The biggest steam locomotive is whistle-stopping across the U.S.

National The biggest steam locomotive is whistle-stopping across the U.S. Updated July 11, 202611:14 AM ET Originally published July 11, 202611:14 AM ET Jeff Lunden Attendees take photographs and admire Union Pacific's Big Boy No. 4014, the world's largest operating steam engine locomotive, during a stop in Philadelphia on July 5, 2026. As part of the celebration for America's 250th anniversary, the steam engine train is on tour for public display in multiple cities and states across the United States. Michelle Gustafson for NPR hide caption toggle caption Michelle Gustafson for NPR Union Pacific Railroad's Big Boy No. 4014– the world's largest operating steam locomotive – has been barnstorming from coast-to-coast in a celebration of America's 250th birthday. Based in Wyoming, the train came east to Philadelphia for the July 4th weekend. On the hottest day of the year – 102 degrees with a heat index that made it feel like 112 – dozens of people camped out by the side of the tracks at Valley Forge National Historical Park to see the train steam by. Many people brought camp chairs and coolers with water, like John Seibert, who came with a couple of friends from a model railroad club. Sponsor Message "It's a once-in-a lifetime experience," he said, "I mean you're never gonna see it again." Many in the crowd checked their smartphones to see the progress of the train on an app, as it made its way down the track. And from miles away, you could hear the whistle. Then, the crowd could see the headlights in the distance. Then the Big Boy, 133 feet long and weighing 1.2 million pounds, came barreling past, bells ringing and steam whistle blaring. Adam Lapham, 25, of Green, Ohio, stands for a photograph taken by his grandfather, James Wallace, 74, in front of a train car connected to Union Pacific's Big Boy No. 4014, the world's largest operating steam engine locomotive, during a stop in Philadelphia. Michelle Gustafson for NPR hide caption toggle caption Michelle Gustafson fo...