49 U.S.C. § 20701 : US Code - Section 20701: Requirements for use

      A railroad carrier may use or allow to be used a locomotive or
    tender on its railroad line only when the locomotive or tender and
    its parts and appurtenances - 
        (1) are in proper condition and safe to operate without
      unnecessary danger of personal injury;
        (2) have been inspected as required under this chapter and
      regulations prescribed by the Secretary of Transportation under
      this chapter; and
        (3) can withstand every test prescribed by the Secretary under
      this chapter.