[jedberg]

There are a bunch of articles about it but nothing scientific. For example:

https://www.bbc.com/news/world-us-canada-42104894

And it turns out I was wrong. There is one spot 21.7 miles away from a road deep in Wyoming.

[bdamm]

This is highly dubious. Logging roads might be considered "roads" but some are passable only by heavy equipment. If you have to stop and repair the road every few hundred meters then I don't think it counts as a road.