S.D. Codified Laws § 49-28-41.1
If the department determines upon its own motion or upon the petition of a resident of this state that it is in the best interests of the state, it may appear before the FMCSA, the secretary, or the board as a party in all proceedings involving the regulation and control of motor carriers in interstate commerce. If any matter is pending before the FMCSA, the secretary, or the board between a resident of this state as petitioner and a motor carrier doing business in this state and engaged in interstate transportation of freights, charging the carrier with any violation of the Interstate Commerce Act, upon application of the petitioner, the department may appear therein and be substituted as a party in place of such petitioners and thereafter the matter shall be prosecuted by the department at the expense of the state in the same manner as though originally begun by it.
SDCL 49-28-41.1