It depends.  The General Statutes of North Carolina set all rural speed limits at 55 m.p.h. and municipal limits at 35 m.p.h.  These can be changed by ordinances enacted by the NCDOT.  Changes, either higher or lower, inside city limits, require the agreement of the municipality and the NCDOT.  If signs are not posted in rural areas, the speed limit is officially 55 m.p.h.  This does not mean it is recommended to drive that fast;  motorists should always drive at reasonable and prudent speeds as dictated by driving conditions.  When this office conducts a speed zone study and recommends a speed limit, we draft the ordinance and submit it to the State Traffic Engineer's office for approval.  When it is approved, our Traffic Services unit installs the speed limit signs.