The department of administrative services shall maintain in the city of Columbus a reasonable supply of motor vehicles designed to carry passengers which shall be made available for the use of any state agency needing transportation facilities of an intermittent or temporary nature. The director of administrative services shall fix the rates of charge for the use of such motor vehicles at a level sufficient to operate, maintain, and replace the fleet of vehicles. Such charges shall be collected by the director and deposited in the state treasury to the credit of the fleet management fund, which is hereby created. The vehicles shall be used only with the permission of the appointing authority and the director. A record of such use shall be kept by the director. The director shall calculate at least once each year a cost per mile of operation for each motor vehicle in the fleet.