S.C. Code Ann. § 57-5-170

In order to protect the national security, the regulations may include provisions to restrict the area of the highway within the limits of the Savannah River Project to vehicular traffic, capable of maintaining the minimum posted speed limit; to designate any and all points of access to and from the segment of highway lying within the area and may provide for a system of closure at points upon the highway so as to enable the department or Atomic Energy Commission to identify vehicles and individuals using the highway and to enable the Department of Transportation or the Atomic Energy Commission to determine the transit time along the highway within the limits of the area.