Ind. Code § 8-23-4-10

Sec. 10. Whenever the department determines that, because of the construction of a new state highway, the relocation of a state highway, or a change in general function or use, a part of the state highway system no longer meets the criteria established in section 2 of this chapter for a highway in the state system but that the highway continues to serve a useful purpose, that part of the system may be transferred to a county highway system or a municipal street system.