In cases of emergency where a state highway is rendered impassable for vehicular traffic by reason of fire, flood, storm or any other unusual condition and when it is necessary to take emergency action to reestablish the highway to a condition to render it passable to traffic, and equipment owned by the state transportation commission suitable for such purpose is not immediately available, the secretary, subject to approval of the state transportation commission, may rent equipment for such purpose at a reasonable rental rate without advertising for bids. In all other cases, the secretary shall advertise for bids before renting equipment and shall rent such equipment from the party submitting the lowest satisfactory bid. Such advertisement for bids shall be in accordance with such rules as may be adopted therefor by the state transportation commission, and bids shall be on such forms and in such manner and accompanied by such guarantee as may be prescribed by the commission.