Magnolia Bridge Replacement Project:
Note: Alternative A was selected as the preferred alternative if full funding is available.
Since 2002, Several Magnolia Bridge alternatives have been studied in the
quest to identify Alternative A as the preferred alternative. A history of
how SDOT narrowed the original 25 project alternatives to a final alignment
choice is provided at the bottom of this page.
Illustrations and brief descriptions of the final
three build alternatives SDOT considered but eliminated in favor of Alternative
A can be viewed by clicking on the links below. These options included Alternative
C, D, and a Rehab Alternative, as well as a “ No
Alternative C (Eliminated from consideration in March 2006):
C combined bridge and surface segments, arcing to the north through the Port’s
property. A bridge would have crossed over 15 th Ave W and the railroad tracks
to the east, and a ramp would have climbed up the Magnolia bluff, connecting
at the existing bridge's western endpoint. A surface road at the alignment's
mid-span would have provided access to the Port property and waterfront
Alternative D (Eliminated from consideration in March 2006):
D involved constructing a new bridge in the form of a long arc north of the
existing bridge. Ramps would have connected the bridge’s mid-span to
provide access to the waterfront and Port of Seattle uplands property.
Rehab Alternative (Eliminated from consideration in March 2006):
Under the Rehab Alternative, the existing bridge pillars and supporting soils
would have been stabilized, and a new bridge deck (roadway) would have been
built along the existing alignment.
"No Build" (Eliminated
from consideration in March 2006
The "No Build" Alternative studies what would happen if the
bridge were not replaced and maintenance continued on the existing bridge.
This alternative helps engineers create a base-line scenario against
which the other alternatives can be compared.
History of Alternative Evaluation
The process to identify the best Magnolia Bridge replacement alternative began
in October 2002, when the project team gathered to brainstorm possible replacement
structures. The key steps described below illustrate how the project team narrowed
the field of alternatives down from 25 original concepts.
- The project team brainstormed a list of 25 alignment possibilities.
- The project team applied "fatal flaw" criteria, eliminating 12
alignments and consolidating the remaining 13 into nine "surviving alignments."
- The project team then developed detailed criteria to evaluate the remaining
nine surviving alignments.
- Evaluation criteria were split into four general categories: Environmental,
Traffic, Urban Design, and Cost.
- Each alignment was evaluated based on all four categories, and the results
of each category were totaled to help prioritize the survivors in terms of
functionality and impacts.
- Four alignments scored well based on the team's criteria evaluation (A,
B, D, and H).
- After further technical review, Mayor Nickels requested on April 14, 2003,
that SDOT eliminate Alternative B from further consideration, citing environmental,
permitting, and legal obstacles.
- In March 2004, SDOT removed Alternative H from consideration because review
of traffic operations found that the option would be unable to handle the
future forecasted traffic demand.
- Because SDOT wanted to evaluate at least three alternatives, the agency
added a version of Alternative C, the next best alternative evaluated during
earlier steps in the process, to Alternative A and D for further study. Alternative
C provided a unique surface/structure combination significantly different
from Alternatives A and D.
- In Spring 2005, SDOT also decided to consider
the Rehabilitation – or
Rehab – Alternative to ensure that a robust range of options would
be evaluated. The Rehab Alternative involved bringing the bridge up to current
load and design standards using the existing bridge structure to the extent
- For several months, SDOT considered two versions of Alternatives A and
D that provided vehicular access to the marina from the bridge, one including
ramps and the other an elevated, signalized intersection. In early March
2005, SDOT decided to drop the intersection options for both alternatives
based on cost/benefit analyses and public opposition.
- In March 2006, in consultation with the Mayor’s office, Alternative A was selected as the preferred alternative, if funding is obtained, for further development and eventual construction.
- In November 2006, SDOT selected a bridge structure type following several public outreach events and consultations with the project's Design Advisory Group and the Seattle Design Commission. The new bridge will use concrete box girders supported by columns that flare out at the top. The two most visible bridge segments (the span crossing over 15th Avenue and the spans climbing the Magnolia Bluff) will be haunched in a gentle arch shape, while the center portion of the bridge will be a straight box shape.