A staff member in clown costumes waves to passengers in Chicago, the United States, on Dec. 18, 2019. To celebrate the forthcoming Christmas holiday season, the Chicago Transit Authority (CTA) has introduced Christmas Train services. (Photos: Xinhua)

A train painted with Christmas patterns is seen in Chicago, the United States, on Dec. 18, 2019. To celebrate the forthcoming Christmas holiday season, the Chicago Transit Authority (CTA) has introduced Christmas Train services.

A staff member in Santa Claus costumes waves to passengers in Chicago, the United States, on Dec. 18, 2019. To celebrate the forthcoming Christmas holiday season, the Chicago Transit Authority (CTA) has introduced Christmas Train services.

Passengers board a Christmas Train in Chicago, the United States, on Dec. 18, 2019. To celebrate the forthcoming Christmas holiday season, the Chicago Transit Authority (CTA) has introduced Christmas Train services.

A boy peers inside a Christmas Train in Chicago, the United States, on Dec. 18, 2019. To celebrate the forthcoming Christmas holiday season, the Chicago Transit Authority (CTA) has introduced Christmas Train services.