(a) No person shall drive a vehicle over any bridge or other elevated structure constituting a part of a highway at a speed which is greater than the maximum speed which can be maintained with safety to the bridge or structure when the structure is signposted as provided in this section.
(b) Upon request from any local authority, the State Highway Commission shall, or upon its own initiative may, conduct an investigation of any bridge or other elevated structure constituting a part of a highway. If it shall find that the structure cannot, with safety to itself, withstand vehicles traveling at the speed otherwise permissible under this subchapter, the commission shall determine and declare the maximum speed of vehicles which the structure can safely withstand and shall cause or permit suitable signs stating the maximum speed to be erected and maintained at a distance of one hundred feet (100') before each end of the structure.
(c) Upon the trial of any person charged with a violation of this section, proof of the determination of the maximum speed by the commission and the existence of the signs shall constitute conclusive evidence of the maximum speed which can be maintained with safety to the bridge or structure.