This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.WEST CHICAGO, Ill. — The world’s largest operating steam locomotive made its way through the Chicago suburbs on Friday. The 133-foot-long Big Boy No. 4014 is part of Union Pacific’s tour to celebrate the 150th anniversary of the First Transcontinental Railroad. The massive train was taken off the tracks on Friday and put on display on the other side of the railroad at the Larry S. Provo Training Center. Hundreds of people packed on to a platform to see the Big Boy roll through. Many said the size and power of the train was what drew them out to see it. Only 25 of these massive Big Boys trains were built. No. 4014, which was delivered to Union Pacific in 1941, was retired in 1961 and later restored to make trips around the country. The train is one of only eight Big Boys still in existence today, and is the only one still operating. It took Union Pacific five years to restore the world’s largest steam locomotive, which dates back to the 1940s. The train will be on display in West Chicago through the weekend until it leaves for Iowa on Tuesday morning. You can track the Big Boy’s route here. The Associated Press contributed to this report.