Expense of operating vehicle used by state officer, employee, or agent

When any state officer, member of a state board or commission, or any subordinate officer, agent, or employee thereof is authorized by law to and does incur, in the discharge of his official duties, any expense incident to traveling in his own motor vehicle, the amount allowed for such expense shall be fixed by the secretary of the Finance and Administration Cabinet which sum shall include depreciation and investment charges incident to the operation of the motor vehicle.