marty Bernard photo.

Rio Grande SD40T-2 #5381 and Southern Pacific/Cotton Belt power at Dalhart, Texas, circa 1983. American-Rails.com collection.

Sources

Foster, Gerald. A Field Guide To Trains. New York: Houghton Mifflin, 1996.

Marre, Louis A. Diesel Locomotives: The First 50 Years, A Guide To Diesels Built Before 1972. Milwaukee: Kalmbach Publishing Company, 1995.

Pinkepank, Jerry A. Diesel Spotter's Guide. Milwaukee: Kalmbach Publishing Company, 1967.

Schafer, Mike. Vintage Diesel Locomotives. Osceola: MBI Publishing, 1998.

Solomon, Brian. American Diesel Locomotive, The. Osceola: MBI Publishing, 2000.

Solomon, Brian. EMD Locomotives. Minneapolis: MBI Publishing Company, 2006.

Solomon, Brian. GE and EMD Locomotives: The Illustrated History. Minneapolis: Voyageur Press, 2014.

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