Tennessee

US 25W carries the unsigned designation of State Route 9 (SR 9) throughout the state.

US 25 splits into US 25W and US 25E on the west side of downtown Newport. Here, SR 32 goes north on US 25E and US 70/SR 9/SR 35 continue on US 25W. The concurrency then has a full interchange with Interstate 40 (I-40; exits 432A–B) before US 411/SR 35 separate and turn south while US 25W/US 70/SR 9 leave Newport and cross into Jefferson County.

Immediately after crossing the county line, they intersect SR 363 in Reidtown and then cross Douglas Lake parallel to the I-40 bridge. After crossing the lake, they intersect SR 113 and then proceed to Dandridge where SR 66 joins the concurrency. US 25W/US 70/SR 9/SR 66 next intersect and become concurrent with SR 92, passing by downtown to the north (SR 66 is unsigned at this intersection). SR 92 separates from the concurrency which proceeds to have another interchange with I-40 (exit 415); SR 66 separates thereafter and runs concurrent to I-40 before leaving Dandridge. US 25W/US 70/SR 9 continue west through rural Jefferson County before coming to an intersection with Snyder Road (which connects to SR 66 and Sevierville) and becoming concurrent with SR 139 before crossing into Sevier County.

Once across the county line, SR 139 separates and turns south toward Kodak while US 25W/US 70/SR 9 continue west to cross into Knox County.

The highway then has an interchange with US 11E/SR 34 in Carter (also known as Trentville) with US 11E joining the concurrency as they enter Knoxville. US 11E/US 25W/US 70/SR 9 then intersect SR 168 (Governor John Sevier Highway) before crossing a bridge over the Holston River. After this section, US 25W/SR 9 leaves the US 11E/US 70 concurrency to join I-40 at exit 394. It travels a short way before leaving I-40 to follow I-640 (exit 385). They then have interchanges with Mall Road (which provides access to Knoxville Center Mall at exit 8), US 441/SR 33/SR 331 (Broadway; which provides access to Fountain City at exit 6), and I-75/I-275 (exit 3A) before separating from I-640 to turn north at exit 3B. US 25W/SR 9 continues through the North Knoxville neighborhood as Clinton Highway and leaves Knoxville to enter Powell. In Powell, they intersect and have a short concurrency with SR 131 before leaving Powell and crossing into Anderson County.

The highway next enters Claxton and becomes a very curvy four-lane undivided highway. In Claxton, US 25W/SR 9 intersects SR 170 and continues north from Claxton, winding its way through rural areas for a few miles to enter Clinton. Here, they intersect SR 61 before going straight through the historic downtown as Main Street. US 25W/SR 9 then leave Clinton, becoming curvy again before going through Medford to enter Rocky Top. In Rocky Top, US 25W/SR 9 goes through downtown to intersect and become concurrent with SR 116. The highway next intersects US 441/SR 71 (which provides access to Norris Lake and Dam) before coming to an interchange where US 25W/SR 9 becomes concurrent with I-75 (exit 129) leaving SR 116 to trace the historical route of US 25W/SR 9.

They cross into Campbell County and enter Caryville where they separate from I-75 (exit 134) and become concurrent with SR 63. Immediately afterward, they intersect the northern end of SR 116 and pass by Cove Lake, Cove Lake State Park, and Caryville Dam before leaving Caryville to enter Jacksboro. In Jacksboro, US 25W/SR 9/SR 63 bypass downtown to the north and go through Jacksboro's main business area before proceeding into downtown LaFollette. There, they separate from SR 63 and turn north, becoming very curvy again as the road enters mountainous terrain to pass through Duff, cross Brushy Mountain Gap, then descend into the valley carved by Lick Creek and the Clear Fork of the Cumberland River. Here, they pass through Habersham then intersect SR 90 at Morley. US 25W/SR 9 finally enters Jellico and have another interchange with I-75 (exit 160) before proceeding to downtown and intersecting SR 297 before turning north and ending at the Kentucky state line, with US 25W continuing north alone into Kentucky.

Kentucky

Upon entry into Whitley County, US 25W runs parallel with and closely follow I-75 for the rest of its course, including the points where it traverses the towns of Williamsburg and Corbin. It continues to parallel Clear Fork as the highway travels down a narrow valley, passing through the communities of Red Ash, Saxton, Pleasant View, and Emlyn. US 25W enters Williamsburg and immediately intersects with KY 92, running concurrently with it as they cross over the Cumberland River and KY 92 leaves the concurrency to head east to Pineville after about one mile (1.6 km). The highway follows the east bank of the river, passes the entrance to downtown and continues north through the Highland Park neighborhood before leaving Williamsburg and intersecting KY 26 near Wofford. It then intersects I-75 (exit 15) with an unusual (for Kentucky) double roundabout interchange before winding its way north through farmland and rural areas. US 25W next intersects with KY 90 (providing access to Cumberland Falls) and KY 1193 before entering Corbin and crossing I-75 for the last time (exit 25). It passes through a business district and some neighborhoods, where it has an intersection with KY 3041 (Corbin Bypass), before meeting back up with KY 26 and passing straight through downtown via a one-way pair between Main Street and Kentucky Avenue. The highway passes through more neighborhoods before crossing Lynn Camp Creek into North Corbin and Laurel County. US 25W passes straight through downtown before coming to an intersection north of town, where US 25E and US 25W reunites to become US 25. However, US 25E continues west of this point to terminate at exit 29 of I-75.^[4][5]