**Background**

In August 1998, the Virginia Department of Transportation (VDOT)
completed a feasibility study to evaluate identified congestion
locations and safety problems along the I-395 and 14th Street corridor
into the District of Columbia. The study identified numerous
improvements to relieve congestion and improve safety affecting I-395,
14th Street Bridge, and the George Washington Memorial Parkway (GWMP).
To implement the results of that study, a Memorandum of Agreement was
executed on December 20, 2000, between the Federal Highway
Administration (FHWA), District of Columbia Department of Public Works
(DCDPW), VDOT, and the National Park Service (NPS) for the environmental
planning and design of the safety and operational improvements to the
14th Street Corridor and its interchange with the GWMP.

**Boundary Channel Humpback Bridge**

The existing Humpback Bridge carries the GWMP over the Boundary Channel
and is a stone-faced, arch shaped concrete structure. The existing
bridge's width varies from 72 feet to 73 feet, measured from
face-to-face of the stone parapets, and has a length of 244 feet. The
bridge accommodates two 14-foot northbound lanes and two 14-foot
southbound lanes, separated by a 4-foot median. The Mount Vernon Trail,
which varies from 6'-0" to 6'-6" in width, runs adjacent to the
northbound lanes, and a similarly varying width sidewalk is located
adjacent to the southbound lanes.

The existing 70-year-old bridge will be removed and replaced with a new
structure similar in appearance to the existing structure. The existing
architectural features of the Humpback Bridge are of a historic nature
and must be incorporated into the new design. The proposed bridge will
carry three northbound lanes (36 feet), two southbound lanes (24 feet),
and a multi-use trail (10 feet). The additional northbound lane is the
proposed acceleration lane for the Southbound I-395 to Northbound GWMP
ramp. In addition, the proposed bridge will accommodate open bank-side
pedestrian underpasses north and south of the Boundary Channel, to
connect the Mount Vernon Trail with the west side of the GWMP and to
provide access to the Columbia Island Marina. These underpasses will
help eliminate pedestrian-vehicle conflicts that presently exist.

**George Washington Memorial Parkway**

The GWMP is a four lane, two-way divided asphalt paved roadway. The
average lane width is 12 feet, with concrete curb along the median and
edges of pavement.

The existing asphalt concrete pavement will be reconstructed on the GWMP
between I‑395 and the Columbia Island Marina Entrance. The vertical
profile of the GWMP at the Humpback Bridge and its approaches will be
designed to meet AASHTO standards for a crest vertical curve with a
design speed of 45 mph. This will require regrading the Southbound I-395
to Northbound GWMP ramp and the Southbound GWMP to Northbound I-395 ramp
to match the new vertical alignment.

Northbound GWMP will be widened to provide an acceleration lane for the
Southbound I-395 to Northbound GWMP ramp. This acceleration lane will
extend across the Humpback Bridge.

At the Columbia Island Marina Entrance, the median opening will be
closed to prohibit left turns at this dangerous intersection. The
existing median will be replaced with landscaping. The pedestrian
crosswalk and associated concrete sidewalk north of the entrance will be
removed. Also, the existing Navy-Marine Memorial/Lady Bird Johnson
parking area east of the GWMP will be removed and restored to match the
surrounding terrain.

**Mount Vernon Trail**

The Mount Vernon Trail is a 9-foot wide asphalt-paved multi-use trail
that is located along the GWMP. The proposed Humpback Bridge will be
designed to carry the Mount Vernon Trail over Boundary Channel. In
addition, the trail will be realigned to provide connections to the
Navy-Marine Memorial, Columbia Island Marina, Boundary Channel Drive,
and the new pedestrian underpasses at the Humpback Bridge approaches.