I-49 in Arkansas

[ozarkman417]

The Ouachita Trail crosses Fourche Mountain east-west, and a road cut would require a long bridge over I-49.

The Ouachita Trail also crosses US-71 at Foran Gap, which functions as a trailhead. A limited-access interstate would displace this trailhead, but it would be simple enough to make a bridge or culvert to allow the trail to cross I-49.

As for creating a trailhead that works with a limited-access highway, I like what Colorado did with the Ten Mile Canyon trailhead off of I-70 at Vail Pass, which doubles as a Rest Area. Such a facility could be placed atop Foran Gap. This would therefore function as a replacement for US-71's Elm Park Rest Area.

[sprjus4]

Not a freeway, but they recently constructed a pedestrian bridge over VA-311 outside Roanoke, VA where the Appalachian Trail crosses. It was previously a crosswalk with advance warning signs on a corner on a 55 mph two lane road. Not exactly the safest condition!

https://maps.app.goo.gl/wU4wU6jV5V8SMSd38

[Rick Powell]

The times I drove the Foran Gap, you can keep it 55 all the way (it's Arkansas) and the big "S" curve on the map is gentle. No issues at all with a freeway through it, but I worry that there would be no alternative through route for slower traffic.

With the number of private entrances and side roads off US 71, I am sure some thought will be given to keeping US 71 as a continuous frontage road, with some consolidation and closing of entrances. IF the freeway closely follows the US 71 alignment, which seems likely. Heck, they may go "all Texas" and create a new frontage road on the other side of the freeway, too. 

[bugo]

If the Foran Gap is so flat, why have they not used it previously?

US 270 and US 71 go through Foran Gap.