© trainspo.comALCo UP 4-6-6-4
Built by ALCo
Overview of the ALCo UP 4-6-6-4
Discover the powerful UP 4-6-6-4 steam locomotive, an icon of the Union Pacific Railroad.
This distinctive locomotive, built by ALCo between 1936 and 1944, features the impressive 4-6-6-4 Whyte notation, showcasing its advanced articulated design for its era.
It boasts a top speed of 110 km/h and an exceptional tractive effort of 433 kN, making it a formidable machine capable of handling heavy loads with ease.
The UP 4-6-6-4 stands as a testament to railway engineering prowess, embodying both power and reliability that defined a significant period in transportation history.
A must-have for railway enthusiasts and collectors, this steam locomotive represents an era of mass transit and industrial development.
Experience the grandeur of the past with this magnificent steam engine, a crucial part of the Union Pacific's rich heritage.
ALCo UP 4-6-6-4 technical specifications
| Value | Imperial / US | |
|---|---|---|
| Built by | ALCo · 1936–1944 | |
| Top speed | 110 km/h68 mph | |
| Tractive effort | 433 kN97,342 lbf | |
| Track gauge | 1,435 mmStandard gauge4 ft 8½ in | |
| Whyte notation | 4-6-6-4 |
Operators of the ALCo UP 4-6-6-4
Railway companies that have operated the UP 4-6-6-4, with the class designation used by each of them.
| Operator | Class | Country |
|---|---|---|
| Union Pacific Railroad | UP Challenger | United States |
ALCo UP 4-6-6-4 photos
Photos © their respective authors, shared on trainspo.com. They may show liveries or variants that differ from the specifications above.
More steam locomotives from ALCo

ALCo
141R
Steam locomotive
100 km/h · 2,150 kW

ALCo
4-8-8-4
Steam locomotive
1941 · 80 km/h

ALCo
CR JF
Steam locomotive
80 km/h

ALCo
USATC S200
Steam locomotive
1942

ALCo
MRSR 2-8-2T
Steam locomotive
1929

ALCo
4-8-4
Steam locomotive
1944
ALCo
4-6-6-4
Steam locomotive
1936–1944 · 70 km/h

ALCo
Union Pacific 9000
Steam locomotive
1926–1930







