A copyright search was done for renewals in film for the years 1957 and 1958. There were no listings for the title Box Car Blues. There's no evidence this continues to be under copyright.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.
{{Information |Description=Scene from the 1930 cartoon ''Box Car Blues''. The boxcar on the runaway train splits in half. |Source=[http://web.archive.org/web/20120308143819/http://bosko.toonzone.net/1930/box_car_blues/ website] [http://web.archive.org...