The Union Pacific Class TTT-6 was a group of 2-10-2 "Santa Fe" type steam locomotives built by the Baldwin Locomotive Works as part of Union Pacific Railroad extensive TTT (Two-Ten-Two) series. These powerful freight engines were designed to haul heavy trains over steep grades and long distances, playing a vital role in the railroad’s operations during the steam era.
History[]
In the early 20th century, the Union Pacific Railroad (UP) was facing new operational challenges. As freight traffic increased and the railroad expanded across the rugged terrain of the American West—particularly through the Wasatch Mountains and Sherman Hill—UP needed more powerful locomotives capable of hauling heavy trains over long, steep grades. By the 1910s, the existing Mallet compound articulateds were powerful but mechanically complex, and the traditional 2-8-0 “Consolidation” types were quickly becoming outdated.
In response, UP engineers—working closely with the Baldwin Locomotive Works—sought a locomotive that could deliver high tractive effort, reliable performance, and a simpler, more maintainable mechanical layout. Their solution was the 2-10-2 wheel arrangement, known on many railroads as the “Santa Fe” type, but internally classified by UP as TTT, short for “Two-Ten-Two.”
Between 1917 and 1924, Union Pacific ordered a total of 144 2-10-2 locomotives, grouped into seven classes: TTT-1 through TTT-7. These locomotives were constructed by three major builders: American Locomotive Company (ALCO) produced 18, Lima Locomotive Works built 37, and Baldwin contributed the largest share with 88. Despite the class distinctions, all shared standard mechanical features, including identical cylinder dimensions, driver diameters, and boiler pressures, providing a consistent and uniform fleet.
The TTT-6 subclass, to which No. #5511 belongs, was part of the later batches in this group. Designed for maximum tractive effort at lower speeds, these engines were ideally suited to mountain railroading and heavy drag freight. With their massive boilers, ten driving wheels, and large tenders, they were built for sustained power over long distances. One notable feature that set 5511 and a few of its sisters apart was their use of Young valve gear—a more compact and efficient alternative to the traditional Walschaerts or Baker gear. While never widely adopted, the Young gear represented UP’s ongoing experimentation with mechanical efficiency and smoother operation.
Locomotives like 5511 were well-suited to the UP’s most demanding routes, particularly between Ogden, Utah, and Green River, Wyoming, where long, steep, and relatively straight grades made full use of the engine’s hauling power. However, their long wheelbase made them less effective on tight curves or at higher speeds, limiting their use to slow, heavy freight rather than fast mainline service.
As dieselization progressed in the mid-20th century, UP gradually began retiring its TTT-series steam locomotives. Most were eventually scrapped, but No. 5511 was the lucky one and managed to escape that fate. It was retired and stored inside the Union Pacific Steam Shop in Cheyenne, Wyoming, where it remained in long-term indoor storage for more than six decades. At one point, the locomotive was temporarily repainted and moved outside onto the Cheyenne turntable for display during a National Railway Historical Society (NRHS) convention. Afterward, it was returned to storage—this time without its boiler jacketing, awaiting an uncertain future.
In 2022, Union Pacific donated No. 5511—along with several other historic pieces, including Challenger 3985—to the Railroading Heritage of Midwest America (RRHMA). It was subsequently moved to Silvis, Illinois, where it now awaits a complete restoration to operational condition.
Today, No. 5511 stands as the last surviving Union Pacific 2-10-2 and one of the few remaining examples of the Santa Fe type in the United States. Once fully restored, it will not only return to steam but also serve as a living testament to Union Pacific’s legacy of mountain railroading and innovation in freight locomotive design.
Roster[]
| Class | Qty. | Road Numbers | Road | Year Built | Builder |
|---|---|---|---|---|---|
| TTT-6 | 10 | 5040-5049 | UP | 1923 | ALCO |
| TTT-6 | 3 | 5050-5052 | UP | 1923 | Baldwin |
| TTT-6 | 37 | 5053-5089 | UP | 1923 | Lima |
| TTT-6 | 8 | 5306-5313 | OSL | 1923 | ALCO |
| TTT-6 | 15 | 5500-5514 | LA&SL | 1923 | Baldwin |
Stock list[]
| Loco No. | Image | Build date | Manufacturer | Status |
|---|---|---|---|---|
| 5075 | 
|
1923 | Lima Locomotive Works | Scrapped |
| 5085 | 
|
1923 | Lima Locomotive Works | Scrapped |
| 5089 | 
|
1923 | Lima Locomotive Works | Scrapped |
| 5508 | 
|
1923 | Baldwin Locomotive Works | Scrapped |
| 5510 | Frameless | 1923 | Baldwin Locomotive Works | Scrapped |
| 5511 | 
|
September 1923 | Baldwin Locomotive Works | Awaiting a restoration to running condition by the Railroading Heritage of Midwest America (RRHMA). |