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.
 There are no restrooms and few water fountains alongside the W&OD Trail in the County.
Restrooms and additional water fountains are available near ball fields and picnic areas along the Four Mile Run Trail.

The W&OD Trail's trailhead (Mile 0) is at the intersection of South Shirlington Road and South Four Mile Run Drive.
The trail starts in the Atlantic Coastal Plain at the trail's lowest elevation:  141 feet (43 m) above sea level.

The trail climbs 195 feet (59 m) in 5.9 miles (9.5 km) while traveling northwest through Arlington County.
While in Arlington, the trail ascends through the Atlantic Seaboard fall line while climbing upstream in the valley of Four Mile Run.
The trail crosses the Run seven times in the valley on bridges whose abutments were constructed before the Civil War by the Alexandria, Loudoun & Hampshire Railroad, a predecessor of the W&OD Railroad.

After crossing Columbia Pike (VA 244), the trail enters a steeply-sloped woodland that covers both sides of the valley.
 Near the end of the woodland, the trail intersects the Bluemont Junction Trail, a 1.3 miles (2.1 km) long paved rail trail that travels to Ballston on the bed of a former W&OD Railroad branch that once ran to Rosslyn and Georgetown.
0.6 miles (1.0 km) past that intersection, the W&OD Trail intersects the Custis Trail, a 4.5 miles (7.2 km) long paved shared use path that travels along Interstate 66 (I-66) (the Custis Memorial Parkway) to Rosslyn and which provides access to Washington, D.C. and the northern end of the Mount Vernon Trail.

After crossing its intersection with the Custis Trail, the W&OD Trail travels northwest near an I-66 soundwall for most of its remaining course in Arlington.
After crossing North Sycamore Street, the W&OD Trail passes the East Falls Church station on Washington Metro's Orange and Silver Lines.

After leaving the fall line, the W&OD Trail enters the Piedmont plateau region near the west corner of the County.
 The trail continues to climb in the Piedmont while traveling northwest through the City of Falls Church and Fairfax County.
 The trail reaches an elevation of 450 feet (140 m) at its crossing of I-66 in Fairfax County.
 When it reaches this point, the trail has risen 309 feet (94 m) while traveling 8.4 miles (13.5 km).

After crossing over I-495 (the Capital Beltway) on a trail bridge and passing Dunn Loring, the trail begins a long descent as it travels through Vienna.
 After leaving Vienna, the trail continues to descend until it reaches Difficult Run (Mile 14.3), where its elevation of 240 feet (73 m) is only about 100 feet (30 m) higher than is the elevation at the trail's origin.

After the trail crosses Difficult Run, it ascends and descends between additional streams (including Sugarland Run, Broad Run, Beaverdam Run, Goose Creek, Sycolin Creek and Tuscarora Creek) as it travels further northwest in the Piedmont through or near Reston, Herndon, Sterling, Ashburn, and Leesburg.
While traveling through Reston, the trail crosses Wiehle Avenue (VA 828) 0.3 miles (0.5 km) northeast of the Wiehle–Reston East station on Washington Metro's Silver Line.

When crossing Tuscarora Creek in Leesburg, the trail's elevatio
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.  There are no restrooms and few water fountains alongside the W&OD Trail in the County. Restrooms and additional water fountains are available near ball fields and picnic areas along the Four Mile Run Trail.
The W&OD Trail's trailhead (Mile 0) is at the intersection of South Shirlington Road and South Four Mile Run Drive. The trail starts in the Atlantic Coastal Plain at the trail's lowest elevation:  141 feet (43 m) above sea level.
The trail climbs 195 feet (59 m) in 5.9 miles (9.5 km) while traveling northwest through Arlington County. While in Arlington, the trail ascends through the Atlantic Seaboard fall line while climbing upstream in the valley of Four Mile Run. The trail crosses the Run seven times in the valley on bridges whose abutments were constructed before the Civil War by the Alexandria, Loudoun & Hampshire Railroad, a predecessor of the W&OD Railroad.
After crossing Columbia Pike (VA 244), the trail enters a steeply-sloped woodland that covers both sides of the valley.  Near the end of the woodland, the trail intersects the Bluemont Junction Trail, a 1.3 miles (2.1 km) long paved rail trail that travels to Ballston on the bed of a former W&OD Railroad branch that once ran to Rosslyn and Georgetown. 0.6 miles (1.0 km) past that intersection, the W&OD Trail intersects the Custis Trail, a 4.5 miles (7.2 km) long paved shared use path that travels along Interstate 66 (I-66) (the Custis Memorial Parkway) to Rosslyn and which provides access to Washington, D.C. and the northern end of the Mount Vernon Trail.
After crossing its intersection with the Custis Trail, the W&OD Trail travels northwest near an I-66 soundwall for most of its remaining course in Arlington. After crossing North Sycamore Street, the W&OD Trail passes the East Falls Church station on Washington Metro's Orange and Silver Lines.
After leaving the fall line, the W&OD Trail enters the Piedmont plateau region near the west corner of the County.  The trail continues to climb in the Piedmont while traveling northwest through the City of Falls Church and Fairfax County.  The trail reaches an elevation of 450 feet (140 m) at its crossing of I-66 in Fairfax County.  When it reaches this point, the trail has risen 309 feet (94 m) while traveling 8.4 miles (13.5 km).
After crossing over I-495 (the Capital Beltway) on a trail bridge and passing Dunn Loring, the trail begins a long descent as it travels through Vienna.  After leaving Vienna, the trail continues to descend until it reaches Difficult Run (Mile 14.3), where its elevation of 240 feet (73 m) is only about 100 feet (30 m) higher than is the elevation at the trail's origin.
After the trail crosses Difficult Run, it ascends and descends between additional streams (including Sugarland Run, Broad Run, Beaverdam Run, Goose Creek, Sycolin Creek and Tuscarora Creek) as it travels further northwest in the Piedmont through or near Reston, Herndon, Sterling, Ashburn, and Leesburg. While traveling through Reston, the trail crosses Wiehle Avenue (VA 828) 0.3 miles (0.5 km) northeast of the Wiehle–Reston East station on Washington Metro's Silver Line.
When crossing Tuscarora Creek in Leesburg, the trail's elevatio
Washington & Old Dominion Railroad Regional Park