49, United States Code, is amended by inserting after section 20153 the following: 20154. Freight train crew size safety standards (a) Minimum crew size Except as provided in subsections (b) and (c), a freight train operated by a Class I railroad may not be operated without a 2-person crew consisting of at least 1 appropriately qualified and certified conductor and 1 appropriately qualified and certified locomotive engineer. (b) Exceptions (1) In general Except as provided in paragraph (2), the requirement under subsection (a) shall not apply with respect to— (A) train operations on track that is not a main line track (as defined in section 20173(a)(2)