Four Mile Run Trail
The Four Mile Run Trail is a 7-mile long, paved shared use path in Arlington County and Falls Church. It runs along Four Mile Run from Benjamin Banneker Park in Falls Church to the Mount Vernon Trail near Ronald Reagan Washington National Airport, where Four Mile Run empties into the Potomac River. The trail runs roughly parallel to parts of the Washington & Old Dominion Railroad Trail as it follows Four Mile Run, sometimes on the other side of the stream. History 
The trail opened on September 4, 1967 as a four-mile, unpaved trail between Roosevelt Street and the Columbia Pike. In 1966, Arlington County was one of 12 urban areas to receive a grant from the Department of the Interior as a demonstration of urban trails, the first such grants ever given. The Four Mile Run Trail was the first of these trails built, making it the nation's first shared use path built with federal funds. Secretary of the Interior Stewart Udall had created the program in hopes that it would build support for trails legislation he was supporting. That legislation later became the National Trail System Act of 1968. The trail was built adjacent to an existing hiking trail and the still extant W&OD railroad tracks. In the following years, the trail was paved and expanded. By mid-1968, the trail had been extended south to Walter Reed Drive, though the bike trail ended at Columbia Pike, and north to N. Van Buren Street in the Falls Church section of Benjamin Banneker Park. By 1971, most sections of the trail were paved, but it still had many low-water crossings and cinder-surfaced sections. By 1976, it was extended to Shirlington. At Shirlington, it crossed I-95 on the Shirlington Overpass which had been opened in 1972. By 1977 it was extended west of Broad Street in Falls Church (along the Washington & Old Dominion (W&OD) right-of-way). In 1980, as part of the construction of seven bridges across Four Mile Run - for Route 1, the Potomac Yard railroad, the main rail line and the George Washington Parkway - the Army Corps of Engineers built a section of the Four Mile Run Trail beneath the bridges from Route 1 to the Mount Vernon Trail. Later that spring, the gap between the new section and I-95 was opened. In 1981-82, the section of trail near Brandymore Castle in Arlington was rebuilt in conjunction with the construction of I-66. The section of trail from the point where Four Mile Run emerges from under I-66 in Arlington County to the bridge over Four Mile Run in Banneker Park then became part of both trails. In the future, Arlington County would like to reroute the W&OD Trail to a separate route outside of the park, thus reducing the amount of joined trail. In 2009, a trail extension was completed near Shirlington that not only linked the end of the Washington & Old Dominion Railroad Trail with the Four Mile Run Trail, but also allowed trail users to pass under the Shirley Highway (Interstate 395) and W. Glebe Road without having to ride on-street in Shirlington and Alexandria. An underpass was originally to be built as part of the 1970's Four Mile Run project that built the I-95 to Mount Vernon Trail section, but it was not built at that time. Notes and references

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Parks in Arlington County, Virginia
Transportation in Arlington County, Virginia
Bike paths in Virginia