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A detour bridge could reduce time and money needed to construct a new Sellwood Bridge, according to project officials.

and , the firms hired by Multnomah County to design and build, respectively, the Sellwood Bridge replacement, recommended a “shoo-fly” bridge be used as a temporary detour during the work, said Mike Pullen, spokesman for Multnomah County.

According to the proposal, the existing Sellwood span would be moved 40 feet to the north to rest on new temporary supports on shore and in the Willamette River. The new bridge could then be built all at once instead of in halves, shrinking the project time frame by a year and, therefore, saving between $5 million and $10 million in labor costs. The proposal was slated to be presented to the Multnomah County Board of Commissioners on Tuesday night.

“There are additional costs for the detour bridge, but that will be offset by the cost savings (by decreasing the construction time frame),” Pullen said.

The shoo-fly bridge proposal would need to be approved by local and federal regulatory agencies and by the Multnomah County board before it could be incorporated into the project plan, Pullen said. The board also would need to approve construction easements along the river for where traffic would be rerouted temporarily.

T.Y. Lin and Slayden used this method of bridge construction previously to replace the Elk Creek Bridge on Oregon Route 38 in Elkton. Other contractors who bid on the Sellwood Bridge project also suggested the use of a detour bridge, Pullen said.

This sort of work is called “accelerated” or “rapid” bridge construction, and is in frequent use, according to Larry Gescher, a Slayden principal. Slayden and Sundt Construction, which are working on the project as a joint venture, would use a patented system from Mammoet USA for jacking up and sliding the bridge from its old supports to new ones, Gescher said.

Gescher said that this process also would make project construction safer because traffic would be detoured to a separate area, and the traffic pattern would remain the same during most of the construction.

“We’re able to put traffic in one spot and leave it in the same place for the duration of the job. People know where they’re supposed to go,” Gescher said.

Pullen said that the detour bridge project would not reduce the number of days (approximately 30) that the bridge would close completely during three years of construction.

This proposal also would make the new bridge safer and eliminate redundant features that would have been necessary in two-phase construction, Pullen said.

“When you build the bridge in halves, there is a seam between the two structures, which is a point of weakness, with more expensive maintenance,” he said.

Pullen said that the temporary bridge would be safer than the existing one because it would not include the latter’s most dangerous portions – cracked concrete on land at both ends.

Pullen said the county is looking for ways to save money on bridge construction because the $290 million project is lacking full funding, according to an agreement finalized in February. The city of Portland will pay between $80 million and $100 million for the project, Multnomah County will pay $127 million, the state of Oregon will pay $30 million and the federal government will pay $11 million.

Clackamas County is slated to pay $22 million for the project, and voters in that county will vote May 17 whether to add a $5 annual vehicle registration fee to cover that amount.