The National Road was the first major improved highway in the United States built by the federal government. Built between 1811 and 1837, the 620-mile (1,000 km) road connected the Potomac and Ohio Rivers and was a main transport path to the West for thousands of settlers. When improved in the 1830s, it became the second U.S. road surfaced with the macadam process pioneered by Scotsman John Loudon McAdam.

John Loudon McAdam was a Scottish civil engineer and road-builder. He invented a new process, "macadamisation", for building roads with a smooth hard surface, using controlled materials of mixed particle size and predetermined structure, that would be more durable and less muddy than soil-based tracks.