Engineers are redesigning the bridge to increase the clearance for ship and barge traffic.
Changing the height affects other aspects of construction such as highway grades, size of onramps, and even Pearson Airfield flight paths. In addition, construction costs increase with the height of the bridge.
Planners must settle on a height before the Jan. 30 deadline to file the permit application with the Coast Guard, The Oregonian reported Tuesday.
In March, after $140 million had been spent during seven years of planning, the Coast Guard said the proposed 95-foot clearance was too low and would block some ships or loads carried on barges.
The Coast Guard must approve the height of bridges on navigable waterways.
Planners have been analyzing possible bridge clearances, calculating effects and costs at each increment. They're narrowing in on a decision of 115 or 116 feet, the newspaper said.
At those clearances, light-rail and Interstate 5 grades would increase slightly. Bridge foundations might have to expand, but not enough to require a new environmental impact statement, planners said.
Still, the $3.5 billion price tag would jump $30 million, not including mitigation expenses to cover upriver businesses.
The river now has more than 2,600 commercial users, and between nine and 11 might be affected at the 115-to-116-foot clearance, officials said. Managers are talking to the businesses.
At 116 feet, the dredging vessel Yaquina could pass below the bridge. But at 115 feet, the bridge could block the dredge used by the Corps of Engineers to maintain shipping channels.
Project managers were confident at a legislative hearing Tuesday at the Oregon State Capitol.
"This is a mega-project, it's a massive project," said Pat Egan, chairman of the Oregon Transportation Commission. "We're going to keep after it, and this is a project that's going to move forward."
In addition to the Coast Guard permit, bridge planners need approval and funding from the Oregon and Washington legislatures and the Federal Transit Administration.
The project is aiming for a Coast Guard permit in mid- to late 2013 and a construction start in 2014, Kris Strickler, CRC Oregon director, told the legislative oversight committee.
The span would save travelers a total of about 6.8 million hours a year stuck in traffic, create 4,200 jobs and avoid a potential loss of two existing bridges in a catastrophic earthquake, Strickler said.
Opponents attending the hearing said afterward that bridge finances and traffic projections don't add up.
"Our biggest concern is the toll revenues," said William "Chris" Girard Jr., president and chief executive of Plaid Pantry convenience stores.
Revenue estimates depend on vastly inflated traffic projections, he said. Revenue shortfalls would force toll increases, that would cut traffic further. And taxpayers, not bondholders, would be liable.
"I've got 70,000 customers a day that are going to make up the difference," Girard said.