When comparing the cost of two items, a shopper needs to know what’s included in the price. The author of a recent letter to a community newspaper wondered why the new Sellwood Bridge has a higher cost than the recently completed Mike O'Callaghan-Pat Tillman Memorial Bridge in Arizona (shown in photo below).
The Arizona bridge is in an iconic location, spanning a steep canyon near the Hoover Dam. The citizen assumed it should cost less to replace the Sellwood Bridge. He encouraged Multnomah County to hire the firm that designed the Arizona bridge to help lower the Sellwood Bridge cost.
When the letter was published, the Sellwood Bridge Project had a cost of $330 million and the final cost of the Arizona bridge was roughly $116 million. The cost of the Sellwood project has since been reduced to $290 million, after the County approved a redesigned Westside interchange and refined the cost estimate. That’s still a big price gap between the two projects.
The letter caused Multnomah County staff to do a bit of research to compare costs of the two projects. What we learned helps explain the cost of the most expensive transportation project in our county’s history.
- Cost Elements: The key difference in the price of the two bridges is that the cost of the Arizona bridge is for the bridge only while the Sellwood estimate includes all project costs. These include a westside intersection with Highway 43 that is still expected to cost roughly $80 million. Other items in the Sellwood estimate include right of way (land and structures), design, and costs to protect the environment. The current cost estimate for just the bridge portion of the Sellwood project is roughly $164 million.
- Year of Estimate: The Arizona bridge costs are from a bid in 2004. The Sellwood Bridge estimates are for 2014, the projected middle year of construction. Costs have risen significantly in the past decade due to inflation which averaged 3 – 4% a year during the decade. Inflation accounts for a cost increase of 40 – 50% over 10 years.
- Geology: The Arizona bridge was built into the solid rock sides of a canyon, so deep foundations were not needed. The river and land piers supporting the new Sellwood Bridge will require deep foundations to support the bridge in river sediment and in a landslide zone on the west side.
- Right of Way: The Arizona bridge was sited on federal land so there was no right of way (property) to buy. The Sellwood Bridge is surrounded by private property, especially on the east side. About $36 million will be spent for Sellwood right of way.
- Construction/Traffic Staging: Because no one lives near the Hoover Dam, construction can happen seven days a week, around the clock. Even with construction easements, the close proximity of residential buildings to the Sellwood Bridge constrains a contractor’s work. Work hours and days will be restricted for the Sellwood construction. Also, the Hoover Dam bridge was in a clear, open site with no existing bridge traffic to keep flowing. The new Sellwood Bridge will be built while maintaining traffic (30,000 vehicles a day) throughout construction. This adds complexity, time and cost.
- Environmental: Due to the presence of protected fish species in the Willamette River, construction of the Sellwood Bridge in-water work will be limited to four months each year, while the Hoover bridge was not. “In-water” work is construction that impacts river sediments, such as pile driving or digging for columns. This adds more complexity, time and cost.
- Demolition: The Sellwood cost includes removal of an old bridge, while the Arizona bridge did not.
- Designer: The letter author suggested Multnomah County contact the designer of the Arizona bridge to give us advice on how to economize our project. We have. The County hired the same bridge engineering firm (T.Y. Lin International) and the same Chief Bridge Engineer (David Goodyear) who designed the Arizona bridge. David is one of the premier bridge designers in the U.S. and we are thrilled to have David and his firm leading the Sellwood design team.
Taking all this into account, it’s clear the costs quoted for the two bridges are not apples to apples. However, all parties agree that the cost of the new Sellwood Bridge should be very closely managed so that taxpayers get maximum value for their investment. The County and its project team are committed to pursuing cost savings throughout design and construction.
