World’s largest operating steam locomotive returns with Home Run Express Tour this month Thu, 06/08/2023 - 12:00am Union Pacific’s famed Big Boy No. 4014, the world’s largest steam locomotive built to haul heavy freight over steep mountain ...PLEASE LOG IN FOR PREMIUM CONTENT. Our website requires visitors to log in to view the best local news. Not yet a subscriber? Subscribe today! Read more about World’s largest operating steam locomotive returns with Home Run Express Tour this month