Business Loop I-90 - Plankinton

The former business route for I-90 at the city of Plankinton looped north from Exits 308 and 310. The western 2.552 miles of the route, consisting of Main Street north and Davenport Street (historic U.S. 16) east double as SD 258. SD 258 is an unsigned municipal and state secondary highway.

The eastern leg of the route follows U.S. 281 between Old Highway 16 and Interstate 90 for 1.3 miles. Signs for the Plankinton business loop were removed by 2009 and South Dakota 258 remains unposted as of 2016.