N.C. Gen. Stat. § 20-144
It shall be unlawful to drive any vehicle upon any public bridge, causeway or viaduct at a speed which is greater than the maximum speed which can with safety to such structure be maintained thereon, when such structure is signposted as provided in this section.
The Department of Transportation, upon request from any local authorities, shall, or upon its own initiative may, conduct an investigation of any public bridge, causeway or viaduct, and if it shall thereupon find that such structure cannot with safety to itself withstand vehicles traveling at the speed otherwise permissible under this Article, the Division shall determine and declare the maximum speed of vehicles which such structure can withstand, and shall cause or permit suitable signs stating such maximum speed to be erected and maintained at a distance of 100 feet beyond each end of such structure. The findings and determination of the Department of Transportation shall be conclusive evidence of the maximum speed which can with safety to any such structure be maintained thereon.
N.C. Gen. Stat. § 20-144