This guide is for general information only and is not legal advice. Laws change — verify current rules with your state DOT or a licensed attorney before relying on this for any legal matter. Read full disclaimer.
The rule
Whether bicycles can ride on an Interstate varies segment-by-segment in South Dakota. South Dakota DOT permits bicycle use on the shoulders of most rural Interstate segments (notably I-90 and I-29 outside metropolitan areas) where no reasonable alternative parallel route exists. Urban Interstate segments through Sioux Falls and Rapid City are signed prohibited. Verify the specific corridor against SDDOT signage before riding.
What this means in practice
Check the South Dakota DOT's bicycle-on-freeways map before you ride. Watch for "no bicycles" signs at on-ramps — they're posted segment-by-segment.