Over two centuries, the route through Cumberland Gap evolved from buffalo trace to Warriors Path, Wilderness Road, Dixie Highway, U.S. Highway 25E, and back again to the Wilderness Road. Since the park's conception in the 1920s, some had hoped to restore the historic trail through the Gap, and 80 years later that goal was achieved. Re-creating the 1780s Wilderness Road required years of fieldwork and research, including use of an 1833 survey and an 1862 Civil War-era map. Standing in the Gap in 1850, U.S. Senator Henry Clay predicted the westward flow of humanity. Restoration work included placing more than 200,000 cubic yards of fill dirt to raise the roadbed to its 18th-century contour and planting tens of thousands of trees. Because U.S. Highway 25E over Cumberland Gap was dangerous, Public Law 93-87 in 1973 directed the National Park Service to build tunnels through Cumberland Mountain to remove traffic from the Gap, and since their opening in 1996, the tunnels have carried more than 11 million vehicles annually.