Tenn. Code Ann. § 54-1-130

In order to promote engineering and design quality and to ensure the maximum benefits of competition by professional engineering and design service firms, the commissioner of transportation is authorized to establish cost principles to be used to determine the reasonableness and allowability of various costs, including overhead rates, salary limits, allowable expense reimbursements and other costs the commissioner may deem necessary to regulate as they are applicable to design and consultant contracts. The overhead rates for professional engineering and design service firms shall not exceed one hundred forty-five percent (145%) of the consultant's direct labor costs. Nothing in this section shall be construed to require competitive bidding of design and consultant contracts.