***ENVIRONMENTAL ASSESSMENT***

***For***

**ROADWAY AND TRAIL SAFETY IMPROVEMENTS**

**GEORGE WASHINGTON MEMORIAL PARKWAY**

***Virginia and Washington, DC***

*Prepared by the*

U.S. Department of Transportation

Federal Highway Administration

Eastern Federal Lands Highway Division

*and the*

U.S. Department of Interior

National Park Service

George Washington Memorial Parkway Unit

*Joint Lead Agencies*

![](media/image1.jpeg){width="6.502083333333333in"
height="4.147222222222222in"}

**March 2002**

*Prepared pursuant to the Council on Environmental Quality's regulations
for implementing the\
National Environmental Policy Act (43 CFR 1500)*

***ENVIRONMENTAL ASSESSMENT***

***For***

**ROADWAY AND TRAIL SAFETY IMPROVEMENTS**

**GEORGE WASHINGTON MEMORIAL PARKWAY**

***Virginia and Washington, DC***

*Prepared by the*

U.S. Department of Transportation

Federal Highway Administration

Eastern Federal Lands Highway Division

![](media/image2.png){width="6.488194444444445in"
height="4.86875in"}*and the*

U.S. Department of Interior

National Park Service

George Washington Memorial Parkway Unit

*Joint Lead Agencies*

**March 2002**

*Prepared pursuant to the Council on Environmental Quality's regulations
for implementing the\
National Environmental Policy Act (43 CFR 1500)*

THIS PAGE INTENTIONALLY LEFT BLANK

**TABLE OF CONTENTS**

[1.0 Purpose and Need for Action 1](#purpose-and-need-for-action)

[A. Introduction 1](#introduction)

[B. Purpose of the Action 1](#purpose-of-the-action)

[C. Need for the Action 5](#need-for-the-action)

[D. Description of the Proposed Action
7](#description-of-the-proposed-action)

[E. Decision To Be Made 7](#decision-to-be-made)

[F. Scoping and Issues 7](#scoping-and-issues)

[2.0 Affected Environment 10](#affected-environment)

[A. Roadways and Ramps 10](#roadways-and-ramps)

[B. Bicycle and Pedestrian Facilities
15](#bicycle-and-pedestrian-facilities)

[C. Historic and Cultural Resources
15](#historic-and-cultural-resources)

[D. Aesthetics and Viewsheds 17](#aesthetics-and-viewsheds)

[E. Land Use 18](#land-use)

[F. Biological Resources 19](#biological-resources)

[G. Water Resources 19](#water-resources)

[H. Physiography, Geology and Soils 20](#physiography-geology-and-soils)

[I. Air Quality 21](#air-quality)

[J. Noise 21](#noise)

[K. Hazardous Materials and Wastes 22](#hazardous-materials-and-wastes)

[L. Energy 22](#energy)

[M. Socioeconomic and Community Features
23](#socioeconomic-and-community-features)

[3.0 Alternatives 24](#alternatives)

[A. Goals and Objectives 24](#goals-and-objectives)

[B. Preliminary Candidate Alternatives
25](#preliminary-candidate-alternatives)

[C. Alternatives for the Columbia Island Marina Entrance
26](#alternatives-for-the-columbia-island-marina-entrance)

[D. Alternatives for the Southbound I-395 Ramp to Northbound GWMP,\
Humpback Bridge and Pedestrian Crossing of the GWMP
28](#alternatives-for-the-southbound-i-395-ramp-to-northbound-gwmp-humpback-bridge-and-pedestrian-crossing-of-the-gwmp)

[E. Alternatives for Additional GWMP Ramp Connection to Northbound\
I-395/Rochambeau Bridge
33](#alternatives-for-additional-gwmp-ramp-connection-to-northbound-i-395rochambeau-bridge)

[F. Alternatives Evaluated but Decision Deferred
34](#alternatives-evaluated-but-decision-deferred)

[4.0 Environmental Effects of Columbia Island Marina Alternatives
37](#environmental-effects-of-columbia-island-marina-alternatives)

[A. Roadways and Ramps 37](#roadways-and-ramps-1)

[B. Bicycle and Pedestrian Facilities
39](#bicycle-and-pedestrian-facilities-1)

[C. Historic and Cultural Resources
39](#historic-and-cultural-resources-1)

[D. Aesthetics and Viewsheds 40](#aesthetics-and-viewsheds-1)

[E. Land Use 40](#land-use-1)

[F. Biological Resources 40](#biological-resources-1)

[G. Water Resources 41](#water-resources-1)

[H. Physiography, Geology and Soils
42](#physiography-geology-and-soils-1)

[I. Air Quality 42](#air-quality-1)

[J. Noise 43](#noise-1)

[K. Hazardous Materials and Wastes
43](#hazardous-materials-and-wastes-1)

[L. Energy 43](#energy-1)

[M. Socioeconomic and Community Features
43](#socioeconomic-and-community-features-1)

[N. Cumulative Impacts 44](#cumulative-impacts)

[O. Comparison of Alternatives 44](#comparison-of-alternatives)

[5.0 Environmental Effects of the Alternatives for the Southbound I-395
Ramp to\
Northbound GWMP, Humpback Bridge and Pedestrian Crossing of the GWMP
47](#environmental-effects-of-the-alternatives-for-the-southbound-i-395-ramp-to-northbound-gwmp-humpback-bridge-and-pedestrian-crossing-of-the-gwmp)

[A. Roadways and Ramps 47](#roadways-and-ramps-2)

[B. Bicycle and Pedestrian Facilities
49](#bicycle-and-pedestrian-facilities-2)

[C. Historic and Cultural Resources
49](#historic-and-cultural-resources-2)

[D. Aesthetics and Viewsheds 51](#aesthetics-and-viewsheds-2)

[E. Land Use 53](#land-use-2)

[F. Biological Resources 53](#biological-resources-2)

[G. Water Resources 55](#water-resources-2)

[H. Physiography, Geology and Soils
57](#physiography-geology-and-soils-2)

[I. Air Quality 58](#air-quality-2)

[J. Noise 58](#noise-2)

[K. Hazardous Materials and Wastes
59](#hazardous-materials-and-wastes-2)

[L. Energy 59](#energy-2)

[M. Socioeconomic and Community Features
59](#socioeconomic-and-community-features-2)

[N. Cumulative Impacts 60](#cumulative-impacts-1)

[O. Comparison of Alternatives 60](#comparison-of-alternatives-1)

[6.0 Environmental Effects of the Southbound GWMP Ramp to Southbound
I-395 Alternatives
67](#environmental-effects-of-the-southbound-gwmp-ramp-to-southbound-i-395-alternatives)

[A. Roadways and Ramps 67](#roadways-and-ramps-3)

[B. Bicycle and Pedestrian Facilities
69](#bicycle-and-pedestrian-facilities-3)

[C. Historic and Cultural Resources
69](#historic-and-cultural-resources-3)

[D. Aesthetics and Viewsheds 70](#aesthetics-and-viewsheds-3)

[E. Land Use 70](#land-use-3)

[F. Biological Resources 70](#biological-resources-3)

[G. Water Resources 71](#water-resources-3)

[H. Physiography, Geology and Soils
71](#physiography-geology-and-soils-3)

[I. Air Quality 71](#air-quality-3)

[J. Noise 71](#noise-3)

[K. Hazardous Materials and Wastes
72](#hazardous-materials-and-wastes-3)

[L. Energy 72](#energy-3)

[M. Socioeconomic and Community Features
72](#socioeconomic-and-community-features-3)

[N. Cumulative Impacts 72](#cumulative-impacts-2)

[O. Comparison of Alternatives 72](#comparison-of-alternatives-2)

[7.0 Environmental Effects of the Northbound I-395 Ramp to Northbound
GWMP Alternatives
75](#environmental-effects-of-the-northbound-i-395-ramp-to-northbound-gwmp-alternatives)

[A. Roadways and Ramps 75](#roadways-and-ramps-4)

[B. Bicycle and Pedestrian Facilities
77](#bicycle-and-pedestrian-facilities-4)

[C. Historic and Cultural Resources
77](#historic-and-cultural-resources-4)

[D. Aesthetics and Viewsheds 77](#aesthetics-and-viewsheds-4)

[E. Land Use 78](#land-use-4)

[F. Biological Resources 78](#biological-resources-4)

[G. Water Resources 78](#water-resources-4)

[H. Physiography, Geology and Soils
79](#physiography-geology-and-soils-4)

[I. Air Quality 79](#air-quality-4)

[J. Noise 79](#noise-4)

[K. Hazardous Materials and Wastes
79](#hazardous-materials-and-wastes-4)

[L. Energy 80](#energy-4)

[M. Socioeconomic and Community Features
80](#socioeconomic-and-community-features-4)

[N. Cumulative Impacts 80](#cumulative-impacts-3)

[O. Comparison of Alternatives 80](#comparison-of-alternatives-3)

[8.0 Mitigation 81](#mitigation)

[A. Historic and Cultural Resources
81](#historic-and-cultural-resources-5)

[B. Vegetation 81](#vegetation-11)

[C. Wetlands and Water Resources 81](#wetlands-and-water-resources)

[D. Socio-economic and Public Use and Enjoyment
82](#socio-economic-and-public-use-and-enjoyment)

[9.0 Environmentally Preferred Alternative
83](#environmentally-preferred-alternative)

[A. Columbia Island Marina 83](#columbia-island-marina)

[B. Southbound I-395 Ramp to Northbound GWMP, Humpback Bridge and
Pedestrian Crossing of the GWMP
83](#southbound-i-395-ramp-to-northbound-gwmp-humpback-bridge-and-pedestrian-crossing-of-the-gwmp)

[C. Southbound GWMP Ramp to Southbound I-395
84](#southbound-gwmp-ramp-to-southbound-i-395-1)

[D. Northbound I-395 Ramp to Northbound GWMP
84](#northbound-i-395-ramp-to-northbound-gwmp-1)

[10.0 Commitments and Resources 85](#commitments-and-resources)

[A. Irreversible and Irretrievable Commitment of Resources
85](#irreversible-and-irretrievable-commitment-of-resources)

[B. Unavoidable Adverse Environmental Effects
85](#unavoidable-adverse-environmental-effects)

[C. Local Short-Term Uses and the Maintenance and Enhancement of
Long-Term Productivity
86](#local-short-term-uses-and-the-maintenance-and-enhancement-of-long-term-productivity)

[11.0 Compliance with Environmental Regulations and Plans
87](#compliance-with-environmental-regulations-and-plans)

[A. National Park Service Organic Act of August 25, 1916
87](#national-park-service-organic-act-of-august-25-1916)

[B. National Environmental Policy Act (NEPA)
87](#national-environmental-policy-act-nepa)

[C. National Historic Preservation Act of 1966
88](#national-historic-preservation-act-of-1966)

[D. Clean Water Act of 1972, as Amended
88](#clean-water-act-of-1972-as-amended)

[E. Executive Order 11990, Protection of Wetlands
88](#executive-order-11990-protection-of-wetlands)

[F. General Bridge Act of 1946 89](#general-bridge-act-of-1946)

[G. Executive Order 11988, Floodplain Management
89](#executive-order-11988-floodplain-management)

[H. Endangered Species Act of 1973 89](#endangered-species-act-of-1973)

[I. Interrelationship with Other Plans and Projects
90](#interrelationship-with-other-plans-and-projects)

[12.0 List of Preparers 92](#list-of-preparers)

[13.0 Public Involvement and Coordination
93](#public-involvement-and-coordination)

[A. Public Involvement 93](#public-involvement)

[B. Agency Coordination 93](#agency-coordination)

[14.0 Selected References 95](#selected-references)

**LIST OF FIGURES**

[Figure 1: Location Map 2](#__RefHeading___Toc5024293)

[Figure 2: Study Area 3](#__RefHeading___Toc5024294)

[Figure 3: Proposed Marina Bridge Section
27](#__RefHeading___Toc5024295)

[Figure 4: Proposed Humpback Bridge Section, Alternative A
29](#__RefHeading___Toc5024296)

[Figure 5: Proposed Humpback Bridge Section, Alternative B
30](#__RefHeading___Toc5024297)

[Figure 6: Proposed Humpback Bridge Replacement Section, Preferred
Alternative 31](#__RefHeading___Toc5024298)

**LIST OF TABLES**

[Table 1: Safety Improvement Goals and Objectives
24](#__RefHeading___Toc5024300)

[Table 2: Weekday Level of Service Results / Peak Hour Volumes\* for
Columbia Island\
Marina Entrance 38](#__RefHeading___Toc5024301)

[Table 3: Comparison of Alternatives -- Columbia Island Marina Entrance
45](#__RefHeading___Toc5024302)

[Table 4: 2025 Speed and Density Results -- Comparison of No Build to
Alternatives for SB I-395\
to NB GWMP 48](#__RefHeading___Toc5024304)

[Table 5: Comparison of Alternatives -- SB I-395 Ramp to NB GWMP and
Humpback Bridge 61](#__RefHeading___Toc5024305)

[Table 6: 2025 Speed and Density Results -- Comparison of No Build to SB
GWMP to SB I-395 Ramp Removal Alternative
68](#__RefHeading___Toc5024311)

[Table 7: Comparison of Alternatives -- SB GWMP Ramp to SB I-395 and NB
I-395 Ramp to\
NB GWMP\* 73](#__RefHeading___Toc5024312)

[Table 8: 2025 Speed and Density Results -- Comparison of No Build to NB
I-395 to NB GWMP Ramp Removal Alternative
76](#__RefHeading___Toc5024314)

# Purpose and Need for Action

## Introduction

The George Washington Memorial Parkway (GWMP) is a linear park located
in Virginia, Maryland and the District of Columbia along the Potomac
River. The park is owned by the Federal government and operated by the
National Park Service (NPS). The GWMP Unit includes four separate
roadway segments -- the George Washington Memorial Parkway, the Mt.
Vernon Memorial Highway, the Clara Barton Parkway and the Spout Run
Parkway -- totaling 38.3 miles and 7,248 acres.

The George Washington Memorial Parkway is mostly located in Virginia, on
the west side of the Potomac River (see Figure 1). The parkway extends
from the Capital Beltway (I-495) on the northern end to Slaters Lane in
the City of Alexandria on the southern end. The Columbia Island portion
of the GWMP is located in the District of Columbia. The Mount Vernon
Memorial Highway is also on the west side of the Potomac in Virginia and
connects Hunting Creek at the south end of Alexandria to Mount Vernon.
The Clara Barton Parkway is located in Maryland, on the east side of the
Potomac. It extends from MacArthur Boulevard west of Carderock Park on
the northwest end to the Chain Bridge across the Potomac River on the
southeast end. Finally, the Spout Run Parkway provides a connection
between the GWMP and Lee Highway/Interstate 66 (I-66) at Spout Run
Creek, north of the Key Bridge. A number of recreational, historical and
memorial sites are also part of the GWMP Unit, including Great Falls
Park, Glen Echo Park, Arlington House, the Clara Barton National
Historic Site, Theodore Roosevelt Island Park and the Lyndon Baines
Johnson (LBJ) Memorial Grove. The Mt. Vernon Trail, a bicycle and
pedestrian route, extends along the GWMP and the Potomac River from
Theodore Roosevelt Island to Mt. Vernon.

The area being investigated focuses on the GWMP in the vicinity of its
intersection with Interstate 395 (I-395), just west of the 14^th^ Street
Bridge over the Potomac River. While collectively referred to as the
14^th^ Street Bridge, the crossing consists of three bridges: the George
Mason Bridge, which carries the southbound lanes of I-395 from the
District of Columbia to Virginia; the Rochambeau Bridge that connects
northbound I-395 to 14^th^ Street; and the Arland D. Williams Jr.
Memorial Bridge (Williams Bridge), which also carries northbound I-395
across the Potomac River from Virginia. The general boundaries of the
Study Area are the Potomac River to the east, the Williams Bridge to the
south, Boundary Channel Drive to the west, and Columbia Island Marina to
the north (see Figure 2).

## Purpose of the Action

The purpose of the proposed action is to identify and evaluate a series
of roadway and bicycle/pedestrian trail modifications to more safely and
efficiently accommodate motorists, bicyclists and pedestrians using the
GWMP in the vicinity of the 14^th^ Street Bridge and Columbia Island
Marina. Potential modifications to meet current public roadway design
and NPS Park Road Standards will also be investigated. The modifications
are intended to address safety concerns in the Study Area and would not
result in any increase in the existing roadway capacity.

[]{#__RefHeading___Toc5024293 .anchor}Figure 1: Location Map

![](media/image5.jpeg){width="6.2375in" height="7.8in"}

*Source: National Park Service, George Washington Memorial Parkway*

[]{#__RefHeading___Toc5024294 .anchor}Figure 2: Study Area

![](media/image6.jpeg){width="6.5in" height="4.875in"}

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## Need for the Action

### 1. Background {#background .unnumbered}

The segment of the GWMP within the Study Area was constructed in 1932,
although a number of modifications have been made to the roadway and
adjacent parklands since that time. The parkway was originally
constructed to commemorate the first president, preserve the natural
setting along the Potomac River and provide a fittingly grand and scenic
entryway for visitors to the nation's capital. Those factors, as well as
its significance as the first parkway constructed and maintained by the
U.S. Government, led to the listing of the GWMP on the National Register
of Historic Places (National Register) in 1981[^1]. Contributing
elements of the GWMP historic resource within the Study Area include the
Boundary Channel Bridge (No. 3300-020P), commonly referred to as the
"Humpback Bridge", and the Navy-Marine Memorial, located just north of
the Humpback Bridge.

As the Washington, DC region has become increasingly urban in character,
the GWMP has become a primary commuter route between Virginia, Maryland
and the District of Columbia. The scenic experience intended by the
parkway's originators is unfortunately lost to most commuters.

With the increase in traffic volumes and speeds, the GWMP now exhibits
interstate traffic characteristics. Regular users of the parkway
commonly display high-speed driving habits. These habits can result in
unsafe traffic maneuvers and accidents. Visitors to the Washington, DC
area, while in the minority in the traffic stream, are also frequent
users of the GWMP. They can be characterized by slower driving speeds
and are typically being pushed along at faster speeds than they would
normally go by the prevailing commuter traffic flows.

### 2. Prior Studies {#prior-studies .unnumbered}

Safety hazards and deficiencies on the GWMP have been documented in
numerous studies conducted over the past 15 years, including four
studies focusing on the Study Area: *Traffic Safety Study* (National
Park Service, 1998), *14^th^ Street Bridge Corridor Improvement
Feasibility Study* (Virginia Department of Transportation, 1998),
*Columbia Island Conceptual Study, George Washington Memorial Parkway*
(Federal Highway Administration, 1993, revised 1994), and *Feasibility
Study of Measures to Improve the Safety, Capacity and Operation of the
14^th^ Street Bridge on I-395 and the I-395 and George Washington
Memorial Parkway Interchange* (Federal Highway Administration, 1986).

### 3. Motorist Safety Concerns {#motorist-safety-concerns .unnumbered}

According to the *Traffic Safety Study*, over the period of time from
1994 to 1996, the George Washington Memorial Parkway system (which
includes the GWMP, the Mt. Vernon Memorial Highway, the Clara Barton
Parkway, and other adjacent parklands operated by National Park Service)
had a total accident rate of 2.25 accidents per million vehicle miles
traveled. This accident rate is average when compared to other similar
roadways. However, the area of the parkway between Memorial Circle and
the I-395 ramps (see Figure 1) was identified as a "high accident
location", where the accident rates were significantly higher than other
segments of the GWMP. Seven of the top ten accident sites on the GWMP
system are located in this segment of the GWMP. The southbound
I-395/George Mason Bridge ramp to northbound GWMP (see Figure 2) was
identified as the site of the most accidents. The Columbia Island Marina
entrance at the GWMP was the seventh most frequent accident site. Also
in the top ten are the northbound GWMP at the ramp to northbound I-395
(Williams Bridge) and the southbound GWMP at the ramp from northbound
I-395. The majority of the accidents involved only property damage,
although some also resulted in personal injuries.

The *14^th^ Street Bridge Corridor Improvement Feasibility Study*
identified the southbound GWMP ramp to southbound I-395 as a frequent
accident location as well. Other frequent accident locations within the
Study Area, documented in the *14^th^ Street Bridge Corridor Improvement
Feasibility Study*, include the left side exit ramp from northbound
I-395 to northbound GWMP.

In addition to the frequency of accidents, a number of the study
locations exhibit operational and design deficiencies that create a
safety hazard and/or result in regular traffic delays and congestion.
Specific locations are summarized below:

-   Southbound I-395 ramp to the northbound GWMP

-   Mainline GWMP at the Humpback Bridge

-   Northbound I-395/Williams Bridge ramp to northbound GWMP

-   Northbound GWMP ramp to southbound I-395

-   Southbound GWMP ramp to southbound I-395

-   Southbound GWMP ramp to northbound I-395

-   Northbound I-395 ramp to southbound GWMP

Safety concerns related to vehicle turning movements are the primary
issue at the intersection of the GWMP and the Columbia Island Marina
entrance. The marina entrance and a large parking area are located on
the western side of the GWMP, just north of the Humpback Bridge.
Vehicles coming out of the marina parking lot can turn left or right
onto the GWMP. Northbound parkway traffic can also turn left into the
marina parking lot. A small parking area serving the Lady Bird Johnson
Park and Navy-Marine Memorial is located on the eastern side of the
GWMP, opposite the Columbia Island Marina entrance. Although vehicles
leaving that parking lot are limited to "Right Turn Only", southbound
GWMP traffic can turn left into the parking lot. Short deceleration and
acceleration lanes are provided on each side of the parkway in both
directions into and out of the parking areas. A left-turn bay is
provided in the northbound direction of the parkway for access to the
Columbia Island Marina. A short acceleration lane on the left side of
the northbound lanes of the parkway, just north of this intersection,
accommodates traffic turning left onto the GWMP from the marina
entrance.

### 4. Bicyclist and Pedestrian Safety Concerns {#bicyclist-and-pedestrian-safety-concerns .unnumbered}

A shared-use bicycle and pedestrian trail system, the Mt. Vernon Trail,
parallels the Potomac River along the eastern edge of the GWMP. For the
most part it is separated from the vehicular roadway by a considerable
distance. At the Humpback Bridge the trail narrows from about eight feet
in width to approximately six feet and is located adjacent to the
vehicle travel lanes. The parkway approaches to the bridge are steep,
resulting in poor sight distance for the motorist and the bicycle trail
user at this location. Only a concrete curb separates bicyclists and
pedestrians from vehicle traffic. The situation is aggravated by the
location of the I-395/George Mason Bridge exit ramp to the northbound
GWMP just south of the Humpback Bridge. Ramp traffic is frequently
backed up at this location and motor vehicle accidents are common,
rendering the adjacent trail an unsafe and unpleasant experience for
users.

The intersection of the GWMP and the Columbia Island Marina entrance
poses an additional hazard for bicycle and pedestrian users of the
parkway. A marked, at-grade crosswalk is located north of the
intersection. It is not used most of the time by trail users traveling
back and forth between the Columbia Island Marina and LBJ Grove on the
western side of the GWMP and the Navy-Marine Memorial on the eastern
side of the parkway. There are no guidance signs leading to the
crosswalk from the main trail or the parking areas on either side of the
road. The crosswalk is connected to the main trail by a narrow asphalt
path along the side of the road. Many bicyclists and pedestrians cross
at the marina entrance, often stopping in the median to wait for a break
in the traffic, where they conflict with oncoming vehicles and turning
vehicles.

## Description of the Proposed Action

The NPS and Federal Highway Administration (FHWA) propose to modify
access ramps, roadway, pedestrian/bicycle trails and parking areas
within the GWMP to correct design deficiencies and satisfy safety
concerns associated with the design and location of the various Parkway
features. The GWMP/I-395 interchange and access ramps, Humpback Bridge,
Columbia Island Marina entrance on the GWMP and other areas within the
Study Area (see Figure 2) will be evaluated for potential modification
and improvement.

## Decision To Be Made

The National Environmental Policy Act of 1969 (NEPA) requires
consideration of the environmental effects of proposed Federal actions.
This Environmental Assessment (EA) has been prepared to assist NPS and
FHWA decision-makers in developing solutions to address the GWMP safety
concerns through the evaluation of various options for accomplishing the
safety improvements and the environmental effects of the preferred
action(s).

## Scoping and Issues

Issues and concerns related to the proposed safety improvements were
identified by NPS and FHWA staff, by other Federal and local agencies
and members of the public consulted during EA development, and by review
of prior investigations within the Study Area.

A set of issues was identified that influenced the development of
alternatives and analysis process. Each of the major issues is discussed
in the following sections.

### 1. GWMP Historic Resource {#gwmp-historic-resource .unnumbered}

The designation of the GWMP as a historic resource, and the prominence
of the Humpback Bridge and Navy-Marine Memorial as contributing elements
of that resource, significantly influences the development of potential
safety improvement alternatives. The State Historic Preservation
Officers (SHPO) for Virginia and the District of Columbia and Advisory
Council on Historic Preservation were consulted early in the
investigations to discuss options for addressing the safety concerns
associated with this segment of the GWMP. Beginning with those initial
discussions, emphasis was placed on minimizing any impacts to the
Humpback Bridge and the vistas of the bridge as seen from the Potomac
River and District of Columbia. As a result, any expansion or
replacement of the Humpback Bridge would take place to the west, with
the eastern edge of the existing bridge as the outer boundary for any
improvements.

### 2. Humpback Bridge Condition {#humpback-bridge-condition .unnumbered}

Boundary Channel Bridge No. 3300-020P or the Humpback Bridge is a
244-foot long, 67-foot wide concrete cantilever-arch structure with
center, suspended span on piled spread footings. It was constructed in
1932 as an original feature of the Parkway and was reconstructed in
1993, consisting of the replacement of the concrete deck and sidewalk
and repair of the concrete tee beams. Four GWMP vehicle travel lanes
cross the bridge, two in each direction. A six-foot wide sidewalk is
also located on each side of the bridge. The east sidewalk connects the
bridge to the Mt. Vernon Trail bicycle and pedestrian route. There are
no connecting sidewalks or paths to the GWMP from the bridge's west
sidewalk.

The FHWA performed the last bridge inspection and load rating of the
Humpback Bridge on May 12, 1999. The bridge was given a good condition
rating with minor deterioration, no load restrictions, and with an
approximate useful life of 25 to 30 years. A visual survey of the
Humpback Bridge was conducted in conjunction with this Environmental
Assessment and related engineering investigations. The complete survey
results are documented in the *GWMP Safety Improvements Existing
Conditions Report* (August 2001).

Based upon the visual survey, the concrete main span deck and sidewalks
are in good condition. Minor transverse cracks were noticed in the deck,
curb median and sidewalk. These cracks are minor shrinkage cracks and
pose no structural or serviceability threat to the deck. Evidence of
efflorescence throughout the underside of the slab was noticed for the
main span. Overall the bottom of the slab and soffit are in fair
condition.

The bridge supporting members, consisting of steel beams encased in
concrete to form composite tee beams that cantilever out from each
bridge pier and a short concrete tee beam "suspended span" bridge
section connecting the two cantilevered bridge sections, appear to be in
fair condition. The concrete on select tee beams is beginning to spall
and chip, exposing the reinforcing steel. It doesn't appear that this
minor beam deterioration is structurally threatening. However, patching
and repairing the spalls in the tee beams is important in maintaining
the serviceability of the bridge. The supporting floor beams and girders
adjacent to the expansion joints show moderate concrete spalls with
exposed reinforcing bar. The concrete spalls in the tee beams and
suspended span should be repaired to prevent further deterioration that
could affect the serviceability of the bridge. The concrete diaphragms
between the tee beams appear to be in good condition, although
efflorescence was observed on several of these elements.

The condition of the concrete in the existing abutments and walls could
not be determined during the survey due to the stone facing. The earth
filled (closed) pier/abutment acts as a gravity retaining wall, which
supports the embankment on both sides of the channel and appears to be
in fair/good condition. Further investigation/inspection is needed to
analyze the condition of the existing abutment and wing walls with
consideration given to any modifications of the structure. A visual
inspection of the bridge piers did not reveal any evidence of foundation
settlement.

Without additional analysis, it is recommended that no additional loads
be added to the Humpback Bridge structure. Any widening of the Humpback
Bridge should be supported by a separate bridge structure and
foundation, but could be attached to the existing bridge. Other
modifications to the Humpback Bridge should not result in any additional
dead loads.

### 3. Maintenance of Traffic {#maintenance-of-traffic .unnumbered}

The maintenance of traffic flow on the GWMP during the construction of
any safety improvements was identified by the NPS and FHWA as a key
requirement, due to the parkway's role as a primary commuter route for
the region. This requirement applies to both vehicular traffic and
pedestrian, bicycle and other traffic on the Mt. Vernon Trail.

# Affected Environment

A detailed description of existing conditions within the Study Area is
included in the *GWMP Safety Improvements Existing Conditions Report*
(August 2001), prepared in conjunction with this Environmental
Assessment. The components of the existing environment that may be
affected by the proposed action are summarized below.

## Roadways and Ramps

### 1. Physical Characteristics and Description {#physical-characteristics-and-description .unnumbered}

Overall, the mainline GWMP consists primarily of asphalt pavement and
concrete curbs with minor sections of concrete surfacing on bridge
decks. There are two vehicle travel lanes in each direction within the
Study Area, separated by a raised grass median, guardrail, or stone
wall, depending on the location. The intersections of the GWMP and
I-395/14^th^ Street Bridge are grade-separated interchanges with ramp
access and egress with the mainline GWMP. Access and egress ramps are
located at the GWMP and southbound I-395/Mason Bridge and the GWMP and
northbound I-395/Williams Bridge. There are no ramps connecting the GWMP
and the Rochambeau Bridge.

Two prior studies -- *Traffic Safety Study* (National Park Service,
August 1998) and *George Washington Memorial Parkway: Virginia,
Maryland, District of Columbia, Engineering Study for Roads and Bridges*
(National Park Service, April 1999) -- respectively describe the
physical characteristics of the Parkway and the physical condition of
the roadways, ramps and bridges in detail. These resources may be
referenced for further information regarding the physical
characteristics of the GWMP.

### 2. Traffic Counts {#traffic-counts .unnumbered}

There are two sources of historical count data that are useful in this
study -- the 1998 *Traffic Safety Study* and the *14^th^ Street Bridge
Corridor Improvement Feasibility Study* (Virginia Department of
Transportation, 1998). The latter study included a thorough analysis of
the traffic activities within the Study Area and will be the primary
source of comparison for this study.

Based on the historic traffic data, there are well-defined morning and
evening peaks in average traffic volume reflecting heavy commuter
traffic. The busiest hours for traffic on the GWMP are from 7:00 AM to
10:00 AM, and from 3:00 PM to 7:00 PM. Average traffic volumes on the
Parkway are extremely light between midnight and 6:00 AM and are
markedly less on the weekends.

An extensive new traffic count program was performed for the Study Area
in March 2001, to supplement historic count data. Eighteen (18) tube
counts were conducted, with the count locations designed to replicate
the 1996 count locations used for the *14^th^ Street Bridge Corridor
Improvement Feasibility Study*. The March 2001 counts were then compared
with several other sources: actual counts and year 2000 projections used
in the 14^th^ Street Bridge Study, actual counts in the 1998 *Traffic
Safety Study*, and VDOT data on primary and interstate routes in the
area. The locations of the tube counts that were conducted for this
study are displayed in Appendix B, Figure B-1.

The 2001 raw traffic counts were balanced across the interchange at GWMP
and I-395 so that the volumes add up appropriately across the
interchange. These volumes were then compared to the year 2000
projections from the *14^th^ Street Bridge Corridor Improvement
Feasibility Study*. Most of the 2001 volumes were within a reasonable
margin (15%) of the year 2000 projections. Appendix B, Figure B-2
displays the existing traffic volumes (Daily/AM Peak Hour/PM Peak Hour).

### 3. Operational Analysis {#operational-analysis .unnumbered}

The Corridor-microscopic Simulation (CORSIM) traffic simulation model
originally developed for the *14^th^ Street Bridge Corridor Improvement
Feasibility Study* was modified to incorporate the new traffic volumes
in the Study Area. CORSIM is a traffic simulation model that allows the
user to analyze complex roadway and/or freeway networks. The output for
this model provides the resulting average density of each link (road
segment) in order to analyze the level of service (LOS) for the freeway
segments. The limits of the simulation model extend to north and south
of the GWMP / I-395 interchange, as well as to the west on I-395 near
the Route 27 underpass, and to the east on I-395 to the Potomac River
Bridges.

The LOS rating of a roadway assigns a value ranging from A for segments
with completely free-flow conditions, to F, which represents a breakdown
in the traffic flow. The levels of service for the AM and PM peak hours
determined by the CORSIM analysis are shown in Appendix B, Figure B-3.
These service levels are very similar to those reported for the year
2000 in the 1998 *14^th^ Street Study*. Along northbound I-395, there
are eight merge, diverge, and/or weave areas; five of which operate at
unacceptable levels of service of E or F in the AM peak. Along
southbound I-395, there are nine merge, diverge, and/or weave areas; two
of which operate at unacceptable levels of service of E or F in the PM
peak.

The specific problem locations reported in the *14^th^ Street Bridge
Corridor Improvement Feasibility Study* and 1998 *Traffic Safety Study*
still apply to 2001 traffic, notably:

-   [Northbound I-395 at the off-ramp to northbound GWMP in the AM peak
    hour\
    ]{.underline}Only 200 feet downstream from the southbound GWMP
    on-ramp to northbound I-395, traffic exiting I-395 to northbound
    GWMP must slow to meet the left exit ramp, which has no auxiliary
    lane to separate the decelerating vehicles from the interstate
    traffic. Although the traffic volume on this ramp is fairly low
    (3800 vehicles per day \[vpd\]), the maneuver is hazardous due to
    the lack of a deceleration lane as well as the limited sight
    distance, which causes vehicles to slow even more on the interstate
    before they exit.

-   [Northbound GWMP at the southbound I-395 off-ramp in the AM and PM
    peak hours\
    ]{.underline}Queues develop on this ramp back to I-395 due to the
    lack of acceleration lane on the Parkway.

-   [Northbound and southbound mainline GWMP at Columbia Island Marina\
    ]{.underline}Currently, northbound GWMP through movements operate at
    LOS F during the AM peak and LOS E during the PM peak. Southbound
    GWMP through movements operate at LOS D for both the AM and PM
    peaks. The traffic entering and exiting the Columbia Island Marina
    and Navy-Marine Memorial parking lots operate at or near
    unacceptable levels of service. It is important to note that
    although the LOS for left turns is poor, the traffic volumes are
    extremely low for left-turning turning vehicles at this
    intersection. Additionally, unsignalized intersections on urban
    roadways frequently operate at LOS E or F in the peak hour. Unlike
    at signalized intersections, this can be acceptable since it
    represents operations for a single movement and not the overall
    intersection.

```{=html}
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-   [Northbound I-395 at the on-ramp from southbound GWMP in the AM peak
    hour\
    ]{.underline}The operational deficiencies at this location are due
    to the lack of acceleration and deceleration lanes for the
    Interstate on and off ramps. Traffic merging onto I-395 from the
    southbound GWMP exit ramp has effectively no acceleration lane,
    therefore causing backups on I-395 due to ramp traffic merging from
    almost a complete stop. Traffic also backs up along the ramp and
    spills back onto the southbound GWMP because of the stop-and-go
    conditions at the I-395 merge area.

-   [Various weave areas along I-395 in the study area from GWMP to the
    ramps at Rte 110\
    ]{.underline}Several weave areas operate at or near unacceptable
    levels of service during the peak hours, including the weaving
    movement from the southbound GWMP ramp to southbound I-395.

### 4. Speed Studies {#speed-studies .unnumbered}

A detailed speed study for the GWMP that included the areas analyzed in
this study was conducted in the *Traffic Safety Study*. The highest
percentages of vehicles traveling 10 miles or more over the posted speed
limit occurred in locations with reduced speed limits (35 to 40 mph).
The posted speed in the Study Area is 40 mph. However, the average
"actual" speed recorded in the vicinity of the Columbia Island Marina
entrance was over 47 mph. The average speeds in both directions jumped
from 45 mph during the morning and evening peak hours (7:00 AM -- 10:00
AM and 4:00 PM -7:00 PM) to 49 mph throughout the rest of the day.

Overall, speeding is considered the greatest safety problem on the
Parkway, although drivers generally seem to maintain a fairly consistent
speed throughout the length of the Parkway, regardless of the posted
speed limit. However, the mixture of slower moving tourists with the
faster moving commuters on the GWMP creates varying driver styles and
the potential for conflicts between vehicles. Due to the lack of NPS
personnel and equipment, high volume traffic conditions, and the basic
design of the Parkway, U.S. Park Police have trouble enforcing the speed
limit.

### 5. Roadway and Ramp Geometric Design {#roadway-and-ramp-geometric-design .unnumbered}

An analysis of geometric design deficiencies, including the Study Area,
was conducted for the *14th Street Bridge Corridor Improvement
Feasibility Study*. Most of the major deficiencies are related to the
interchange or ramp geometry, and are summarized below.

-   [Southbound I-395 ramp to northbound GWMP]{.underline}\
    The length of the deceleration lane for this ramp is less than
    engineering design standards. There is no acceleration lane on the
    GWMP for traffic entering the parkway from this ramp. The lack of an
    acceleration lane on the GWMP for merging traffic results in
    frequent queues on the ramp and extending back to the mainline
    segment of southbound I-395/George Mason Bridge during peak periods.

-   [Mainline GWMP at the Humpback Bridge]{.underline}\
    The existing vertical profile of the Humpback Bridge and its
    approaches is well below the recommended minimum design speed for
    this portion of the GWMP, particularly the northbound lanes. The
    bridge approaches are designed for 20 miles per hour (mph) while the
    bridge itself has a 30 mph design speed. The posted speed limit for
    the bridge and its approaches is 40 mph. The limited sight distance
    coupled with the intersection of the southbound I-395 ramp to the
    Parkway and its deficiencies just south of the Humpback Bridge raise
    multiple safety concerns for this portion of the GWMP.

-   [Northbound I-395 ramp to northbound GWMP]{.underline}\
    This left-exit ramp has no deceleration lane and, due to the curved
    alignment on the approach to the exit, sight distance is limited.
    Low speeds and high delays on this segment of northbound I-395
    result due to the tendency for exiting vehicles to decelerate more
    abruptly than anticipated by through-freeway vehicles. The
    acceleration lane length where this ramp merges with northbound GWMP
    is also substandard. In addition, the proximity of this ramp to the
    northbound GWMP exit ramp to southbound I-395 creates additional
    vehicle conflicts.

-   [Northbound GWMP ramp to southbound I-395]{.underline}\
    As discussed above, this ramp is too close to the prior northbound
    I-395 to northbound GWMP on-ramp. The conflicts between vehicles
    entering and exiting the GWMP as well as the substandard
    deceleration lane length of this ramp create an accident hazard at
    this location.

-   [Southbound GWMP ramp to southbound I-395\
    ]{.underline}The deceleration and acceleration lengths of this ramp
    are shorter than current design standards and pose a safety concern.
    This ramp is also part of a 3,800-foot long segment of I-395 between
    the northbound GWMP and VA Route 27/Pentagon off-ramps that contains
    five consecutive weaving sections and nine different ramp junctions.
    The higher than normal lane changing activity at this location
    significantly slows operations through this portion of I-395 and
    frequently results in accidents.

-   [Southbound GWMP ramp to northbound I-395]{.underline}\
    Accidents occur at the end of this ramp, at the merge with I-395,
    and on the southbound GWMP at the diverge or deceleration lane for
    this ramp. The lack of a merge area at the end of the ramp is a
    problem at this location, as well as the proximity of this GWMP exit
    to the adjacent on-ramp for southbound I-395 traffic entering the
    southbound GWMP.

-   [Southbound I-395 ramp to southbound GWMP]{.underline}\
    Potential problems at this location include the lack of advance and
    visible signage for the vehicles merging onto southbound GWMP from
    the northbound I-395 exit ramp. Additionally, the ramp merges with
    high-speed traffic on the southbound Parkway lanes with no
    merge/acceleration lane provided.

### 6. Accident Information {#accident-information .unnumbered}

All three of the prior studies that have been used as a resource for
this analysis provide useful accident information for the GWMP. Accident
records maintained by the U.S. Park Police for the years 1997 through
July 2001 were also reviewed as well as VDOT accident data for the Study
Area (1997-2002). Overall, the GWMP has a fair safety performance
record. Over the period of time from 1994 to 1996, the GWMP system
(which includes the GWMP, the Mt. Vernon Memorial Highway, the Clara
Barton Parkway, and other adjacent parklands operated by National Park
Service) had a total accident rate of 2.25 accidents per million vehicle
miles traveled. This accident rate is average when compared to other
similar roadways. However, in the segment of the parkway between
Memorial Circle and the I-395 ramps, which includes the Study Area, a
number of "high accident locations" have been identified, where the
accident rates were significantly higher than other comparable segments
of the GWMP.

A brief summary of the accident history and problems associated with the
accident locations within the Study Area is provided below. Accidents on
this segment of the GWMP are documented in Appendix C.

-   [Northbound GWMP at the ramp from southbound I-395 (George Mason
    Bridge)]{.underline}\
    This site is the location of the most accidents on the entire GWMP
    system (286 accidents between 1994 and July 2001). All accidents
    that occurred at this location, except one, were between motor
    vehicles (i.e., no pedestrians involved) and most involved property
    damage only. The majority of accidents were during the AM and PM
    peak hours and were rear-end collisions (approximately 95%).
    Commonly listed contributing factors include "Driver failed to give
    full time and attention" and "Driver followed to closely".\
    \
    Location-specific problems included the lack of adequate merge ramps
    for the traffic merging into the northbound GWMP mainline flows. In
    addition, merging traffic immediately encounters an upgrade leading
    into the Humpback Bridge (specifically difficult during wet
    conditions).

-   [GWMP at Columbia Island Marina/Navy-Marine Memorial/Lady Bird
    Johnson Park]{.underline}\
    Accidents at this location were primarily between vehicles (although
    there was an incidence of a pedestrian/vehicle accident during the
    study period). Of the accidents involving other motor vehicles,
    rear-end collisions were the most common type of collision reported.
    If contributing factors were indicated, the most frequent factors
    were "Driver - failed to give full time and attention", "Driver too
    fast for conditions" and "Driver followed to closely".\
    \
    Problems at the intersection are specifically related to the high
    volume of vehicles on the GWMP. Left-turns and U-turns are difficult
    and dangerous because they involve crossing opposing traffic flows.
    In addition, there are site-related problems at this location. There
    is a lack of guidance signs leading pedestrians to the crosswalk
    from parking areas on the side of the road. On a related note, very
    few pedestrians use the marked crosswalk. Sight distances are
    limited to the south of the site by the presence of the Humpback
    Bridge over Boundary Channel.

-   [GWMP Mainline at the Humpback Bridge]{.underline}\
    The Humpback Bridge span is a frequent accident location, in both
    the northbound and southbound directions. Approximately 20% of the
    accidents involved some kind of personal injury. As with other
    locations, there was a predominance of rear-end collisions.
    Contributing factors include "Driver - failed to give full time and
    attention", "Driver too fast for conditions" and "Driver followed to
    closely".

-   [Northbound I-395 ramp to northbound GWMP]{.underline}\
    The majority of the accidents occurring at this ramp (23 total
    between 1994 and July 2001) result in property damage only and are
    rear-end collisions. The lack of a deceleration lane on I-395 is the
    reason for the problems at this ramp. In addition, the acceleration
    lane for this ramp is inadequate for vehicles entering the GWMP,
    which must merge with high-speed traffic on the mainline lanes of
    the parkway. The proximity of this ramp to the northbound GWMP exit
    ramp to southbound I-395 creates additional conflicts for traffic
    using this ramp.

-   [Northbound GWMP at the ramp to southbound I-395]{.underline}\
    This location was the scene of 20 accidents between 1994 and
    July 2001. The accidents were a mixture of vehicle-to-vehicle
    collisions (rear-end and sideswipe) and collisions between a vehicle
    and a fixed object such as a guardrail. The substandard deceleration
    lane and proximity of this ramp to the prior northbound I-395 to
    northbound GWMP on-ramp cause the problems at this location.

-   [Southbound GWMP ramp to southbound I-395]{.underline}\
    The substandard deceleration lane length is a problem at this
    location. As a result, accidents are most common on the southbound
    GWMP at the diverge/deceleration lane for this ramp. Accidents also
    occur at the end of this ramp, where the merge area onto mainline
    I-395 is inadequate, and where the ramp is part of a series of
    closely-spaced on- and off-ramps results in multiple weaving
    movements for traffic entering and exiting southbound I-395.

## Bicycle and Pedestrian Facilities

An extensive network of pedestrian and bicycle paths is currently
provided adjacent to the GWMP in the Study Area. The shared-use pathway
system is frequented by walkers, joggers, tourists, naturalists, in-line
skaters and recreational and commuter bicyclists. Major pedestrian and
bicyclist attractions in the Study Area include the LBJ Memorial Grove
and Columbia Island Marina, and Gravelly Point and Roaches Run Waterfowl
Sanctuary, located to the south of the Study Area.

The Mt. Vernon Trail, the main pedestrian-bicycle route on the GWMP, is
nine feet wide for most of the Study Area. The trail narrows
considerably, to about six feet, as it crosses the Humpback Bridge.
There is no protective separation between the trail and the roadway. The
AASHTO *Guide for the Development of Bicycle Facilities* (AASHTO, 1999)
recommends a width of 10 feet for a two-directional shared use path. A
12 to 14 foot wide path is desirable when there is substantial use by
bicycles, joggers, and pedestrians, use by large maintenance vehicles
and/or steep grades. When the distance between a vehicular roadway and
the shared use path is less than five feet, a physical barrier is
recommended to separate vehicular traffic from bicycle and pedestrian
traffic.

The GWMP approaches to the Humpback Bridge are steep and do not work
well with the vertical curvature of the bridge. These factors contribute
to poor sight distance for both the GWMP motorist and for the Mt. Vernon
Trail user. The transition of the trail to the sidewalk of the bridge is
substandard as well.

There is an at-grade pedestrian crossing of the mainline GWMP within the
Study Area. It is located just north of Columbia Island Marina entrance.
Pedestrians and bicyclists find it difficult to cross the Parkway. Heavy
traffic volumes and high vehicle speeds create a barrier for pedestrians
and bicyclists and make the crossing difficult.

## Historic and Cultural Resources

The Study Area and its immediate environs have been subject to human
occupation since prehistoric times. Historic maps provide a detailed
history of the area since the mid-nineteenth century. Changes to the
landscape since that time have largely been the result of activities
such as grading, dredging, filling, mining and construction.

Prior to 1924, the southern end of Columbia Island and the GWMP lands to
the north of I-395 and the George Mason Bridge were the open waters of
the Potomac River. Other land within the Study Area was low-lying marsh.
A stream known as Roaches Run flowed in a north-south direction west of
the Boundary Channel lagoon in the area where VA 110 and the Pentagon
north parking lot are now located. Another stream fed into Roaches Run
from the west, just north of the Pentagon. Columbia Pike intersected a
road following the alignment of today's U.S. Route 1 in the vicinity of
the current Route 1/I-395 interchange. From there, the road extended
eastward to the Potomac River. The Long Bridge carried the road across
the Potomac about where the RF&P railroad bridge now sits. Columbia
Island was created in 1924 when the U.S. Army Corps of Engineers dredged
the Potomac River navigational channel and side-cast the spoils to the
west. A small lagoon and Boundary Channel were formed by the creation of
Columbia Island. Roaches Run and the second stream were filled in 1942
during the construction of the Pentagon. Boundary Channel was also
enlarged as a result of dredging during the construction of the
Pentagon.

A detailed discussion of the historical development of the lands within
the Study Area is included in the *GWMP Safety Improvements Existing
Conditions Report* (August 2001).

### 1. GWMP Historic Resource {#gwmp-historic-resource-1 .unnumbered}

The GWMP was established in 1930 by the U.S. Congress as a memorial to
George Washington, connecting the areas where he spent much of his time:
Mount Vernon, his residence; Washington, D.C, the nation's capital; and
Great Falls, location of the Potomac Canal, which he helped design and
build. The initial section of the parkway, known as the Mount Vernon
Memorial Highway, opened in November 1932 and extended from the
Arlington Memorial Bridge to Mount Vernon. Most of the northern section
of the parkway, from the Memorial Bridge to the Capital Beltway, was
opened in 1966.

The initial Mount Vernon Memorial Highway segment of the GWMP was listed
on the National Register of Historic Places in 1981. It had previously
been identified as a historic resource of the District of Columbia in
1964. The remaining portions of the GWMP were listed on the National
Register in 1995. It is significant as the first parkway constructed and
maintained by the U.S. Government, as a work of landscape architecture,
and as a memorial to George Washington. Specifically, the significance
of the parkway closely relates to the long and continuous city planning
effort for the Washington, DC region. The GWMP has additional
significance as a designed entryway into the nation's capital and the
grand approach it provides to the monumental core of the capital. George
Washington's association with the Potomac River corridor and the
District of Columbia is another major factor that elevates the
significance of the parkway. Finally, the GWMP has significance as an
instrument of conservation and protection of the natural resources of
the Potomac River. By its very existence, the parkway prevents
development along the river corridor and the potentially detrimental
impacts of that development to the corridor's natural resources.

GWMP National Register elements include the Humpback Bridge. The GWMP
and the bridge are also within the viewsheds of other National Register
resources in the area, including the Pentagon, Arlington National
Cemetery and the LBJ Memorial Grove. Although not constructed in
connection with the original segment of the GWMP, the Navy-Marine
Memorial on the southern end of Columbia Island is also a contributing
element of the GWMP National Register resource. Erected in 1934 on the
lands of the GWMP, the sculpture is a unique and striking specimen among
the abundance of memorial art in the Washington, DC region.

Detailed discussions of the GWMP and its historical significance are
found in the *Historic Resource Study: Rock Creek and Potomac Parkway,
George Washington Memorial Parkway, Suitland Parkway and
Baltimore-Washington Parkway* (U.S. Department of Interior, 1990) and
the *Cultural Landscape Report, Mount Vernon Memorial Highway* (EDAW,
1986).

### 2. Archaeological Resources {#archaeological-resources .unnumbered}

The construction of roads, bridges across the Potomac River, the
Pentagon Reservation and the GWMP itself involved extensive cutting,
filling and grading. Filling activities may have covered archaeological
sites, protecting them from shallow surface disturbances. Cutting may
have destroyed archaeological sites. Although these activities, and
human activity in general, have altered the landscape throughout its
history, archaeological sites may still exist in or near the Study Area,
although the extensive ground-moving activities in the area may have
destroyed them.

### 3. Historic Resources {#historic-resources .unnumbered}

In addition to the GWMP, a number of other historic resources are
located immediately adjacent to the GWMP. Most resources are related to
the growth of Washington, DC as the nation's capital and the federal
government's role in that development or are federally designated
memorials and monuments. Historic resources in proximity to the Study
Area include the Pentagon, Arlington National Cemetery and Arlington
House, the Arlington Memorial Bridge, the LBJ Memorial Grove, the
National Airport Complex, the Lincoln Memorial, the Jefferson Memorial,
East and West Potomac Parks and the Tidal Basin, the National Mall
Historic District, and the L'Enfant Plan of Washington or the Squares,
Circles, Streets, Vistas and Other Delineated Elements Created by the
Plan of the Federal City.

These and other resources are listed on various federal and local
historic registers including the National Register of Historic Places,
the District of Columbia (DC) Inventory of Historic Sites, the Virginia
Landmarks Register and the Arlington County Inventory of Historic
Resources. A more comprehensive listing of historic and cultural
resources in the vicinity of the Study Area is included in Appendix D.

## Aesthetics and Viewsheds

The GWMP was constructed, in part, to provide a fittingly grand approach
to Washington, DC. Its alignment and original landscape elements were
designed to frame a series of planned vistas of the National Capital and
its monumental core. Today much of the parkway, including the
landscaping, is relatively unaltered from its original construction and
siting. It should be noted, however, that much change has taken place on
the lands adjacent to the parkway -- including dense urban development
in areas such as Crystal City and Rosslyn, the construction of I-395,
and the construction of National Airport and the Pentagon -- that has
compromised some of the GWMP's original character.

The GWMP is also an element in the viewsheds of numerous surrounding
historic resources. The Study Area forms the foreground for the views
from the Pentagon river terrace across the Potomac River to the
Washington, DC monumental core. It is also within the viewshed of the
LBJ Memorial Grove and Arlington National Cemetery. Finally, the GWMP is
part of the background of vistas formed by the L'Enfant Plan of
Washington. Vistas include the primary intersecting vistas from the
Capitol along the National Mall to the western horizon and from the
White House along President's Park to the southern horizon.

## Land Use

The area immediately surrounding the intersection of the GWMP and the
14^th^ Street Bridge is devoted to the park and recreation uses of the
GWMP. The areas adjacent to the GWMP, in Arlington, VA and Washington,
DC, include a mixture highly developed urbanized areas and parklands and
open space. Land use categories in the vicinity of the Study Area
include:

-   Park and open space,

-   Federal government facilities,

-   Residential (single family and multi-family),

-   Commercial office, hotel and retail, and

-   Industrial.

The GWMP itself is a major park and recreation resource, primarily
devoted to passive recreation activities and memorial functions such as
the Navy-Marine Memorial, Lady Bird Johnson Memorial Park and the LBJ
Memorial Grove. Recreation facilities within the Study Area include the
Columbia Island Marina and boat launching facility and the Mt. Vernon
Trail.

Roaches Run Waterfowl Sanctuary, a 53-acre lake created by the Civilian
Conservation Corps in the 1930's, is located immediately south of the
Study Area. Other federal parklands and open space include East and West
Potomac Parks, the Jefferson Memorial and the National Mall and
Smithsonian museum complex located across the Potomac River in
Washington, DC. The Army-Navy Country Club is located to the southwest.
A county park, Virginia Highlands, is also located to the southwest.

Interstate 395 and the Pentagon and Arlington National Cemetery separate
the Study Area from adjacent residential areas. Other federal facilities
in the vicinity include National Airport, Fort Myer Military Reservation
and the federal office complex adjacent to the National Mall in
Washington, DC. The closest residential neighborhoods are Aurora
Highlands/Pentagon City and Crystal City, located southwest of the study
area. The residential neighborhoods are a high-density mixture of
single-family dwellings and multi-family dwellings and apartments. Those
areas also contain a concentration of commercial office, hotel and
retail land uses.

A small pocket of industrial land use is located immediately south of
the Study Area and I-395. This area, which includes the site of the
former Twin Bridges Marriott Hotel, is largely undeveloped, although
Arlington County is currently developing a master recreation plan for
the area.

### 1. Arlington County Zoning {#arlington-county-zoning .unnumbered}

The Arlington County Zoning Map designates the portion of the GWMP
within the Study Area and the surrounding Pentagon Reservation,
Arlington National Cemetery and I-395 as a Special District (S-3A). The
strip of land directly south of the Study Area, between I-395 and the
Roaches Run Waterfowl Sanctuary is zoned a combination of Limited
Industrial (CM), Commercial Office Building, Hotel and Apartment
(C-0-1.5), Light Industrial (M-1) and Service Industrial (M-2).

## Biological Resources

### 1. Vegetation {#vegetation .unnumbered}

Vegetation within the Study Area is comprised primarily of lawn and
ornamental plantings. Remnants of the original landscape plantings
remain, including four large-caliper specimen trees -- three American
elms (*Ulmus americana*) and a flowering pear (*Pyrus calleryana*) --
that flank the Humpback Bridge on the Potomac River side. Additional
specimens include flowering dogwood (*Cornus florida*) and pin oak
(*Quercus palustris*).

Natural vegetation fringes Boundary Channel and the lagoon and includes
wetland vegetation (floodplain forest associations and aquatic herbs),
as well as white oaks (*Quercus alba*), black locusts (*Robinia
pseudoacacia*) and tulip poplars (*Liriodendron tulipifera*).

### 2. Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species .unnumbered}

Wildlife found within the portion of the GWMP within the Study Area is
limited to species associated with urban environments, such as birds,
squirrels and other small animals. The Roaches Run Waterfowl Sanctuary
is located just south of I-395, adjacent to the GWMP, and is also under
the jurisdiction of the NPS. The area is not considered a unique habitat
for any wildlife species.

There are no state or federally listed rare, threatened or endangered
species known to inhabit the Study Area. A list of Natural Heritage
Resources of Arlington County, including federal and state protected
species, is provided in the *GWMP Safety Improvements Existing
Conditions Report* (August 2001).

### 3. Wetlands {#wetlands .unnumbered}

The U.S. Fish and Wildlife Service (FWS), National Wetlands Inventory
(NWI) map data classifies the Boundary Channel and lagoon as a
lacustrine, limnetic, unconsolidated bottom, permanent-tidal (L1UBV)
wetland, approximately 39 acres in size. A small lacustrine, littoral,
emergent, nonpersistent, semipermanent-tidal (L2EM2T) wetland of
approximately 2 acres is found adjacent to the Boundary Channel
shoreline, north of the LBJ Memorial Grove parking lot. The Potomac
River is classified as a riverine, tidal, unconsolidated bottom,
permanent-tidal (R1UBV) wetland.

## Water Resources

The Study Area is within the Arlington and Alexandria City Drainages
watershed. That watershed, in turn, is part of the Middle Potomac,
Potomac River and Chesapeake Bay watersheds. The Potomac River is tidal
along the segment adjacent to the Study Area and experiences a mean
tidal range of approximately 3 feet (1.5 feet above and below MSL).
There are no national or state designated wild and scenic rivers in the
vicinity of the GWMP and 14^th^ Street Bridge.

Groundwater is encountered approximately 20 to 25 feet below the
surface, although groundwater is not used as a source of water supply in
the region. Arlington County purchases its water from the City of Falls
Church, VA, which is supplied by the Washington Aqueduct by drawing
water from the Potomac River. Arlington County drinking water meets or
surpasses all federal and state drinking water standards.

### 1. Floodplains {#floodplains .unnumbered}

The Study Area encompasses two water bodies: the Potomac River and
Boundary Channel. The Federal Emergency Management Agency (FEMA)
designates the 100-year base flood elevation to be approximately 13 feet
above mean sea level (MSL) in the vicinity of the Study Area. The
100-year floodplain encompasses portions of Columbia Island adjacent to
Boundary Channel, including the marina parking lot and dock areas and
the shoreline surrounding the Navy-Marine Memorial. Flood Zone B,
defined as the areas between the limits of the 100-year flood and
500-year flood or certain other areas subject to 100-year flood,
includes the open areas adjacent to the Columbia Island Marina and its
parking lot as well as the area surrounding the Navy-Marine Memorial.

### 2. Coastal Zone Management {#coastal-zone-management .unnumbered}

The Virginia Coastal Resources Management Program was established in
1986 to protect and manage an area known as Virginia's "Coastal Zone"
which encompasses 29 counties, including Arlington County, 15 cities and
43 towns and all of the waters to the three-mile Territorial Sea
boundary. The Study Area is contained in the Potomac River basin of the
Chesapeake Bay watershed. The tidal portion of the river extends from
the mouth of the Chesapeake Bay to Chain Bridge in Washington, DC. As
such, the Virginia portions of the Study Area are within the Virginia
Coastal Zone. The District of Columbia was excluded from the original
Coastal Zone legislation[^2] and is not required to have a coastal zone
management program.

### 3. Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area .unnumbered}

Arlington County is responsible for delineating Chesapeake Bay
Preservation Areas (CBPA's) and adopting programs that implement the
performance criteria specified in the language of the Chesapeake Bay
Preservation Act. CBPA's are divided into two designations by
Commonwealth of Virginia regulation: Resource Protection Areas (RPA's)
and Resource Management Areas (RMA's). The District of Columbia does not
designate Chesapeake Bay Preservation Areas.

A RPA includes extremely sensitive areas such as major streams, rivers,
lakes and wetlands as well as a 100-foot buffer surrounding them. While
the Arlington County CBPA does not include federal properties such as
the GWMP, the Potomac River and Boundary Channel shorelines and a
100-foot buffer around them would qualify as a RPA if the CBPA
designations were applied.

## Physiography, Geology and Soils

The Study Area and GWMP are located in the Atlantic Coastal Plain
physiographic province. In general, the Coastal Plain province is flat,
defined by terraces at several different locations, including the
Arlington Ridge to the west of the Pentagon Reservation. The low-lying
area encompassing the Study Area has been altered extensively by human
activity and no longer resembles the natural landform of the area.

The geologic formation underlying the Study Area is designated as part
of the Potomac Formation on the *Simplified Geologic Map of Arlington
County, VA and Vicinity* (Arlington County, 1999). The geology of the
Study Area itself is designated as artificial fill. The artificial fill
category is described as heterogeneous materials found in large areas
regraded, leveled, or filled for construction. It also includes fill of
marshes or low-lying areas and those formerly mined for sand, gravel or
clay.

Most soils in Arlington County include some percentage of urban land
intermixed with the native soil profile. Urban land is designated as
soils completely covered by concrete, asphalt, buildings or other
impervious surfaces. The soils within the Study Area are part of the
Urban Land-Sassafras-Neabsco complex. The mapping unit is designated as
the Urban land-Udorthents complex, 2 to 15 percent slopes and consists
of areas where more than 85 percent of the surface is Urban land. The
Udorthents consist of material that has been graded, cut, filled, or
otherwise disturbed during urbanization.

## Air Quality

The GWMP is located approximately 125 miles from the Atlantic Ocean.
Good air dispersion parameters occur in the region, with typical wind
speeds of 5 to 15 miles per hour (mph) predominantly from a general
northerly or southerly direction. Overall air quality can be considered
fair, but problems with specific pollutants exist in the area. The
metropolitan Washington, DC region exceeds the National Ambient Air
Quality Standards (NAAQS) for ozone and has been designated a Serious
Non-Attainment Area for ozone by the U.S. Environmental Protection
Agency (EPA). The region is in compliance for the other pollutants
considered in the NAAQS.

The Environmental Protection Agency (EPA) approved the National Capital
Region State Implementation Plan (SIP) on December 15, 2000. The EPA
also approved the region's request to extend the ozone attainment date
to November 15, 2005. On June 20, 2001 the National Capital Region
Transportation Planning Board (TPB) approved amendments to the 2000
Constrained Long-Range Plan (CLRP) and FY2001-2006 Transportation
Improvement Program (TIP) to include the proposed short- and mid-term
safety improvements associated with the 14^th^ Street Bridge/I-395 and
GWMP/I-395 interchange to the region's transportation plan and TIP. As
the proposed improvements do not result in an expansion of the regional
transportation system capacity, they are not anticipated to affect
conformity with the SIP.

## Noise

Vehicular traffic noise on the GWMP and I-395 and aircraft noise from
planes approaching and departing from National Airport are the most
common type of noise in the Study Area. Other noise sources include rail
traffic from the adjacent Metro and RF&P tracks. Information on existing
noise levels was drawn from existing published studies. No new field
measurements were taken. The aircraft noise is an intermittent source
that is superimposed upon the relatively constant ambient traffic noise
and accounts for only periodic sharp increases in noise levels.

The Metropolitan Washington Airports Authority completed a *Noise
Compatibility Study* for National Airport in 1990. Additional noise
analysis was conducted as part of the *Environmental Assessment for
Airport Traffic Control Tower and Related Terminal Improvements*
(Ricondo and Associates, 1993). Noise modeling done in conjunction with
the terminal improvements environmental assessment reflected compliance
with the Airport Noise and Capacity Act of 1990, which directed the
Federal Aviation Administration (FAA) to phase out the operation of
Stage 2 aircraft by the end of 1999. While the projected year 2000 noise
levels reflect an increase in the use of widebody (i.e., Boeing 767's)
operations at National Airport, they also reflect the introduction of
the quieter Stage 3 aircraft. The average day-night sound level (Ldn)
measured in decibels on the A-scale or dBA, the metric used by the FAA
to measure noise levels, is predicted to be 65 Ldn or less in the Study
Area.

Monitoring of noise levels in the vicinity of the Study Area was also
conducted in conjunction with the preparation of the *Environmental
Assessment of the Pentagon Reservation Master Plan* (DMJM-3D/I, 1991).
The monitoring site closest to the Study Area was in the Pentagon north
parking lot. The maximum noise levels at that site are associated with
National Airport operations. The average equivalent sound level (L~eq~)
measured at that location was 62 L~eq~ for the AM peak (with aircraft
making a south takeoff from National Airport), 75 L~eq~ for mid-day
(with aircraft making a north takeoff from National Airport) and 77
L~eq~ for the PM peak (with aircraft making a north takeoff). An
additional monitoring site was located southwest of the Study Area,
adjacent to I-395 and in the vicinity of Federal Office Building 2
(FOB2) or the Navy Annex. That site reflects noise generated by traffic
on I-395. Noise measurements at that location were 69 L~eq~ in the AM
peak, 70 L~eq~ at mid-day and 71 L~eq~ in the PM peak.

## Hazardous Materials and Wastes

A Phase I Environmental Site Assessment (ESA) was conducted of the
portion of the GWMP encompassing the Study Area. The assessment included
buildings associated with the Columbia Island Marina facility, which is
located on Columbia Island. These buildings include a main concession
building, restroom facilities and two small storage sheds.

Neither evidence of any historical land use that involved the
manufacture, use, or disposal of hazardous materials or hazardous wastes
on the property was found, nor any evidence that suggests the presence
of recognized environmental conditions based on the past use of the
property. The assessment did reveal evidence of recognized environmental
conditions -- the presence of underground storage tanks (USTs) and
aboveground storage tanks (ASTs) -- in connection with the current use
of the Columbia Island Marina portion of the Study Area for motorboat
docking/storage.

The USTs are used for the storage of gasoline, for refueling the
motorboats that use the marina, while the ASTs are used for storage of
used motor oil and fuel oil storage. According to NPS records, the USTs
and ASTs and piping appear to be in compliance with current local and
federal regulations. There was one historical recognized environmental
condition associated with the property, also related to the Columbia
Island Marina. This closed leaking UST was reported on the environmental
regulatory record search report. Although there are no dates indicating
when this case was opened or closed, it is known that this leaking UST
case has been closed. As such, it is believed that this reported leaking
UST case is not a current recognized environmental condition.

## Energy

Energy requirements associated with the Study Area relate to the amount
of energy required to operate and maintain buildings and other permanent
facilities (i.e., the outbuildings at the marina), the operation of
maintenance vehicles and equipment, including grounds maintenance
equipment, and the operation of other NPS vehicles. Energy is also
required for the operation of motor vehicles traversing the Study Area.

Energy sources utilized include electricity and petroleum products
(heating oil and fuels). The operations related to the Study Area are
dependent upon the continued availability of the existing energy
sources.

## Socioeconomic and Community Features

The GWMP and its associated uses primarily influence the surrounding
areas of Arlington County and areas of Washington, DC at the other end
of the 14^th^ Street Bridge(s). The recreation and open space features
of the GWMP have a broader influence and function as a regional park
resource. The GWMP is also a major component of the regional
transportation network.

### 1. Environmental Justice {#environmental-justice .unnumbered}

Executive Order 12898, Federal Actions to Address Environmental Justice
in Minority and Low-Income Populations, directs all federal agencies to
determine whether a proposed action would have an adverse or
disproportionate impact on minority and/or low-income populations. It
also directs agencies to ensure that representatives of an affected
community have every opportunity to provide input regarding the impact
of the proposed project.

There are no minority or low-income populations within the Study Area.
Within Arlington County, the majority of county residents (69%) consider
themselves to be of the white race; minority races include black or
African American (9%), Asian (9%) or multi-racial (8%). The median
household income, as reported in the 1997 Economic Census, was \$57,244.
The 2000 population of Arlington County was 189,453 persons, based on
2000 Census of Population estimates.

# Alternatives

This study has evolved from a series of investigations by the FHWA and
NPS dating back to the mid-1980's that documented safety and engineering
deficiencies in the segment of the GWMP from the southern end of
Columbia Island to the GWMP/I-395 interchange. Each of the studies
included recommendations for improvements to the GWMP to eliminate the
safety and design deficiencies. Those recommendations formed the basis
for an initial set of safety improvement alternatives.

Coordination meetings with public agencies having jurisdiction over the
Study Area were held in the summer of 2001 to review the initial set of
improvement alternatives and gauge agency reactions to the potential
alternatives. At the same time, two public information meetings were
also held to determine the level of public interest in the project and
initiate public comment on the possible alternatives.

## Goals and Objectives

Goals and objectives for the project were developed based upon the
specific problems associated with the Study Area, a review of goals and
objectives outlined by the FHWA and the NPS at the beginning of the
current investigations, and a review of relevant goals and objectives
associated with previous investigations in the Study Area. Specific
goals include:

1.  Improve safety for motorists, pedestrians, bicyclists and other GWMP
    users.

2.  Improve transportation system efficiency.

3.  Protect and preserve the scenic, historic and recreational aspects
    of the GWMP and surrounding historic resources.

4.  Protect and preserve natural features of the GWMP.

Objectives related to the various goals are summarized in Table 1.

[]{#__RefHeading___Toc5024300 .anchor}Table 1: Safety Improvement Goals
and Objectives

+-----------------------+----------------------------------------------+
| **GOALS**             | **OBJECTIVES**                               |
+-----------------------+----------------------------------------------+
| 1.  Improve safety    | -   Reduce the number of accidents and       |
|     for motorists,    |     incidents: motorists-motorists,          |
|     pedestrians,      |     motorists-pedestrians/bicyclists, and    |
|     bicyclists and    |                                              |
|     other GWMP users. |   pedestrian/bicyclist-pedestrian/bicyclist. |
|                       |                                              |
|                       | -   Eliminate or reduce the hazard potential |
|                       |     of roadway, trail or Parkway features.   |
+-----------------------+----------------------------------------------+
| 2.  Improve           | -   Improve traffic operations at problem    |
|     transportation    |     locations on the GWMP, especially peak   |
|     system            |     period traffic, consistent with the      |
|     efficiency.       |     alleviation of safety hazards and        |
|                       |     deficiencies.                            |
|                       |                                              |
|                       | -   Improve pedestrian/bicycle mobility.     |
+-----------------------+----------------------------------------------+
| 3.  Protect and       | -   Minimize impacts to scenic, historic or  |
|     preserve the      |     recreational elements of the GWMP,       |
|     scenic, historic  |     including visual impacts to surrounding  |
|     and recreational  |     historic resources (i.e., GWMP, the      |
|     aspects of the    |     Pentagon, Arlington National Cemetery,   |
|     GWMP and          |     East-West Potomac Park, etc.) that       |
|     surrounding       |     include the Columbia Island portion of   |
|     historic          |     the GWMP in their viewshed(s).           |
|     resources.        |                                              |
|                       | -   Maintain navigation in Boundary Channel  |
|                       |     to/from the Columbia Island Marina.      |
+-----------------------+----------------------------------------------+
| 4.  Protect and       | -   Minimize impacts on trees, wetlands,     |
|     preserve natural  |     floodplains, riparian areas, Potomac     |
|     features of the   |     River water quality and other natural    |
|     GWMP.             |     features.                                |
+-----------------------+----------------------------------------------+

## Preliminary Candidate Alternatives

Potential safety improvement options for each of the areas of concern
within the Study Area (see Figure 2) have been developed using the
recommendations identified in prior studies as a starting point. One of
the prior studies, the 1998 *14^th^ Street Bridge Corridor Improvement
Feasibility Study,* was initiated in 1996 as a result of special
Congressional legislation[^3] that directed action be taken to reduce
congestion and improve safety and traffic operations in the 14^th^
Street/I-395 corridor, including the I-395/GWMP interchange. The study
recommended a number of short- and long-term improvements for I-395,
14^th^ Street and the GWMP. To implement those recommendations, a
Memorandum of Agreement (MOA) was executed on December 20, 2000 between
the Federal Highway Administration (FHWA), District of Columbia
Department of Public Works (DCDPW), the Virginia Department of
Transportation (VDOT) and the NPS for the environmental planning and
design of the safety and operational improvements, including the I-395
interchange with the GWMP.

Ten potential projects have been developed from those identified in the
1998 feasibility study, prioritized as short-, mid- and long-term
improvements, and recommended for implementation by the FHWA:

*Short-term Improvements*

1.  Construct acceleration lane on northbound I-395 for ramp from
    southbound GWMP to northbound I-395.

2.  Improve signage on I-395 in Virginia.

3.  Improve signage on I-395 in the District of Columbia.

4.  Improve signal timing on 14th Street, between Constitution and C
    Streets, in the District of Columbia.

*Mid-term Improvements*

5.  Remove the ramp from northbound I-395 to northbound GWMP.

6.  Remove the ramp from southbound GWMP to southbound I-395.

7.  Replace the Humpback Bridge and construct an acceleration lane on
    northbound GWMP for the ramp from southbound I-395 to northbound
    GWMP. Also construct Mt. Vernon Trail underpasses connecting the
    east and west sides of the parkway.

8.  Close the entrance into the Columbia Island Marina from the GWMP and
    construct a new entrance and bridge from Boundary Channel Drive over
    Boundary Channel to the marina. Also close the small parking lot
    serving the Navy-Marine Memorial on the western side of the parkway.

*Long-term Improvements*

9.  Widen the northbound I-395 bridge over the GWMP as it approaches the
    Williams Bridge.

10. Widen the Williams Bridge through the addition of one through lane
    and one acceleration lane for the ramp from the northbound GWMP to
    northbound I-395.

The projects that correspond to the mid-term improvements listed above,
numbers four through eight, comprise the initial set of safety
improvement alternatives evaluated by this EA. Short-term improvements
are currently being implemented by the FHWA and VDOT. Since the issues
being evaluated and the purpose and need of this EA are strictly
concerned with improving the safety of GWMP roadway and trail
operations, rather than expanding its traffic-carrying capacity,
additional traffic analysis and environmental documentation will be
conducted before any long-term modifications or capacity improvements
for I-395, the Williams Bridge or the other 14^th^ Street bridges are
implemented.

A potential connection between the GWMP (either northbound or
southbound) and northbound I-395/Rochambeau Bridge has also been
considered in prior studies to alleviate congestion and weaving activity
on the inbound segment of I-395 between the GWMP and Williams Bridge.
The *14^th^ Street Bridge Corridor Improvement Feasibility Study*
recommended the northbound GWMP to northbound I-395/Rochambeau Bridge
ramp connection while a southbound GWMP to northbound I-395/Rochambeau
Bridge ramp connection was identified in the 1986 *Feasibility Study of
Measures to Improve the Safety, Capacity and Operation of the 14^th^
Street Bridge on I-395 and the I-395 and George Washington Memorial
Parkway Interchange*.

[]{.mark}

Additional alternatives have been identified based upon an analysis of
traffic counts and forecasts, geometric design standards, accident
information, and input from agency and public involvement. Proposed
vehicular and pedestrian improvement alternatives are listed in Table
E-1, Appendix E, grouped by the location they address within the Study
Area. Additional information on the preliminary alternatives and the
evaluation process is included in the *GWMP Safety Improvements Study
Candidate Alternatives Report*, prepared in conjunction with this EA.

Each of the preliminary alternatives were considered relative to the
goals and objectives of this study -- the expected safety benefit,
traffic impacts, practical operational ability, and potential impacts on
scenic/historic and natural features of the GWMP and adjacent properties
-- and relative to its financial impact. Of the preliminary GWMP safety
improvement options, those determined to be the most viable and
reasonable options for improving safety on the GWMP for motorists and
pedestrians have been retained for further evaluation. Alternatives
inconsistent with the goals and objectives of the study, alternatives
contrary to GWMP management objectives or review agency objectives, and
alternatives not considered environmentally or economically feasible
have been eliminated from further consideration.

Drawings depicting the proposed alternatives retained for evaluation in
this EA are located in Appendix A.

## Alternatives for the Columbia Island Marina Entrance

### 1. No Action Alternative {#no-action-alternative .unnumbered}

Under the No Action Alternative, no changes would be made to the
Columbia Island Marina entrance and related circulation/turning
patterns. The small parking lot serving the Navy-Marine Memorial and
Lady Bird Johnson Park would be retained as well. The safety concerns
associated with turning traffic at the marina entrance would not be
addressed.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance .unnumbered}

The proposed action would include the permanent closing of the Columbia
Island Marina entrance at the GWMP and construction of a new entrance on
Boundary Channel Drive, to the west (see drawings in Appendix A). The
existing entrance roadway to the marina parking lot and boat ramp would
be removed. The reclaimed roadway would be re-vegetated with grass,
consistent with the groundcover of the surrounding open space areas.

A two-lane vehicular bridge would be constructed over Boundary Channel
to connect Boundary Channel Drive with the existing marina parking lot
(see Figure 3). The bridge would accommodate two vehicle travel lanes
(one in each direction) and a sidewalk on one side. It would be designed
to blend with the character of the GWMP National Register historic
resource as well as adjacent National Register resources (i.e., LBJ
Memorial Grove and the Pentagon).

Boundary Channel Drive is part of the Pentagon Reservation and under the
jurisdiction of Department of Defense (DOD). A permit has been requested
from the DOD Directorate of Real Estate and Facilities for access from
Boundary Channel Drive for the new Columbia Island Marina entrance and
bridge. The NPS maintains a parking area for the LBJ Grove and
pedestrian bridge across Boundary Channel that are accessed via Boundary
Channel Drive under a similar permit agreement.

It should be noted that, due to the terrorist attack on the Pentagon of
September 11, 2002, DOD has initiated plans to realign Virginia Route
110 (VA 110) to decrease its proximity to the Pentagon (see Figure 2).
While a final alignment has not been established, the relocation may
require modifications to Boundary Channel Drive and/or the
I-395/Boundary Channel Drive interchange that could also affect the
design for the new marina entrance. As an interim safety measure and
until a final alignment has been determined, the FHWA and NPS propose to
reconfigure the Columbia Island Marina entrance on the GWMP to right
turns only (see Appendix A). The center median of the GWMP would be
closed to turning traffic as discussed previously. Once the relocation
of VA 110 is completed, the new marina entrance would be constructed.

A bus turnaround located adjacent to the existing marina entrance
roadway and parking lot would be removed in conjunction with the interim
modifications to the marina entrance. Public buses no longer serve the
Columbia Island Marina and the turnaround serves no useful purpose.

[]{#__RefHeading___Toc5024295 .anchor}Figure 3: Proposed Marina Bridge
Section

![](media/image7.jpeg){width="6.246527777777778in"
height="2.9409722222222223in"}

### 3. Alternatives Eliminated from Further Consideration {#alternatives-eliminated-from-further-consideration .unnumbered}

#### Signalize Entrance

The installation of traffic signals at the GWMP/marina intersection is a
relatively low-impact option that would provide for a safer intersection
and more efficient traffic flow in this area. However, it is a priority
of the NPS to keep the Parkway flowing freely without any traffic
signals. The portion of the GWMP that travels through the City of
Alexandria is the exception to this policy because the city has
jurisdiction over this stretch of parkway. For general GWMP application,
both the operational and aesthetic factors make traffic signalization
and/or automated vehicle message signs an undesirable option.

## Alternatives for the Southbound I-395 Ramp to Northbound GWMP, Humpback Bridge and Pedestrian Crossing of the GWMP

### 1. No Action Alternative {#no-action-alternative-1 .unnumbered}

Under the No Action Alternative, no modifications would be made to the
southbound I-395 ramp to northbound GWMP. The safety and design
deficiencies associated with the ramp would not be addressed. The
Humpback Bridge would remain in its existing configuration. The bridges
vertical sight distance deficiencies would remain as well. No
modifications would be made to the Mt. Vernon Trail crossing of the
Humpback Bridge. The at-grade, pedestrian[^4] crossing of the GWMP would
remain in its present location to the north of the marina entrance.
Pedestrian safety concerns associated with the existing trail and
crosswalk would not be addressed.

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge .unnumbered}

Alternative A involves widening the Humpback Bridge on the west side of
the existing bridge through the construction of an additional,
self-supporting bridge section (see Appendix A). The widened structure
would accommodate a northbound acceleration lane for the I-395 ramp, two
northbound vehicle travel lanes and two southbound vehicle travel lanes
(see Figure 4). A median barrier would separate the northbound and
southbound GWMP lanes. Modification of the horizontal alignment of the
GWMP to the north and south of the Humpback Bridge would be required to
accommodate the wider bridge structure.

The expanded bridge would accommodate a 10-foot wide Mt. Vernon Trail
crossing and a physical barrier or guardrail between the trail and
vehicular traffic. Both the median barrier and the trail barrier would
be constructed in a style and material(s) compatible with the GWMP
historic resource and the character of the existing bridge.

[]{#__RefHeading___Toc5024296 .anchor}Figure 4: Proposed Humpback Bridge
Section, Alternative A

![](media/image8.jpeg){width="6.499305555555556in"
height="2.704861111111111in"}

The existing at-grade crosswalk would be eliminated and pedestrian
underpasses would be constructed to the north and south of the Humpback
Bridge. The underpasses would be lighted and equipped for the potential
use of security devices. Sidewalks/trails would be constructed to
connect the Columbia Island Marina parking lot with the Mt. Vernon Trail
and Navy-Marie Memorial, via the northern underpass. Modifications to
the Mt. Vernon Trail would be made to link the existing trail with both
underpasses. A new trail connection would be constructed along the
southern edge of the Boundary Channel lagoon to link the
Pentagon/Boundary Channel Drive with the GWMP and Mt. Vernon Trail via
the southern underpass. All trail connections would be 9-feet wide,
consistent with the Mt. Vernon Trail width standard. The small,
six-stall parking lot serving the Navy-Marine Memorial would be
eliminated in this alternative.

Alternative A also involves adjusting the vertical profile of the
Humpback Bridge and approaches to increase the sight distance.
Modification of the GWMP ramps with I-395 (i.e., northbound GWMP ramp to
southbound I-395, southbound GWMP ramp to southbound I-395 and
southbound I-395 ramp to southbound GWMP) would be required to
transition from the new vertical alignment.

Unless additional structural analysis of the Humpback Bridge is
conducted, it is recommended that no additional dead loads be added to
the Humpback Bridge structure. Filling and grading required to adjust
the vertical approaches to the bridge should incorporate the use of
lightweight fill or decking material so as to not increase the dead load
on the bridge.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge .unnumbered}

Alternative B involves constructing a second bridge across Boundary
Channel, parallel to the Humpback Bridge (see Appendix A). The existing
bridge structure would be modified to accommodate the northbound
acceleration lane for the I-395 off-ramp, two northbound travel lanes
and a widened Mt. Vernon Trail and a barrier between the trail and
vehicle travel lanes (see Figure 5). The new span would accommodate the
two southbound GWMP travel lanes. The design style and material(s) of
the new bridge would be similar to that of the Humpback Bridge.

The northbound and southbound vehicle travel lanes of the GWMP would be
realigned to meet the new bridge structure. Modification of the
southbound GWMP ramp to southbound I-395 and the Columbia Island Marina
entrance would also be required to transition from the new alignment.
Additionally, the vertical profile of the Humpback Bridge and its
approaches would be modified to conform to recommended design standards.
Modification of the GWMP ramps with I-395 (i.e., northbound GWMP ramp to
southbound I-395, southbound GWMP ramp to southbound I-395 and
southbound I-395 ramp to southbound GWMP) would also be required to
transition from the new vertical alignment. Unless additional structural
analysis of the Humpback Bridge is conducted, it is recommended that no
additional dead loads be added to the Humpback Bridge structure. Filling
and grading required to adjust the vertical approaches to the bridge
should incorporate the use of lightweight fill or decking material so as
to not increase the dead load on the bridge.

This alternative also involves eliminating the existing at-grade
crosswalk and constructing pedestrian underpasses to the north and south
of the Humpback Bridge. As with Alternative A, the underpasses would be
lighted and equipped for the potential use of security devices.
Sidewalks/trails would be constructed to connect the Columbia Island
Marina parking lot with the Mt. Vernon Trail and Navy-Marie Memorial,
via the northern underpass. Modifications to the Mt. Vernon Trail would
be made to link the existing trail with both underpasses. A new trail
connection would be constructed along the southern edge of the Boundary
Channel lagoon to link the Pentagon/Boundary Channel Drive with the GWMP
and Mt. Vernon Trail via the southern underpass. All trail connections
would be 9-feet wide, consistent with the Mt. Vernon Trail width
standard. The small, six-stall parking lot serving the Navy-Marine
Memorial would be eliminated in this alternative.

[]{#__RefHeading___Toc5024297 .anchor}Figure 5: Proposed Humpback Bridge
Section, Alternative B

![](media/image9.jpeg){width="6.752083333333333in"
height="1.9006944444444445in"}

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge .unnumbered}

The Preferred Alternative involves the demolition of the Humpback Bridge
and construction of a replacement bridge structure to include: a widened
Mt. Vernon Trail crossing (with a physical barrier between the trail and
vehicular travel lanes), a northbound acceleration lane for the ramp
from southbound I-395 to northbound GWMP, two northbound travel lanes
and two southbound travel lanes (see Figure 6 and Appendix A). The
vertical profile and sight distance deficiencies of the existing bridge
would be corrected and addressed in the design of the new bridge and the
GWMP approaches.

The design of the new bridge would also incorporate north and south
pedestrian trail underpasses and the trail connections discussed in
Alternative A and Alternative B. The small parking lot serving the
Navy-Marine Memorial would also be eliminated in this alternative.

### 5. Alternatives Eliminated from Further Consideration {#alternatives-eliminated-from-further-consideration-1 .unnumbered}

#### Realign Ramp

This alternative involves the realignment of the ramp approximately 250
feet south of its current location. Although the realigned ramp would
incorporate compound horizontal curves that would serve to slow exiting
southbound I-395 traffic to some degree, the new acceleration lane on
the GWMP would still be substandard. Implementation of this option would
also result in a new deficiency on the GWMP; the distance between the
realigned ramp and the prior northbound GWMP to southbound I-395 ramp
would become substandard.

[]{#__RefHeading___Toc5024298 .anchor}Figure 6: Proposed Humpback Bridge
Replacement Section,\
Preferred Alternative

![](media/image10.jpeg){width="6.499305555555556in"
height="2.723611111111111in"}

#### Adjust Humpback Bridge Vertical Profile

The vertical curve of the GWMP as it approaches and descends the bridge
crossing of the Boundary Channel and Columbia Island Marina inlet
exceeds current roadway standards, hence the name "Humpback Bridge".
Adjusting the vertical profile of the bridge and its approaches, without
modifying or replacing the bridge structure itself, would eliminate the
roadway grade and sight distance deficiencies in this segment of the
GWMP and provide some improvement in motorist safety and traffic
operations. It would also, however, require modification of the
southbound I-395 to northbound GWMP ramp and southbound GWMP to
southbound I-395 ramp to meet the new vertical alignment of the mainline
Parkway. In addition, it does not address the more critical deficiency
in this segment of the Parkway; the lack of a merge/acceleration lane
for the southbound I-395 to northbound GWMP ramp. Eliminating the sight
distance deficiency without addressing the ramp merge deficiency may
pose more of a hazard, as the limited sight distance serves to slow
approaching northbound traffic.

#### Construct Separate Pedestrian Bridge Over Boundary Channel

Although providing a separate Mt. Vernon Trail crossing of Boundary
Channel would eliminate the pedestrian-vehicle conflicts on the Humpback
Bridge, that improvement is the most costly of the pedestrian access
options investigated and results in greater potential impacts to GWMP
historic and natural resources, particularly the viewshed(s) of the GWMP
and adjacent historic resources. It was therefore eliminated from
further consideration.

#### No Build with Pedestrian Modifications

While a wider Mt. Vernon Trail crossing can be accommodated on the
Humpback Bridge by reducing the width of the existing vehicle travel
lanes, this option only addresses the pedestrian-vehicle safety
conflicts associated with the bridge and the GWMP. Other safety concerns
related to the bridge, such as the vertical sight distance deficiency
and deficiencies associated with the southbound I-395 to northbound GWMP
ramp, are not addressed with this alternative. Those safety problems
would remain. Therefore, this alternative was eliminated from further
consideration.

#### Signalize Existing Crosswalk

As discussed in the previous section, the installation of traffic
signals on the GWMP, including pedestrian-activated signals, is not
supported by the NPS for aesthetic and operational reasons. Furthermore,
the crosswalk is located outside of the logical circulation path used by
pedestrians and bicyclists traveling between the Columbia Island Marina,
Navy-Marine Memorial and the Mt. Vernon Trail. Even with signalization,
it may be bypassed for the more direct crossing at the Columbia Island
Marina entrance.

#### Modify Existing Crosswalk: Construct Pedestrian Underpass

The construction of a pedestrian underpass, in the vicinity of the
existing at-grade crosswalk, was also considered as an option to
alleviate current pedestrian-vehicle safety conflicts. Due to the
relative flatness of the Parkway at the existing crosswalk, an underpass
would take the form of a tunnel beneath the existing roadway. The
transition from the at-grade trails to a tunnel would be difficult to
achieve and costly, and result in the addition of the tunnel structure
to the view of the GWMP as seen from the Potomac River and District of
Columbia. In addition, a pedestrian crossing at this location would
still be outside of the logical circulation path between the eastern and
western sides of the Parkway. It is likely at-grade crossings of the
GWMP and conflicts with motor vehicles would continue further south,
closer to the Columbia Island Marina entrance and the Humpback Bridge.

#### Relocate Crossing: Construct Pedestrian Underpass North of the Humpback Bridge

The construction of a single pedestrian underpass, located north of the
Humpback Bridge, was considered as a solution to address the
pedestrian-vehicle conflicts associated with the existing at-grade GWMP
crosswalk. This solution does not, however, provide any additional
opportunities for bicyclists and pedestrians to access the GWMP and the
Mt. Vernon Trail from the Pentagon and other points to the south and
west in Arlington County. Arlington County and DOD officials and local
bicyclist groups have expressed a desire to link the Mt. Vernon Trail
with adjacent, non-NPS trails and routes.

#### Modify/Relocate Crosswalk: Construct Pedestrian Overpass

The construction of a grade-separated pedestrian crossing, in the form
of an overpass, was considered as an option to alleviate current
pedestrian-vehicle safety conflicts. Two locations were identified: the
general location of the existing at-grade crosswalk and adjacent to the
northern end of the Humpback Bridge. Although an overpass would be less
costly to construct than an underpass, the visual costs and impacts on
the GWMP and adjacent National Register historic resources were
determined to be too great to consider this option further.

## Alternatives for Additional GWMP Ramp Connection to Northbound I-395/Rochambeau Bridge

### 1. Alternatives Eliminated from Further Consideration {#alternatives-eliminated-from-further-consideration-2 .unnumbered}

#### New Ramp from Southbound GWMP to Northbound I-395/Rochambeau Bridge

A new ramp connection between the southbound GWMP and northbound I-395
Rochambeau Bridge approach was considered in the 1986 *Feasibility Study
of Measures to Improve the Safety, Capacity and Operation of the 14^th^
Street Bridge on I-395 and the I-395 and George Washington Memorial
Parkway Interchange* to alleviate congestion on inbound I-395/Williams
Bridge and the GWMP. Although the construction of a new ramp at this
location would likely reduce queues on the GWMP during peak periods at
the existing southbound GWMP to northbound I-395/Williams Bridge ramp by
providing additional inbound access to the District of Columbia via the
Rochambeau Bridge, it serves primarily to reduce weaving activity on the
inbound Williams Bridge.

As discussed in the 1986 feasibility study, there is no practical way to
enforce the use of one ramp over the other, if the additional ramp were
constructed, except by physically prohibiting the weave movement between
14^th^ Street and I-395 on each bridge. If the weave movement were
prohibited through the construction of a physical barrier, with no
additional modifications to the 14^th^ Street Bridge corridor, no
significant improvement in traffic conditions was expected to result.
The construction of this new ramp connection is also projected to be
difficult to construct, given the limited space available and proximity
of other ramps and roadways in this segment of the GWMP, and would
require the widening of the Rochambeau Bridge. The cost associated with
the construction of the ramp was anticipated to be prohibitively
expensive relative to the traffic and safety improvements that would be
achieved. Finally, any improvement proposal that involves the widening
of one of the 14^th^ Street-Potomac River bridge crossing is expected to
be highly controversial to local stakeholders. The National Capital
Region Transportation Planning Board (TPB) has expressed the desire that
an environmental impact statement (EIS) and public outreach effort be
conducted as part of the evaluation of any bridge widening proposal. The
TPB has also requested that improvement proposals for the 14^th^ Street
Bridge corridor evaluate increased reliance on transit as an alternative
to bridge widening. In addition, the NPS-GWMP unit indicated they do not
support construction of new ramp access to/from the Parkway or other
improvements that may result in additional traffic volumes on the GWMP.
A new ramp would be considered a significant impact to the parkway
facility.

Due to the limited improvement to motorist safety on the GWMP and the
potential controversy a new ramp from the GWMP to the Rochambeau Bridge
would generate, this option was not considered further as part of this
EA.

#### New Ramp from Northbound GWMP to Northbound I-395/Rochambeau Bridge

A new ramp connection between the northbound GWMP and northbound I-395
Rochambeau Bridge approach was recommended in the *14^th^ Street Bridge
Corridor Improvement Feasibility Study* to alleviate congestion and
weaving activity on inbound I-395 between the GWMP and Williams Bridge.
The construction of a new ramp at this location was investigated because
of the high volume of District-bound traffic using the northbound GWMP
to northbound I-395/Williams Bridge ramp in the peak period and
resulting queues that form on the Parkway, as well as the existing
ramp's geometric deficiencies. The construction of the additional I-395
entrance ramp from the GWMP is also projected to increase motorist
safety and decrease weaving movements between 14^th^ Street and I-395 on
the Williams Bridge by providing a direct ramp connection to the
Rochambeau Bridge for motorists destined for 14^th^ Street.

Due to the limited distance between the Williams and Rochambeau Bridges
and the approximately 19 feet difference in elevation between the GWMP
and the Rochambeau Bridge, a ramp connecting the two roadways would
likely extend to the Potomac River shoreline or beyond before merging
with the bridge deck and result in significant land-disturbing activity.
Additional widening of the Rochambeau Bridge across the Potomac River
would also be necessary to provide an acceleration lane for the merging
traffic. As with the previously dismissed option to construct a ramp
connection between the southbound GWMP and inbound Rochambeau Bridge,
the cost of the proposed ramp is projected to be much greater than the
safety and traffic benefits that would be realized on the GWMP and is
likely to be controversial to local policymakers and motorists.
Therefore, this option was eliminated from further consideration.

## Alternatives Evaluated but Decision Deferred

The closure of two ramps at the GWMP and I-395 interchange -- the
southbound GWMP exit ramp to southbound I-395 and the northbound I-395
exit ramp to northbound GWMP -- were identified in the *14^th^ Street
Bridge Corridor Improvement Feasibility Study* as an option to improve
motorist safety. The NPS has deferred selection of a preferred
alternative or action/no action for the proposed ramp closures until the
completion of a more extensive evaluation by the FHWA of the
transportation needs of the I-395/14^th^ Street corridor in Virginia and
the District of Columbia, including the GWMP/I-395 interchange.
Therefore, no preferred alternative has been selected at this time.

### 1. Southbound GWMP Ramp to Southbound I-395 {#southbound-gwmp-ramp-to-southbound-i-395 .unnumbered}

#### No Action Alternative

The safety and design deficiencies associated with the southbound GWMP
ramp to southbound I-395 would not be addressed under the No Action
Alternative and the ramp would continue in operation.

#### Deferred Alternative: Eliminate Ramp

This alternative involves closing the southbound GWMP exit ramp to
southbound I-395. Traffic currently utilizing this ramp would be
diverted to the following alternate routes:

11. Southbound GWMP to southbound Virginia Route 27 (VA 27) to
    southbound I-395.

12. Southbound GWMP to southbound VA 27 to southbound Boundary Channel
    Drive to southbound I-395. Traffic bound for U.S. Route 1 (Route 1)
    or the Crystal City area of Arlington County, south of the existing
    ramp and the Study Area, could use southbound GWMP to southbound VA
    27 to southbound Boundary Channel Drive to southbound Old Jefferson
    Davis Highway to access Route 1/Crystal City.

As noted previously, DOD has initiated plans to realign VA 110 to
decrease its proximity to the Pentagon. While a final alignment has not
been established, the relocation may require modifications to Boundary
Channel Drive and/or the I-395/Boundary Channel Drive interchange that
could affect the use of Boundary Channel Drive as an alternate route
between the GWMP and I-395. This ramp closure alternative would not be
implemented until the plans for relocating VA 110 are complete and
impacts to Boundary Channel Drive can be assessed.

#### Alternatives Eliminated from Further Consideration

##### Lengthen the Deceleration Lane {#lengthen-the-deceleration-lane .unnumbered}

The extension of the existing, substandard deceleration lane for this
ramp would improve the present geometric deficiency on the GWMP. Despite
the geometric deficiencies, the ramp currently operates at an acceptable
level of service. The weaving section where this ramp merges with
southbound I-395, however, operates at an unacceptable level of service.
Constructing the deceleration lane on the GWMP would do nothing to
address that deficiency and would require the widening or replacement of
the Humpback Bridge. Therefore, this option was eliminated from further
consideration.

### 2. Northbound I-395 Ramp to Northbound GWMP {#northbound-i-395-ramp-to-northbound-gwmp .unnumbered}

#### No Action Alternative

Under the No Action Alternative, the northbound I-395 ramp to northbound
GWMP would continue in operation. The safety and design deficiencies
associated with the ramp would not be addressed.

#### Deferred Alternative: Eliminate Ramp

This alternative involves closing the left-side exit ramp from
northbound I-395 to northbound GWMP. Traffic currently utilizing this
ramp would be diverted to the following alternate routes:

1.  Northbound I-395 to VA 27 to northbound GWMP.

2.  Northbound I-395 to northbound Boundary Channel Drive to northbound
    VA 27 to northbound GWMP.

As with the proposed southbound GWMP to southbound I-395 ramp closure,
this alternative also relies on Boundary Channel Drive as an alternate
means of accessing I-395 from the GWMP. The ramp closure would not be
implemented until DOD plans for relocating VA 110 are complete and
impacts to Boundary Channel Drive can be assessed.

# Environmental Effects of Columbia Island Marina Alternatives

## Roadways and Ramps

### 1. Future (2025) Traffic Conditions Analysis {#future-2025-traffic-conditions-analysis .unnumbered}

Year 2001 traffic counts and historical traffic projections were used to
develop the future (2025) traffic projections for the future conditions
traffic model. In the *14^th^ Street Bridge Corridor Improvement
Feasibility Study* (Virginia Department of Transportation, 1998),
traffic was projected from 1996 to 2000, and again to the year 2020. The
study utilized the Metropolitan Washington Council of Governments
(MWCOG) travel-forecasting model to develop these growth rates. The
growth rates from this report were utilized to determine the growth in
traffic from 2001 to 2025 during the peak hours. The 2025 projected peak
hour traffic is shown in the figure found in Appendix B, Figure B-4.
There are several locations at which 2001 traffic counts were taken and
no future projection has been developed. These locations had not been
included in the *14^th^ Street Study*, and therefore, no future traffic
projection has been made.

A CORSIM model was developed using the projected 2025 traffic volumes
with no roadway improvements. This analysis will be the baseline from
which the various improvement alternatives will be compared. A figure
depicting the results of the LOS analysis is found in Appendix B, Figure
B-5. The heavier traffic volumes overload the road network, especially
I-395 northbound in the AM where the bottleneck at GWMP causes severe
backups along the Interstate. At that location several design and
capacity deficiencies cause the traffic congestion; the interstate
decreases from four lanes to three lanes, an on-ramp from the GWMP with
a short acceleration lane is located only 200 feet downstream of the
lane drop, and an off-ramp to the GWMP with no deceleration lane is
located 200 feet downstream of the on-ramp.

The intersection of the GWMP and the Columbia Island Marina entrance was
analyzed using Highway Capacity Software (HCS) 2000, which is based on
the standard Highway Capacity Manual (HCM) methodology for analyzing
intersections, and utilizing AM and PM peak hour turning movement counts
collected in August 2001. Although the peak period for traffic using the
marina entrance may be on the weekend, the traffic on the GWMP peaks
during the weekday rush hours. It is also standard engineering practice
to analyze an intersection based on the weekday peak hours, and not on a
weekend peak.

### 2. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance .unnumbered}

No change to existing traffic operations would result. Traffic entering
and exiting the marina and memorial parking lots operate at or near
unacceptable levels of service, as indicated in Figure B-5, Appendix B.
The intersection would operate at LOS F for the northbound GWMP traffic
and LOS D for southbound GWMP traffic. The conflicts between turning
vehicles and the mainline GWMP traffic flows would also remain.

### 3. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-1 .unnumbered}

The high traffic volumes on the GWMP at the unsignalized marina entrance
intersection make left turns in and out of the Columbia Island Marina
and Navy-Marine Memorial parking lot difficult and unsafe. The
intersection was analyzed for the existing (2001) conditions, future
(2025) no-build conditions, as well as the Preferred Alternative (2025),
which involves the closure of the GWMP median (right in/out) as an
interim safety measure and the permanent closure of the marina entrance
on the GWMP and Navy-Marine Memorial parking lot as the preferred,
long-term measure. The future marina entrance traffic was determined
using the growth rate already developed on the GWMP in the vicinity of
the marina, as described in the 'Future (2025) Traffic Conditions
Analysis' section of this report. Table 2 details the results of the
traffic operations analysis.

[]{#__RefHeading___Toc5024301 .anchor}Table 2: Weekday Level of Service
Results / Peak Hour Volumes\* for Columbia Island Marina Entrance

+----------------+-------+-------+-------+--------+--------+---------+
|                | **Exi |       | **No  |        | **I    |         |
|                | sting |       | Build |        | nterim |         |
|                | (20   |       | (20   |        | (2     |         |
|                | 01)** |       | 25)** |        | 025)** |         |
|                |       |       |       |        |        |         |
|                |       |       |       |        | *      |         |
|                |       |       |       |        | *Right |         |
|                |       |       |       |        | In &   |         |
|                |       |       |       |        | Right  |         |
|                |       |       |       |        | out**  |         |
+----------------+-------+-------+-------+--------+--------+---------+
|                | AM    | PM    | AM    | PM     | AM     | PM      |
+----------------+-------+-------+-------+--------+--------+---------+
| NB Lefts -- NB | D /   | F /   | D /   | F / 32 | n/a    | n/a     |
| GWMP to marina | 12    | 28    | 12    |        |        |         |
+----------------+-------+-------+-------+--------+--------+---------+
| WB Rights --   | F / 7 | E /   | F / 7 | F / 14 | n/a    | n/a     |
| Navy-Marine    |       | 12    |       |        |        |         |
| Memorial       |       |       |       |        |        |         |
| parking lot to |       |       |       |        |        |         |
| NB GWMP        |       |       |       |        |        |         |
+----------------+-------+-------+-------+--------+--------+---------+
| EB Lefts --    | F / 3 | F /   | F / 3 | F / 14 | n/a    | n/a     |
| marina to NB   |       | 12    |       |        |        |         |
| GWMP           |       |       |       |        |        |         |
+----------------+-------+-------+-------+--------+--------+---------+
| EB Rights --   | D /   | F /   | D /   | F / 43 | D / 15 | F / 57  |
| marina to SB   | 12    | 37    | 12    |        |        |         |
| GWMP           |       |       |       |        |        |         |
+----------------+-------+-------+-------+--------+--------+---------+

\* peak hour volume in vph (vehicles per hour)

Note: Right turns from northbound GWMP to the Navy-Marine Memorial
parking lot and from the southbound GWMP to the marina are not included
because they are free-flow turning movements. Left turns into and out of
the Navy-Marine Memorial parking lot are prohibited.

Eliminating the left turns at this intersection and providing right
turns only, as an interim measure, removes most of the conflict points
between vehicles, thus creating a safer intersection. The left turns
into and out of the marina would be rerouted to become right turns at
the marina entrance. This additional traffic on the southbound GWMP
right-turn movement does not significantly affect its operation, since
it is a free-flow movement. The mainline GWMP would remain at LOS D for
southbound traffic and LOS F for northbound traffic.

Eliminating the entrance completely and relocating it to Boundary
Channel Drive, as a long-term measure, would have the greatest safety
benefit for the GWMP, although the northbound and southbound through
traffic on the GWMP would remain at or near unacceptable levels of
service due to the heavy mainline traffic volumes. Relocating the marina
entrance would result in increased traffic on Boundary Channel Drive.
The peak marina traffic, however, is on the weekend so there would be
little conflict with weekday, peak period commuter traffic.

The long-term option to relocate the marina entrance assumes Boundary
Channel Drive, which is under DOD jurisdiction, remains open to
non-Pentagon traffic. The FHWA has submitted a request to the DOD, on
behalf of the NPS, for a permit for access to Boundary Channel Drive for
a new Columbia Island Marina entrance and vehicular bridge across
Boundary Channel.

##### Maintenance of Traffic {#maintenance-of-traffic-1 .unnumbered}

The proposed interim measure to reconfigure the marina entrance to limit
turning movements to right turns only and close the existing GWMP median
break would require temporary reductions in mainline GWMP lane widths
and at the marina entrance. The construction is not anticipated to have
a significant on GWMP or marina traffic operations.

The construction of the new marina entrance and bridge would temporarily
affect traffic patterns on Boundary Channel Drive and within the marina
parking lot. Travel lanes on Boundary Channel Drive would be temporarily
reduced in width due to construction activities. No road closures are
anticipated. The new entrance would also result in the loss of
approximately six parking spaces at the Columbia Island Marina. Travel
lanes on the mainline GWMP in the vicinity of the marina would also be
temporarily reduced during the removal of the existing entrance and
median. No road closures are anticipated.

## Bicycle and Pedestrian Facilities

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-1 .unnumbered}

The Mt. Vernon Trail and other pedestrian/bicycle facilities within the
Study Area, as well as related safety deficiencies, would remain in
their current condition.

[]{.mark}

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-2 .unnumbered}

This alternative does not involve any modifications to the Mt. Vernon
Trail or other pedestrian/bicycle facilities. The existing facilities
would remain in their current condition.

## Historic and Cultural Resources

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-2 .unnumbered}

No impact to historic or cultural resources is anticipated.

[]{.mark}

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-3 .unnumbered}

Construction of the new marina entrance and bridge across Boundary
Channel would impact the historic setting of the GWMP. Consultation with
the Advisory Council on Historic Presentation (Advisory Council) and
Virginia and District of Columbia State Historic Preservation Officers
(SHPO) has been initiated in compliance with Section 106 of the National
Historic Preservation Act. The design of the new bridge, construction
plans and details would be executed in conjunction with the terms and
conditions of a memorandum of agreement (MOA) between the FHWA, NPS,
Advisory Council and District of Columbia and Virginia SHPO's that would
outline the measures to be taken to mitigate potential impacts to the
historic resources.

Past grading and filling activity have extensively modified the land
within the Study Area. It is not anticipated to have a high potential
for the presence of undisturbed cultural or archaeological resources.

## Aesthetics and Viewsheds

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-3 .unnumbered}

The aesthetic condition and viewshed of the GWMP and adjacent historic
resources would remain in their current condition.

[]{.mark}

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-4 .unnumbered}

The interim configuration of the marina entrance would benefit Parkway
aesthetics slightly, due to the elimination of pavement in the GWMP and
at the marina entrance. Construction of a new marina entrance and bridge
across Boundary Channel would create a new element within the GWMP
historic resource and in the viewsheds of adjacent historic resources:
LBJ Memorial Grove, the Pentagon and Arlington National Cemetery (see
also Environmental Effects, *Historic and Cultural Resources*).

While the design of the new bridge and entrance would be compatible with
the existing character of the GWMP and other historic resources, the
visual setting of the GWMP and Columbia Island would be affected by the
construction of the new entrance, as well as views from the Pentagon and
LBJ Memorial Grove. Areas cleared of vegetation during the construction
process would be replanted once the new entrance is complete, to
minimize visual impacts.

## Land Use

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-4 .unnumbered}

No change to existing Land use patterns is anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-5 .unnumbered}

No change to existing land use patterns is anticipated, either for the
interim marina alternations (e.g., right in/right out) or the
construction of a new entrance from Boundary Channel Drive and vehicular
bridge over Boundary Channel.

## Biological Resources

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-5 .unnumbered}

##### Vegetation {#vegetation-1 .unnumbered}

No change to existing vegetation would result.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-1 .unnumbered}

No change to existing wildlife is anticipated.

##### Wetlands {#wetlands-1 .unnumbered}

No impact to wetland resources is anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-6 .unnumbered}

##### Vegetation {#vegetation-2 .unnumbered}

The interim option to limit turning movements at the existing entrance
to right in/out would result in the closure and re-vegetation of the
center GWMP median at the marina entrance. The median would likely be
planted with turf grass, consistent with the treatment of the adjacent
median areas. This modification is anticipated to have a minimal benefit
to existing vegetation resources, but would increase the amount of
landscaped area by approximately 5,900 square feet (SF) or 0.1 acres
(AC).

The construction of a new marina entrance from Boundary Channel Drive
would result in the clearing of approximately 6,500 SF or 0.1 AC of
mixed woodland vegetation adjacent to Boundary Channel within the path
of the proposed entrance bridge. Once the new bridge is constructed,
disturbed areas would be re-vegetated. Removal of the existing marina
entrance roadway would increase the amount of landscaped area by
approximately 0.8 AC.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-2 .unnumbered}

While existing vegetation would be cleared on each side of Boundary
Channel for the proposed new entrance bridge, loss of that resource is
not anticipated to have an adverse impact on wildlife inhabiting the
area surrounding the Columbia Island Marina. Disturbed areas would be
replanted with vegetation consistent with that removed in order to
provide the same type of wildlife habitat that would be destroyed.
Construction of the bridge would also affect aquatic wildlife found in
Boundary Channel; however those impacts are anticipated to be temporary.
There are no state or federally listed rare, threatened or endangered
species known to inhabit the Study Area.

##### Wetlands {#wetlands-2 .unnumbered}

Construction of the new entrance bridge over Boundary Channel to the
marina would take place within the Boundary Channel wetland resource. No
wetlands would be destroyed, however temporary impacts to the wetlands
and associated aquatic vegetation and wildlife would result. The
construction of the new bridge would comply with the conditions of
Section 401 and 404 of the Clean Water Act, if necessary. A wetlands
permit would be obtained from the U.S. Army Corps of Engineers for the
construction activity. The proposed action would also comply with
applicable state and local permit requirements.

## Water Resources

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-6 .unnumbered}

##### Floodplains {#floodplains-1 .unnumbered}

No impact to floodplains is anticipated.

##### Coastal Zone Management {#coastal-zone-management-1 .unnumbered}

No Coastal Zone impacts are anticipated.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-1 .unnumbered}

No Chesapeake Bay impacts are anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-7 .unnumbered}

##### Floodplains {#floodplains-2 .unnumbered}

Construction of the new entrance bridge over Boundary Channel to the
marina would take place within Flood Zone A12, area of 100-year flood,
as indicated on the FEMA Flood Insurance Rate Map for the Study Area. A
permit would be required from the U.S. Army Corps of Engineers for the
construction activity. A bridge permit from the U.S. Coast Guard would
also be required.

##### Coastal Zone Management {#coastal-zone-management-2 .unnumbered}

The Arlington County portions of the Study Area are located within the
Virginia Coastal Zone. The Federal Coastal Zone Management Act requires
development projects of Federal agencies that take place within the
Coastal Zone be consistent with the applicable state coastal zone
management program to the maximum extent practicable. The Virginia
Coastal Resources Management Program is a network of existing state laws
and policies though which the Commonwealth of Virginia manages its
coastal resources. Proposed actions that comply with the applicable
state laws and policies[^5] are considered to be consistent with the
Virginia Coastal program. The District of Columbia is not subject to the
Coastal Zone Management Act. The proposed safety improvements would be
constructed in accordance with Commonwealth of Virginia and District of
Columbia stormwater management, sedimentation and erosion control and
other water quality protection laws and policies.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-2 .unnumbered}

The proposed new marina entrance is located on government-owned property
that is exempt from Arlington County Chesapeake Bay Preservation
regulations. Construction and other activities related to the
implementation of the proposed safety improvements would comply with
local stormwater management, sedimentation and erosion control and other
water quality protection regulations.

## Physiography, Geology and Soils

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-7 .unnumbered}

No disturbance to soils is anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-8 .unnumbered}

Minor soil disturbance would occur during the reconfiguration of the
marina entrance from the GWMP and removal of the pavement in the GWMP
median for the interim entrance modifications (right in/out). An area of
approximately 0.3 AC would be impacted by the interim modifications.
Soils would be disturbed during the construction of the new entrance
bridge and the removal of the existing marina entrance driveway.
Approximately 3.9 AC would be disturbed. All demolition and construction
activities would incorporate erosion control measures to minimize soils
loss.

## Air Quality

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-8 .unnumbered}

No change to air quality levels is anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-9 .unnumbered}

The proposed action does not increase the capacity of the GWMP
transportation system; air quality levels would remain essentially the
same as present conditions as a result of the construction of the new
marina entrance. Minor, temporary increases in dust and other air
emissions would result from construction activities. Construction
activities would be conducted in accordance with the FHWA's Standard
Specifications for Construction of Roads and Bridges on Federal Highway
Projects (1996) and would comply with applicable local, state and
federal regulations.

## Noise

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-9 .unnumbered}

No change in existing noise sources or noise levels is anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-10 .unnumbered}

Existing noise levels would increase temporarily during the construction
of the new marina entrance and bridge across Boundary Channel. The
rerouting of traffic to the new entrance would result in minor increases
in noise levels on I-395, VA 27 and Boundary Channel Drive, due to the
additional vehicle traffic. The increases in noise levels are not
anticipated to be significant.

## Hazardous Materials and Wastes

No evidence of historical land use involving hazardous materials or
hazardous wastes was found within the Study Area. Implementation of the
proposed action would not require the disturbance or relocation of any
of the existing, recognized environmental conditions -- USTs and ASTs --
found at the Columbia Island Marina. Therefore, no disturbance or
generation of hazardous materials or hazardous wastes are anticipated to
occur with either the implementation of any of the safety improvements
or under "no-action" conditions.

## Energy

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-10 .unnumbered}

No change in energy consumption is anticipated.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-11 .unnumbered}

Energy consumption would temporarily increase during construction of the
new marina entrance and bridge. No significant change in long-term
energy consumption is anticipated.

## Socioeconomic and Community Features

### 1. No Action: Retain Existing Marina Entrance {#no-action-retain-existing-marina-entrance-11 .unnumbered}

No change to socioeconomic or community features is anticipated. The
public would continue to be exposed to the safety hazards associated
with the current GWMP transportation and circulation systems.

### 2. Preferred Alternative: New Entrance {#preferred-alternative-new-entrance-12 .unnumbered}

Construction jobs associated with the relocation of the marina entrance
and construction of the entrance bridge across Boundary Channel would
have a short-term benefit to local construction workers and the local
economy.

If turning movements in and out of the Columbia Island Marina were
limited to right turns only, as an interim safety improvement measure,
marina access/egress options would be reduced. The change in traffic
patterns is not anticipated to adversely impact traffic operations. The
marina situation would be similar to other locations on the GWMP, such
as Gravelly Point and the Teddy Roosevelt Island parking lot, where
access is only possible from one direction of the Parkway. In the long
term, marina-bound visitors would be rerouted to the new entrance via a
less direct route. Since the majority of marina traffic travels in
non-peak periods, the rerouting is not anticipated to result in greater
congestion on the Study Area road network.

[]{.mark}

## Cumulative Impacts

The proposed mid-term safety improvements identified for the Study Area
are intended to complement the short-term and long-term safety
improvements proposed by the FHWA for the I-395/GWMP interchange and
14^th^ Street Bridge to enhance overall motorist and pedestrian safety
within the corridor. No increase in the traffic-carrying capacity of the
GWMP would result from the implementation of the preferred marina
entrance alternative. It is not anticipated to contribute to any
cumulative impacts.

Implementation of the proposed safety improvements would create a safer
environment for the users of the other GWMP facilities proposed by the
NPS in the vicinity of the Study Area as well as current GWMP users.
Those facilities -- a (non-motorized) boathouse and comfort station --
would utilize the existing mainline roadway network, although the
construction of vehicular and pedestrian connections may be necessary to
link the new facilities with existing parking and trail resources.

The selection of the preferred alternative to relocate the Columbia
Island Marina entrance to Boundary Channel Drive is contingent upon
approval of the proposed entrance location by DOD, which controls access
to Boundary Channel Drive. Any changes to Boundary Channel Drive would
also require coordination with proposed plans to realign VA 110 to
decrease its proximity to the Pentagon. Other planned improvements for
the Pentagon Reservation are primarily concerned with the renovation of
the existing Pentagon building. No major new structures are anticipated
that, when combined with the impacts of the proposed marina re-location
would result in significant cumulative impacts.

Undeveloped parcels in the vicinity of the Study Area include the former
Twin Bridges Marriott site and the Arlington County "North Tract" site.
Both are located to the southwest of the Study Area, at the north end of
Crystal City. Arlington County plans to redevelop the North Tract as a
public park and recreation facility. The county is also investigating
the acquisition of the Twin Bridges Marriott site. Upgrade of the
existing transportation network, including Old Jefferson Davis Highway,
is under investigation as well. The upgrade of Old Jefferson Davis
Highway would facilitate access to Boundary Channel Drive and the
preferred new marina entrance. Development of the two parcels for park
and recreation uses would be compatible with the use of the GWMP and
would not be anticipated to result in significant cumulative impacts.

## Comparison of Alternatives

A comparison of the No Action Alternative and the Preferred Build
Alternative is provided in Table 3.

[]{#__RefHeading___Toc5024302 .anchor}Table 3: Comparison of
Alternatives -- Columbia Island Marina Entrance

  -------------- --------------- ----------------------- -----------------------
  **Evaluation   **No Action     **Preferred             
  Factor**       Alternative**   Alternative: New        
                                 Entrance**              

                                 *Interim Action --      *Long-term Action --
                                 Right In/Out*           New Entrance from
                                                         Boundary Channel Drive*

  Navigation     No impact is    No impact is            No impact is
  Impacts        anticipated.    anticipated.            anticipated. Boundary
                                                         Channel is not
                                                         navigable by marina
                                                         traffic at the proposed
                                                         bridge location. USCG
                                                         bridge permit would be
                                                         required.

  Maintenance of No impact is    GWMP and marina would   Boundary Channel Drive
  Traffic        anticipated.    remain open during      and marina would remain
                                 construction activities open during
                                 to modify the marina    construction of new
                                 entrance and GWMP       entrance/bridge.
                                 median.                 

  Motorist       Safety hazards  Motorist safety         Motorist safety
  Safety and     and accident    improved with           improved with the
  Traffic        potential       elimination of left     elimination marina
  Operations     associated with turns in/out of marina. entrance on GWMP.
                 marina entrance Access to marina would  Conflicts between
                 would remain.   be eliminated from the  marina traffic and
                                 northbound GWMP.        mainline GWMP traffic
                                                         would be eliminated.
                                                         Marina-bound traffic
                                                         would be rerouted to
                                                         the new entrance via a
                                                         less direct route.

  Alternate      No impact is    Northbound vehicles on  Marina traffic would be
  Routes         anticipated.    GWMP destined for and   rerouted to the new
                                 exiting the marina      entrance via
                                 would have to use       I-395/Route 27/Boundary
                                 alternate route.        Channel Drive.
                                 Traffic increases on    Permission of DOD
                                 alternate routes would  required to access
                                 be minimal.             marina from Boundary
                                                         Channel Drive.

  Historic and   No impact is    No impact is            Consultation with
  Cultural       anticipated.    anticipated.            Advisory Council and VA
  Resources                                              and DC SHPO's required.
                                                         No adverse impacts to
                                                         historic/cultural
                                                         resources are
                                                         anticipated; new bridge
                                                         design would be
                                                         compatible with
                                                         historic resource(s).
                                                         Concurrence with SHPO
                                                         would be sought for
                                                         determination of "no
                                                         adverse effect".

  Aesthetics and No impact is    No impact is            New entrance bridge
  Viewsheds      anticipated.    anticipated.            would be new element in
                                                         GWMP and Pentagon
                                                         viewsheds; new bridge
                                                         design would be
                                                         compatible with
                                                         historic resources.

  Vegetation     No impact is    GWMP median would be    New entrance/bridge
                 anticipated.    re-vegetated after      construction results in
                                 removal of existing     clearing of
                                 turn lanes. Landscaped  approximately 0.1 AC of
                                 area would increase by  mixed woodland
                                 approximately 0.1 AC.   vegetation adjacent to
                                                         Boundary Channel.
                                                         Cleared areas would be
                                                         re-planted following
                                                         construction
                                                         completion.

  Wildlife and   No impact is    No impact is            No impact is
  Threatened &   anticipated.    anticipated.            anticipated.
  Endangered                                             
  Species                                                

  Wetlands       No impact is    No impact is            Boundary Channel
                 anticipated.    anticipated.            wetlands impacted by
                                                         bridge construction.
                                                         USACOE permit would be
                                                         required.
  -------------- --------------- ----------------------- -----------------------

Table 3: Comparison of Alternatives -- Columbia Island Marina Entrance

  ----------------------- --------------- ------------------------- -----------------------
  **Evaluation Factor**   **No Action     **Preferred Alternative:  
                          Alternative**   New Entrance**            

                                          *Interim Action -- Right  *Long-term Action --
                                          In/Out*                   New Entrance from
                                                                    Boundary Channel Drive*

  Water                   No impact is    Minor decrease in         New bridge located in
  Resources/Floodplains   anticipated.    impervious surface on     100-year floodplain;
                                          GWMP. Modifications would USACOE permit would be
                                          be constructed in         required. Improvements
                                          accordance with DC        would be constructed in
                                          stormwater management,    accordance with VA and
                                          sedimentation and erosion DC stormwater
                                          control and other water   management,
                                          quality protection laws   sedimentation and
                                          and policies.             erosion control and
                                                                    other water quality
                                                                    protection laws and
                                                                    policies. Net reduction
                                                                    in impervious surface
                                                                    of approximately 0.3 AC
                                                                    in marina area due to
                                                                    removal of existing
                                                                    entrance driveway
                                                                    pavement.

  Geology/Soils           No impact is    Minor soils disturbance   Soils disturbance of
                          anticipated.    (0.3 AC) for median       approximately 3.9 AC
                                          removal and construction  during construction of
                                          of entrance               new entrance/bridge.
                                          modifications. Erosion    Erosion control
                                          control measures would be measures would be
                                          incorporated during       incorporated during
                                          construction and          construction and
                                          disturbed areas           disturbed areas
                                          re-vegetated.             re-vegetated.

  Air Quality             No impact is    Existing air quality      Existing air quality
                          anticipated.    levels would remain       levels would remain
                                          essentially the same.     essentially the same.

  Noise                   No impact is    Existing noise levels     Rerouting of
                          anticipated.    would remain essentially  marina-bound traffic
                                          the same.                 would result in
                                                                    negligible decrease in
                                                                    traffic noise on GWMP
                                                                    and negligible increase
                                                                    along alternate routes.

  Hazardous Materials and No impact is    No impact is anticipated. No impact is
  Wastes                  anticipated.                              anticipated.

  Energy                  No impact is    No significant impact is  No significant impact
                          anticipated.    anticipated.              is anticipated.

  Socioeconomic and       The public      Traffic hazards on the    Minor benefit from
  Community Features      would continue  GWMP would be reduced,    construction-related
                          to be subject   making it safer for       jobs and purchases. No
                          to safety       Parkway users.            long-term economic
                          hazards                                   impact is anticipated.
                          associated with                           The public would no
                          the current                               longer be subject to
                          GWMP                                      safety hazards
                          circulation                               associated with the
                          systems.                                  current GWMP
                                                                    circulation systems.

  Temporary Impacts       No impact is    Temporary lane reductions Temporary lane
                          anticipated.    and/or closures may be    reductions and/or
                                          required during           closures may be
                                          construction of entrance  required during
                                          modifications. Minor,     construction of new
                                          temporary noise increases bridge. Minor,
                                          would result during       temporary impacts to
                                          demolition/construction   air quality during
                                          activities.               construction of
                                                                    entrance modifications.
                                                                    Minor, temporary noise
                                                                    increases would result
                                                                    during construction
                                                                    activities. Energy
                                                                    consumption would
                                                                    temporarily increase
                                                                    during construction of
                                                                    the new marina entrance
                                                                    and bridge.

  Cumulative Impacts      No impact is    Safer environment for     Safer environment for
                          anticipated.    vehicular and pedestrian  vehicular and
                                          users of the GWMP would   pedestrian users of the
                                          result. No adverse        GWMP would result.
                                          impacts are anticipated.  Marina access enhanced
                                                                    by potential Old
                                                                    Jefferson Highway
                                                                    improvements under
                                                                    investigation by
                                                                    Arlington County. No
                                                                    adverse impacts are
                                                                    anticipated.

  Cost                    Not applicable  \$170,000                 \$3,350,000
  ----------------------- --------------- ------------------------- -----------------------

# Environmental Effects of the Alternatives for the Southbound I-395 Ramp to Northbound GWMP, Humpback Bridge and Pedestrian Crossing of the GWMP

## Roadways and Ramps

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications .unnumbered}

No change to existing traffic operations would result. The ramp and GWMP
would operate at LOS F as indicated in Figure B-6, Appendix B for the no
build condition. Existing geometric and safety deficiencies would also
remain.

### 2. All Alternatives {#all-alternatives .unnumbered}

The three alternatives evaluated for this ramp,

-   Alternative A, widen existing bridge;

-   Alternative B, construct a second, parallel bridge; and

-   Preferred Alternative, replace existing bridge

are the same in terms of a traffic operations analysis. All involve a
wider bridge crossing of the Boundary Channel inlet, which eliminates
the geometric deficiencies for this ramp and allows for a longer
acceleration lane without realigning the ramp.

Figure B-6, Appendix B shows the level of service improvement as a
result of the proposed ramp alternatives. The LOS on the ramp is
significantly improved from a LOS F to a LOS D in the AM peak. In the PM
peak, the LOS improved from an F to borderline C/D. The longer
acceleration lanes in the improvement scenarios allow vehicles to merge
more easily, thus reducing the queues that develop along the ramp.
However, northbound GWMP continues to operate at LOS F even with the
ramp improvements due to the heavy mainline volumes.

In addition to the level of service analysis, an analysis of average
speed and density was performed on the southbound I-395 to northbound
GWMP movement in order to further compare the alternatives to the
no-build scenario. As shown in Table 4, the results are reported for the
affected portion of the model; the link of I-395 before the ramp, the
ramp itself, and the GWMP link after the ramp merges.

In the AM peak, speed improved by about 16 mph over a 0.65-mile length
of roadway. In this same section, density improved by about 40 percent.
In the PM peak, speed improved by about 3 mph over a 0.73-mile section.
In this same section, density improved by about 8 percent.

In the AM peak CORSIM models, the section of roadway analyzed was 0.65
miles in length. The time it takes to travel this 0.65-mile section of
roadway improved by 1.3 minutes for the AM peak. In the PM peak models,
the section of roadway analyzed was 0.73 miles in length. The time it
takes to travel this 0.73-mile section of roadway improved only by 0.2
minutes for the PM peak.

[]{#__RefHeading___Toc5024304 .anchor}Table 4: 2025 Speed and Density
Results -- Comparison of No Build to Alternatives for SB I-395 to NB
GWMP

  ------------------- ---------------- ----------------- -----------------
                      Average speed    Average density   Length of
                      difference       difference        affected area

  SB I-395 to NB GWMP                                    

  AM                  15.6 mph         39.5 %            0.65 mi

  PM                  3.4 mph          8.2 %             0.73 mi
  ------------------- ---------------- ----------------- -----------------

Note: AM & PM peak hours were simulated in different models. As a
result, the endpoints of the models may be in slightly different
positions, causing the "Length of Affected Area" to be slightly
different between the AM & PM peak hour models.

##### Maintenance of Traffic {#maintenance-of-traffic-2 .unnumbered}

Maintenance of traffic (MOT) plans would be developed to manage traffic
on the GWMP during the construction of any of the ramp/bridge
alternatives. For Alternative A, additional structural analysis of the
Humpback Bridge is necessary to determine the feasibility of maintaining
traffic loads on the existing structure while the widening and the
construction of pedestrian underpasses are underway. Without further
analysis, it is recommended that a temporary bridge be installed to
maintain GWMP traffic flow during construction. A temporary bridge would
be located to the west of the existing bridge and proposed expansion
area. A reduction in the GWMP speed limit would be required for the
duration of construction activities to correspond to the 35 mph design
speed of the temporary bridge.

For Alternative B, traffic flows on the GWMP roadway and the Mt. Vernon
Trail would be maintained in their current configuration during
construction of the parallel bridge span and its horizontal and vertical
approaches. Construction of the pedestrian underpasses would also
commence on the western side of the span(s). Once the new span is
complete, southbound GWMP traffic would be shifted to the new structure
and modifications to the existing Humpback Bridge/Mt. Vernon Trail and
its approaches undertaken, by reducing lane widths and shifting travel
lanes between the eastern and western sides of the existing bridge. By
constructing a new span that is physically separated from the Humpback
Bridge, the impacts to existing traffic patterns and flows are
minimized. A reduction in the GWMP speed limit would be required,
however, for the duration of construction activities.

If the Humpback Bridge were replaced with a new structure, as in the
Preferred Alternative, a temporary bridge across the Boundary Channel
inlet would be required to maintain GWMP/Mt. Vernon Trail traffic. The
temporary bridge would be located to the west of the proposed
replacement bridge. Northbound and southbound GWMP travel lanes and the
Mt. Vernon Trail would be diverted to the temporary bridge for the
duration of the construction period. This alternative would result in
the greatest disruption of existing traffic patterns and flows.

## Bicycle and Pedestrian Facilities

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-1 .unnumbered}

The Mt. Vernon Trail and other pedestrian/bicycle facilities within the
Study Area, as well as related safety deficiencies, would remain in
their current condition.

### 2. All Alternatives {#all-alternatives-1 .unnumbered}

The three alternatives evaluated for this location

-   Alternative A, widen existing bridge;

-   Alternative B, construct a second, parallel bridge; and

-   Preferred Alternative, replace existing bridge

include similar pedestrian/bicycle trail improvements. All involve a
wider bridge crossing of the Boundary Channel inlet, which eliminates
the geometric deficiencies for this ramp and allows for a longer
acceleration lane without realigning the ramp. For each alternative, the
Mt. Vernon Trail would be widened as it crosses the Humpback Bridge and
a barrier constructed between the trail and vehicle travel lanes to
eliminate the existing safety deficiencies. In Alternative A and the
Preferred Alternative, the trail would be widened to 10 feet. In
Alternative B the trail would be widened to (±) 12 feet.
Pedestrian/bicyclist conflicts with vehicular traffic associated with
the existing at-grade crosswalk between the east and west sides of the
GWMP would also be eliminated in this alternative, through the
construction of pedestrian trail underpasses to the north and south of
the bridge structure(s). The small parking lot serving the Navy-Marine
Memorial would also be eliminated in this alternative. Accessible
sidewalk/trail connections would be constructed to connect the Columbia
Island Marina parking lot with the Mt. Vernon Trail and Navy-Marie
Memorial, via the northern underpass. The pedestrian/bicyclist
connection between the Mt. Vernon Trail, the Pentagon and Arlington
County would be enhanced through the construction of a new trail
connection along the southern edge of the Boundary Channel lagoon
linking the Pentagon/Boundary Channel Drive with the GWMP via the
southern underpass. All trail connections would be 9-feet wide,
consistent with the Mt. Vernon Trail width standard.

## Historic and Cultural Resources

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-2 .unnumbered}

No impact to historic or cultural resources is anticipated.

[]{.mark}

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge-1 .unnumbered}

The widening of the Humpback Bridge across Boundary Channel, would
directly impact the Humpback Bridge, a contributing element of the GWMP
historic resource. Consultation with the Advisory Council and Virginia
and District of Columbia SHPO's has been initiated in compliance with
Section 106 of the National Historic Preservation Act. The design of the
modifications to the Humpback Bridge, construction plans and details
would be executed in conjunction with the terms and conditions of a MOA
between the FHWA, NPS, Advisory Council and District of Columbia and
Virginia SHPO's outlining the measures to be taken to address effects to
the historic resources.

The eastern façade of the Humpback Bridge would remain in place,
although it would be modified by the addition of the pedestrian/bicycle
underpasses. The parapet wall along the eastern side of the Humpback
Bridge would be extended to the north and south of its current location
in conjunction with the re-grading of the GWMP approaches to the bridge
to eliminate the vertical sight deficiencies. The height of the wall
would also be extended to provide increased safety for Mt. Vernon Trail
users. Modifications to the structure would be similar in character and
materials to the existing bridge.

The western or Pentagon side of the Humpback Bridge would be demolished
and the bridge widened by (±) 19 feet. The new structure would be
similar to the existing Humpback Bridge in shape and massing, in order
to minimize the appearance of the bridge alternations as seen from the
Columbia Island Marina and Pentagon river terrace. The stone facing from
the western side of the bridge would be removed prior to demolition for
potential reuse on the new façade.

Pedestrian and bicycle circulation patterns surrounding the Navy-Marine
Memorial, a contributing element of the GWMP historic resource, would
also be modified to provide a transition and trail connection between
the Mt. Vernon Trail, new pedestrian underpasses and Columbia Island
Marina. The new trail connections would be designed and constructed to
minimize disturbances to the Navy-Marine Memorial and views of the GWMP
as seen from the District of Columbia.

With respect to cultural or archaeological resources, past grading and
filling activity have extensively modified the land within the Study
Area. It is not anticipated to have a high potential for the presence of
undisturbed cultural or archaeological resources.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge-1 .unnumbered}

The construction of a second bridge across Boundary Channel, parallel to
the existing Humpback Bridge would indirectly impact the Humpback
Bridge. The proposed action would also impact the historic setting of
the GWMP and adjacent historic resources (i.e., the Pentagon and LBJ
Memorial Grove). Consultation with the Advisory Council and Virginia and
District of Columbia SHPO's has been initiated. The design of the
modifications to the Humpback Bridge and the new bridge, construction
plans and details would be executed in conjunction with the terms and
conditions of a MOA between the FHWA, NPS, Advisory Council and District
of Columbia and Virginia SHPO's outlining the measures to be taken to
address effects to the historic resources.

The eastern façade of the Humpback Bridge would remain in place,
although it would be modified by the addition of the pedestrian/bicycle
underpasses. The parapet wall along the eastern side of the Humpback
Bridge would be extended to the north and south of its current location
in conjunction with the re-grading of the GWMP approaches to the bridge.
The height of the wall would also be extended. All modifications to the
structure would be similar in character and materials to the existing
bridge.

The western or Pentagon side of the Humpback Bridge would be obscured by
the parallel bridge structure. The new structure would be separated from
the existing bridge by approximately one foot. It would be reflective of
the Humpback Bridge in shape and massing and faced with similar
materials (e.g., stone-faced), in order to minimize the appearance of
the bridge alternations as seen from the Columbia Island Marina and
Pentagon river terrace. It should be noted the proximity of the two
bridges to one another and limited access between the spans is projected
to compromise the ability to complete maintenance work on the historic
resource as well as the new bridge.

Pedestrian and bicycle circulation patterns surrounding the Navy-Marine
Memorial would also be modified to provide a transition and trail
connection between the Mt. Vernon Trail, new pedestrian underpasses and
Columbia Island Marina. The new trail connections would be designed and
constructed to minimize disturbances to the Navy-Marine Memorial and
views of the GWMP as seen from the District of Columbia.

With respect to cultural or archaeological resources, past grading and
filling activity have extensively modified the land within the Study
Area. It is not anticipated to have a high potential for the presence of
undisturbed cultural or archaeological resources.

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge-1 .unnumbered}

This alternative would result in the replacement of the Humpback Bridge
with a new bridge across Boundary Channel. The existing bridge would be
demolished, a direct impact to the GWMP historic resource and the
bridge. The proposed action would also alter the GWMP setting within the
views and vistas of adjacent historic resources, including the Pentagon,
LBJ Memorial Grove, Arlington National Cemetery, East and West Potomac
Park, and other historic resources of the District of Columbia.
Consultation with the Advisory Council and Virginia and District of
Columbia SHPO's has been initiated. The design of the new bridge and
related elements, construction plans and details would be executed in
conjunction with the terms and conditions of a MOA between the FHWA,
NPS, Advisory Council and District of Columbia and Virginia SHPO's
outlining the measures to be taken to mitigate the impacts to the
historic resources.

The new bridge would be similar in design and materials to the Humpback
Bridge. The eastern or Potomac River edge of the new structure would not
be located any farther east than the eastern façade of the existing
bridge, to minimize impacts to the adjacent Navy-Marine Memorial.
Multi-use trails would be constructed to pass beneath the new bridge and
provide grade-separated crossing of the GWMP. Pedestrian and bicycle
circulation patterns surrounding the Navy-Marine Memorial would also be
modified to provide a transition and trail connection between the Mt.
Vernon Trail, new trail underpasses and Columbia Island Marina. The new
trail connections would be designed and constructed to minimize
disturbances to the Navy-Marine Memorial.

With respect to cultural or archaeological resources, past grading and
filling activity have extensively modified the land within the Study
Area. It is not anticipated to have a high potential for the presence of
undisturbed cultural or archaeological resources.

## Aesthetics and Viewsheds

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-3 .unnumbered}

The aesthetic condition and viewshed of the GWMP and adjacent historic
resources would remain in their current condition.

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge-2 .unnumbered}

The appearance of the eastern or Potomac River façade of the Humpback
Bridge, a contributing element of the GWMP and prominent component of
the viewsheds of the Washington, DC monumental core as seen from East
and West Potomac Park and other points within the District of Columbia,
would be altered by the addition of the pedestrian/bicycle trail
underpasses and modifications to the existing bridge's eastern parapet
wall. All modifications to the structure would be similar in character
and materials to the existing bridge, to minimize visual impacts.

The western view of the Humpback Bridge, as seen from the Pentagon river
terrace and LBJ Memorial Grove is a prominent element in the viewsheds
of those two historic resources. Although the western side of the
Humpback Bridge would be demolished, the expanded bridge structure would
be designed to mimic the existing façade. Reuse of the stone facing from
the existing façade may also serve to minimize the visual impact of the
bridge modifications.

The original landscape elements of the GWMP were designed to frame and
enhance the parkway elements, including the Humpback Bridge. The mature
specimen trees flanking the Potomac River side of the bridge and
Boundary Channel inlet are remnants of the original GWMP plantings.
Construction of the pedestrian underpasses beneath the Humpback Bridge
and the new bridge would require the removal of some of those plantings.
While the alignment of the underpasses and associated trails have been
sited to minimize impacts on existing vegetation as much as possible,
some impacts are unavoidable. Mixed woodland vegetation on the western
or Pentagon side of the bridge would also be cleared to accommodate the
new bridge span, which would affect the views of the bridge from the
Pentagon. Cleared areas adjacent to the bridge and underpasses would be
landscaped once construction activities are complete to mitigate visual
impacts.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge-2 .unnumbered}

As with Alternative A, the appearance of the Potomac River façade of the
Humpback Bridge would be altered by the addition of the
pedestrian/bicycle trail underpasses and modifications to the existing
bridge's eastern parapet wall. All modifications to the structure would
be similar in character and materials to the existing bridge, to
minimize visual impacts. The western or Pentagon side of the Humpback
Bridge would be obscured by the new bridge structure. The new structure
would be reflective of the existing Humpback Bridge in shape, massing
and materials, in order to minimize the changes to the Pentagon and LBJ
Memorial Grove viewsheds.

The construction of the pedestrian underpasses and related Mt. Vernon
Trail modifications associated with Alternative B would also unavoidably
impact original plantings of the GWMP that remain adjacent to the
Humpback Bridge on the Potomac River side as well as mixed woodland
vegetation on the Pentagon side of the bridge. Landscape elements
removed during construction would be replanted once construction is
complete to mitigate visual impacts.

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge-2 .unnumbered}

Alternative C would have the greatest potential visual impact on the
GWMP historic resource and adjacent historic resources. The Humpback
Bridge would be replaced with a new structure. The design of the new
bridge would be reminiscent of the Humpback Bridge in scale, massing and
materials. The pedestrian underpasses and other new elements would be
designed as integral components of the new bridge, to ensure their fit
and compatibility. As with the other Humpback Bridge alternatives,
mature specimen trees dating to the 1930's that flank the existing
bridge on the Potomac River side would need to be removed. Vegetation on
the Pentagon side of the bridge would also be cleared as part of
construction activities. Landscaped areas adjacent to the bridge that
would be cleared during construction would be replanted once
construction is complete to mitigate the visual impacts.

## Land Use

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-4 .unnumbered}

No change to existing land use patterns is anticipated.

### 2. All Alternatives {#all-alternatives-2 .unnumbered}

No change to existing land use patterns is anticipated to result from
the implementation of any of the proposed Humpback Bridge improvements
other modifications in its location.

## Biological Resources

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-5 .unnumbered}

##### Vegetation {#vegetation-3 .unnumbered}

No change to existing vegetation would result.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-3 .unnumbered}

No change to existing wildlife is anticipated.

##### Wetlands {#wetlands-3 .unnumbered}

No impact to wetland resources is anticipated.

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge-3 .unnumbered}

##### Vegetation {#vegetation-4 .unnumbered}

Widening the Humpback Bridge and adding the pedestrian underpasses would
result in the removal of approximately 1.78 AC of mixed woodland
vegetation on the Pentagon side of the existing bridge.

The proposed pedestrian underpasses would also impact the specimen trees
on the Potomac River side of the bridge. While the alignment of the
underpasses and associated trails have been sited to minimize impacts on
existing vegetation as much as possible, the location of the existing
bridge abutments, topographic conditions and tunnel cover requirements
make the impacts unavoidable. The removal of four trees, a pin oak
(*Quercus palustris*) of approximately 80 inches diameter at breast
height (dbh), two American elms (*Ulmus americana*) of approximately 120
inches dbh and 150 inches dbh, and a 25-inch dbh flowering dogwood
(*Cornus florida*) would be necessary. Other trees located adjacent to
the bridge and the proposed tunnels would be protected during
construction to minimize impacts to them. Once the bridge widening and
underpasses are completed, the cleared areas would be re-planted.

The construction of the temporary bridge and roadway to re-route GWMP
traffic around the construction site would require the clearing of an
additional 0.3 AC of mixed woodland vegetation. The cleared area would
be re-planted once construction is completed.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-4 .unnumbered}

Disturbed areas would be re-vegetated after the bridge widening is
complete. It is anticipated that loss of the existing vegetation
resources would not have an adverse impact on wildlife inhabiting the
GWMP. The bridge widening would also temporarily affect aquatic wildlife
found in Boundary Channel. There are no state or federally listed rare,
threatened or endangered species known to inhabit the Study Area.

##### Wetlands {#wetlands-4 .unnumbered}

Filling of approximately 1,400 SF or 0.03 AC within the Boundary Channel
wetland would be required for the foundations of the expanded bridge
structure. Additional construction activity would take place on and over
the waters of Boundary Channel. Construction activities would comply
with the conditions of Section 401 and 404 of the Clean Water Act, if
necessary. A wetlands permit would be required from the U.S. Army Corps
of Engineers for the construction activity. The proposed action would
also comply with applicable state and local permit requirements.

Temporary filling of approximately 900 SF of wetland would also be
required for the temporary construction bridge and roadway. The
necessary permits would be obtained for the temporary filling and the
wetland would be restored once construction was completed.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge-3 .unnumbered}

##### Vegetation {#vegetation-5 .unnumbered}

The construction of a new bridge structure parallel to the Humpback
Bridge and pedestrian underpasses would result in the removal
approximately 1.84 AC of mixed woodland vegetation on the Pentagon side
of the existing bridge.

As discussed in the previous section, the proposed pedestrian
underpasses would impact mature trees on the Potomac River side of the
bridge. The underpasses and related trails follow the same approximate
alignment as in Alternative A and result in the same impacts to the
mature trees located on each side the Boundary Channel inlet. The
removal of an 80-inch dbh pin oak (*Quercus palustris*), two American
elms (*Ulmus americana*) of approximately 120 inches dbh and 150 inches
dbh, and a 25-inch dbh flowering dogwood (*Cornus florida*) would be
necessary. Other trees located adjacent to the bridge and the proposed
tunnels would be protected during construction to minimize impacts to
them. Once the bridge widening and underpasses are completed, the
cleared areas would be re-planted.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-5 .unnumbered}

Once the new bridge span and underpasses are constructed, disturbed
areas would be re-vegetated. It is anticipated that loss of the existing
vegetation resources would not have an adverse impact on wildlife
inhabiting the GWMP. Construction of the additional span would also
temporarily affect aquatic wildlife found in Boundary Channel. There are
no state or federally listed rare, threatened or endangered species
known to inhabit the Study Area.

##### Wetlands {#wetlands-5 .unnumbered}

Construction of the parallel bridge span across Boundary Channel would
require filling of approximately 1,900 SF within the Boundary Channel
wetland for the bridge foundations. Additional work would take place on
and over the waters of Boundary Channel. Construction activities would
comply with the conditions of Section 401 and 404 of the Clean Water
Act, if necessary. A wetlands permit would be required from the U.S.
Army Corps of Engineers for the construction activity. The proposed
action would also comply with applicable state and local permit
requirements.

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge-3 .unnumbered}

##### Vegetation {#vegetation-6 .unnumbered}

Replacement of the Humpback Bridge would result in the clearing of trees
and other vegetation on both sides of the new structure. The eastern or
river face of the new structure would be located in approximately the
same position as the existing bridge face in order to minimize the
impact to existing planting, although constructing a new bridge allows
greater flexibility in the location of the underpasses and related
trails. Those features have been located to minimize the loss of
existing plantings, particularly the specimens on the Potomac River side
of the bridge. However, three trees, the 80-inch dbh pin oak (*Quercus
palustris*), the 25-inch dbh flowering dogwood (*Cornus florida*) and a
multi-trunk flowering pear (*Pyrus calleryana*) would be impacted.
Protective measures such as the use of pile shoring and other measures
would be taken during the construction of the bridge to minimize
additional impacts to vegetation. Approximately 1.77 AC of mixed
woodland vegetation would be also need to be removed on the Pentagon
side of the new bridge. Once the new bridge and underpasses are
constructed, cleared areas would be re-planted.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-6 .unnumbered}

Existing vegetation would be cleared on each side of Boundary Channel
for the proposed new GWMP bridge. Loss of that resource, however, is not
anticipated to have an adverse impact on wildlife inhabiting the Study
Area. Disturbed areas would be replanted with vegetation consistent with
that removed in order to provide the same type of wildlife habitat.
Construction of the bridge would also temporarily affect aquatic
wildlife found in Boundary Channel. There are no state or federally
listed rare, threatened or endangered species known to inhabit the Study
Area; therefore there would be no impact.

##### Wetlands {#wetlands-6 .unnumbered}

Construction of the new bridge would require filling of approximately
1,400 SF within the Boundary Channel wetland for the bridge foundations.
Additional work would take place on and over the waters of Boundary
Channel. Construction activities would comply with the conditions of
Section 401 and 404 of the Clean Water Act, if necessary. A wetlands
permit would be required from the U.S. Army Corps of Engineers for the
construction activity. The proposed action would also comply with
applicable state and local permit requirements.

Temporary filling of approximately 900 SF of wetland would also be
required for the temporary construction bridge and roadway. The
necessary permits would be obtained for the temporary filling activity
and the wetland would be restored once construction was completed.

## Water Resources

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-6 .unnumbered}

##### Floodplains {#floodplains-3 .unnumbered}

No impact to floodplains is anticipated.

##### Coastal Zone Management {#coastal-zone-management-3 .unnumbered}

No Coastal Zone impacts are anticipated.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-3 .unnumbered}

No Chesapeake Bay impacts are anticipated.

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge-4 .unnumbered}

##### Floodplains {#floodplains-4 .unnumbered}

Construction of the foundations and piers of the expanded bridge
structure would take place within the 100-year floodplain, at the
Boundary Channel shoreline. A permit would be required from the U.S.
Army Corps of Engineers for the construction activity. A bridge permit
from the U.S. Coast Guard would also be required.

##### Coastal Zone Management {#coastal-zone-management-4 .unnumbered}

The Arlington County portions of the Study Area are located within the
Virginia Coastal Zone. The Federal Coastal Zone Management Act requires
development projects of Federal agencies that take place within the
Coastal Zone be consistent with the applicable state coastal zone
management program to the maximum extent practicable. The Virginia
Coastal Resources Management Program is a network of existing state laws
and policies though which the Commonwealth of Virginia manages its
coastal resources. Proposed actions that comply with the applicable
state laws and policies are considered to be consistent with the
Virginia Coastal program. The District of Columbia is not subject to the
Coastal Zone Management Act. The proposed safety improvements would be
constructed in accordance with applicable Commonwealth of Virginia and
District of Columbia stormwater management, sedimentation and erosion
control and water quality protection laws and policies.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-4 .unnumbered}

The proposed Humpback Bridge alternatives are located on
government-owned property that is exempt from Arlington County
Chesapeake Bay Preservation regulations. Remaining Humpback Bridge and
other safety improvements proposed for Columbia Island are located in
the District of Columbia, which does not designate Chesapeake Bay
Preservation Areas. However, construction and other activities related
to the implementation of the proposed safety improvements would comply
with local stormwater management, sedimentation and erosion control and
other water quality protection regulations.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge-4 .unnumbered}

##### Floodplains {#floodplains-5 .unnumbered}

Construction of the parallel bridge span across Boundary Channel would
involve construction within the 100-year floodplain, at the Boundary
Channel shoreline, for bridge foundations and piers. A permit would be
required from the U.S. Army Corps of Engineers for the construction
activity. A bridge permit from the U.S. Coast Guard would also be
required.

##### Coastal Zone Management {#coastal-zone-management-5 .unnumbered}

The proposed action would comply with the Virginia Coastal Zone
Management Program to the maximum extent practicable. The proposed
safety improvements would be constructed in accordance with applicable
Virginia and District of Columbia stormwater management, sedimentation
and erosion control and water quality protection laws and policies.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-5 .unnumbered}

The proposed Humpback Bridge alternatives are partially located on
government-owned property in Virginia that is exempt from Arlington
County Chesapeake Bay Preservation regulations and partially located in
the District of Columbia, which does not designate Chesapeake Bay
Preservation Areas. However, construction and other activities related
to the implementation of the proposed safety improvements would comply
with local stormwater management, sedimentation and erosion control and
other water quality protection regulations.

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge-4 .unnumbered}

##### Floodplains {#floodplains-6 .unnumbered}

Construction of the new bridge would involve construction within the
100-year floodplain for bridge foundations and piers. A permit would be
required from the U.S. Army Corps of Engineers for the construction
activity. A bridge permit from the U.S. Coast Guard would also be
required.

##### Coastal Zone Management {#coastal-zone-management-6 .unnumbered}

The proposed action would comply with the Virginia Coastal Zone
Management Program to the maximum extent practicable. The proposed
safety improvements would be constructed in accordance with applicable
Virginia and District of Columbia stormwater management, sedimentation
and erosion control and water quality protection laws and policies.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-6 .unnumbered}

The proposed Humpback Bridge alternatives are partially located on
government-owned property in Virginia that is exempt from Arlington
County Chesapeake Bay Preservation regulations and partially located in
the District of Columbia, which does not designate Chesapeake Bay
Preservation Areas. However, construction and other activities related
to the implementation of the proposed safety improvements would comply
with local stormwater management, sedimentation and erosion control and
other water quality protection regulations.

## Physiography, Geology and Soils

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-7 .unnumbered}

No disturbance to soils is anticipated.

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge-5 .unnumbered}

Soil disturbance would result from site clearing and grading activities
related to the widening of the Humpback Bridge and the construction of a
pedestrian underpass to the north and south of the bridge crossing and
other related Mt. Vernon Trail modifications. Approximately 10.1 AC
would be disturbed. The modification of the GWMP vertical profile at its
approaches to the Humpback Bridge(s) would require the placement of fill
and related grading activities along the mainline GWMP roadway alignment
as well. Demolition and construction activities would incorporate
erosion control measures to minimize soils loss. Disturbed areas would
be re-vegetated once construction activities are complete.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge-5 .unnumbered}

Soil disturbance, filling and grading activities would result from site
clearing and construction activities related to the construction of a
second bridge over the Boundary Channel inlet, parallel to the Humpback
Bridge and other modifications at this location. Approximately 10.5 AC
would be disturbed. Construction activities would incorporate erosion
control measures to minimize soils loss. Disturbed areas would be
re-vegetated once construction activities are complete.

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge-5 .unnumbered}

Soil disturbance would result in the disturbance of approximately 9.9 AC
due to demolition, clearing, filling/grading and other activities
related to the construction of a new GWMP bridge over the Boundary
Channel inlet and other modifications at this location. Demolition and
construction activities would incorporate erosion control measures to
minimize soils loss. Disturbed areas would be re-vegetated once
construction activities are complete.

## Air Quality

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-8 .unnumbered}

No change to air quality levels is anticipated.

### 2. All Alternatives {#all-alternatives-3 .unnumbered}

The three alternatives evaluated for this location

-   Preferred Alternative A, widen existing bridge;

-   Alternative B, construct a second, parallel bridge; and

-   Preferred Alternative, replace existing bridge

Are generally the same in terms of air quality impacts. None of the
alternatives expand the capacity of the GWMP transportation system. No
changes to air quality levels are anticipated as a result of the
implementation of any of the three alternatives, except for minor,
temporary increases in dust and other air emissions associated with
construction activities.

From the construction emissions standpoint, the Preferred Alternative
would involve more extensive demolition and construction activities and,
as a result, have a greater impact on local air quality than
Alternatives A or B. Construction activities related to each of the
alternatives would be conducted in accordance with the FHWA's Standard
Specifications for Construction of Roads and Bridges on Federal Highway
Projects (1996) and would comply with applicable local, state and
federal regulations.

## Noise

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-9 .unnumbered}

No change in existing noise sources or noise levels is anticipated.

### 2. All Alternatives {#all-alternatives-4 .unnumbered}

The three alternatives evaluated for this location

-   Preferred Alternative A, widen existing bridge;

-   Alternative B, construct a second, parallel bridge; and

-   Preferred Alternative, replace existing bridge

are similar in terms of noise impacts. Existing noise levels would
increase temporarily during the construction of the acceleration lane
and bridge improvements. The speed with which a vehicle would travel the
segment of roadway encompassing the ramp -- the segment of southbound
I-395 before the ramp, the ramp to the GWMP and the GWMP segment after
the ramp merge -- improved slightly with the addition of the
acceleration lane, by approximately 16 mph (1.3 minutes) in the AM peak
and 3 mph (0.2 minutes) in the PM peak. That increase in vehicle speeds
would result in a corresponding slight increase in traffic-related noise
levels within the Study Area, although below the approximately 20 mph
increase necessary to produce a readily noticeable (i.e., 5 dBA)
increase in noise levels[^6].

## Hazardous Materials and Wastes

No evidence of historical land use involving hazardous materials or
hazardous wastes was found within the Study Area. The proposed actions
would not require the disturbance or relocation of any of the existing,
recognized environmental conditions -- USTs and ASTs -- found at the
Columbia Island Marina. Therefore, no disturbance or generation of
hazardous materials or hazardous wastes are anticipated to occur with
either the implementation of any of the proposed safety improvements or
under "no-action" conditions.

## Energy

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-10 .unnumbered}

No change in energy consumption is anticipated.

### 2. All Build Alternatives {#all-build-alternatives .unnumbered}

Energy consumption would temporarily increase during the construction of
any of the proposed Humpback Bridge improvements and construction of
related roadway and Mt. Vernon Trail improvements. No significant change
in long-term energy consumption is anticipated.

## Socioeconomic and Community Features

### 1. No Action: Keep Existing Bridge with No Modifications {#no-action-keep-existing-bridge-with-no-modifications-11 .unnumbered}

No change to socioeconomic or community features is anticipated. The
public would continue to be exposed to the safety hazards associated
with the current GWMP transportation and circulation systems.

### 2. Alternative A: Widen Existing Bridge {#alternative-a-widen-existing-bridge-6 .unnumbered}

Construction jobs associated with the widened bridge would have a
short-term benefit to local construction workers and the local economy.
No long-term economic benefit to local community is anticipated. NPS
bridge maintenance costs would not be anticipated decrease
significantly, since the 70-year-old Humpback Bridge would comprise the
majority of the structure. Its useful life expectancy is approximately
25 to 30 years.

### 3. Alternative B: Construct a Second, Parallel Bridge {#alternative-b-construct-a-second-parallel-bridge-6 .unnumbered}

Construction jobs associated with the parallel bridge would have a
short-term benefit to local construction workers and the local economy.
While lower, long-term NPS maintenance costs would be anticipated for
the new bridge span, which would have a 75 to 100 year life expectancy,
maintenance of the 70 year old Humpback Bridge span that would remain
would also be required. The anticipated life expectancy of the historic
bridge is approximately 25 to 30 years. At that time a major renovation
or replacement of the Humpback Bridge would be required.

### 4. Preferred Alternative: Replace Existing Bridge {#preferred-alternative-replace-existing-bridge-6 .unnumbered}

Construction jobs associated with the new bridge would have a short-term
benefit to local construction workers and the local economy. The longer
and more extensive construction period required for a new bridge would
produce slightly greater benefits than the shorter-term parallel bridge
or bridge widening efforts.

In the long-term, a new bridge would incur lower maintenance costs for
the NPS than the 70-year-old Humpback Bridge. The expected useful life
of a new bridge would be 75 to 100 years, greater than the 25 to 30 year
life expectancy of the Humpback Bridge.

## Cumulative Impacts

The proposed mid-term safety improvements identified for the Study Area
are intended to complement the short-term and long-term safety
improvements proposed by the FHWA for the I-395/GWMP interchange and
14^th^ Street Bridge to enhance overall motorist and pedestrian safety
within the corridor. No increase in the traffic-carrying capacity of the
GWMP would result from the implementation of the preferred replacement
bridge alternative. It is not anticipated to contribute to any
cumulative impacts.

Implementation of the proposed safety improvements would create a safer
environment for the users of the other GWMP facilities proposed by the
NPS in the vicinity of the Study Area as well as current GWMP users.
Those facilities -- a (non-motorized) boathouse and comfort station --
would utilize the existing mainline roadway network, although the
construction of vehicular and pedestrian connections may be necessary to
link the new facilities with existing parking and trail resources.

Planned improvements for the adjacent Pentagon Reservation are primarily
concerned with the renovation of the existing Pentagon building. No
major new structures are anticipated that, when combined with the
impacts of the proposed ramp, bridge and trail improvements would result
in significant cumulative impacts.

Undeveloped parcels in the vicinity of the Study Area include the former
Twin Bridges Marriott site and the Arlington County "North Tract" site.
Both are located to the southwest of the Study Area, at the north end of
Crystal City. Arlington County plans to redevelop the North Tract as a
public park and recreation facility. The county is also investigating
the acquisition of the Twin Bridges Marriott site. Upgrade of the
existing transportation network, including Old Jefferson Davis Highway,
is under investigation as well. The upgrade of Old Jefferson Davis
Highway would facilitate access to the GWMP. Development of the two
parcels for park and recreation uses would be compatible with the use of
the GWMP and would not be anticipated to result in significant
cumulative impacts.

## Comparison of Alternatives

A comparison of the No Action Alternative and the Preferred Build
Alternative is provided in Table 5.

[]{#__RefHeading___Toc5024305 .anchor}Table 5: Comparison of
Alternatives -- SB I-395 Ramp to NB GWMP and Humpback Bridge

+---------+-----------+--------------+---------------+---------------+
| **Eva   | **No      | *            | **Alternative | **Preferred   |
| luation | Action    | *Alternative | B**           | Alternative** |
| F       | Alte      | A**          |               |               |
| actor** | rnative** |              |               |               |
+---------+-----------+--------------+---------------+---------------+
|         |           | *Widen       | *Construct a  | *Replace      |
|         |           | Existing     | Second,       | Existing      |
|         |           | Bridge,      | Parallel      | Bridge,       |
|         |           | Construct    | Bridge,       | Construct     |
|         |           | Underpass    | Construct     | Underpass     |
|         |           | North &      | Underpass     | North & South |
|         |           | South of     | North & South | of Humpback   |
|         |           | Humpback     | of Humpback   | Bridge and    |
|         |           | Bridge and   | Bridge and    | Modify        |
|         |           | Modify       | Modify        | Vertical      |
|         |           | Vertical     | Vertical      | Profile of    |
|         |           | Profile of   | Profile of    | Bridge and    |
|         |           | Bridge and   | Bridge and    | Approaches*   |
|         |           | Approaches*  | Approaches*   |               |
+---------+-----------+--------------+---------------+---------------+
| Roadway | No change | Design speed | Design speed  | Design speed  |
| Hor     | to        | = 50 mph     | = 50 mph      | = 50 mph      |
| izontal | h         |              |               |               |
| Al      | orizontal | New          | New alignment | New alignment |
| ignment | a         | alignment    | would require | would require |
|         | lignment; | would        | minor         | minor         |
|         | existing  | require      | modifications | modifications |
|         | design    | minor        | to SB GWMP    | to SB GWMP    |
|         | speed is  | m            | ramp to       | ramp to       |
|         | adequate  | odifications | SBI-395 and   | SBI-395 and   |
|         | for       | to SB GWMP   | Columbia      | Columbia      |
|         | posted    | ramp to      | Island Marina | Island Marina |
|         | speed     | SBI-395 and  | entrance.     | entrance.     |
|         | limit.    | Columbia     |               |               |
|         |           | Island       |               |               |
|         |           | Marina       |               |               |
|         |           | entrance.    |               |               |
+---------+-----------+--------------+---------------+---------------+
| Roadway | No change | Design speed | Design speed  | Design speed  |
| V       | to        | = 50 mph     | = 50 mph      | = 50 mph      |
| ertical | vertical  |              |               |               |
| Al      | a         | Sight        | Sight         | Sight         |
| ignment | lignment; | distance     | distance      | distance      |
|         | sight     | deficiencies | deficiencies  | deficiencies  |
|         | distance  | would be     | would be      | would be      |
|         | def       | eliminated.  | eliminated.   | eliminated.   |
|         | iciencies | New          | New alignment | New alignment |
|         | would     | alignment    | would require | would require |
|         | remain.   | would        | modifications | modifications |
|         |           | require      | to SB GWMP    | to SB GWMP    |
|         |           | m            | ramp to SB    | ramp to SB    |
|         |           | odifications | I-395, NB     | I-395, NB     |
|         |           | to SB GWMP   | GWMP ramp to  | GWMP ramp to  |
|         |           | ramp to SB   | SB I-395 and  | SB I-395 and  |
|         |           | I-395, NB    | SB I-395 ramp | SB I-395 ramp |
|         |           | GWMP ramp to | to SB GWMP.   | to SB GWMP.   |
|         |           | SB I-395 and |               |               |
|         |           | SB I-395     |               |               |
|         |           | ramp to SB   |               |               |
|         |           | GWMP.        |               |               |
+---------+-----------+--------------+---------------+---------------+
| Str     | No impact | Lightweight  | Lightweight   | Not           |
| uctural | is        | fill would   | fill would be | Applicable    |
| Impact  | an        | be used on   | used on       |               |
| to      | ticipated | Humpback     | Humpback      |               |
| H       |           | Bridge so as | Bridge so as  |               |
| umpback |           | to not       | to not        |               |
| Bridge  |           | increase the | increase the  |               |
|         |           | dead load on | dead load on  |               |
|         |           | the bridge.  | the bridge.   |               |
+---------+-----------+--------------+---------------+---------------+
| Nav     | No impact | Existing     | Existing      | Existing      |
| igation | is        | vertical     | vertical      | vertical      |
| Impacts | an        | bridge       | bridge        | bridge        |
|         | ticipated | clearance    | clearance     | clearance     |
|         |           | would be     | would be      | would be      |
|         |           | maintained.  | maintained.   | maintained.   |
|         |           | USCG bridge  | USCG bridge   | USCG bridge   |
|         |           | permit would | permit would  | permit would  |
|         |           | be required. | be required.  | be required.  |
+---------+-----------+--------------+---------------+---------------+
| Main    | No impact | G            | GWMP/Humpback | GWMP/Humpback |
| tenance | is        | WMP/Humpback | Bridge and    | Bridge and    |
| of      | an        | Bridge and   | Mt. Vernon    | Mt. Vernon    |
| Traffic | ticipated | Mt. Vernon   | Trail would   | Trail would   |
|         |           | Trail would  | remain open   | remain open   |
|         |           | remain open  | during        | during        |
|         |           | during       | construction  | construction  |
|         |           | construction | activities.   | activities. A |
|         |           | activities.  | Temporary     | temporary     |
|         |           | Temporary    | lane          | bridge over   |
|         |           | lane         | redu          | Boundary      |
|         |           | reduc        | ction/closure | Channel would |
|         |           | tion/closure | and reduction | be required   |
|         |           | and          | in GWMP speed | during        |
|         |           | reduction in | limit would   | construction  |
|         |           | GWMP speed   | be required   | of new bridge |
|         |           | limit would  | during        | for GWMP and  |
|         |           | be required  | construction. | Mt. Vernon    |
|         |           | during       | This          | Trail         |
|         |           | c            | alternative   | traffic.      |
|         |           | onstruction. | would have    | Temporary     |
|         |           | Additional   | the least     | lane          |
|         |           | structural   | impact of the | redu          |
|         |           | analysis of  | three build   | ction/closure |
|         |           | the Humpback | alternatives  | and reduction |
|         |           | Bridge is    | on GWMP       | in GWMP speed |
|         |           | necessary to | traffic flow. | limit would   |
|         |           | determine    |               | also be       |
|         |           | the          |               | required      |
|         |           | feasibility  |               | during        |
|         |           | of           |               | construction. |
|         |           | maintaining  |               |               |
|         |           | traffic      |               |               |
|         |           | loads on the |               |               |
|         |           | existing     |               |               |
|         |           | structure    |               |               |
|         |           | during       |               |               |
|         |           | c            |               |               |
|         |           | onstruction. |               |               |
|         |           | Without      |               |               |
|         |           | further      |               |               |
|         |           | analysis, a  |               |               |
|         |           | temporary    |               |               |
|         |           | bridge is    |               |               |
|         |           | recommended. |               |               |
+---------+-----------+--------------+---------------+---------------+

Table 5: Comparison of Alternatives -- SB I-395 Ramp to NB GWMP and
Humpback Bridge

  -------------- ---------------------- --------------- ---------------- ---------------------
  **Evaluation   **No Action            **Alternative   **Alternative    **Preferred
  Factor**       Alternative**          A**             B**              Alternative**

                                        *Widen Existing *Construct a     *Replace Existing
                                        Bridge,         Second, Parallel Bridge, Construct
                                        Construct       Bridge,          Underpass North &
                                        Underpass North Construct        South of Humpback
                                        & South of      Underpass North  Bridge and Modify
                                        Humpback Bridge & South of       Vertical Profile of
                                        and Modify      Humpback Bridge  Bridge and
                                        Vertical        and Modify       Approaches*
                                        Profile of      Vertical Profile 
                                        Bridge and      of Bridge and    
                                        Approaches*     Approaches*      

  Motorist       Safety hazards and     Motorist safety Motorist safety  Motorist safety
  Safety and     accident potential     improved with   improved with    improved with the
  Traffic        associated with ramp   the elimination the elimination  elimination of ramp
  Operations     and bridge would       of ramp and     of ramp and      and sight distance
                 remain. Traffic        sight distance  sight distance   deficiencies. LOS on
                 congestion on the      deficiencies.   deficiencies.    I-395 off ramp would
                 I-395 off ramp and     LOS on I-395    LOS on I-395 off improve from F to D
                 outbound George Mason  off ramp would  ramp would       in the AM peak and F
                 Bridge would continue. improve from F  improve from F   to borderline C/D in
                                        to D in the AM  to D in the AM   the PM peak. Queues
                                        peak and F to   peak and F to    that develop along
                                        borderline C/D  borderline C/D   the ramp and George
                                        in the PM peak. in the PM peak.  Mason Bridge would be
                                        Queues along    Queues that      reduced. Northbound
                                        the ramp and    develop along    GWMP continues to
                                        George Mason    the ramp and     operate at LOS F due
                                        Bridge would be George Mason     to the heavy mainline
                                        reduced.        Bridge would be  volumes. Moderate
                                        Northbound GWMP reduced.         improvement in
                                        continues to    Northbound GWMP  traffic speed and
                                        operate at LOS  continues to     density in AM peak
                                        F due to the    operate at LOS F and small increase in
                                        heavy mainline  due to the heavy PM peak.
                                        volumes.        mainline         
                                        Moderate        volumes.         
                                        improvement in  Moderate         
                                        traffic speed   improvement in   
                                        and density in  traffic speed    
                                        AM peak and     and density in   
                                        small increase  AM peak and      
                                        in PM peak.     small increase   
                                                        in PM peak.      

  Pedestrian &   Safety hazards         Pedestrian and  Pedestrian and   Pedestrian and
  Bicyclist      associated with Mt.    bicyclist       bicyclist safety bicyclist safety
  Safety         Vernon Trail crossing  safety improved improved with    improved with widened
                 of Humpback Bridge and with widened    widened          trail/barrier across
                 at-grade               trail/barrier   trail/barrier    Humpback Bridge and
                 pedestrian/bicyclist   across Humpback across Humpback  construction of
                 crossing of the GWMP   Bridge and      Bridge and       underpasses and trail
                 would remain.          construction of construction of  connections.
                                        underpasses and underpasses and  
                                        trail           trail            
                                        connections.    connections.     

  Historic and   No impact to the GWMP  Consultation    Consultation     Consultation with
  Cultural       historic resource      with Advisory   with Advisory    Advisory Council and
  Resources      and/or Humpback Bridge Council and VA  Council and VA   VA and DC SHPO's
                 contributing element   and DC SHPO's   and DC SHPO's    required. Adverse
                 is anticipated.        required. The   required.        effect with physical
                                        western face of Indirect adverse destruction of the
                                        the Humpback    effect on the    Humpback Bridge would
                                        Bridge would be Humpback Bridge  result; MOA would be
                                        demolished; no  would result     executed to address
                                        other adverse   from             replacement-in-kind
                                        effect is       construction of  and other measures to
                                        anticipated.    parallel bridge. be taken to address
                                        Design of       Preventative     effects to historic
                                        expanded bridge maintenance of   resources.
                                        would be        historic         
                                        compatible with resource would   
                                        the design and  be compromised   
                                        materials of    due to limited   
                                        the historic    access between   
                                        resource. MOA   spans leading to 
                                        would be        deterioration.   
                                        executed        MOA would be     
                                        between FHWA,   executed         
                                        NPS, Advisory   outlining        
                                        Council and VA  measures to be   
                                        and DC SHPO's   taken to address 
                                        outlining       effects to       
                                        measures to be  historic         
                                        taken to        resources.       
                                        address effects                  
                                        to historic                      
                                        resources.                       
  -------------- ---------------------- --------------- ---------------- ---------------------

Table 5: Comparison of Alternatives -- SB I-395 Ramp to NB GWMP and
Humpback Bridge

+---------+-----------+--------------+---------------+---------------+
| **Eva   | **No      | *            | **Alternative | **Preferred   |
| luation | Action    | *Alternative | B**           | Alternative** |
| F       | Alte      | A**          |               |               |
| actor** | rnative** |              |               |               |
+---------+-----------+--------------+---------------+---------------+
|         |           | *Widen       | *Construct a  | *Replace      |
|         |           | Existing     | Second,       | Existing      |
|         |           | Bridge,      | Parallel      | Bridge,       |
|         |           | Construct    | Bridge,       | Construct     |
|         |           | Underpass    | Construct     | Underpass     |
|         |           | North &      | Underpass     | North & South |
|         |           | South of     | North & South | of Humpback   |
|         |           | Humpback     | of Humpback   | Bridge and    |
|         |           | Bridge and   | Bridge and    | Modify        |
|         |           | Modify       | Modify        | Vertical      |
|         |           | Vertical     | Vertical      | Profile of    |
|         |           | Profile of   | Profile of    | Bridge and    |
|         |           | Bridge and   | Bridge and    | Approaches*   |
|         |           | Approaches*  | Approaches*   |               |
+---------+-----------+--------------+---------------+---------------+
| Aes     | No impact | Expanded     | New bridge    | Replacement   |
| thetics | is        | bridge and   | span and      | bridge and    |
| and     | ant       | pedestrian   | pedestrian    | pedestrian    |
| Vi      | icipated. | underpasses  | underpasses   | underpasses   |
| ewsheds |           | would result | would result  | would be new  |
|         |           | in           | in minor      | element in    |
|         |           | minor        | to-moderate   | the GWMP, DC  |
|         |           | -to-moderate | change to the | and Pentagon  |
|         |           | change to    | GWMP, DC and  | viewsheds.    |
|         |           | GWMP, DC and | Pentagon      | Design of new |
|         |           | Pentagon     | viewsheds.    | elements      |
|         |           | viewsheds.   | Design of new | would be      |
|         |           | Design of    | elements      | subject to    |
|         |           | new elements | would be      | terms and     |
|         |           | would be     | subject to    | conditions of |
|         |           | subject to   | terms and     | MOA.          |
|         |           | terms and    | conditions of |               |
|         |           | conditions   | MOA.          |               |
|         |           | of MOA (see  |               |               |
|         |           | Historic and |               |               |
|         |           | Cultural     |               |               |
|         |           | Resources).  |               |               |
+---------+-----------+--------------+---------------+---------------+
| Veg     | No impact | Four mature  | Four mature   | Three mature  |
| etation | is        | specimen     | specimen      | specimen      |
|         | ant       | trees on     | trees on      | trees on      |
|         | icipated. | Potomac      | Potomac River | Potomac River |
|         |           | River side   | side of       | side of       |
|         |           | of existing  | existing      | existing      |
|         |           | bridge would | bridge would  | bridge would  |
|         |           | be removed:  | be removed:   | be removed:   |
|         |           |              |               |               |
|         |           | 2 American   | 2 American    | 1 multi-trunk |
|         |           | elms (*Ulmus | elms (*Ulmus  | flowering     |
|         |           | a            | americana*) - | pear (*Pyrus  |
|         |           | mericana*) - | (±) 120" dbh  | calleryana*)  |
|         |           | (±) 120" dbh | and 150" dbh  |               |
|         |           | and 150" dbh |               | 1 flowering   |
|         |           |              | 1 flowering   | dogwood       |
|         |           | 1 flowering  | dogwood       | (*Cornus      |
|         |           | dogwood      | (*Cornus      | florida)* -   |
|         |           | (*Cornus     | florida)* -   | (±) 25" dbh   |
|         |           | florida)* -  | (±) 25" dbh   |               |
|         |           | (±) 25" dbh  |               | 1 pin oak     |
|         |           |              | 1 pin oak     | (*Quercus     |
|         |           | 1 pin oak    | (*Quercus     | palustris*) - |
|         |           | (*Quercus    | palustris*) - | (±) 80" dbh   |
|         |           | p            | (±) 80" dbh   |               |
|         |           | alustris*) - |               | Approximately |
|         |           | (±) 80" dbh  | Approximately | 1.77 AC of    |
|         |           |              | 1.84 AC of    | mixed         |
|         |           | A            | mixed         | woodland      |
|         |           | pproximately | woodland      | vegetation on |
|         |           | 1.78 AC of   | vegetation on | Pentagon side |
|         |           | mixed        | Pentagon side | of Boundary   |
|         |           | woodland     | of Boundary   | Channel       |
|         |           | vegetation   | Channel       | Bridge would  |
|         |           | on Pentagon  | Bridge would  | be cleared.   |
|         |           | side of      | be cleared.   | Potential     |
|         |           | Boundary     | Potential     | adverse       |
|         |           | Channel      | adverse       | effect on     |
|         |           | Bridge would | effect on     | cultural      |
|         |           | be cleared.  | cultural      | landscape is  |
|         |           | Potential    | landscape is  | anticipated.  |
|         |           | adverse      | anticipated.  | MOA may be    |
|         |           | effect on    | MOA may be    | needed to     |
|         |           | cultural     | needed to     | address       |
|         |           | landscape is | address       | impact to     |
|         |           | anticipated. | impact to     | historic      |
|         |           | MOA may be   | historic      | planting      |
|         |           | needed to    | planting      | plans.        |
|         |           | address      | plans.        |               |
|         |           | impact to    |               |               |
|         |           | historic     |               |               |
|         |           | planting     |               |               |
|         |           | plans.       |               |               |
+---------+-----------+--------------+---------------+---------------+
| W       | No impact | No impact is | No impact is  | No impact is  |
| ildlife | is        | anticipated. | anticipated.  | anticipated.  |
| and     | ant       |              |               |               |
| Thr     | icipated. |              |               |               |
| eatened |           |              |               |               |
| &       |           |              |               |               |
| End     |           |              |               |               |
| angered |           |              |               |               |
| Species |           |              |               |               |
+---------+-----------+--------------+---------------+---------------+
| W       | No impact | 1,400 SF of  | 1,900 SF of   | 1,400 SF      |
| etlands | is        | Boundary     | Boundary      | Boundary      |
|         | ant       | Channel      | Channel       | Channel       |
|         | icipated. | wetlands     | wetlands      | wetlands      |
|         |           | impacted by  | impacted by   | impacted by   |
|         |           | bridge       | bridge        | bridge        |
|         |           | expansion.   | construction. | construction. |
|         |           | USACOE       | USACOE permit | USACOE permit |
|         |           | permit would | would be      | would be      |
|         |           | be required. | required.     | required.     |
+---------+-----------+--------------+---------------+---------------+

Table 5: Comparison of Alternatives -- SB I-395 Ramp to NB GWMP and
Humpback Bridge

+---------+-----------+--------------+---------------+---------------+
| **Eva   | **No      | *            | **Alternative | **Preferred   |
| luation | Action    | *Alternative | B**           | Alternative** |
| F       | Alte      | A**          |               |               |
| actor** | rnative** |              |               |               |
+---------+-----------+--------------+---------------+---------------+
|         |           | *Widen       | *Construct a  | *Replace      |
|         |           | Existing     | Second,       | Existing      |
|         |           | Bridge,      | Parallel      | Bridge,       |
|         |           | Construct    | Bridge,       | Construct     |
|         |           | Underpass    | Construct     | Underpass     |
|         |           | North &      | Underpass     | North & South |
|         |           | South of     | North & South | of Humpback   |
|         |           | Humpback     | of Humpback   | Bridge and    |
|         |           | Bridge and   | Bridge and    | Modify        |
|         |           | Modify       | Modify        | Vertical      |
|         |           | Vertical     | Vertical      | Profile of    |
|         |           | Profile of   | Profile of    | Bridge and    |
|         |           | Bridge and   | Bridge and    | Approaches*   |
|         |           | Approaches*  | Approaches*   |               |
+---------+-----------+--------------+---------------+---------------+
| Water   | No impact | Widened      | Additional    | New bridge    |
| Resourc | is        | bridge       | bridge span   | located in    |
| es/Floo | ant       | /foundations | located in    | 100-year      |
| dplains | icipated. | located in   | 100-year      | floodplain;   |
|         |           | 100-year     | floodplain;   | USACOE permit |
|         |           | floodplain;  | USACOE permit | would be      |
|         |           | USACOE       | would be      | required.     |
|         |           | permit would | required.     | Underpasses   |
|         |           | be required. | Underpasses   | would be      |
|         |           | Underpasses  | would be      | located in a  |
|         |           | would be     | located in a  | flood-prone   |
|         |           | located in a | flood-prone   | area.         |
|         |           | flood-prone  | area.         |               |
|         |           | area.        | Improvements  | Improvements  |
|         |           | Improvements | would be      | would be      |
|         |           | would be     | constructed   | constructed   |
|         |           | constructed  | in accordance | in accordance |
|         |           | in           | with VA and   | with VA and   |
|         |           | accordance   | DC stormwater | DC stormwater |
|         |           | with VA and  | management,   | management,   |
|         |           | DC           | sedimentation | sedimentation |
|         |           | stormwater   | and erosion   | and erosion   |
|         |           | management,  | control and   | control and   |
|         |           | s            | other water   | other water   |
|         |           | edimentation | quality       | quality       |
|         |           | and erosion  | protection    | protection    |
|         |           | control and  | laws and      | laws and      |
|         |           | other water  | policies. Net | policies. Net |
|         |           | quality      | reduction in  | reduction in  |
|         |           | protection   | impervious    | impervious    |
|         |           | laws and     | surface of    | surface of    |
|         |           | policies.    | approximately | approximately |
|         |           | Net          | 1,500 SF in   | 0.3 AC in     |
|         |           | reduction in | vicinity of   | vicinity of   |
|         |           | impervious   | Humpback      | Humpback      |
|         |           | surface of   | Bridge due to | Bridge due to |
|         |           | a            | removal of    | removal of    |
|         |           | pproximately | existing      | existing      |
|         |           | 0.4 AC in    | pavement      | pavement      |
|         |           | vicinity of  | areas.        | areas.        |
|         |           | Humpback     |               |               |
|         |           | Bridge due   |               |               |
|         |           | to removal   |               |               |
|         |           | of existing  |               |               |
|         |           | pavement     |               |               |
|         |           | areas.       |               |               |
+---------+-----------+--------------+---------------+---------------+
| Geolog  | No impact | Soils        | Soils         | Soils         |
| y/Soils | is        | disturbance  | disturbance   | disturbance   |
|         | ant       | of           | of            | of            |
|         | icipated. | a            | approximately | approximately |
|         |           | pproximately | 10.5 AC       | 9.9 AC during |
|         |           | 10.1 AC      | during bridge | bridge        |
|         |           | during       | construction. | construction. |
|         |           | bridge       | Erosion       | Erosion       |
|         |           | expansion.   | control       | control       |
|         |           | Erosion      | measures      | measures      |
|         |           | control      | would be      | would be      |
|         |           | measures     | incorporated  | incorporated  |
|         |           | would be     | during        | during        |
|         |           | incorporated | construction  | construction  |
|         |           | during       | and disturbed | and disturbed |
|         |           | construction | areas         | areas         |
|         |           | and          | re-vegetated. | re-vegetated. |
|         |           | disturbed    |               |               |
|         |           | areas        |               |               |
|         |           | r            |               |               |
|         |           | e-vegetated. |               |               |
+---------+-----------+--------------+---------------+---------------+
| Air     | No impact | Existing air | Existing air  | Existing air  |
| Quality | is        | quality      | quality       | quality       |
|         | ant       | levels would | levels would  | levels would  |
|         | icipated. | remain       | remain        | remain        |
|         |           | essentially  | essentially   | essentially   |
|         |           | the same.    | the same.     | the same.     |
+---------+-----------+--------------+---------------+---------------+
| Noise   | No impact | Existing     | Existing      | Existing      |
|         | is        | noise levels | noise levels  | noise levels  |
|         | ant       | would remain | would remain  | would remain  |
|         | icipated. | essentially  | essentially   | essentially   |
|         |           | the same.    | the same.     | the same.     |
+---------+-----------+--------------+---------------+---------------+
| Ha      | No impact | No impact is | No impact is  | No impact is  |
| zardous | is        | anticipated. | anticipated.  | anticipated.  |
| Ma      | ant       |              |               |               |
| terials | icipated. |              |               |               |
| and     |           |              |               |               |
| Wastes  |           |              |               |               |
+---------+-----------+--------------+---------------+---------------+
| Energy  | No impact | No           | No            | No            |
|         | is        | significant  | significant   | significant   |
|         | ant       | change in    | change in     | change in     |
|         | icipated. | long-term    | long-term     | long-term     |
|         |           | energy       | energy        | energy        |
|         |           | consumption  | consumption   | consumption   |
|         |           | is           | is            | is            |
|         |           | anticipated. | anticipated.  | anticipated.  |
+---------+-----------+--------------+---------------+---------------+
| Socioe  | The       | Minor        | Minor benefit | Minor benefit |
| conomic | public    | benefit from | from          | from          |
| and     | would     | construc     | constru       | constru       |
| Co      | continue  | tion-related | ction-related | ction-related |
| mmunity | to be     | jobs and     | jobs and      | jobs and      |
| F       | subject   | purchases.   | purchases. No | purchases No  |
| eatures | to safety | No long-term | long-term     | long-term     |
|         | hazards   | economic     | economic      | economic      |
|         | a         | benefit to   | benefit to    | benefit to    |
|         | ssociated | local        | local         | local         |
|         | with the  | community is | community is  | community is  |
|         | current   | anticipated. | anticipated.  | anticipated.  |
|         | GWMP      |              |               |               |
|         | ci        | The public   | The public    | The public    |
|         | rculation | would no     | would no      | would no      |
|         | systems.  | longer be    | longer be     | longer be     |
|         |           | subject to   | subject to    | subject to    |
|         |           | safety       | safety        | safety        |
|         |           | hazards      | hazards       | hazards       |
|         |           | associated   | associated    | associated    |
|         |           | with the     | with the      | with the      |
|         |           | current GWMP | current GWMP  | current GWMP  |
|         |           | circulation  | circulation   | circulation   |
|         |           | systems.     | systems.      | systems.      |
+---------+-----------+--------------+---------------+---------------+

Table 5: Comparison of Alternatives -- SB I-395 Ramp to NB GWMP and
Humpback Bridge

+---------+-----------+--------------+---------------+---------------+
| **Eva   | **No      | *            | **Alternative | **Preferred   |
| luation | Action    | *Alternative | B**           | Alternative** |
| F       | Alte      | A**          |               |               |
| actor** | rnative** |              |               |               |
+---------+-----------+--------------+---------------+---------------+
|         |           | *Widen       | *Construct a  | *Replace      |
|         |           | Existing     | Second,       | Existing      |
|         |           | Bridge,      | Parallel      | Bridge,       |
|         |           | Construct    | Bridge,       | Construct     |
|         |           | Underpass    | Construct     | Underpass     |
|         |           | North &      | Underpass     | North & South |
|         |           | South of     | North & South | of Humpback   |
|         |           | Humpback     | of Humpback   | Bridge and    |
|         |           | Bridge and   | Bridge and    | Modify        |
|         |           | Modify       | Modify        | Vertical      |
|         |           | Vertical     | Vertical      | Profile of    |
|         |           | Profile of   | Profile of    | Bridge and    |
|         |           | Bridge and   | Bridge and    | Approaches*   |
|         |           | Approaches*  | Approaches*   |               |
+---------+-----------+--------------+---------------+---------------+
| Te      | No impact | Temporary    | Temporary     | Temporary     |
| mporary | is        | height       | height        | height        |
| Impacts | ant       | restriction  | restriction   | restriction   |
|         | icipated. | of the       | of the        | of the        |
|         |           | Boundary     | Boundary      | Boundary      |
|         |           | Channel for  | Channel for   | Channel for   |
|         |           | formwork and | formwork and  | formwork and  |
|         |           | scaffolding  | scaffolding   | scaffolding   |
|         |           | during       | during        | during        |
|         |           | construction | construction  | construction  |
|         |           | activities.  | activities.   | activities.   |
|         |           |              |               |               |
|         |           | Clearing of  | Minor,        | Clearing of   |
|         |           | a            | temporary     | approximately |
|         |           | pproximately | impacts to    | 0.3 AC of     |
|         |           | 0.3 AC of    | air quality   | mixed         |
|         |           | mixed        | during bridge | woodland      |
|         |           | woodland     | construction. | would be      |
|         |           | would be     |               | required for  |
|         |           | required for | Minor,        | temporary     |
|         |           | temporary    | temporary     | bridge and    |
|         |           | bridge and   | noise         | roadway. The  |
|         |           | roadway. The | increases     | cleared area  |
|         |           | cleared area | would result  | would be      |
|         |           | would be     | during        | re-graded and |
|         |           | re-graded    | construction  | landscaped    |
|         |           | and          | activities.   | when          |
|         |           | landscaped   |               | construction  |
|         |           | when         | Energy        | is complete.  |
|         |           | construction | consumption   |               |
|         |           | is complete. | would         | Temporary     |
|         |           |              | temporarily   | filling of    |
|         |           | Temporary    | increase      | 900 SF of     |
|         |           | filling of   | during        | wetland for   |
|         |           | 900 SF of    | construction  | temporary     |
|         |           | wetland for  | of the        | bridge and    |
|         |           | temporary    | proposed      | roadway would |
|         |           | bridge and   | improvements. | be required.  |
|         |           | roadway      |               | The wetland   |
|         |           | would be     |               | would be      |
|         |           | required.    |               | restored when |
|         |           | The wetland  |               | construction  |
|         |           | would be     |               | is complete.  |
|         |           | restored     |               |               |
|         |           | when         |               | Minor,        |
|         |           | construction |               | temporary     |
|         |           | is complete. |               | impacts to    |
|         |           |              |               | air quality   |
|         |           | Minor,       |               | during        |
|         |           | temporary    |               | demolition of |
|         |           | impacts to   |               | old bridge    |
|         |           | air quality  |               | and           |
|         |           | during       |               | construction  |
|         |           | bridge       |               | of new        |
|         |           | expansion.   |               | bridge.       |
|         |           |              |               |               |
|         |           | Minor,       |               | Minor,        |
|         |           | temporary    |               | temporary     |
|         |           | noise        |               | noise         |
|         |           | increases    |               | increases     |
|         |           | would result |               | would result  |
|         |           | during       |               | during        |
|         |           | demolition   |               | demolition    |
|         |           | and          |               | and           |
|         |           | construction |               | construction  |
|         |           | activities.  |               | activities.   |
|         |           |              |               | This          |
|         |           | Energy       |               | alternative   |
|         |           | consumption  |               | would have    |
|         |           | would        |               | the greatest  |
|         |           | temporarily  |               | temporary     |
|         |           | increase     |               | noise impact. |
|         |           | during       |               |               |
|         |           | construction |               | Energy        |
|         |           | of the       |               | consumption   |
|         |           | proposed     |               | would         |
|         |           | i            |               | temporarily   |
|         |           | mprovements. |               | increase      |
|         |           |              |               | during        |
|         |           |              |               | construction  |
|         |           |              |               | of the        |
|         |           |              |               | proposed      |
|         |           |              |               | improvements. |
+---------+-----------+--------------+---------------+---------------+
| Cum     | No impact | Safer        | Safer         | Safer         |
| ulative | is        | environment  | environment   | environment   |
| Impacts | ant       | for          | for vehicular | for vehicular |
|         | icipated. | vehicular    | and           | and           |
|         |           | and          | pedestrian    | pedestrian    |
|         |           | pedestrian   | users of the  | users of the  |
|         |           | users of the | GWMP would    | GWMP would    |
|         |           | GWMP would   | result. GWMP  | result. GWMP  |
|         |           | result. GWMP | access would  | access would  |
|         |           | access would | be enhanced   | be enhanced   |
|         |           | be enhanced  | by potential  | by potential  |
|         |           | by potential | Old Jefferson | Old Jefferson |
|         |           | Old          | Davis Highway | Davis Highway |
|         |           | Jefferson    | improvements  | improvements  |
|         |           | Davis        | by Arlington  | by Arlington  |
|         |           | Highway      | County. No    | County. No    |
|         |           | improvements | adverse       | adverse       |
|         |           | by Arlington | impacts are   | impacts are   |
|         |           | County. No   | anticipated.  | anticipated.  |
|         |           | adverse      |               |               |
|         |           | impacts are  |               |               |
|         |           | anticipated. |               |               |
+---------+-----------+--------------+---------------+---------------+

Table 5: Comparison of Alternatives -- SB I-395 Ramp to NB GWMP and
Humpback Bridge

  -------------- --------------- ---------------- ---------------- ----------------
  **Evaluation   **No Action     **Alternative    **Alternative    **Preferred
  Factor**       Alternative**   A**              B**              Alternative**

                                 *Widen Existing  *Construct a     *Replace
                                 Bridge,          Second, Parallel Existing Bridge,
                                 Construct        Bridge,          Construct
                                 Underpass North  Construct        Underpass North
                                 & South of       Underpass North  & South of
                                 Humpback Bridge  & South of       Humpback Bridge
                                 and Modify       Humpback Bridge  and Modify
                                 Vertical Profile and Modify       Vertical Profile
                                 of Bridge and    Vertical Profile of Bridge and
                                 Approaches*      of Bridge and    Approaches*
                                                  Approaches*      

  Maintenance                    The existing     Long-term        Maintenance
  Cost                           Humpback Bridge  maintenance      costs would be
                                 would comprise   costs            reduced for a
                                 the majority of  anticipated to   new bridge, with
                                 the modified     remain the same  an est. 75-100
                                 bridge           or increase, due year life
                                 structure.       to need to       expectancy.
                                 Long-term        maintain both    Additional
                                 maintenance      existing         long-term
                                 costs would not  Humpback Bridge  maintenance
                                 be expected to   and new bridge.  costs would be
                                 decrease         Est. 25-30 year  incurred for
                                 significantly.   remaining life   underpasses and
                                 Est. 25-30 year  expectancy for   new trails.
                                 remaining life   Humpback Bridge  
                                 expectancy for   and 75 to 100    
                                 Humpback Bridge. year life        
                                 Additional       expectancy for   
                                 long-term        new bridge.      
                                 maintenance      Additional       
                                 costs would be   long-term        
                                 incurred for     maintenance      
                                 underpasses and  costs would be   
                                 new trails.      incurred for     
                                                  underpasses and  
                                                  new trails.      

  Construction                   \$5,990,000      \$6,780,000      \$10,390,000
  Cost                                                             
  -------------- --------------- ---------------- ---------------- ----------------

# Environmental Effects of the Southbound GWMP Ramp to Southbound I-395 Alternatives

Due to weaving/safety issues, the removal of this ramp has been
recommended. The NPS has deferred the selection of a preferred
alternative or action/no action for the proposed ramp closure until the
completion of a more extensive evaluation by the FHWA of the I-395
corridor in Virginia and the District of Columbia. The following
analysis is provided for information purposes.

## Roadways and Ramps

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open .unnumbered}

No change to existing traffic operations would result. The ramp and GWMP
would operate at LOS A during the AM and PM peak periods for the no
build condition. The weave section where the ramp merges with southbound
I-395 would operate at LOS F/E (AM/PM) as indicated in Figure B-6,
Appendix B.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp .unnumbered}

While the ramp itself operates effectively, the 280-foot weave at the
end of the ramp where it meets I-395 is anticipated to operate at
unacceptable levels of service by 2025, as shown in Figure B-5. The
projected traffic volumes on the ramp are the lowest of all the ramps in
the GWMP/I-395 interchange: 190 and 180 vehicles per hour (vph) for AM
and PM peak hours, respectively. If this ramp were removed, the
alternate route a driver would take would involve diverting traffic from
southbound GWMP to I-395 by way of VA 27. For drivers destined for Route
1 and other points east of VA 27, a driver would be diverted from the
southbound GWMP to VA 27 to Boundary Channel Drive to I-395/Route 1/Old
Jefferson Davis Highway.

##### Traffic Operations Impacts {#traffic-operations-impacts .unnumbered}

Figure B-7, Appendix B shows the level of service results for this
alternative. The removal of the ramp slightly improves the LOS on
southbound I-395 for the AM peak in the vicinity of the prior ramp
junction. The removal of the ramp actually causes the level of service
on southbound GWMP to decrease from a D (No-Build) to an E (Ramp
Closure) for the PM peak. This degradation occurs because the
methodology of analyzing the existing ramp junction is different than
the proposed basic freeway section. The threshold at which a section of
roadway becomes an E is based on the type of freeway section; a basic
freeway section (with no ramps), a freeway-ramp junction, or a weave
section. The threshold of LOS D/E for a basic freeway section is 32
pc/mi/ln whereas the threshold of LOS D/E is 35 pc/mi/ln for a
freeway-ramp junction. A driver anticipates more friction at ramp
junctions, which causes the level of service criteria to shift to allow
more vehicles/lane/mile based on driver expectancy. As a result, the LOS
of a roadway section without a ramp junction reaches an E at a lower
threshold than a section of roadway with a ramp junction.

The level of service is based on the density of the vehicles and is
expressed as vehicles/lane/mile. In the No-Build scenario, the
deceleration lane carries little traffic (low density) while the main
lanes of southbound GWMP carry heavy traffic (higher density). If the
deceleration lane is removed, only the heavy-volume, higher density main
lanes are left, causing a slight increase in the total density of the
road section.

In addition to the level of service analysis, an analysis of average
speed and density was performed in order to compare the alternative
(ramp removal) to the no-build scenario. The results are shown in Table
6. The results are reported for the portion of the model affected by the
alternative.

Along southbound GWMP, removing the ramp causes very little, if any,
improvement in speed and density for the AM and PM peak hours over the
approximately 0.4-mile section of the Parkway affected by the ramp
removal, which removes 190 and 180 vph from the SB I-395 flow in 2025
during the AM and PM peaks, respectively. The improvement to traffic is
slightly greater for the portion of I-395 at the southbound end of the
ramp. In the AM, speed improved by about 6 mph and density improved by
about 12 percent for the section of I-395 affected by the ramp removal.
In the PM, speed improved by 2 mph and density by 11 percent for the
affected section of I-395.

In addition to speed and density impacts, the ramp closure would
eliminate geometric deficiencies associated with the current ramp design
on both the GWMP and I-395.

##### Impact on Alternate Routes {#impact-on-alternate-routes .unnumbered}

If the southbound GWMP ramp to southbound I-395 were eliminated, most
drivers would take VA 27 to access southbound I-395 from the southbound
GWMP. Traffic volumes on VA 27 and Boundary Channel Drive were
investigated to determine the impact of the rerouted southbound GWMP
traffic on alternate routes. While the two roadways were not included in
the CORSIM modeling, average daily traffic (ADT) data was available for
each and was used to evaluate the change in traffic volumes if the ramp
were closed. Growth rates for VA 27 and Boundary Channel Drive were not
determined in the *14^th^ Street Bridge Corridor Improvement Feasibility
Study* and CORSIM model. As a result, the existing year (2001) traffic
volumes have been utilized to evaluate the change in traffic volumes.

[]{#__RefHeading___Toc5024311 .anchor}Table 6: 2025 Speed and Density
Results -- Comparison of No Build to SB GWMP to SB I-395 Ramp Removal
Alternative

  ----------------- ------------------ ------------------ -----------------
                    **Average speed    **Average density  **Length of
                    difference**       difference**       affected area**

  GWMP SB                                                 

  AM                -0.07 mph          1.5 %              0.43 mi

  PM                2.1 mph            -3.3 %             0.43 mi

  I-395 SB                                                

  AM                6.2 mph            12.4 %             0.28 mi

  PM                0.4 mph            3.9 %              0.22 mi
  ----------------- ------------------ ------------------ -----------------

Note: AM & PM peak hours were simulated in different models. As a
result, the endpoints of the models may be in slightly different
positions, causing the "Length of Affected Area" to be slightly
different between the AM & PM peak hour models.

Year 2001 peak hour volumes for the southbound GWMP ramp to southbound
I-395 are 120 vph for both the AM and PM periods. According to the VDOT
*Year 2000 Annual Average Daily Traffic Volume Estimates*, VA 27 carried
20,000 to 31,000 vph eastbound and 25,000 to 31,000 vph westbound
between I-395 and Boundary Channel Drive in the year 2000. The design
hourly volume for this section is 2,000-2,700 vph eastbound and
2,800-3,700 vph westbound. In the AM peak, approximately 420 vehicles
travel southbound on Boundary Channel Drive. In the PM peak,
approximately 660 vph travel southbound on Boundary Channel Drive. If
the southbound GWMP ramp to southbound I-395 were eliminated,
approximately 56 vehicles would be displaced to westbound VA 27 and 64
vehicles would be displaced to southbound Boundary Channel Drive during
the AM peak hour to reach their ultimate destinations on I-395 and/or
Route 1. The estimates of diverted traffic is based upon the traffic
split identified in the *14^th^ Street Bridge Corridor Improvement
Feasibility Study* origin-destination analysis applied to 2001 balanced
traffic volumes. The diversion of ramp traffic would increase westbound
AM peak traffic on VA 27 by approximately 2% and on southbound Boundary
Channel Drive by 15%. Approximately 17 vehicles would be displaced to VA
27 and 103 vehicles would be displaced to Boundary Channel Drive during
the PM peak period. The displacement of traffic would increase PM peak
traffic by 1% on VA 27 and by 16% on Boundary Channel Drive.

It should be noted that, in order to maintain consistency in traffic
movement, both the southbound GWMP ramp to southbound I-395 and the
northbound I-395 ramp to northbound GWMP should either remain or be
removed. This is based on driver expectancy of the same return trip to
an interstate once their vehicle has exited from the interstate.

## Bicycle and Pedestrian Facilities

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-1 .unnumbered}

There are no pedestrian/bicyclist facilities associated with this ramp.
The Mt. Vernon Trail and other pedestrian/bicycle facilities within the
Study Area, as well as related safety deficiencies, would remain in
their current condition.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-1 .unnumbered}

This alternative does not involve any modifications to the Mt. Vernon
Trail or other pedestrian/bicycle facilities. The existing facilities
would remain in their current condition.

## Historic and Cultural Resources

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-2 .unnumbered}

No impact to historic or cultural resources is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-2 .unnumbered}

No impact to historic or cultural resources is anticipated by the
closure of this ramp.

## Aesthetics and Viewsheds

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-3 .unnumbered}

The aesthetic condition and viewshed of the GWMP and adjacent historic
resources would remain in their current condition.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-3 .unnumbered}

Although not a prominent visual element of the parkway, the closure of
the ramp, removal of ramp pavement and revegetation of the area would
have a minor, positive impact on the aesthetic condition of the GWMP.

## Land Use

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-4 .unnumbered}

No change to existing land use patterns is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-4 .unnumbered}

No change to existing land use patterns is anticipated to result.

## Biological Resources

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-5 .unnumbered}

##### Vegetation {#vegetation-7 .unnumbered}

No change to existing vegetation would result.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-7 .unnumbered}

No change to existing wildlife is anticipated.

##### Wetlands {#wetlands-7 .unnumbered}

No impact to wetland resources is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-5 .unnumbered}

##### Vegetation {#vegetation-8 .unnumbered}

Once the ramp is closed, the existing pavement would be removed and the
area re-vegetated. The ramp area would likely be planted with turf
grass, consistent with the treatment of the adjacent interchange areas.
This modification is anticipated to have a minimal benefit to existing
vegetation resources, but would increase the amount of landscaped area
by approximately 0.6 acres AC.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-8 .unnumbered}

While the former ramp area would be re-vegetated, the replacement turf
grass cover provides minimal wildlife value and is not anticipated to
have any effect on existing wildlife communities.

##### Wetlands {#wetlands-8 .unnumbered}

No impact to wetland resources is anticipated.

## Water Resources

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-6 .unnumbered}

##### Floodplains {#floodplains-7 .unnumbered}

No impact to floodplains is anticipated.

##### Coastal Zone Management {#coastal-zone-management-7 .unnumbered}

No Coastal Zone impacts are anticipated.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-7 .unnumbered}

No Chesapeake Bay impacts are anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-6 .unnumbered}

##### Floodplains {#floodplains-8 .unnumbered}

No impact to floodplains is anticipated.

##### Coastal Zone Management {#coastal-zone-management-8 .unnumbered}

No Coastal Zone impacts are anticipated.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-8 .unnumbered}

No Chesapeake Bay impacts are anticipated.

## Physiography, Geology and Soils

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-7 .unnumbered}

No disturbance to soils is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-7 .unnumbered}

Minor soil disturbance would result from the demolition of the ramp
pavement. Erosion control measures would be incorporated to minimize
soils loss. Disturbed areas would be re-vegetated once demolition
activities are complete.

## Air Quality

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-8 .unnumbered}

No change to air quality levels is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-8 .unnumbered}

Minor increases in dust and other air emissions would result from
demolition activities associated with the removal of the ramp. Emissions
increases would be temporary in duration and would comply with the
FHWA's Standard Specifications for Construction of Roads and Bridges on
Federal Highway Projects (1996) and with applicable local, state and
federal regulations.

## Noise

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-9 .unnumbered}

No change in existing noise sources or noise levels is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-9 .unnumbered}

Existing noise levels would increase temporarily during the demolition
of the existing ramp. The rerouting of traffic to VA 27 and Boundary
Channel Drive associated with the closure of this ramp would result in
minor increases in noise levels on those roadways, due to the additional
vehicle traffic. The increases in noise levels are not anticipated to be
significant.

## Hazardous Materials and Wastes

No evidence of historical land use involving hazardous materials or
hazardous wastes was found within the Study Area. The proposed actions
would not require the disturbance or relocation of any of the existing,
recognized environmental conditions -- USTs and ASTs -- found at the
Columbia Island Marina in the Study Area. Therefore, no disturbance or
generation of hazardous materials or hazardous wastes are anticipated to
occur with either the implementation of any of the safety improvements
or under "no-action" conditions.

## Energy

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-10 .unnumbered}

No change in energy consumption is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-10 .unnumbered}

Energy consumption would temporarily increase during demolition of the
ramp. No significant change in long-term energy consumption is
anticipated.

## Socioeconomic and Community Features

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-11 .unnumbered}

No change to socioeconomic or community features is anticipated. The
public would continue to be exposed to the safety hazards associated
with the current GWMP transportation and circulation systems.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-11 .unnumbered}

Construction jobs associated with the demolition of the ramp would have
a short-term benefit to local construction workers and the local
economy. In the long term, motorists would be rerouted to more heavily
traveled alternate routes, VA 27 and Boundary Channel Drive/Jefferson
Davis Highway, where they would experience increased traffic volumes and
less direct routing to their final destinations, particularly for those
destined for the Route 1 corridor and Crystal City.

## Cumulative Impacts

The proposed ramp closure is not anticipated to contribute to
significant cumulative impacts in the vicinity of the Study Area.

## Comparison of Alternatives

A comparison of the No Action Alternative and the Preferred Build
Alternative is provided in Table 7.

[]{#__RefHeading___Toc5024312 .anchor}Table 7: Comparison of
Alternatives -- SB GWMP Ramp to SB I-395 and NB I-395 Ramp to NB GWMP\*

+--------------+-----------+--------------+-----------+--------------+
| **Evaluation | **S       |              | **N       |              |
| Factor**     | outhbound |              | orthbound |              |
|              | GWMP Ramp |              | I-395     |              |
|              | to        |              | Ramp to   |              |
|              | S         |              | N         |              |
|              | outhbound |              | orthbound |              |
|              | I-395**   |              | GWMP**    |              |
+--------------+-----------+--------------+-----------+--------------+
|              | **No      | **Preferred  | **No      | **Preferred  |
|              | Action    | Al           | Action    | Al           |
|              | Alte      | ternative:** | Alte      | ternative:** |
|              | rnative** |              | rnative** |              |
+--------------+-----------+--------------+-----------+--------------+
|              |           | *Eliminate   |           | *Eliminate   |
|              |           | Ramp*        |           | Ramp*        |
+--------------+-----------+--------------+-----------+--------------+
| Motorist     | Safety    | Motorist     | Safety    | Motorist     |
| Safety and   | hazards   | safety       | hazards   | safety       |
| Traffic      | and       | improved     | and       | improved     |
| Operations   | accident  | with the     | accident  | with the     |
|              | potential | elimination  | potential | elimination  |
|              | a         | of ramp.     | a         | of ramp.     |
|              | ssociated |              | ssociated |              |
|              | with ramp | Peak hour    | with ramp | Peak hour    |
|              | would     | traffic on   | would     | traffic on   |
|              | remain.   | westbound VA | remain.   | eastbound VA |
|              |           | 27 projected |           | 27 projected |
|              |           | to increase  |           | to increase  |
|              |           | by           |           | by           |
|              |           | a            |           | a            |
|              |           | pproximately |           | pproximately |
|              |           | 2% in AM     |           | 15% in AM    |
|              |           | peak and 1%  |           | peak and 12% |
|              |           | in PM peak   |           | in PM peak   |
|              |           | due to ramp  |           | due to ramp  |
|              |           | closure.     |           | closure.     |
|              |           |              |           |              |
|              |           | Peak hour    |           | Peak hour    |
|              |           | traffic on   |           | traffic on   |
|              |           | southbound   |           | northbound   |
|              |           | Boundary     |           | Boundary     |
|              |           | Channel      |           | Channel      |
|              |           | Drive        |           | Drive        |
|              |           | projected to |           | projected to |
|              |           | increase by  |           | increase by  |
|              |           | 15% in the   |           | 11% in the   |
|              |           | AM peak and  |           | AM peak and  |
|              |           | by 16% in    |           | by 41% in    |
|              |           | the PM peak. |           | the PM peak. |
+--------------+-----------+--------------+-----------+--------------+
| Alternate    | No impact | Alternate    | No impact | Alternate    |
| Routes       | is        | route        | is        | route        |
|              | ant       | required     | ant       | required     |
|              | icipated. | between GWMP | icipated. | between      |
|              |           | and I-395.   |           | I-395 and    |
|              |           | In order to  |           | GWMP. In     |
|              |           | maintain     |           | order to     |
|              |           | consistency  |           | maintain     |
|              |           | in traffic   |           | consistency  |
|              |           | movement and |           | in traffic   |
|              |           | driver       |           | movement and |
|              |           | e            |           | driver       |
|              |           | xpectations, |           | e            |
|              |           | both the SB  |           | xpectations, |
|              |           | GWMP ramp to |           | both the SB  |
|              |           | SB I-395 and |           | GWMP ramp to |
|              |           | the NB I-395 |           | SB I-395 and |
|              |           | ramp to NB   |           | the NB I-395 |
|              |           | GWMP should  |           | ramp to NB   |
|              |           | either be    |           | GWMP should  |
|              |           | closed or    |           | either be    |
|              |           | remain open. |           | closed or    |
|              |           |              |           | remain open. |
+--------------+-----------+--------------+-----------+--------------+
| Historic and | No impact | No impact is | No impact | No impact is |
| Cultural     | is        | anticipated. | is        | anticipated. |
| Resources    | ant       |              | ant       |              |
|              | icipated. |              | icipated. |              |
+--------------+-----------+--------------+-----------+--------------+
| Aesthetics   | No impact | No impact is | No impact | No impact is |
| and          | is        | anticipated. | is        | anticipated. |
| Viewsheds    | ant       |              | ant       |              |
|              | icipated. |              | icipated. |              |
+--------------+-----------+--------------+-----------+--------------+
| Vegetation   | No impact | Interchange  | No impact | Interchange  |
|              | is        | area would   | is        | area would   |
|              | ant       | be           | ant       | be           |
|              | icipated. | re-vegetated | icipated. | re-vegetated |
|              |           | after        |           | after        |
|              |           | removal of   |           | removal of   |
|              |           | ramp.        |           | ramp.        |
+--------------+-----------+--------------+-----------+--------------+
| Wildlife and | No impact | No impact is | No impact | No impact is |
| Threatened & | is        | anticipated. | is        | anticipated. |
| Endangered   | ant       |              | ant       |              |
| Species      | icipated. |              | icipated. |              |
+--------------+-----------+--------------+-----------+--------------+
| Wetlands     | No impact | No impact is | No impact | No impact is |
|              | is        | anticipated. | is        | anticipated. |
|              | ant       |              | ant       |              |
|              | icipated. |              | icipated. |              |
+--------------+-----------+--------------+-----------+--------------+
| Water        | No impact | S            | No impact | S            |
| Resources    | is        | edimentation | is        | edimentation |
| /Floodplains | ant       | measures     | ant       | measures     |
|              | icipated. | would be     | icipated. | would be     |
|              |           | incorporated |           | incorporated |
|              |           | during ramp  |           | during ramp  |
|              |           | removal.     |           | removal.     |
|              |           | Minor        |           | Minor        |
|              |           | decrease in  |           | decrease in  |
|              |           | impervious   |           | impervious   |
|              |           | surface      |           | surface      |
|              |           | cover on the |           | cover on the |
|              |           | GWMP (0.6    |           | GWMP (0.4    |
|              |           | AC).         |           | AC).         |
+--------------+-----------+--------------+-----------+--------------+
| G            | No impact | Minor soils  | No impact | Minor soils  |
| eology/Soils | is        | disturbance  | is        | disturbance  |
|              | ant       | during       | ant       | during       |
|              | icipated. | demolition   | icipated. | demolition   |
|              |           | of the ramp. |           | of the ramp. |
|              |           | Erosion      |           | Erosion      |
|              |           | control      |           | control      |
|              |           | measures     |           | measures     |
|              |           | would be     |           | would be     |
|              |           | incorporated |           | incorporated |
|              |           | and          |           | and          |
|              |           | disturbed    |           | disturbed    |
|              |           | areas        |           | areas        |
|              |           | r            |           | r            |
|              |           | e-vegetated. |           | e-vegetated. |
+--------------+-----------+--------------+-----------+--------------+
| Air Quality  | No impact | Existing air | No impact | Existing air |
|              | is        | quality      | is        | quality      |
|              | ant       | levels would | ant       | levels would |
|              | icipated. | remain       | icipated. | remain       |
|              |           | essentially  |           | essentially  |
|              |           | the same.    |           | the same.    |
+--------------+-----------+--------------+-----------+--------------+

\* The NPS has deferred the selection of a preferred alternative or
action/no action for the proposed ramp closures until the completion of
a more extensive evaluation by the FHWA of the I-395 corridor in
Virginia and the District of Columbia. The comparisons in this table are
provided for information purposes.

Table 7: Comparison of Alternatives -- SB GWMP Ramp to SB I-395 and NB
I-395 Ramp to NB GWMP\*

  --------------- --------------- ------------------------- --------------- -------------------------
  **Evaluation    **Southbound                              **Northbound    
  Factor**        GWMP Ramp to                              I-395 Ramp to   
                  Southbound                                Northbound      
                  I-395**                                   GWMP**          

                  **No Action     **Preferred               **No Action     **Preferred
                  Alternative**   Alternative:**            Alternative**   Alternative:**

                                  *Eliminate Ramp*                          *Eliminate Ramp*

  Noise           No impact is    Rerouting of ramp traffic No impact is    Rerouting of ramp traffic
                  anticipated.    would result in           anticipated.    would result in
                                  negligible decrease in                    negligible decrease in
                                  traffic noise on GWMP and                 traffic noise on GWMP and
                                  negligible increase along                 negligible increase along
                                  alternate routes.                         alternate routes.

  Hazardous       No impact is    No impact is anticipated. No impact is    No impact is anticipated.
  Materials and   anticipated.                              anticipated.    
  Wastes                                                                    

  Energy          No impact is    Energy consumption would  No impact is    Energy consumption would
                  anticipated.    temporarily increase      anticipated.    temporarily increase
                                  during demolition of the                  during demolition of the
                                  ramp. No significant                      ramp. No significant
                                  change in long-term                       change in long-term
                                  energy consumption is                     energy consumption is
                                  anticipated.                              anticipated.

  Socioeconomic   No impact is    No impact is anticipated. No impact is    No impact is anticipated.
  and Community   anticipated.                              anticipated.    
  Features                                                                  

  Temporary       No impact is    Minor, temporary impacts  No impact is    Minor, temporary impacts
  Impacts         anticipated.    to air quality during     anticipated.    to air quality during
                                  ramp removal. Minor,                      ramp removal. Minor,
                                  temporary noise increases                 temporary noise increases
                                  would result during                       would result during
                                  demolition/construction                   demolition/construction
                                  activities.                               activities.

  Cumulative      No impact is    No impact is anticipated. No impact is    No impact is anticipated.
  Impacts         anticipated.                              anticipated.    

  Construction                    \$350,000                                 \$210,000
  Cost                                                                      
  --------------- --------------- ------------------------- --------------- -------------------------

\* The NPS has deferred the selection of a preferred alternative or
action/no action for the proposed ramp closures until the completion of
a more extensive evaluation by the FHWA of the I-395 corridor in
Virginia and the District of Columbia. The comparisons in this table are
provided for information purposes.

# Environmental Effects of the Northbound I-395 Ramp to Northbound GWMP Alternatives

As with the previously discussed ramp closure alternative, the NPS has
deferred its decision on ramp closures at the GWMP/I-395 interchange
until the completion of a more extensive I-395 corridor study by the
FHWA. The following analysis is provided for information purposes.

## Roadways and Ramps

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-12 .unnumbered}

No change to existing traffic operations would result. The ramp and GWMP
would operate at LOS B during the AM and PM peak periods for the no
build condition. The weave section where the ramp merges with northbound
GWMP would operate at LOS E/F (AM/PM) as indicated in Figure B-6,
Appendix B.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-12 .unnumbered}

Due to safety/design issues, the removal of this ramp is also under
consideration. While the ramp itself operates effectively, it has
several design characteristics that cause safety/operational concerns on
either end of the ramp; no deceleration lane at I-395 and a 420-foot
weave at GWMP. As shown in Figure B-5, the section of I-395 prior to the
exit ramp is anticipated to operate at LOS F for the AM and PM peaks in
2025 and the weave movement on the GWMP is expected to operate at LOS E
and D in the AM and PM peak hours, respectively.

The projected traffic volumes on the ramp are the third lowest of all
the ramps in the GWMP/I-395 interchange: 360 and 370 vph for AM and PM
peak hours, respectively. If this ramp were removed, the alternate route
a driver would take would involve diverting traffic from northbound
I-395 to northbound GWMP via VA 27. Drivers on I-395 originating from
Route 1 and other points east of VA 27 would be diverted to GWMP via
northbound Boundary Channel Drive and VA 27.

##### Traffic Operations Impacts {#traffic-operations-impacts-1 .unnumbered}

Figure B-8, Appendix B shows the level of service results for this
alternative. Note that the model limits for northbound I-395 in the AM
peak were originally set in the CORSIM models east of Route 27 and the
limits for the PM peak were set east of Boundary Channel Drive. As a
result, operational improvements are reported up to these limits.

The removal of the ramp improves the density of the section of I-395
just prior to the ramp, but not enough to raise the LOS above F.
However, the ramp closure removes approximately 6 percent of the total
traffic from I-395 northbound east of Route 27 in the AM and PM peak.
This decrease in traffic reduces the length of queuing along I-395
northbound in the AM peak hour, thus improving the LOS for I-395 from
Route 27 to Route 110.

The ramp closure eliminates the weave on northbound GWMP, and improves
the LOS along the GWMP in that weave area from an E (weave area) to D
(weave removed) for the AM peak hour, and from a D to C for the PM peak
hour.

In addition to the level of service analysis, an analysis of average
speed and density was performed in order to compare the alternative
(ramp closure) to the no-build scenario. Table 8 shows the results of
the speed and density analysis for this alternative. The results are
reported for the portion of the model affected by the alternative.

Along northbound GWMP, removing the ramp causes an improvement in speed
of approximately 3 and 2 mph for the AM and PM peak hours, respectively,
over the approximately 0.3-mile section of the Parkway affected by the
ramp removal. The density of traffic in this section improved by 13 and
11 percent, for the AM and PM peak hours, respectively.

The improvement to traffic is greater for northbound I-395. In the AM,
speed improved by about 12 mph and density improved by about 38 percent
for the 1.7-mile section of I-395 affected by the ramp removal, which
removes 360 vph in the AM peak in 2025. In the PM, speed improved by
about 5 mph and density by 20 percent for the 0.3-mile section of I-395
affected by the ramp closure, which removes 370 vph in the PM peak in
2025. As stated above, the model limits for northbound I-395 in the AM
peak were originally set in the CORSIM models east of Route 27 and the
limits for the PM peak were set east of Boundary Channel Drive, and the
results are therefore reported up to these limits.

In addition to speed and density impacts, the ramp closure would
eliminate geometric deficiencies associated with the current ramp design
on both the GWMP and I-395.

[]{.mark}

##### Impact on Alternate Routes {#impact-on-alternate-routes-1 .unnumbered}

If the northbound I-395 ramp to northbound GWMP were eliminated, most
drivers would take VA 27 to access northbound GWMP. As with the
southbound GWMP ramp to southbound I-395, the existing year (2001)
traffic volumes have been utilized to evaluate the change in traffic
volumes. An additional alternate route utilizes northbound Boundary
Channel Drive to access VA 27 from I-395.

[]{#__RefHeading___Toc5024314 .anchor}Table 8: 2025 Speed and Density
Results -- Comparison of No Build to NB I-395 to NB GWMP Ramp Removal
Alternative

  ------------- ------------------ -------------------- ------------------
                Average speed      Average density      Length of affected
                difference         difference           area

  GWMP NB                                               

  AM            3.3 mph            13.1 %               0.31 mi

  PM            2.0 mph            10.9 %               0.31 mi

  I-395 NB                                              

  AM            11.6 mph           37.9 %               1.70 mi

  PM            5.2 mph            20.0 %               0.30 mi
  ------------- ------------------ -------------------- ------------------

Note: AM & PM peak hours were simulated in different models. As a
result, the endpoints of the models may be in slightly different
positions, causing the "Length of Affected Area" to be slightly
different between the AM & PM peak hour models.

Year 2001 peak hour volumes for the ramp are 290 vph in the AM hour and
240 vph in the PM hour. The design hourly volume for VA 27 between I-395
and Boundary Channel Drive is 2,000-2,700 vph eastbound and 2,800-3,700
vph westbound. In the AM peak, approximately 530 vehicles travel
northbound on Boundary Channel Drive. In the PM peak, approximately 330
vehicles travel northbound on Boundary Channel Drive. If the northbound
I-395 ramp to northbound GWMP were eliminated, approximately 290
vehicles would be displaced to eastbound VA 27 during the AM peak
period. Of that total, approximately 232 would access VA 27 directly
from I-395 while about 58 vehicles would be displaced from I-395 to
northbound Boundary Channel Drive to VA 27. This would increase
eastbound AM peak traffic on VA 27 by approximately 15% and on
northbound Boundary Channel Drive by 11%. In the PM peak hour, 240
vehicles would be displaced to eastbound VA 27. Of that total,
approximately 106 vehicles access VA 27 from I-395 and 134 vehicles
would access VA 27 via I-395 and northbound Boundary Channel Drive
during the PM peak period. The displacement of traffic would increase PM
peak traffic by about 12% on VA 27 and by about 41% on Boundary Channel
Drive.

As with the proposed southbound GWMP to southbound I-395 ramp closure,
in order to maintain consistency in traffic movement, both that ramp and
the northbound I-395 ramp to northbound GWMP should either remain or be
removed. This is based on driver expectancy of the same return trip to
an interstate once their vehicle has exited from the Interstate.

## Bicycle and Pedestrian Facilities

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-13 .unnumbered}

There are no pedestrian/bicyclist facilities associated with this ramp.
The Mt. Vernon Trail and other pedestrian/bicycle facilities within the
Study Area, as well as related safety deficiencies, would remain in
their current condition.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-13 .unnumbered}

This alternative does not involve any modifications to the Mt. Vernon
Trail or other pedestrian/bicycle facilities. The existing facilities
would remain in their current condition.

## Historic and Cultural Resources

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-14 .unnumbered}

No impact to historic or cultural resources is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-14 .unnumbered}

No impact to historic or cultural resources is anticipated by the
closure of this ramp.

## Aesthetics and Viewsheds

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-15 .unnumbered}

The aesthetic condition and viewshed of the GWMP and adjacent historic
resources would remain in their current condition.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-15 .unnumbered}

Although not a prominent visual element of the parkway, the closure of
the ramp, removal of ramp pavement and revegetation of the area would
have a minor, positive impact on the aesthetic condition of the GWMP.

## Land Use

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-16 .unnumbered}

No change to existing land use patterns is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-16 .unnumbered}

No change to existing land use patterns is anticipated to result.

## Biological Resources

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-17 .unnumbered}

##### Vegetation {#vegetation-9 .unnumbered}

No change to existing vegetation would result.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-9 .unnumbered}

No change to existing wildlife is anticipated.

##### Wetlands {#wetlands-9 .unnumbered}

No impact to wetland resources is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-17 .unnumbered}

##### Vegetation {#vegetation-10 .unnumbered}

Once the ramp is closed, the existing pavement would be removed and the
area re-vegetated. The ramp area would likely be planted with turf
grass, consistent with the treatment of the adjacent interchange areas.
This modification is anticipated to have a minimal benefit to existing
vegetation resources, but would increase the amount of landscaped area
by approximately 0.4 acres AC.

##### Wildlife and Threatened and Endangered Species {#wildlife-and-threatened-and-endangered-species-10 .unnumbered}

While the former ramp area would be re-vegetated, the replacement turf
grass cover provides minimal wildlife value and is not anticipated to
have any effect on existing wildlife communities.

##### Wetlands {#wetlands-10 .unnumbered}

No impact to wetland resources is anticipated.

## Water Resources

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-18 .unnumbered}

##### Floodplains {#floodplains-9 .unnumbered}

No impact to floodplains is anticipated.

##### Coastal Zone Management {#coastal-zone-management-9 .unnumbered}

No Coastal Zone impacts are anticipated.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-9 .unnumbered}

No Chesapeake Bay impacts are anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-18 .unnumbered}

##### Floodplains {#floodplains-10 .unnumbered}

No impact to floodplains is anticipated.

##### Coastal Zone Management {#coastal-zone-management-10 .unnumbered}

No Coastal Zone impacts are anticipated.

##### Chesapeake Bay Preservation Area {#chesapeake-bay-preservation-area-10 .unnumbered}

No Chesapeake Bay impacts are anticipated.

## Physiography, Geology and Soils

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-19 .unnumbered}

No disturbance to soils is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-19 .unnumbered}

Minor soil disturbance would result from the demolition of the ramp
pavement. Erosion control measures would be incorporated to minimize
soils loss. Disturbed areas would be re-vegetated once demolition
activities are complete.

## Air Quality

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-20 .unnumbered}

No change to air quality levels is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-20 .unnumbered}

Minor increases in dust and other air emissions would result from
demolition activities associated with the removal of the ramp. Emissions
increases would be temporary in duration and would comply with the
FHWA's Standard Specifications for Construction of Roads and Bridges on
Federal Highway Projects (1996) and with applicable local, state and
federal regulations.

## Noise

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-21 .unnumbered}

No change in existing noise sources or noise levels is anticipated.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-21 .unnumbered}

Existing noise levels would increase temporarily during the demolition
of the existing ramp. The rerouting of traffic to VA 27 and Boundary
Channel Drive associated with the closure of this ramp would result in
minor increases in noise levels on those roadways, due to the additional
vehicle traffic. The increases in noise levels are not anticipated to be
significant.

## Hazardous Materials and Wastes

No evidence of historical land use involving hazardous materials or
hazardous wastes was found within the Study Area. The proposed actions
would not require the disturbance or relocation of any of the existing,
recognized environmental conditions -- USTs and ASTs -- found at the
Columbia Island Marina in the Study Area. Therefore, no disturbance or
generation of hazardous materials or hazardous wastes are anticipated to
occur with either the implementation of any of the safety improvements
or under "no-action" conditions.

## Energy

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-22 .unnumbered}

No change in energy consumption is anticipated.

### 2. Preferred Alternative: Close Ramp {#preferred-alternative-close-ramp .unnumbered}

Energy consumption would temporarily increase during demolition of the
ramp. No significant change in long-term energy consumption is
anticipated.

## Socioeconomic and Community Features

### 1. No Action: Keep Ramp Open {#no-action-keep-ramp-open-23 .unnumbered}

No change to socioeconomic or community features is anticipated. The
public would continue to be exposed to the safety hazards associated
with the current GWMP transportation and circulation systems.

### 2. Deferred Alternative: Close Ramp {#deferred-alternative-close-ramp-22 .unnumbered}

Construction jobs associated with the demolition of the ramp would have
a short-term benefit to local construction workers and the local
economy. In the long term, motorists would be rerouted to more heavily
traveled alternate routes, VA 27 and Boundary Channel Drive/Jefferson
Davis Highway, where they would experience increased traffic volumes and
slightly less direct routing to their final destinations.

## Cumulative Impacts

The proposed ramp closure is not anticipated to contribute to
significant cumulative impacts in the vicinity of the Study Area.

## Comparison of Alternatives

A comparison of the No Action Alternative and the Preferred Build
Alternative is provided in Table 7.

# Mitigation

## Historic and Cultural Resources

In order to prevent potential adverse impacts to historic resources, the
FHWA EFLHD and the NPS initiated coordination with the Advisory Council
on Historic Preservation (Advisory Council) and the Virginia and
District of Columbia State Historic Preservation Offices (SHPO).
Consultation has also taken place with the District of Columbia
Commission of Fine Arts and the National Capital Planning Commission.

A memorandum of agreement (MOA) would be developed between the FHWA,
NPS, Advisory Council and District of Columbia and Virginia SHPO's to
address impacts to the GWMP historic resource as a result of the
implementation of the preferred safety improvement alternative(s).
Potential impacts include the construction of the new marina entrance
and bridge over Boundary Channel Drive, demolition of the Humpback
Bridge over Boundary Channel and replacement-in-kind with a new bridge,
alteration of circulation patterns adjacent to the Humpback Bridge and
Navy-Marine Memorial, and removal of historic plantings. The design of
the proposed safety improvements, construction plans and details would
be executed in conjunction with the terms and conditions of the MOA.

## Vegetation

In order to minimize any adverse impacts to vegetation, the preferred
alternative safety improvements have been located to minimize the
removal of trees and other vegetation necessary to accomplish the
proposed action. Trees and other plants located adjacent to construction
areas would be protected to minimize impacts to them. Landscape plans
would be developed to restore and stabilize the cleared or disturbed
areas. Adverse impacts to the remaining original GWMP plantings and the
historic planting plans would be coordinated with the Advisory Council
and the Virginia and District of Columbia SHPO's. Impacts to the
cultural landscape would be addressed in a MOA between the FHWA, NPS,
Advisory Council and the two SHPO's.

## Wetlands and Water Resources

The proposed safety improvements would be constructed in accordance with
applicable Commonwealth of Virginia and District of Columbia stormwater
management, sedimentation and erosion control and other water quality
protection laws and policies. Safety improvements implemented in areas
under the jurisdiction of the Commonwealth of Virginia would comply with
state Coastal Zone policies to the maximum extent practicable.

Construction activities would comply with the conditions of Section 401
and 404 of the Clean Water Act, if necessary. Permits would be obtained
from the U.S. Army Corps of Engineers for filling within the Boundary
Channel wetland and construction within the 100-year floodplain. Bridge
permits would also be obtained from the U.S. Coast Guard for the
construction of the new bridges across Boundary Channel (i.e., Humpback
Bridge replacement and new marina entrance bridge). The proposed action
would also comply with applicable state and local permit requirements.

Implementation of the preferred safety improvements would result in a
net decrease in impervious surface cover within the Study Area. Areas of
excess roadway pavement and other paved areas along the GWMP and at the
Columbia Island Marina would be removed in conjunction with the proposed
modifications.

## Socio-economic and Public Use and Enjoyment

In order to minimize disruption to commuters and other users of the
GWMP, measures would be taken to maintain access to the GWMP, the Mt.
Vernon Trail, Columbia Island Marina, the Navy-Marine Memorial and other
areas affected by the implementation of the proposed safety improvements
and construction activities. Measures include the provision of a
temporary road, trail and bridge across Boundary Channel during the
replacement of the Humpback Bridge to maintain traffic flows on the GWMP
and pedestrian/bicycle traffic on the Mt. Vernon Trail. Temporary
reductions in roadway or trail widths or closures of segments of the Mt.
Vernon Trail may, however, be necessary in order to complete the
proposed modifications. Any closures or other potential impacts would be
scheduled to occur during off-peak times, to minimize impacts on GWMP
traffic.

The proposed replacement bridge would maintain the same vertical
clearance between the water surface and the bridge as the existing
Humpback Bridge. While water access to the Columbia Island Marina via
Boundary Channel would be maintained during the proposed replacement of
the Humpback Bridge, clearance beneath the bridge would be temporarily
reduced due to the placement of concrete formwork and scaffolding
necessary for construction. Periodic, temporary closures of the inlet
may also be required due to demolition or other construction activities.

# Environmentally Preferred Alternative

The environmentally preferred alternative is determined by applying the
criteria suggested in the National Environmental Policy Act of 1969
(NEPA), which is guided by the Council on Environmental Quality (CEQ)
regulations. CEQ regulations provide direction that the "environmentally
preferred alternative is the alternative that would promote the national
environmental policy as expressed in NEPA's Section 101. Generally, this
means the alternative that causes the least damage to the biological and
physical environment. It also means the alternative that best protects,
preserves and enhances historic, cultural and natural resources."[^7]

## Columbia Island Marina

The No Action Alternative, which maintains the status quo regarding the
Columbia Island Marina entrance location and configuration, is the
environmentally preferred alternative since it provides for the
preservation of the GWMP's historic, cultural, and natural resources and
maximizes protection of the biological and physical environment. The No
Action Alternative does not, however, address the purpose and need for
the proposed action. The safety of Parkway and Mt. Vernon Trail users
would still be at risk and the accident potential at the marina entrance
would not be addressed. Although the Preferred Alternative, Construction
of a New Columbia Island Marina Entrance, would impact historic and
cultural resources, vegetation and wetland/water resources in the Study
Area, it would eliminate the safety concerns associated with the
existing marina entrance location and configuration. Excess pavement
within the marina area would also be removed as part of the Preferred
Alternative, which would reduce the amount of impervious surface cover
in this part of the GWMP. It is believed that through the use of
mitigation and best management practices, any environmental effects
related to the implementation of the Preferred Alternative would be
minimized and no significant impacts would result.

## Southbound I-395 Ramp to Northbound GWMP, Humpback Bridge and Pedestrian Crossing of the GWMP

The No Action Alternative, which maintains the status quo regarding the
southbound I-395 ramp to northbound GWMP, the Humpback Bridge and
pedestrian crossings of the GWMP, is the environmentally preferred
alternative since it provides for the preservation of the Parkway's
historic, cultural, and natural resources and maximizes protection of
the biological and physical environment. The No Action Alternative does
not, however, address the purpose and need for the proposed action. The
safety deficiencies and accident potential of the GWMP access ramp would
not be addressed. Likewise, the safety concerns associated with the
existing at-grade pedestrian crosswalk would remain. The Preferred
Alternative, which would replace the Humpback Bridge with a wider bridge
that would include a northbound acceleration lane for the GWMP access
ramp, a wider Mt. Vernon Trail and new trail connections to
grade-separated pedestrian underpasses beneath the bridge, would impact
historic and cultural resources, vegetation and wetland/water resources
in the Study Area. It would also, however, correct safety deficiencies
related to the design of the existing access ramp and Humpback Bridge
and provide a safer, more convenient pedestrian connection between the
east and west sides of the GWMP.

The inclusion of the pedestrian underpasses in the bridge design and new
trail segments would provide a direct connection between the Mt. Vernon
Trail and other bicycle/pedestrian trail resources adjacent to the Study
Area in Arlington County that minimizes the trail users interaction with
motor vehicles. Removal of the small parking lot serving the Navy-Marine
Memorial and excess pavement along the mainline GWMP, recommended in the
Preferred Alternative, would reduce the amount of impervious surface
cover in this segment of the GWMP. It is believed that through the use
of mitigation and best management practices, any environmental effects
related to the implementation of the Preferred Alternative would be
minimized and no significant impacts would result.

## Southbound GWMP Ramp to Southbound I-395

The NPS has deferred the selection of a preferred alternative or
action/no action for the proposed ramp closure until the completion of a
more extensive evaluation by the FHWA of the I-395 corridor in Virginia
and the District of Columbia.

## Northbound I-395 Ramp to Northbound GWMP

The NPS has deferred the selection of a preferred alternative or
action/no action for the proposed ramp closure until the completion of a
more extensive evaluation by the FHWA of the I-395 corridor in Virginia
and the District of Columbia.

# Commitments and Resources

## Irreversible and Irretrievable Commitment of Resources

The implementation of the preferred alternatives would result in the
irreversible and irretrievable commitment of federal funds, for the
planning, design and construction of the proposed actions. Congress has
authorized approximately \$23.6 million for the planning, design and
construction of the proposed actions. If it is determined the preferred
alternative(s) would not result in significant environmental impacts,
construction would begin in October 2003.

Resources in the form of construction materials and labor, fuels and
other energy sources for vehicles and equipment would also be committed
with the implementation of the preferred alternatives.

## Unavoidable Adverse Environmental Effects

The implementation of the preferred alternatives would result in
unavoidable construction-related impacts to: GWMP circulation and
traffic; vegetation; floodplains; soils; local air quality; and noise
levels. Most of these impacts are anticipated to of temporary duration
and of minor intensity.

Long-term permanent impacts to historic resources, viewsheds, wetlands,
and traffic patterns would also result. The Humpback Bridge, a
contributing element of the GWMP historic resource, would be demolished.
The character of the GWMP historic resource would be altered by the
construction of the new GWMP bridge across Boundary Channel as well as
the construction of a new entrance bridge to the Columbia Island Marina.
The viewsheds of the Pentagon and LBJ Memorial Grove would also be
altered by the introduction of the new bridges. Views westward across
the Potomac River from the Washington, DC monumental core would also be
similarly affected. Construction of the replacement GWMP bridge across
Boundary Channel would also result in the permanent loss of
approximately 1,400 SF of wetlands and the temporary loss of an
additional 900 SF of wetland area. Finally, local traffic patterns on
the GWMP, I-395, VA 27 and Boundary Channel Drive would be altered if
the proposed ramp closures were implemented. Direct access between
northbound I-395 and northbound GWMP and between southbound GWMP and
southbound I-395 would be eliminated. Traffic volumes on the alternative
routes -- VA 27 and Boundary Channel Drive -- would increase. Eastbound
VA 27 volumes would increase moderately, by approximately 15% in the AM
peak and 12% in the PM peak. Westbound VA 27 volumes would have minor
increases of 2% in the AM peak and 1% in the PM peak. Northbound
Boundary Channel Drive volumes would increase by approximately 11% in
the AM peak and 41% in the PM peak. Southbound volumes would increase
moderately by 15% and 16% in the respective peak periods.

## Local Short-Term Uses and the Maintenance and Enhancement of Long-Term Productivity

While the implementation of the preferred alternatives would require a
significant, short-term investment of construction dollars and
materials, in the long-term, the safety of motorists, pedestrians,
bicyclists and others using the GWMP would be enhanced. Long-term
accident rates for this segment of the GWMP, identified as a high
accident location, would be anticipated to decline. Maintenance costs
associated with the 70-year-old Humpback Bridge would also be reduced
with the construction of the new GWMP bridge over the Boundary Channel
inlet. The anticipated life of the new structure is 75 to 100 years,
compared to the estimated 25-year remaining life of the Humpback Bridge.

# Compliance with Environmental Regulations and Plans

There is no General Management Plan in force for the GWMP. The
Capper-Cramton Act, the GWMP enabling legislation, defines three major
roles for the park:

1.  To preserve the Potomac River shoreline from pollution and
    commercial development;

2.  To provide for a variety of recreational needs of the Washington, DC
    metropolitan area; and

3.  To provide a scenic memorial roadway to the nation's capital and the
    Mt. Vernon estate.

It is the current mission of the GWMP to protect those values and the
unique character of the Parkway.

Ensuring the GWMP is maintained and operated in a safe manner supports
its continued use and enjoyment as a scenic, recreational and
transportation resource. Maintenance activities must, however, also be
sensitive to the natural features and resources that are the setting for
the parkway and its recreational functions. The proposed actions would
be undertaken consistent with the following regulations and plans.

## National Park Service Organic Act of August 25, 1916

This act states that the fundamental purpose of national parks is "to
conserve the scenery and the natural and historic objects and the
wildlife therein and to provide for the enjoyment of the same in such
manner and by such means as will leave them unimpaired for the enjoyment
of future generations".

## National Environmental Policy Act (NEPA)

This environmental assessment (EA) and resultant decision documents
provide disclosure of the decision-making process and potential
environmental consequences of the alternatives. This EA will be
available for a 30-day public review and comment period, after which the
NPS would decide if the proposed action is significant enough to prepare
an environmental impact statement (EIS). If an EIS is not required, the
NPS National Capital Region Director and the FHWA Eastern Federal Lands
Highway Division Engineer would jointly sign a Finding of No Significant
Impact (FONSI). Together this EA and the FONSI would conclude the NEPA
compliance process for this project.

All comments and/or questions can be directed to either:

Jack Van Dop

Environmental Specialist

Federal Highway Administration

Eastern Federal Lands Highway Division

21400 Ridgetop Circle

Sterling, VA 20166-6511

FAX (703) 404-6217

Audrey Calhoun

Superintendent

George Washington Memorial Parkway Unit

National Park Service

Turkey Run Park

McLean, VA 22101

FAX (703) 289-2598

## National Historic Preservation Act of 1966

This act requires federal agencies to establish programs for evaluating
and nominating properties to the National Historic Register of Historic
Places. Section 106 of the act mandates that federal agencies take into
account the effects of their actions on properties listed on the
National Register or eligible to be listed and to give the Advisory
Council on Historic Preservation a reasonable opportunity to comment on
said actions, if appropriate.

The FHWA and NPS have consulted with the Advisory Council on Historic
Preservation and District of Columbia and Commonwealth of Virginia State
Historic Preservation Officers (SHPO) regarding the proposed actions and
would complete any proposed safety improvements in accordance with
National Register of Historic Places standards and criteria. A
memorandum of agreement (MOA) would be executed between the FHWA, NPS,
Advisory Council on Historic Preservation and DC and Virginia SHPO
specifying the conditions under which the proposed actions would be
implemented and mitigation measures necessary for the project.

## Clean Water Act of 1972, as Amended

The act seeks to restore and maintain the chemical, physical, and
biological integrity of the nation's water by a variety of means.
Section 404 of the act directs wetlands protection by authorizing the
U.S. Army Corps of Engineers to prohibit or regulate, through a permit
process, discharge of dredged or fill material into the waters of the
United States, including wetlands. Actions described in this document
would comply with the requirements of Section 404 of the Clean Water Act
and other applicable federal, state and local agencies.

Water quality in the project area would be protected by the
implementation of erosion and sediment controls, such as silt fencing,
straw bales and sediment traps, as needed. Disturbed areas would be
stabilized by reseeding and mulching. A sedimentation and erosion
control plan would be prepared as part of the construction documents for
the project(s).

Construction of the preferred new GWMP bridge over Boundary Channel
would require the permanent filling of approximately 1,400 SF of
wetlands for the bridge abutments and the temporary filling of
approximately 900 SF of wetlands for a temporary road and bridge across
Boundary Channel to maintain GWMP traffic during construction. A permit
would be obtained from the U.S. Army Corps of Engineers for the filling
activity. Temporary fill areas would be restored once construction
activities are complete.

## Executive Order 11990, Protection of Wetlands

This EO requires federal agencies minimize the destruction, loss or
degradation of wetlands, and to preserve and enhance the natural and
beneficial values of wetlands in carrying out the agency\'s mission,
including agency construction and improvement actions. If there is no
practicable alternative to the proposed action, the agency is required
to take all practicable measures to minimize harm to wetlands that may
result from the action.

The proposed GWMP bridge over Boundary Channel (Humpback Bridge
replacement) would require the permanent filling of approximately 1,400
SF of wetlands and the temporary filling of approximately 900 SF of
wetland area. No alternative exists to carry the mainline GWMP across
the Boundary Channel inlet. The bridge would be constructed in the same
general location as the existing bridge and would incorporate design
features to minimize the amount of filling required. Due to its use as a
major commuter route, the GWMP would remain open during construction of
the proposed replacement bridge. A temporary bridge over Boundary
Channel would also be required to maintain traffic the flow.

## General Bridge Act of 1946

This act requires the Secretary of Transportation approve the location
and plans of any bridge over navigable waters of the United States in
order to preserve the public right of navigation and to prevent
interference with interstate and foreign commerce. The Secretary of
Transportation delegated the approval and permitting authority to the
U.S. Coast Guard in 1967.

[]{.mark}

The new GWMP bridge over Boundary Channel would be constructed in the
same general location as the existing Humpback Bridge. No abutments or
other bridge elements would be constructed within Boundary Channel to
impede navigation. The boat clearance height of the existing bridge
would be maintained. A permit would be obtained from the U.S. Coast
Guard for the construction of the new GWMP bridge over Boundary Channel
to replace the Humpback Bridge. A bridge permit would also be required
for the construction of the Columbia Island Marina entrance bridge over
Boundary Channel.

## Executive Order 11988, Floodplain Management

This executive order (EO) requires federal agencies determine whether
proposed actions, including construction and improvements, would occur
in a floodplain. If the proposed action is located in a floodplain, the
agency is required to consider alternatives to avoid adverse effects and
incompatible development in the floodplains. If there is no practicable
alternative to siting in a floodplain, the agency is required to design
or modify its action in order to minimize potential harm to or within
the floodplain.

The proposed new GWMP bridge over Boundary Channel (Humpback Bridge
replacement) and the proposed Columbia Island Marina entrance bridge
over Boundary Channel are both sited within the 100-year floodplain. No
alternative exists to carry the mainline GWMP across the Boundary
Channel inlet. The bridge would be constructed in the same general
location as the existing bridge and would incorporate design features to
withstand flooding impacts. The bridge roadway would be elevated above
the 100-year flood level. While the proposed Columbia Island Marina
entrance bridge is located within the 100-year floodplain, the existing
parking lot, docks and marina support facilities are also located within
the floodplain. In the event of a flood, the use of marina facilities
would be limited and access potentially prohibited as a safety measure.
Emergency access and egress would be possible via the GWMP.

## Endangered Species Act of 1973

Section 7 of the Endangered Species Act directs all federal agencies to
use their authority in furtherance of the purposes of the act by
carrying out programs for the conservation of rare, threatened and
endangered species. Federal agencies are required to consult with the
U.S. Fish and Wildlife Service to ensure that any actions authorized,
funded and/or carried out by the agency do not jeopardize the continued
existence of any listed species or critical habitat.

There are no state or federally listed rare, threatened or endangered
species known to inhabit the project area. Informal consultation
pursuant to the Endangered Species Act was initiated via a letter
request to the U.S. Fish and Wildlife Service, Chesapeake Bay Field
Office.

## Interrelationship with Other Plans and Projects

A review was conducted of plans and reports developed by other agencies
to help identify any proposed projects or activities with the potential
to impact this study's findings and recommendations. The following
reports and studies that were assessed as part of this review.

-   The October 2001 *Designing for Security in the Nation's Capital*
    report, developed by an Interagency Task Force of the National
    Capital Planning Commission (NCPC), made recommendations for safety
    and security.

-   The *Arlington County Master Transportation Plan* was adopted by the
    County in 1986 and is an element of the Arlington County
    Comprehensive Plan.

-   The *Arlington County Bicycle Transportation Plan*, completed in
    1994, is a revision of the bicycle transportation elements contained
    in the 1986 Master Transportation Plan.

-   The *Comprehensive Plan for the National Capital Parks, Open Space,
    and Natural Features Element Update*, was developed by the NCPC and
    was adopted in 2001. It established federal planning policies and
    recommendations related to parks, open spaces and natural features.

-   The report, *Paved Recreation Trails of the National Capital
    Region,* provided recommendations for improvements and coordination
    for a multi-use trail system. The National Park Service prepared the
    1990 document.

-   The *Memorials and Museum Master* establishes policies for the
    siting and design of new memorials throughout the District of
    Columbia. The 1997 *Plan* is a collaborative effort of the National
    Capital Planning Commission, the Commission of Fine Arts and the
    National Capital Memorial Commission.

The section below identifies projects and policies included within the
reports with the potential to impact the project areas.

### 1. *Paved Recreation Trails of the National Capital Region* {#paved-recreation-trails-of-the-national-capital-region .unnumbered}

-   G10: Widen the Mount Vernon Trail wherever possible to 10 feet, or
    at least 8 feet. In areas of heaviest use (near the city center and
    major bridges) widen to 12 feet.

-   G20: This is identified as a top priority project. If the Boundary
    Channel or Humpback Bridge is rebuilt, accommodate trail access from
    all four quadrants as well as 12 foot wide sidewalks for trail use
    protected from vehicle traffic by appropriate barriers. Grade
    separated crossings under the Humpback Bridge with connections to
    the marina and to the Pentagon/Arlington County. Night lighting for
    safety.

-   G34: Work with the General Services Administration, the Defense
    Department, Arlington County, and others as necessary to complete
    both a north-south and an east-west trail route near the Pentagon.

### *2. Arlington County Master Transportation Plan* {#arlington-county-master-transportation-plan .unnumbered}

The Plan identifies needs for new or improved pedestrian and biking
trails, including the following in the study area.

-   Columbia Island/Lady Bird Johnson Park: A connection would be
    provided to the Potomac shoreline and the Mount Vernon Trail by
    using the existing pedestrian bridge across Boundary Channel to
    Columbia Island and the LBJ Grove in the District of Columbia.

### *2. Arlington County Bicycle Transportation Plan* {#arlington-county-bicycle-transportation-plan .unnumbered}

The Plan includes projects for the GWMP as identified in the NPS *Paved
Recreation Trails of the National Capital Region* report to eliminate
barriers to bicycles and link regional activity centers.

-   No. 2: Bicycle underpass on the southern side of the Humpback
    Bridge.

-   No. 3: A Columbia Pike-Pentagon-Boundary Channel connector bicycle
    route via the south side of the Boundary Channel lagoon and the
    Humpback Bridge underpass.

-   No. 4: A GWMP crossing via a bicycle-pedestrian overpass in the
    vicinity of the RF&P railroad bridge linking the Mt. Vernon Trail
    with Old Jefferson Davis Highway and Boundary Channel Drive.

### 3. *Comprehensive Plan for the National Capital Parks, Open Space, and Natural Features Element Update* {#comprehensive-plan-for-the-national-capital-parks-open-space-and-natural-features-element-update .unnumbered}

The NCPC plan includes the following policies:

-   Natural shoreline areas in the National Capital Open Space System
    should be retained in their natural condition or be appropriately
    landscaped for a distance of 150 to 200 feet from the water's edge,
    if possible.

-   Existing large parking areas, such as the Pentagon's north parking
    lot along Boundary Channel, should be removed as soon as possible
    and the areas restored to a landscaped condition with active or
    passive recreational uses.

-   The GWMP should be maintained as a scenic historic landscape
    corridor, serving not only as a spectacular gateway artery to the
    Nation's Capital but also preserving its important historic
    associations.

### 4. *Memorials and Museum Master Plan* {#memorials-and-museum-master-plan .unnumbered}

-   A candidate memorial site was identified at a location described as
    the "Virginia side of the 14^th^ Street Bridge near the location of
    the old Twin Bridges Marriott.

# List of Preparers

**Federal Highway Administration**

Jack Van Dop, Environmental Specialist

Hala Elgaaly, P.E., Bridge Engineer

**George Washington Memorial Parkway**

Audrey Calhoun, Superintendent

Jacqueline Lavelle, Concessions Specialist

Matt Virta, Cultural Resource Manager

Ann Brazinski, Natural Resource Manager

Tim Buechner, Historical Architect

**Parsons, Brinckerhoff, Quade and Douglas, Inc.**

Timothy Ramey, P.E., Project Manager

Christine Hoeffner, AICP, ASLA, Lead Planner

Kristin Belfield, Transportation Engineer

Jessica Juriga, Civil Engineer

John Michels, P.E., Structural Engineer

**Applied Environmental, Inc.**

David S. Rosa, P.E., Environmental Engineer

# Public Involvement and Coordination

## Public Involvement

In accordance with NPS Director's Order No. 12, Conservation Planning,
Environmental Impact Analysis, and Decision-making and NPS-12, Handbook
to Director's Order 12, efforts have been made to involve the interested
and affected public in the planning and preliminary design of the
proposed action(s) and the environmental assessment process.

Initial public meetings were held in June 2001 for scoping purposes and
to generate public interest and public comments. Fourteen people
attended the first meeting, held in Arlington County, VA, and five
people attended the second meeting, held in the District of Columbia.

In addition, a newsletter announcing the initial public meetings and
identifying the areas of the GWMP under investigation was mailed to
members of the public and other organizations with interest in the
study. The mailing list from the newsletter was compiled from names
provided by the NPS, GWMP unit, the FHWA Eastern Federal Lands Highway
Division, and Arlington County Department of Public Works. Material was
also published on the World Wide Web sites of the NPS and FHWA. Requests
for comments were included in both the newsletter and the web site.
Written comments obtained through the public involvement process are
summarized in Appendix F.

The EA will be made available for review to the interested and affected
public, including affected agencies and tribes, for a minimum of 30
days, beginning March 28, 2002. A public meeting is scheduled for March
28, 2002 in Arlington County, VA. The purpose of the meeting is to
inform the public of the actions that have taken place since the prior
public meetings and to review the safety improvement alternatives being
evaluated by the NPS and FHWA.

## Agency Coordination

Consultation and coordination has occurred with a number of agencies and
organizations having jurisdictional approval authority relative to
proposed actions or anticipated to have a vested interest in the project
plans and decision process.

The following agencies and organizations were contacted, by letter
inquiry, for information to assist in identifying important issues,
developing alternatives, analyzing impacts and assessing interest in the
outcome of the investigations. Copies of responses received are included
in Appendix G.

-   U.S. Department of Transportation, Federal Highway Administration,
    DC Division Office

-   U.S. Department of Interior, National Park Service, National Capital
    Region

-   U.S. Fish and Wildlife Service

-   U.S. Army Corps of Engineers

-   U.S. Department of Defense, Pentagon Reservation

-   U.S. Coast Guard

-   Arlington County, Virginia, Department of Public Works

-   District of Columbia, Department of Public Works

-   District of Columbia, Office of Planning

-   District of Columbia, Department of Parks and Recreation

-   District of Columbia, Department of Health, Environmental Health
    Administration

-   DC State Historic Preservation Officer

-   Advisory Council on Historic Preservation

-   Virginia State Historic Preservation Officer

-   Virginia Department of Transportation, Northern Virginia District

-   Virginia Department of Conservation and Recreation

-   City of Alexandria, Parks and Recreation Commission

-   Arlington National Cemetery

-   National Capital Planning Commission

-   U.S. Commission of Fine Arts

-   Metropolitan Washington Council of Governments

-   Washington Metropolitan Area Transit Administration

-   Metropolitan Washington Airports Authority

-   National Trust for Historic Preservation

Meetings were held throughout the alternatives development and
evaluation process with representatives of the organizations listed
below, to keep them informed of the planning and preliminary engineering
progress and solicit informal comments on the various safety improvement
alternatives.

-   U.S. Department of Interior, National Park Service, George
    Washington Memorial Parkway Staff

-   U.S. Department of Interior, National Park Service, National Capital
    Region Staff

-   U.S. Department of Defense, Directorate of Real Estate and
    Facilities, Pentagon Reservation

-   Arlington County, Virginia, Department of Public Works

-   Arlington County, Virginia, Bicycle Advisory Committee

-   Advisory Council on Historic Preservation

-   District of Columbia State Historic Preservation Officer

-   Virginia State Historic Preservation Officer

-   National Capital Planning Commission

-   U.S. Commission of Fine Arts

-   Charles E. Smith Realty Companies

# Selected References

Applied Environmental, Inc., "Phase 1 Environmental Site Assessment,
George Washington Memorial Parkway," March 2001.

Bellomo-McGee, Inc., "14^th^ Street Bridge Corridor Improvement
Feasibility Study," Virginia Department of Transportation, August 1998.

Bellomo-McGee, Inc., "14^th^ Street Bridge Corridor Improvement
Feasibility Study, CORSIM Model," 1998.

Bellomo-McGee, Inc., "George Washington Memorial Parkway Columbia Island
Trail and Roadway Study", U.S. Department of Interior, National Park
Service, March 1986.

District of Columbia Department of Consumer and Regulatory Affairs,
Historic Preservation Division, "District of Columbia, Inventory of
Historic Sites," 1997 and October 1999 Update.

District of Columbia Department of Public Works, "Bridge Inspection
Report, I-395/George Mason Bridge/Potomac River, Bridge No. 1133,"
December 1998.

District of Columbia Department of Public Works, "Bridge Inspection
Report, I-395/Rocheambeau Bridge/Potomac River, Bridge No. 169-1, April
1999.

District of Columbia Department of Public Works, "Bridge Inspection
Report, I-395/Williams Bridge/Potomac River, Bridge No. 170-1," May
1999.

DMJM-3D/I, "Final Environmental Assessment of the Pentagon Reservation
Master Plan," Department of Defense, Washington Headquarters Service,
May 28, 1991.

EDAW, " Cultural Landscape Report, Mount Vernon Memorial Highway," U.S.
Department of Interior, National Park Service, 1986.

Federal Emergency Management Agency, "Flood Insurance Rate Map (FIRM),
District of Columbia, Washington DC," Community-Panel Number 110001
015B, November 15, 1985.

National Capital Planning Commission, "Comprehensive Plan for the
National Capital, Parks Open Space, and Natural Features Element
Update," Final Draft, 2001.

Parsons Brinckerhoff Quade and Douglas, Inc., "George Washington
Memorial Parkway Safety Improvements Existing Conditions Report", U.S.
Department of Transportation, Federal Highway Administration and U.S.
Department of Interior, National Park Service, August 2001.

Parsons Brinckerhoff Quade and Douglas, Inc., "George Washington
Memorial Parkway Safety Improvements Candidate Alternatives Report",
U.S. Department of Transportation, Federal Highway Administration and
U.S. Department of Interior, National Park Service, March 2002.

Ricondo & Associates, "Final Environmental Assessment Airport Traffic
Control Tower Site Selection and Related Terminal Improvements,"
Metropolitan Washington Airports Authority, Washington National Airport,
October 1993.

Robert Peccia and Associates, "Traffic Safety Study, George Washington
Memorial Parkway, Virginia, Washington, DC, Maryland," U.S. Department
of the Interior, National Park Service, August 1998.

U.S. Department of the Interior, National Park Service, "Historic
Resource Study, Rock Creek and Potomac Parkway, George Washington
Memorial Parkway, Suitland Parkway, Baltimore-Washington Parkway",
January 1990.

U.S. Department of Transportation, Federal Highway Administration,
"Bridge Inspection Report, George Washington Memorial Parkway over
Boundary Channel (Humpback Bridge), Structure No. 3300-020P."

U.S. Department of Transportation, Federal Highway Administration,
"Engineering Study for George Washington Memorial Parkway," Volume 1:
Summary and Report, Volume 2: Appendices A & B (excerpts), Volume 3:
Appendices C to G (excerpts), May 15, 1989.

U.S. Department of Transportation, Federal Highway Administration,
"Columbia Island Conceptual Study, George Washington Memorial Parkway,"
February 1993, revised March 1994 and May 1994.

U.S. Department of Transportation. Federal Highway Administration.
Engineering Study for Roads and Bridges, George Washington Memorial
Parkway, Volume 1 of 2. April 1999.

U.S. Department of Transportation, Federal Highway Administration,
"Feasibility Study of Measures to Improve the Safety, Capacity and
Operation of the 14^th^ Street Bridge on I-395 and the I-395 and George
Washington Memorial Parkway Interchange," March 1986.

U.S. Department of Transportation, Federal Highway Administration,
"Highway Traffic Noise in the U.S., Problem and Response," April 2000.

Virginia Department of Transportation, "Bridge Inspection Report,
I-395/George Washington Memorial Parkway, Structure No. 2004" (SBL),
April 6, 2000.

Virginia Department of Transportation, "Bridge Inspection Report,
I-395/George Washington Memorial Parkway, Structure No. 2050" (NBL),
July 21, 2000.

[^1]: The initial Mt. Vernon Highway segment of the GWMP, from the
    Arlington Memorial Bridge to Mt. Vernon, was listed on the National
    Register in 1981. The remaining portions of the GWMP were listed on
    the National Register in 1995.

[^2]: 16 USC 1453

[^3]: Public Law 106-113.

[^4]: The use of the term pedestrian applies to all users of the GWMP
    and its trails: walkers and joggers, bicyclists and others.

[^5]: State laws and policies applicable to the proposed action include:
    Virginia Marine Resources Commission, Subaqueous Lands Management
    and Wetlands Management regulations; Virginia Department of
    Conservation and Recreation, Non-point Source Pollution Control
    regulations; and Chesapeake Bay Preservation Act regulations.

[^6]: U.S. Department of Transportation, Federal Highway Administration.
    *Traffic Noise in the United States: Problem and Response*. April
    2000.

[^7]: "Forty Most Asked Questions Concerning CEQ's National
    Environmental Policy Act Regulations" (40 CFR 1500-1508), Federal
    Register Vol. 46, No. 55, 18026-18038, March 23, 1981.