C.R.S. § 39-26-710

(1) The following shall be exempt from taxation under the provisions of part 1 of this article: (a) The sale of construction and building materials to a common carrier by rail operating in interstate or foreign commerce for use by the common carrier in construction and maintenance of its railroad tracks; however, any actual use of such construction and building materials shall, at the time of the actual use, be subject to the tax imposed by part 2 of this article and any use tax imposed pursuant to article 2 of title 29 , C.R.S.; (b) The sale of tangible personal property that is to be affixed or attached as a component part of a locomotive, a freight car, railroad work equipment, or other railroad rolling stock; and (c) The sale of locomotives, freight cars, railroad work equipment, and other railroad rolling stock used or purchased for use in interstate commerce by a railroad company. (2) The following shall be exempt from taxation under the provisions of part 2 of this article: (a) The storage, use, or consumption of any tangible personal property that is to be affixed or attached as a component part of a locomotive, a freight car, railroad work equipment, or other railroad rolling stock; and (b) The storage, use, or consumption of locomotives, freight cars, railroad work equipment, and other railroad rolling stock used or purchased for use in interstate commerce by a railroad company.