What is the name of the oldest highway in which states?

The oldest highway in the United States is the National Road, also known as U.S. Route 40. It was established in the early 19th century, originally connecting Cumberland, Maryland, to Vandalia, Illinois. Today, it runs through several states, including Maryland, Pennsylvania, West Virginia, Ohio, Indiana, and Illinois. The road played a significant role in westward expansion and transportation in early American history.