Whenever the legendary Big Boy #UP4014 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 - click to learn more: ⬇️ up.com/news/heritage/4014-runs-on-own-steam-260807