Hi no greed, my vision is not the best (actually, it’s awful following possibly botched cataract surgery back in March), but when I first read your post I thought it read 120 instead of I20.
Just to clarify: the area being discussed in the New Yorker article is just south of where I-20 crosses the river, right near the Six Flags Over Georgia parking lot. This location is about 3 miles west of the the I-20 / I-285 interchange, and about 9 miles west of downtown Atlanta.
Most Atlantans I think refer to I-285 (which encircles the city) as “The Perimeter” or “The Perimeter Highway”, so the river location being discussed is about 3 miles outside the Perimeter.
Jmo