This subchapter governs the scope and content of program grant agreements and contracts and the means of determining whether costs of a proposed project will be eligible for reimbursement with traffic safety funds pursuant to a grant agreement or a contract with the department. They shall not be construed to enlarge, diminish, modify, or alter the power or authority of the department or any substantive rights of any person, organization, or political jurisdiction. This subchapter does not apply to purchase order contracts awarded in accordance with Government Code, Chapter 2155.