Photo taken on July 29, 2019 shows part of the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

Engineers work on the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States, on July 29, 2019. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

An engineer is seen on the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States, on July 29, 2019. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

Enthusiasts gather at the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States, on July 29, 2019. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

Photo taken on July 29, 2019 shows part of the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

Enthusiasts gather near the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States, on July 29, 2019. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

Enthusiasts gather near the historic Big Boy No. 4014 steam locomotive in West Chicago, Illinois, the United States, on July 29, 2019. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)

The historic Big Boy No. 4014 steam locomotive stops in West Chicago, Illinois, the United States, on July 29, 2019. The Big Boy No. 4014 steam locomotive spent three days in West Chicago during a tour to commemorate the 150th anniversary of the completion of the transcontinental railroad. (Photo by Joel Lerner/Xinhua)