U.S. Code of Federal Regulations
Regulations most recently checked for updates: Jan 27, 2020
§ 231.25 - Track motorcars (self-propelled 4-wheel cars which can be removed from the rails by men).
§ 231.27 - Box and other house cars without roof hatches or placed in service after October 1, 1966.
§ 231.28 - Box and other house cars with roof hatches built or placed in service after October 1, 1966.