Forest Service maps indicate which ones are gated, though not how overgrown they are. Note earlier comment about hard vs easy, in this case more applicable to research than hiking effort. Gifford Pinchot Mt Adams district has a ton of gated forest roads at low altitude that will be melted out fairly early. While the roads were all for logging so the forest won't be old growth, it could be reasonably mature second growth. And some aren't gated but are blocked by berms to keep drivers out.
Trip recommendations, current conditions, and other trail related Q&A