(a) No person shall operate a vehicle over any bridge or other elevated structure constituting a part of a street at a speed which is greater then the maximum speed that can be maintained with safety to such bridge or structure, when such structure is posted with authorized signs stating such maximum speed. Such signs shall be erected and maintained at a distance of at least 100 feet before each end of such structure.
(b) Upon the trial of any person charged with a violation of this section, proof of the determination of the maximum speed and the existence of such signs shall constitute prima-facie evidence of the maximum speed which can be maintained with safety to such bridge or structure. (ORC 4511.23)