(a) The Department may conduct an investigation of any public or private bridge, causeway, viaduct or other elevated structure which crosses any public highway regardless of the owner or the owners of said bridge, causeway, viaduct or elevated structure and regardless of what government has jurisdiction over it.
(b) If it finds that a public structure set forth in subsection (a) of this section cannot safely withstand vehicles traveling at the speed permissible under the Code, or cannot withstand vehicular gross weights, including carried load, permissible under the Code, the Department shall determine and declare the maximum speed or gross weight, including carried load, or both, of vehicles which such structure can withstand and shall cause or permit signs stating such maximum speed or gross weight, including carried load, to be erected and maintained before the entrance to such structure.