South Dakota Highway 34 is a state route that runs parallel to Interstate 90 across the entire state of South Dakota. It begins at the Wyoming border west of Belle Fourche, as a continuation of Wyoming Highway 24 (WYO 24). The eastern terminus is at the Minnesota border east of Egan, or southwest of Airlie, Minnesota, where it continues as Minnesota State Highway 30 (MN 30). It is just over 419 miles (674 km) in length, making it the longest state highway in South Dakota.

Interstate 90 (I-90) in the US state of South Dakota traverses east–west through the southern half of the state.