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SC 340 begins at an intersection with SC 403 (Oates Highway) north-northwest of Timmonsville, within Darlington County. It travels to the northeast and crosses Middle Swamp and Myrtle Branch before an interchange with Interchange 20 (I-20). It crosses over Jeffries Creek and High Hill Creek before entering the city limits of Darlington. There, it intersects U.S. Route 52 (US 52; Governor Williams Highway). It crosses some railroad tracks before it meets its northern terminus, an intersection with SC 34 (Pearl Street).[2]