Title 40, Chapter 6, Section 185
(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 such bridge or structure, when such structure is posted as
provided in this Code section.
(b) The Department of Transportation may conduct an investigation of
any bridge or other elevated structure constituting a part of a
highway, and, if it shall thereupon find that such structure cannot,
with safety to itself, withstand vehicles traveling at the speed
otherwise permissible under this chapter, the department shall
determine and declare the maximum speed of vehicles which such
structure can safely withstand and shall cause or permit suitable
signs stating such maximum speed to be erected and maintained before
each end of such structure.
(c) Upon the trial of any person charged with a violation of
subsection (a) of this Code section, proof of determination of the
maximum speed by the department and the existence of such signs
shall constitute conclusive evidence of the maximum speed which can
be maintained with safety to such bridge or structure.