43 Tex. Admin. Code § 15.194
If allocated funds remain after reimbursement of all of a county's listed transportation infrastructure projects, the county may use the unexpended balance for any transportation project in the county if within one year after the date of submission of the written certification required by § 15.193 of this subchapter (relating to Certification of Completion), the county submits in writing to the department a proposed amendment to the agreement under § 15.191 of this subchapter (relating to Agreement) that identifies the additional project and contains the information required by § 15.188(b)(2) and (4) of this subchapter (relating to Application Procedure) for that project, and the department and county execute the proposed amendment.
43 Tex. Admin. Code § 15.194