Section 218.123 - General train crew size safety requirements(a)General. Each railroad shall comply with the requirements of this subpart and may adopt its own rules or practices consistent with the requirements of this subpart. If any person, as defined in § 218.9 (including, but not limited to, each railroad, railroad officer, supervisor, and employee), violates any requirement of a railroad rule or practice implementing the requirements of this subpart, that person shall be considered to have violated the requirements of this subpart.(b)Two-person train crew size safety requirement. Except as provided in this subpart, each train shall be assigned a minimum of two crewmembers.(c)Hazardous materials. For the purposes of this paragraph (c), a tank car containing residue of a hazardous material as defined in § 171.8 of this title is not considered a loaded car. The exceptions in §§ 218.125 and 218.127 are not applicable, and the exceptions in § 218.129 apply as specified therein, when any train is:(1) A high-hazard flammable train (HHFT) as defined in § 171.8 of this title;(2) Transporting twenty (20) or more loaded tank cars or loaded intermodal portable tanks of any one or any combination of the hazardous materials identified in § 232.103(n)(6)(i)(B) of this chapter; or(3) Transporting one or more car loads of rail-security sensitive materials (RSSM) as defined in § 1580.3 of this title.(d)Location of crewmember(s) when the train is moving. A train crewmember that is not operating the train may be located anywhere outside of the operating cab of the controlling locomotive when the train is moving if: (1) The train crewmember is on the train, except when the train crewmember cannot perform the duties assigned without temporarily disembarking from the train;(2) The train crewmember and a locomotive engineer in the cab of the controlling locomotive can directly communicate with each other;(3) The train crewmember can continue to perform the duties assigned; and(4) The location does not violate any Federal railroad safety law, regulation, or order.