; (B) 1 tank car or intermodal portable tank load with a material toxic or poisonous by inhalation; (C) 1 or more cars loaded with high-level radioactive waste or spent nuclear fuel; (D) 10 or more cars loaded with explosives; (E) 5 or more tank cars loaded with a flammable gas; or (F) 20 or more cars loaded with any combination of flammable liquids, flammable gases, or explosives. (6) High-level radioactive waste; spent nuclear fuel The terms high-level radioactive waste and spent nuclear fuel have the meanings given to a type B package or a fissile material package , respectively, in section 173.403 of title 49, Code of Federal Regulations. (7) Material toxic or poisonous by inhalation The term material toxic or poisonous by inhalation has the meaning given the term Material poisonous by inhalation or Material toxic by inhalation in section 171.8 of title 49, Code of Federal Regulations. (b) Rulemaking Not later than 1 year after the date of the enactment of the Railway Safety Act of 2023 , the Secretary, in consultation with appropriate Federal agencies, shall issue regulations that— (1) rescind the requirements set forth in paragraphs (4) and (5) of section 174.310(a) of title 49, Code of Federal Regulations, with respect to tank cars carrying hazardous materials other than Class 3 flammable liquids; (2) revise the requirements set forth in section 174.310(a)(2) of title 49, Code of Federal Regulations— (A) to limit all trains to a maximum speed of 50 miles per hour