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1991 CA/T FSEIS
U.S. Department of Transportation, Central Artery
(Interstate 93)/Third Harbor Tunnel (Interstate 90) Project,
Boston, Massachusetts: Final Supplemental Environmental
Impact Statement (Boston: Mass. Dept. of Public Works,
January 1991), pp. 8-13.
Background: The following extract from the FSEIS
explains the reasons the state chose Scheme
Z as the final design for the Charles River
crossing.
3 PROJECT CHANGES AND
REFINEMENTS
Since 1985, the design of the Preferred Alternative has
been developed to improve traffic operations, to mitigate
potential impacts further, and to address issues identified
for further design study in the approved 1985 FEIS/R. The
Final SEIS describes the alternative designs considered
after the approved 1985 FEIS/R in developing the Proposed
Action. Part II of this Final SEIS contains a detailed
analysis of the three major changes -- Area North of
Causeway Street (crossings of the Charles River), South
Boston Bypass Road, and toll plaza relocation -- along with
a comprehensive evaluation of alternatives considered for
materials disposal.
This Final SEIS describes design changes since the
approved 1985 FEIS/R and further design refinements since
the Draft SEIS/R. The effort since publication of the Draft
SEIS/R has been to focus on those major issues that have
been of concern throughout the lengthy project review
process that began nearly 9 years ago. Two of those issues
-- the Charles River crossing and materials disposal at
Spectacle Island -- have generated the most public and
agency review comments, and the plans for both have been
substantially improved since the Draft SEIS/R.
3.1 Area North Of Causeway
Street/Charles River Crossing
Since the Draft SEIS/R, design refinements have resulted
in fewer impacts to the river and both its north and south
banks. In response to the U.S. Coast Guard, USACE, and other
agency and public comments, long-span bridges have been
incorporated into the design (see Figure S.2), reducing the
number of support piers in the river (see Figure S.3). (See
also Sections 14.2.1 and 14.3.1 of the 1990 FSEIR.) The
northbound Ramp W-CN has been eliminated, reducing the
overall bulk and size of the river crossing. Ramp CS on the
north bank has been relocated to eliminate encroachment of
this ramp on the Charles River and to facilitate
construction of the proposed riverside walkway/bikeway in a
sunlit rather than shaded area.
3.1.1 Alternatives
Considered
Overview. The Charles River crossing is one of the three
major design changes since the approved 1985 FEIS/R. Part II
of the 1990 FSEIR contains a complete analysis of design
alternatives for this area, including full environmental
analyses of the most promising options. This area also is
one of the subjects of Part III of the 1990 FSEIR which
includes the Final Section 4(f) Evaluation. A total of 32
design options for connections between the Central Artery
and Leverett Circle/Storrow Drive were considered for
overall viability. In 31 of the options, 1-93 is carried on
new bridges across the Charles River and the Central Artery
North Area Project (CANA) ramps provide connections between
1-93 and Route 1. An all-tunnel concept also was developed.
It was determined to be not workable because of the
following reasons: construction of mainline tunnels appears
to entail a high risk of damage and prolonged disruption to
the Orange Line tunnel; the weaving sections on 1-93 would
be shorter than the current high-level bridge weaves which
are being improved by CANA; there would be serious conflicts
with commuter rail lines in Charlestown; and there would be
major construction conflicts with Charles River navigation
and North Station rail service, The all-tunnel scheme does
not avoid parkland and has major construction impacts on
parks; it would also add at least $1.2 billion to the
project cost. A more detailed discussion of the assessment
of the all-tunnel alternatives is contained in Section 6.2.8
of this Final SEIS.
After the Draft SEIS/R, attention focused on the
comparison between two schemes, T Modified and Z Modified,
as a result of public and review agency comments.
Alternative T Modified (Charles River tunnel concept) uses
tunnel connections behind North Station to connect Storrow
Drive with the downtown Artery and makes the connections to
the north in a tunnel under the Charles River. Alternative Z
Modified (viaduct concept), the Proposed Action, makes both
the northbound and southbound connections on viaduct on the
north side of the river. These options were first examined
in the Draft SEIS/R as to their constructibility, effects on
traffic and transportation, and impacts on Charles River
open space and other environmental resources. Both schemes
relocate the main river crossing near the railroad crossing
to North Station and remove the existing 1-93 bridge. This
alignment of mainline bridges concentrates transportation
facilities in a narrower corridor allowing the expansion of
Paul Revere Landing Park, but it affects the Millers River
as a result. Z Modified minimizes conflicts with pedestrian
access to the MDC locks walkway at the new Charles River dam
from Causeway Street, while T Modified has a highway exit
ramp between the MBTA station and the park entrance. On the
north bank of the Charles River, neither of the options
would substantially impede pedestrian circulation on a
permanent basis; the Z Modified alignment would cover a
broader area than T Modified, but both schemes have
essentially the same functional effect on public use of the
Charles River and its open space corridor (see Figure
S.4).
During the construction period, all of the options would
result in temporary disruptions of pedestrian circulation at
various locations for short periods of time; T Modified
would result in a major negative construction period impact
to the Charles River. Scheme Z Modified is the most
constructible solution involving substantially less
disruption to vehicular and commuter railroad traffic than
other alternatives.
Z Modified provides the best overall solution to traffic
operations and is the only scheme that provides adequate
mainline weaves between the Sumner/Callahan Tunnels and
Storrow Drive. As described in the Section 4(f) Evaluation,
scheme Z Modified is functionally equivalent to scheme T
Modified with regard to the 4(f) properties affected, while
T Modified has major park access impacts at Causeway Street
and substantially worse construction period impacts on
parkland. Z Modified has lesser overall land use impacts and
essentially the same long-term aquatic resource impacts to
the Millers and Charles Rivers and to other impact
categories. Z Modified has substantially fewer construction
period impacts to transportation facilities and aquatic
resources. Through a comprehensive mitigation program, the
Proposed Action will result in a substantially improved
Charles River corridor as well as a better transportation
system.
3.12 Mitigation
A comprehensive mitigation plan for effects of the
project in this area, particularly on parklands, has been
developed to go along with the design modifications that
have directly reduced those impacts. The Department and the
MDC have agreed on these comprehensive measures. The MDC
will take a lead role in the planning, design, construction,
ownership, and management of the new parklands created. A
Citizens Advisory Committee and Bridge Design Review
Committee will participate actively in further detailed
design.
Specific portions of the mitigation are compensation
measures for impacts on previous CANA project commitments
(see Figure 3.5). They are: the acquisition of private land
on the north bank of the Charles River; a pedestrian
connection under the North Washington Street bridge to Tudor
Wharf; walkways across the MBTA railroad bridge; an improved
path along the Charles River and redeveloped entrance to the
Millers River; and improvement of the areas underneath the
viaducts, with access from Rutherford Avenue.
Other portions of the mitigation commitment address
Artery/Tunnel Project impacts on the extension of the park
corridor, both in specific locations and as a whole. They
include the improvements to bridge and ramp designs
mentioned in Section 3.1, above. Noise barriers will be
incorporated, subject to design review.
- Paul Revere Landing Park, south bank, will be
reconfigured and expanded south to Causeway Street and
east to Lovejoy Wharf, where walkways and ferry terminals
will be constructed. The new south bank pedestrian
environment will extend upstream under the bridges as far
as the MBTA walkways, and a structure under the bridges
will house an active use such as a visitors center or
food vending. A new Portal Plaza will be created on
Causeway Street, and a pedestrian underpass will be
provided at the North Washington Street bridge from
Lovejoy Wharf to the North End Park.
- Paul Revere Landing Park, north bank, will be
reconfigured, restored, enhanced, and expanded westward
to the new highway bridge and a pedestrian underpass to
Tudor Wharf provided. The Department will pay for master
planning of the Charles River Basin extension and will
pay for the design and construction of new parks on the
MDC-owned Nashua Street and GSA parcels and the newly
acquired north bank waterfront. Many improvements will be
made prior to highway construction. The MDC maintenance
facility will be relocated from the GSA parcel.
- Leverett Circle will be reconfigured, relandscaped,
and enlarged. Pedestrian overpasses will be reconstructed
with one or two new overpasses on the Nashua Street
parcel. Historic buildings will be improved at the old
dam, and site improvements including new walkways will be
made on each side.
- MBTA pedestrian walkways will be extended on each
side of the railroad bridge, and a pedestrian bridge will
be provided from O'Brien Highway, under the arches of the
MBTA Green Line viaduct to the GSA parcel.
- A 100-foot-wide strip of private river front land in
the North Point area will be acquired and developed as
parkland. As indicated by master planning, the MBTA
bridge stub will be improved as a park or removed from
the river. A 100-foot buffer zone will be created next to
the loop ramps.
- Improvements to the Charles River lagoons for skating
and swimming will be studied, and Lee Pool will be
improved and enlarged.
- The Longfellow Bridge will be lighted and
restored.
3.l.3 Progress Since The 1990
FSEIR
The visual and environmental impacts of Z Modified
continued to be the most frequent concern expressed by both
supporters and opponents of the project in response to the
1990 FSEIR. Comments ranged from adjustment of ramps or
mitigation features to complete replacement with an
all-tunnel alternative.
In terms of its scale and aesthetics, the interchange
structure under Z Modified is over 400 feet from the nearest
community, Charlestown, and over 1,500 feet from residential
development at Lechmere Canal and more than 2,400 feet from
the rest of the East Cambridge residential neighborhood. It
will be visible from only a marginally greater surrounding
area than the existing 1-93, and will be virtually hidden
from view in East Cambridge. From Charlestown, the views
from the edge of the community will be primarily of the
elevated mainlines, much as they are at present, but of a
larger structure.
The area of scheme Z Modified's elevated interchange is
49 acres, of which the loop rams account for 25 acres; in
comparison, the CANA project interchange (no-build) covers
40 acres overall, its loop ramps 22 acres. In both CANA and
scheme Z Modified, approximately 1 acre of viaduct would be
located behind North Station, but this would not preclude
development.
There is a strong commitment by the Department to
high-quality design of the bridges, both as seen from a
distance and by park users underneath them, and these
bridges have the potential to create a positive gateway to
Boston for drivers and to become objects of civic pride.
Design of ramps and the surrounding buffer strip provide
many opportunities for a higher-quality appearance than is
typical for standard highway interchanges and for screening
much of the inner ramp system and underlying structure from
view, While the interchange is higher than current adjacent
warehouse uses, plans for North Point in Cambridge and the
North Station area m Boston include buildings more than
twice the height of the ramp system.
The 1990 FSEIR contains an analysis of shadows of the
bridge structures on the Charles River which concludes that
they are of limited extent. Subsequent shadow studies using
the same CADD model show that 3 PM December shadows
(worst-case) would extend only to the median of New
Rutherford Avenue and not to residences in Charlestown. The
effect of shadows on navigation had been raised in
connection with the earlier bridge design with more piers in
the river. Consultation with the U.S. Coast Guard and MDC
personnel concerned with navigation in the river concluded
that shadows would not be a major problem with bridge piers
located as committed in the 1990 FSEIR.
Mainline Tunnel Alternatives. The inadequacy of
mainline tunnel schemes has become more evident with the
submittal of additional tunnel schemes just prior to and
during the 1990 FSEIR review process.
An all-tunnel crossing scheme (4.02) was submitted to the
Department in sketch form by Mr. Stephen Kaiser of
Cambridge, Massachusetts, shortly before publication of the
Draft SEIS/R. Reasons why this scheme was not acceptable are
explained in the 1990 FSEIR, Chapter IIB-1.3. Two additional
schemes were recently submitted in sketch form (5.01 and
3.0) and are analyzed in Section 6.2.8 of this Final
SEIS.
Mr. Kaiser prepared a list of 24 design, construction,
and operational issues and problems attendant with his
original all-tunnel scheme. The additional schemes attempt
to improve the most serious operational issue, very
inadequate weaving sections south of Causeway Street, and
the constructibility problem, but none of the issues is
adequately addressed in the revised schemes.
Mainline tunnel options 3.0, 4.02, and 5.01 pose many
distinct construction problems which threaten service and
structural integrity of the MBTA Orange Line tunnel and
commuter rail facilities and require the underpinning of the
piers supporting the 1-93 bridge over the Charles River,
Analysis of the more recent schemes (5.01 and 3.0), which
increase the separation between the highway tunnels and the
Orange Line, strengthens the conclusion that an all-tunnel
scheme would have major and potentially unsolvable
construction problems of extraordinary magnitude for reasons
detailed in Section 6.2.8 of this volume. Similarly,
multiple tunnel connections under the North Station railroad
platforms would disrupt commuter rail service for 2 years or
more. Navigation would be largely disrupted for prolonged
periods over many years by a large floating dredging
platform, and tube fabrication would disrupt the proposed
North Point development area, the GSA park site, and the
Charles River Recreational Area upstream of the railroad
bridge for the duration of Artery/Tunnel Project
construction, which would be extended by 2 to 4 years. In
addition, 1-93 bridge pier replacement and tunnel excavation
could damage the lock mechanisms at the dam.
Even if these construction problems could be overcome,
the tunnel scheme would not result in an acceptable highway
design. Scheme 4.02 was improved during further study but
still had very inadequate weaves on the mainlines south of
Causeway Street, and would permanently conflict with
commuter rail service north of the Gilmore Bridge. These
problems are intrinsic to lowering the profile of the
mainlines to provide adequate cover under the river. The
complex geometry of the stacked tunnels in schemes 3.0 and
5.01 does not provide for required clearances. Even if a
side ventilation concept is assumed, which would conflict
with several ramp connections, these schemes still would
result in mainline and ramp roadway grades too steep for
acceptable traffic operations. Also, short weaves would
remain.
The all-tunnel alternatives also have major Section 4(f)
parkland and historic impacts, including the following: a
permanent taking of part of the Nashua Street park parcel
for an open boat ramp connection to Leverett Circle,
disruption of the Charles River Extension Recreation Area
and GSA park parcel during sunken tube construction,
prolonged restriction of access to all of the Charles River
from the Harbor, structural risk to the historic Registry
Building, substantial effect on or possible foreclosure of
the development of a new sports arena at North Station,
relocation of Nashua Street, and tunnel construction very
close to the Spaulding Rehabilitation Hospital and new
Suffolk County jail, potentially damaging those buildings.
There would also likely be probable adverse impacts from
ventilation structures to the Causeway/North Washington
Streets Historic District and Paul Revere Landing Park, as
well as disruption of the park and walkway across the new
dam during construction, Two to five ventilation buildings
would be needed throughout the Area North of Causeway
Street.
In addition, the suggested benefits of the mainline
tunnel options in creating large areas of future parkland
above the highway tunnel, depend in part on bringing very
large quantities of soil to the area after construction and
creating two large hills above the ramps, some of which
would be so close to the existing ground surface that they
would normally be designed as open boat or surface roadways.
Given realistic assessment of cost and materials disposal
logistics, the additional ventilation requirements and
importation of cover material for these mounds may make it
infeasible to convert these essentially surface roadways to
tunnels.
Traverse Street Ramp. The 1990 FSEIR contains an
analysis of traffic impacts of reducing the footprint of the
Charles River crossing by eliminating the Traverse Street
ramp (and its counterpart in scheme T Modified). It was
concluded that the environmental benefits of removing the
ramp outweigh the effects on traffic. Because further design
study may make it possible to reincorporate the ramp without
increasing Section 4(f) impacts, the Department will
continue to evaluate this aspect of the crossing (the
analysis contained in the 1990 FSEIR is sufficient to assess
the environmental consequences of replacing the ramp).
The 1990 FSEIR contains an analysis of surface
intersections with and without the Traverse Street ramp. It
concluded that the effect of removing the ramp would result
in some additional congestion at certain local intersections
and warrant left turn restrictions at City Square and Keany
Square. However, no intersection would experience service
failure.
Since the 1990 FSEIR, further analysis of surface
intersections without the W-CN ramp has lead to revisions in
predicted PM peak hour intersection delays without the W-CN
ramp and for the no-build case (Table 1.14 in Part IIB-I).
At City Square, the earlier analysis of build conditions has
been confirmed (125 seconds of delay with W-CN compared to
119 seconds without the ramp, assuming a peak hour
prohibition of northbound left turns to the I-93 on-ramp;
the no-build estimate has been revised downward to 92
seconds. At Keany Square, further analysis concludes that
without W-CN, southbound as well as northbound and westbound
left turns should be prohibited, resulting in a 48-second
delay, or 55 percent less than with the ramp. The Keany
Square no-build case had been incorrectly analyzed as
resulting in gridlock; there would instead be 83 seconds of
delay in the no-build case. The 1990 FSEIR comparison to the
no-build should accordingly be revised: delays without the
W-CN ramp would be higher than the no-build only at City
Square, while Lowell Square would have the same delay as in
the no-build. This does not change the overall conclusion
stated above.
In addition, new analyses of traffic and air quality
impacts were performed for the peak hour 2010 year condition
at the intersection of Mystic Avenue and Assembly Square
Drive and Lombardi Street. These analyses concluded that
while there would be 275 more vehicles per hour on Mystic
Avenue without ramp W-CN than with the ramp, no violation of
the Ambient Air Quality Standard would occur. Further, the
exclusion of the ramp should not have any significant air
quality impact when compared to the future no-build
scenario.
Current Status. Because the Department is
committed to creating a Charles River crossing that is as
aesthetically pleasing and environmentally sensitive as
possible, potential modifications to scheme Z Modified will
continue to be evaluated as the project progresses. The
Bridge Design Review Committee includes members of the
communities surrounding the Charles River crossing,
representatives of interested agencies and associations,
architects and engineers, and is responsible for identifying
and evaluating potential modifications to scheme Z Modified
which might further lessen the environmental and aesthetic
impacts of the crossing.
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