Vehicles or a combination of vehicles with divisible loads in excess of the width, length, or height requirements of chapter 321 may be moved on the highways of this state if the department or permit-issuing authority determines there is a special or emergency situation which warrants the issuance of a special permit. The combined gross weight or gross weight on any one axle or group of axles may exceed the limits established in section 321.463, subject to the limits and routes established by the permit-issuing authority.