SC 303 ALT: Appeared in 1942 as new primary routing including new construction, running from SC 303 north via River St Ext to Mill St west to Memorial Ave north to end at SC 64 (now US 17 ALT and SC 64 Bus) in Walterboro.
In 1947, SC 303 ALT was downgraded to S-15-36. The Rivers St portion is now part of S-15-59.
SC 303 ALT is shown but not labeled on the 1942 Official, but oddly no road is shown on the 1943 Colleton County map. However, SC 303 ALT is explicitly mentioned in the 1948 SCDOT Annual Report.