close Historic Big Boy steam locomotive draws crowds on America 250 tour Union Pacific's Big Boy No. 4014, the world's largest operating steam locomotive, is making its first East Coast tour as part of America 250 celebrations. Rail fans traveled from multiple states to see the historic engine in Illinois. NEW You can now listen to Fox News articles! WEST CHICAGO, Illinois – Union Pacific's Big Boy No. 4014, the world's largest operating steam locomotive, is making its first tour of the East