Florida). Corridor Q, carrying US 460, runs through Mercer County, entering the state from Giles County, Virginia and then reentering Virginia at Tazewell County. Work continues on the long-delayed Corridor H, which will carry US 48 from Weston to the Virginia line near Wardensville. As of 2018, a section from Weston to Kerens just past Elkins, and another section from Wardensville to Davis are complete. Other projects under development are a four-lane upgrade of US 35 from Scott Depot to the Ohio River at Point Pleasant, which is about two-thirds complete; a four-lane upgrade of WV 10 from Logan to Man and then of WV 80 from Man to Gilbert, which is about half completed; and four-lane upgrades to US 52 from Bluefield to Williamson, known as the "King Coal Highway" and from Williamson to Huntington, known as the "Tolsia Highway" which are many years from completion. A project known as the "Coalfields Expressway" is also ongoing, and will carry US 121 from Beckley west across Raleigh, Wyoming, and McDowell counties, entering Virginia near Bishop. Rail lines in the state used to be more prevalent, but many lines have been discontinued because of increased automobile traffic. Many old tracks have been converted to rail trails for recreational use, although the coal-producing areas still have railroads running at near capacity. Amtrak's Cardinal roughly parallels I-64's path through the state. MARC trains serve commuters to Washington, D.C. in the eastern panhandle. In 2006 Norfolk Southern along with the West Virginia and U.S. Government approved a plan to modify many of the rail tunnels in West Virginia, especially in the southern half of the state, to allow for double-stacked cars (see inter-modal freight). This is expected to also help bring economic growth to the southern half of the state. An Intermodal Freight Facility is located at Prichard, just south of Huntington. Because of the mountainous nature of the entire state, West Virginia has several notable tunnels and bridges. The most famous of these is the New River Gorge Bridge, which was at a time the longest steel single-arch bridge in the world with a 3,031-foot (924 m) span. The bridge is also pictured on the West Virginia state quarter. The Fort Steuben Bridge (Weirton-Steubenville Bridge) was at the time of its construction one of only three cable-stayed steel girder trusses in the United States. "The Veterans Memorial Bridge was designed to handle traffic