S.C. Code § 57-5-720
The Department of Transportation shall construct the highways in the state highway primary system and the highways in the state highway secondary system to standards commensurate with the amount and types of traffic services to be rendered by the highways in the respective systems, it being the declared policy of the State that the highways in the state highway secondary system shall be constructed by less expensive standards than the highways in the state highway primary system, thus enabling the State to construct a larger mileage of all-weather farm-to-market roads from the available funds.
In recognition of budgetary restraints, the Department of Transportation, its commission, officers, and employees, are granted the discretionary authority to relax design and construction standards with respect to highway projects in the secondary state highway system. The exercise of the discretionary authority to relax design and construction standards shall not give rise to any liability on the part of the department, its commission, officers, or employees.
S.C. Code § 57-5-720