Big Boy And The Big Easy. On the afternoon of Friday, August 20, 2021, Union Pacific Railroad's 4-8-8-4 4014 (Big Boy) crossed the Mississippi River over Huey P. Long Bridge with the city of New Orleans in the background. This is the largest operating steam engine in the world, and is touring the UP's system to show its 2013-2019 restoration to crowds in communities across the United States.