U.S. Route 431 in Tennessee

U.S. Route 431 (US 431) in Tennessee totals an estimated 116 mi through Lincoln, Marshall, Maury, Williamson, Davidson, and Robertson counties in Middle Tennessee.

Alabama state line to Nashville
US 431 runs concurrently with US 231 upon entry into Tennessee from Madison County, Alabama, where the concurrency begins. The state line also marks the beginning of a secret concurrency with, and the southern terminus of unsigned State Route 10 (SR 10). The two U.S. Routes plus SR 10 do not split until they reach downtown Fayetteville. While US 231 goes into a north-northeasterly path, US 431 turns northwest into Marshall County, bypassing around Lewisburg, and later into northeastern Maury and into Williamson County. It traverses the city of Franklin, Tennessee before entering the Metropolitan Nashville and Davidson County area.

In Nashville, US 431, known as Hillsboro Pike, traverses the exit 3 interchange on I-440, and eventually merges into US 70/SR 1 before entering the downtown area. US 431 then joins US 31 and US 41A onto the James Robertson Parkway. After crossing I-24's exit 47 interchange, US 431 then follows US 41 (SR 11) and US 31W towards the northern suburbs.

Nashville to the Kentucky state line
US 431, now paired with a secret SR 65 designation, then follows Trinity Lane, crossing the I-65/I-24 exit 87 interchange, and turns right onto Whites Creek Pike. A few miles later, it intersects Briley Parkway (SR 155)] and Old Hickory Boulevard near Whites Creek. Like most major routes in and out of Nashville, US 431 crosses Old Hickory Boulevard. twice, the first time in the southern suburbs, and the other in the north. US 431/SR 65 continues northward to traverse I-24's Joelton interchange, exit 35, before entering Robertson County.

It traverses the Springfield area, running concurrently with US 41 (SR 11) through town. It then splits off again, and US 431 continues north to the Kentucky state line, which marks the northern terminus of SR 65.

Concurrencies and secret designations
In Tennessee, when a US Highway runs concurrently with a state highway, the state highway's designation is not signed, but is a secret designation. Along US 431 in Tennessee, the secret designations include:
 * SR 10 from the Alabama state line to Fayetteville (in association with US 231);
 * SR 50 from Fayetteville to Lewisburg;
 * SR 106 from Lewisburg to the US 70S/SR 1 junction in Nashville;
 * SR 1 in downtown Nashville (in association with US 70S);
 * SR 24 in downtown Nashville (with US 70);
 * SR 11 from downtown Nashville to the Trinity Lane intersection (in association with US 31/US 41/US 41A, and US 31W/US 41, including James Robertson Parkway), and through downtown Springfield (with US 41);
 * SR 65 from Nashville to the Kentucky state line;
 * SR 76 from downtown Springfield to the north side of Springfield.