Heritage
August 7, 2026
Union Pacific’s Big Boy No. 4014 Runs on Its Own Steam
Diesel locomotives assist with braking, switching and showcasing commemorative locomotives
Whenever Union Pacific's legendary Big Boy No. 4014 rolled through towns this year during its historic coast-to-coast tour, one question almost always followed: "Why are there modern diesel engines traveling behind the world’s largest operating steam locomotive?”
It's a fair question: Big Boy is a fully functional 1941-era steam locomotive that provides nearly 100% of all pulling power on tour. In fact, Big Boy has traveled several times without diesels, including between Ogden, Utah, to Green River, Wyoming, during this year’s 14-state tour that attracted millions of spectators.
So why do diesels often tag along with Big Boy? The answer is fourfold:
Dynamic braking: The Big Boy crew often uses the diesel locomotives’ modern-day dynamic braking system to save wear and tear on the historic locomotive and passenger cars’ brake shoes, which are custom made and pricey to replace.
Commemorative Locomotives: When Big Boy goes on tour, it gives Union Pacific a chance to showcase its “commemorative locomotives,” which are painted in bright, custom-colored designs to honor milestones, historical figures and organizations. During the last tour, Big Boy was accompanied by both Union Pacific and Norfolk Southern locomotives that celebrated America’s 250th anniversary, along with No. 1616 that honors President Abraham Lincoln, the founder of Union Pacific.
Switching operations: During long journeys, there are times when cars need to be added, removed or repositioned in Big Boy’s train consist. It’s easier and faster to do it with the help of diesels.
Range: Unlike days of yore, the infrastructure that once kept steam engines operating across the country, including coal and water towers, no longer exist. The Steam Team accounts for this by refilling the locomotive’s water tender and its two auxiliary water cars every night, but there are times the diesels are used to extend Big Boy’s range.
The bottom line is that Big Boy doesn’t need the diesels to run, but they provide modern-day support that helps keep this living piece of railroad history running on the rails, turning heads and inspiring a new generation of railroaders to come.