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
Bicycles are permitted on Interstate highways in Idaho. ITD permits bicycle travel on the paved shoulders of rural Interstate segments in Idaho — including I-15, I-84, I-86, and I-90 — where no reasonable alternative exists. Urban Interstate segments through Boise and Coeur d'Alene are signed prohibited; long tunnels and certain bridges are individually posted.
What this means in practice
Interstate cycling is legal in Idaho, but ride only where you have a wide, clean shoulder and exit at the first signed bicycle exit when conditions deteriorate.