Design guidance from the Federal Highway Administration recommends a protected bike lane or shared use path for people biking when a road has a speed limit of 30 miles per hour or more. This data specifically shows answers about the existence of protected bike lanes on state roadways, and not shared use paths.
Data is from the 2021 Bicycle Friendly State survey and asked "Are protected or separated bike lanes installed on any state-controlled roadway in your state?" Some states, such as Ohio and Washington, have shared use paths adjacent to state roadways, but did not report them based on the specific phrasing of the question.