Interstate 640 (I-640) is an east–west auxiliary Interstate Highway in Knoxville, Tennessee. It serves as a bypass for Interstate 40 around Downtown Knoxville, and is also an alternative route for traffic passing between I-40 and I-75. All trucks carrying hazardous cargo through Knoxville are required to use I-640. It has a total length of 10.8 miles (17.4 km), and runs approximately 3 miles (4.8 km) north of downtown through the northern neighborhoods of Knoxville.
For its first 2.9 miles (4.7 km), I-640 has a concurrency with I-75, although exits along this segment are numbered according to the former’s mileage. For the rest of its length, the interstate maintains an unsigned concurrency with U.S. Route 25W (US 25W). Both of these highways were rerouted from their original alignments upon I-640’s completion.
The route that is now I-640 was first planned by the city of Knoxville in 1945, and initiated by the Federal Aid Highway Act of 1956, along with most of the Interstate Highway System. Initial construction work began in the early 1960s, and for many years, only 2 miles (3.2 km) of the highway was open to traffic. Work on the remainder of I-640 began in 1977, and the last section was completed in 1982.
I-640 has three lanes in each direction for its entire length, in addition to auxiliary lanes between some interchanges. Average annual daily traffic (AADT) counts range from between 87,000 vehicles near the highway’s midpoint to 66,000 vehicles at the eastern terminus. Unlike the other Interstate Highways in Knoxville, however, I-640 rarely experiences severe congestion.
I-640 begins west of Downtown Knoxville at a directional T interchange with I-40 and I-75, where the latter continues onto a concurrency with I-640. Along this section, I-640 is treated as the primary route, with exits numbered according to its mileage. Initially heading northwest, the interstate immediately passes under State Route 169 (SR 169, Middlebrook Pike) without an interchange. A short distance beyond this point, the highway turns north and crosses a CSX railroad mainline, intersecting with SR 62 (Western Avenue) a short distance later. It then veers northeast into the southern fringes of Dutch Valley, running along the northern base of Sharp’s Ridge. About
1+1⁄2 miles (2.4 km) later, I-640 reaches an unusual three-level combination interchange, commonly known as the Sharp’s Gap Interchange, with US 25W (Clinton Highway), I-75, and the northern terminus of I-275.
At this interchange, I-75 splits off, heading north towards Lexington, Kentucky, and US 25W and SR 9 begin an unsigned concurrency with I-640. Also at this interchange, SR 9 continues onto an unsigned concurrency with US 25W north to Clinton. The highway then shifts slightly east-northeast, and a few miles later, has an interchange with US 441 (Broadway). A short distance later, I-640 crosses a Norfolk Southern Railway mainline. Some distance later, the freeway turns almost directly east. It then reaches an interchange with Washington Pike and Millertown Pike; access between the two is provided via frontage roads on both sides of the interstate. The highway then gradually shifts south, and a few miles later, crosses another Norfolk Southern mainline and US 11W (Rutledge Pike) without intersecting this route. I-640 then reaches its eastern terminus at a directional T interchange with I-40 on the eastern outskirts of Knoxville. Here, US 25W and SR 9 continue onto a brief unsigned concurrency with I-40, heading eastward towards Asheville, North Carolina.