World’s Largest Operating Steam Locomotive: Big Boy 4014 Climbing Sullivan’s Curve in Cajon Pass

Union Pacific Big Boy 4014 pulls a Rail Giants Train Museum excursion up-grade through Sullivan’s Curve while ascending Cajon Pass on October 12th, 2019. By several standards the Big Boys built for the Union Pacific by Alco were among the largest, heaviest and most powerful steam locomotives ever built. Of the original production run of 25 only eight exist today, and of those 4014 is the only one to have been restored to operation. It is the largest and heaviest operating steam locomotive in the world today. 4014 was preserved on static display for 52 years at Rail Giants Train Museum in Pomona, California until restoration by the UP Steam program in Cheyenne, Wyoming between 2014 and 2019.