Interstate Highway 26

Interstate Highway 26

Interstate Highway 26

As traffic congestion increased on the heavily traveled U.S. Highway 23 corridor between Asheville, North Carolina and Johnson City, Tennessee, so did the need for an alternate route. Motorists needed a safer and quicker path between the two cities. Safety and mobility were the main concerns. 

Tennessee Department of Transportation chose HDR to design a five-mile extension of Interstate Highway 26 in Unicoi County, Tennessee. The new route began at the North Carolina/Tennessee border, near the Appalachian Trail. It headed north toward Johnson City. 

Our design cut travel time significantly. It also provided a safe environment for the traveling public. We designed a four-lane, divided interstate facility with a 14-foot median in rugged terrain that included one interchange, one truck inspection area and two scenic overlooks. 

Building in the Appalachian Mountains required challenging geotechnical work. It included core oriented drilling. Our engineers spent a large amount of time testing and drilling the terrain to ensure the proposed roadway would not encounter rockslide issues. This also resulted in minimizing future maintenance costs.

Due to the mountainous terrain and associated roadway grades, we included two runaway-truck ramps. To minimize the risk of runaways, we kept the maximum horizontal grade below six percent. 

The project winds through an extremely remote area that supports an abundance of wildlife. For this reason, we provided wildlife passage culverts. Now, local fauna can cross beneath the interstate.  Two scenic overlooks were also installed so motorists could stop and enjoy the beauty of the Appalachian Mountains.


Award of Excellence, Federal Highway Administration


Interstate Highway 26
Tennessee Department of Transportation

Unicoi County, TN
United States

5 miles