Between Charleston and Beaufort
Going south from Charleston towards Beaufort on Highway 17, there is an (approximate) 25 mile stretch with maximum speeds of 50 and sometimes 45. Ironically, some of this stretch is four lane highway, surrounded by nothing more than woods and swamp. In other words, the speed limit has no real relation to what a reasonable speed limit should be.
Out-of-state drivers are easy prey for the troopers/police as they drive through, at what must seem to them to be a natural speed, of 65 or 70. Although the official speed limit is ridiculous, you will be ticketed (I believe over $200) for going 10 miles over the limit.