South Carolina Highway 642, also known as Dorchester Road, is a major state highway in North Charleston and Summerville. The road runs for 19.1 miles from U.S. 78 in North Charleston, SC to U.S. 17 Alt southwest of Summerville, SC. Dorchester Road is a heavily congested highway during morning and evening traffic periods. In Summerville, it narrows to a two lane road, creating a bottleneck of traffic in Dorchester County.

Current plans call for widening of the road from Summerville to U.S. 17-Alt.