Articulated Steam Locomotives Debut

The articulation featured two more sets of driving wheels and a "hinged" frame that permitted bigger boilers, yet allowed the locomotives to negotiate sharp curves. This advancement was a boon to trains traveling notoriously steep grades with curves, like those east of Ogden, Utah. The use of articulated steam locomotives reached its peak in the 1940s, with the introduction of Union Pacific’s powerful 4000-class “Big Boys," the most successful articulated steam locomotive ever built.

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Around the same time, Southern Pacific created a new innovation with cab placement. Since SP locomotives burned oil rather than coal, fuel was pumped from the tender to the firebox. This allowed Southern Pacific to move the cab to the front of the locomotive. The locomotives were designed to operate in the Sierra Nevada Mountains, but were so fast and powerful that they worked the entire system from 1910 until the 1950s.

In 2012, Union Pacific celebrates the shared stories that have shaped our country since 1862. To mark our 150th anniversary, we invite you to explore how the nation’s largest railroad came to be and how UP continues to build America with innovation and tenacity, touching the lives of nearly every citizen.