U.S. Route 321 (US 321) is a branch of U.S. Route 21. It stretches 516.9 miles (831.9 km) from Hardeeville, South Carolina, to Lenoir City, Tennessee, with both cities serving as its southern endpoints. The road reaches its northernmost point in Elizabethton, Tennessee, near Johnson City.  Due to its unusual "north–south–north" path, US 321 crosses Interstate 40 and U.S. Route 70 three different times. Its purpose varies by state: it acts as an alternate route to interstates in South Carolina, serves as a major highway in North Carolina, and provides a scenic drive in Tennessee. 

Interstate 40 (I-40) is a major east-west transcontinental highway in the United States, running for 2,556.61 miles (4,114.46 km). It is the third-longest interstate highway in the country, following Interstate 90 and Interstate 80. I-40 stretches across eight states: California, Arizona, New Mexico, Texas, Oklahoma, Arkansas, Tennessee, and North Carolina.

Key Information:

Western Terminus: The western end of I-40 is at Interstate 15 in Barstow, California.

Eastern Terminus: The eastern terminus is in Wilmington, North Carolina, where I-40 terminates at a concurrency with U.S. Route 117 (US 117) and North Carolina Highway 132 (NC 132).

Major Cities Served:

I-40 passes through or near several major cities across the country, including:

Flagstaff, Arizona

Albuquerque, New Mexico

Amarillo, Texas

Oklahoma City, Oklahoma

Little Rock, Arkansas

Memphis, Tennessee

Nashville, Tennessee

Knoxville, Tennessee

Asheville, North Carolina

Winston-Salem, North Carolina

Greensboro, North Carolina

Durham, North Carolina

Raleigh, North Carolina

Wilmington, North Carolina

Significance:

Transportation Corridor: I-40 is an important transportation route for freight and passenger traffic, linking the southeastern and southwestern United States. It connects many major cities and serves as a critical route for travel across the country.

Scenic and Historical Areas: In addition to its role in modern transportation, I-40 also passes through many scenic and historical areas, including parts of Route 66 in Arizona and New Mexico, offering travelers access to both natural beauty and American history.

I-40 plays a vital role in connecting key regions of the U.S., facilitating trade, travel, and commerce across multiple states.