(a) A state agency may pay an expense under this subchapter by:
(1) reimbursing the employee as provided by Subsection (b);
(2) directly paying the expense as provided by Subsection (c); or
(3) directly paying the expense in advance of travel as provided by Subsection (d).
(b) If a state agency reimburses a state employee, the agency shall submit receipts to the comptroller on request in the manner required by the comptroller. A state agency is not required to submit receipts for mass transit, taxi, or limousine fares.

(c) A state agency may request a commercial transportation company to furnish transportation to the agency’s state employees and to bill the agency monthly for that transportation. The state agency shall require the company to submit an invoice to the agency listing the points of origin and destination for each trip and the taxes charged. The agency shall submit those invoices to the comptroller on request and in the manner required by the comptroller.
(d) A state agency may directly pay a commercial transportation company before the travel of a state employee if the payment would result in a lower transportation expense. The comptroller may adopt rules that authorize advance payments in other circumstances.
(e) If a reimbursement to a state employee for a transportation expense would not be authorized, a direct payment to a commercial transportation company for the same expense is prohibited.
(f) A state agency may not pay or reimburse the expense of transporting a state employee by rented or public conveyance if the transportation is provided by a person who is not a commercial transportation company.