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The Preferred Alternative has been refined and a Final EIS has been prepared (including responding to comments that
were submitted about the Draft EIS). Refinements have been made to the
plan to ensure it complies with local, state and federal regulations. Approval by FHWA is expected in late summer 2010.
The project is now at the point of deciding what type of bridge the replacement structure should be. Previous bridge type
discussions took place during Phase 1. In a city of bridges,
choosing a new bridge design is a major decision that will have a lasting impact.
Any new bridge must meet the following criteria:
- Cross-section without a raised center median
- Cost of the bridge structure less than $170 million*
- No long term traffic closures
- Construction footprint must minimize impacts to adjacent businesses and residences
- Versatile cross-section to accommodate future streetcar
*Includes river span, east approach, temporary construction, demolition of existing bridge and buildings within the
alignment, design and construction engineering, contingency and inflation to the year 2014. Full cost of the project is
estimated at $330 million.
There are eleven bridge types currently under consideration that are possible with new construction techniques and the
alignment chosen in the preferred alternative. The alignment will be approximately 15 feet south of the existing Tacoma
Street centerline to allow for continuous traffic flow at the crossing throughout construction. The possible bridge types
include deck structures (no superstructure above the deck) and thru structures (support structure above the deck).
The renderings of the bridge types are for illustrative purposes only - they are not meant to depict the final designs
and they do not include design details like color, texture, lighting, etc. Additionally, the interchange with Hwy. 43
will require that the bridge deck be wider on the west end of the bridge to give vehicles enough space to queue before
turning. This additional deck width is not illustrated in the renderings. Renderings with additional bridge views will
be available later this year.
Girder Bridges
Box and Plate Girder bridges are clean, modern, and cost-effective to construct and maintain. These bridges can be steel
or concrete. Their straightforward, functional form allows a blank canvas for deck features. Their classical arch profile
offers options for architectural detail in the shape of the girders and piers, slopes, shadows, and textures. These
bridges’ moderate price and flexibility in accommodating varying deck widths make them a common bridge type throughout
the world. The Glen Jackson Memorial Bridge (I-205) and the Bybee Boulevard Bridge are examples of concrete box girder
bridges. The Abernethy Bridge (Oregon City I-205 Freeway Bridge), is an example of a steel plate girder bridge.
Delta Frame bridges, sometimes called Y-Leg, are in the girder family. These concrete structures are named for the unique
look achieved by their Y-shaped piers. This bridge design offers a high level of architectural interest for a moderate
price. This bridge would be a new bridge type in Portland (similar to the Alsea Bay Bridge in Waldport, Oregon).
Arch Bridges
Deck Arch bridges offer a classical architectural style. The arch form is a very popular style, especially in Oregon,
which offers broad opportunity for deck features and architectural detail in color, texture, and shadow. Arch bridges
limit navigational channel clearance more than other bridge types. Southwest Portland’s Vista Bridge is an example of a
Deck Arch bridge.
Through Arch bridges offer a striking profile and create an iconic gateway presence. They are more expensive to build
than other bridge types and the arches and hangers require more intensive maintenance. This type allows for a slender
deck depth with cables providing support from above. This bridge type has limited construction staging options. The
Fremont Bridge is an example of this bridge type.
Extradosed Bridges
Extradosed bridges are a cross between a box girder bridge and a cable-stayed bridge design. This light and elegant form
can be constructed with either concrete or steel. Concrete and steel extradosed bridges are in the upper to moderate
price range. The design creates architectural interest by stringing support cables from short pylons above the box girder
deck. This bridge type has limited construction staging options and the layout is more challenging with the variable
roadway width of the preferred alternative. This would be a new bridge type in Portland.
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