The Washington and Old Dominion Railroad Regional Park is a linear regional park in Northern Virginia. The park's primary feature is the Washington and Old Dominion Railroad Trail (abbreviated as W&OD Trail), an asphalt-surfaced paved rail trail that runs through densely populated urban and suburban communities as well as through rural areas. Most of the trail travels on top of the rail bed of the former Washington and Old Dominion Railroad, which closed in 1968. Although the park is long, it is only about wide. The rail trail is approximately wide through much of its length and is a shared use path that is suitable for walking, running, cycling, and roller skating. A crushed bluestone–surfaced bridle path travels near the paved trail in the park's most westerly . The path is suitable for horseback riding and mountain biking. NOVA Parks (formerly named the Northern Virginia Regional Park Authority (NVRPA)) administers and maintains the park and its trails. NOVA Parks keeps most of the parkland surrounding the trails in a natural state. The park authority has placed alongside the paved trail a series of mile markers and a number of interpretative exhibits that describe the historic and natural features of the park (see Washington and Old Dominion Railroad Stations for locations of historical markers near the W&OD Trail). The headquarters office of the park is near the southwest side of the trail at Smith's Switch Road in Ashburn. A park rest stop is adjacent to the trail near the park's headquarters. Route The W&OD Trail begins in the Nauck neighborhood near the Shirlington section of Arlington County, close to the boundary between the County and the City of Alexandria. The trail ends in Purcellville in western Loudoun County. Its route largely parallels the routes of the Potomac River and Virginia State Route 7 (VA 7). The trail connects at its origin to the paved Four Mile Run Trail, which travels eastward through Arlington along a stream embankment to meet the Mount Vernon Trail at Ronald Reagan Washington National Airport, near the Potomac River. The start of the trail is also accessible from the Shirlington exit (Exit 6) of Interstate 395 (I-395) (the Henry G. Shirley Memorial Highway). The trail parallels the more curving and hilly Four Mile Run Trail throughout its route in Arlington. Although they coincide in several locations, the two trails generally travel on opposite sides of the Run.