A few miles north of the state line, in Fayetteville, US 231 and 431 split again, with 431 heading northwest in combination with State Route 50. In the town of Petersburg, the combined route briefly joins with State Route 129; the trio head a few miles northwest before SR-129 splits off to the west. From here, US 431/SR 50 travels through mountainous and largely undeveloped territory in south central Tennessee until arriving in Lewisburg. On the east side of Lewisburg, it joins with U.S. Route 31A; the combined routes form part of a bypass around the eastern side of Lewisburg. This portion is named Ellington Parkway, and it forms brief unions with State Routes 272 and 11, plus a longer-lasting combination with State Route 106. Meanwhile, SR 50 splits off to travel through downtown Lewisburg, rejoining US 431 on the north side of town.