US 40, also known as the National Road, is a major east-west highway in the United States. It stretches approximately 3,000 miles from Atlantic City, New Jersey, to San Francisco, California. Established in the early 19th century, it played a crucial role in westward expansion and the development of the American transportation network. The highway passes through several states, including Pennsylvania, Ohio, and California. It connects various cities and towns, serving as a vital route for commerce and travel. Today, US 40 is part of the larger U.S. Highway System and continues to be an important thoroughfare for both local and long-distance traffic.