S.C. Code Ann. § 58-15-1690

Whenever any department or subdivision shall require a railroad, under the provisions of this article, to construct an overhead bridge or underpass, such railroad shall begin work thereon within sixty days after receipt of the order of such department or subdivision. And in case such railroad shall not comply with such order within the period specified, the department or subdivision may proceed with the work and, upon its completion, bill the railroad for its proportion thereof and the railroad shall pay such bill, together with interest at the rate of seven per cent per annum from the date of the completion of the work. But before the railroad is required under this provision to proceed with the construction of such grade separation structure the estimated pro rata share of the department or subdivision shall be arranged for and appropriated.