The Union Pacific Big Boy No. 4014 locomotive rolled into Altoona on Tuesday, July 23 to large crowds. Train fans of all ages were treated the world’s largest steam engine at the Union Pacific yard adjacent to the 1400 Block of Spooner Avenue. Union Pacific’s historic Big Boy is touring the Union Pacific system in 2019 to commemorate the transcontinental railroad's 150th anniversary. The No. 4014 locomotive is the world’s only operating Big Boy steam engine, one of only nine ever constructed.