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Burnside Bridge task force recommends 'long span' design, no temporary bridge

The Earthquake Ready Burnside Bridge task force looked at four types of bridges and has chosen the long span alternative for the replacement bridge.
Credit: Multnomah County
The long span alternative could include two tied arch spans as shown here.

PORTLAND, Ore. — In the interest of making the upcoming Burnside Bridge replacement resilient to a major earthquake, a task force on Monday recommended moving forward with a long span bridge alternative.

The recommendation came after 18 months of work. The task force and a Multnomah County project team have met 16 times to discuss alternatives for the Earthquake Ready Burnside Bridge Project.

The long span bridge would replace the existing bridge in the same location and alignment, said Multnomah County spokesperson Mike Pullen. 

"The long span alternative has the fewest support columns of four alternatives that were studied," Pullen explained. "Fewer columns avoids costly construction in geotechnical hazard zones near the Willamette River, and restricted spaces between lanes of Interstate 5 and the Union Pacific Railroad tracks on the east side." 

Fact sheet: Understanding the long span bridge alternative

The reasons task force members chose the long span alternative include:

  • Locating fewer columns in liquefiable soils gives it the least risk from soil movement during an earthquake
  • It is the lowest cost of four build alternatives ($825 million compared to as high as $950 million for the most expensive option)
  • The reduced number of columns also benefits Waterfront Park users, crime prevention, and preservation of the Burnside Skatepark
  • Additional deck width over the river provides a safer facility for bicyclists, pedestrians and other users
  • Reduced impacts to natural resources due to fewer columns in the river

Pullen said the task force is still working on options to mitigate the long span’s impacts on views, because a superstructure will be required above the bridge deck to support the longer horizontal span. 

"Questions of the structure’s scale and relation to adjacent neighborhoods will be dealt with in the Bridge Type Selection phase which begins this fall, and during final design," Pullen said. 

Watch: Simulation of Burnside Bridge collapse following earthquake

The project should not include a temporary bridge during construction, the task force decided. That temporary bridge would carry less than half of existing Burnside Bridge traffic and would cost about $90 million. It would also add two years of construction time to the project.

The public will get to weigh in on the task force recommendations through an open house and survey in August. A policy group of elected and appointed leaders will vote on the preferred alternative in October.

If the long span option is chosen, a bridge type with a superstructure above the bridge deck will be necessary. Options would include a tied arch, like the Fremont Bridge, or a cable-stayed structure, like the Tilikum Crossing.

The bridge type selection should be complete in 2021. Design work will stretch from 2021-2024, and then with construction should begin in 2024. Building the new bridge should take about 4-1/2 years.

The task force also studied three other build alternatives: an enhanced seismic retrofit of the existing bridge, a replacement movable bridge on the same alignment with short spans and a replacement movable bridge with an extension of Northeast Couch Street.

Last summer, a group of Portland State University Master of Architecture students got a chance tor reimagine what the bridge would look like.

RELATED: What could a new Burnside Bridge look like? PSU students pitch creative ideas to county leaders

Pullen said task force members represent neighborhoods, business districts, and interests including auto commuters, transit users, pedestrians, bicyclists and social service agencies. He said bridge history and input from organizations based near the bridge are also take into account.

Watch: County plans to quake-proof Burnside Bridge (June 2019)

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