Skyline Drive was originally lined with miles of chestnut log guardrails. However, the guardrails rotted and were removed in the 1950s and not replaced. The Marys Rock Tunnel was partially lined with concrete in 1958 to prevent icicles in the winter and water seepage in the summer. In 1983, the Federal Highway Administration began work to replace several of the original stone walls on the drive with concrete walls that used the original stone as a veneer. The road was added to the National Register of Historic Places on April 28, 1997. On September 22, 2005, Skyline Drive was designated a National Scenic Byway. Skyline Drive was designated a National Historic Landmark in October 2008 for its pioneering place in the development of national parks in the eastern United States.