See the original story from KOIN here.
PORTLAND, Ore. -- They connect us, they transport us, and they keep Portland moving.
By Oregon Department of Transportation (ODOT) and Multnomah County's count, more than half-a-million cars cross Portland's downtown bridges every day.
"We're a river city," Multnomah County spokesman Mike Pullen said.
However, the majority of those bridges, according to Pullen, are at risk, and he cannot rule out the possibility of collapse.
"We have a major issue with seismic vulnerability," ODOT bridge engineer Bruce Johnson said.
Scientists say a massive earthquake is in our future. In a worst-case scenario, engineers believe portions of bridges, like the Hawthorne and Steel which have yet to be retrofitted for extra strength, could fall into the Willamette River.
"It is possible that the deck surface that you drive on could slide off of the pier, so it would actually collapse," Johnson said.
Portland's downtown bridges are maintained by three different agencies. Multnomah County maintains the Sellwood, Hawthorne, Morrison, Burnside and Broadway bridges. ODOT maintains the Ross Island, Marquam and Fremont bridges. Union Pacific Railroad maintains the Steel Bridge.
According to ODOT and Multnomah County officials, only two downtown bridges have received seismic upgrades, Marquam and Burnside. Every downtown Portland bridge was built before anything was known about the earthquake threat off the coast of Washington and Oregon.
"It's like a time bomb," Portland State University Research Professor Rob McCaffrey said. "But we can't see the timer."
McCaffrey, a geophysicist, says that "time bomb" will unleash a magnitude 8 or 9 earthquake with "shaking could last for 4 or 5 minutes."
Johnson says there will be no way to cross the river for days -- if not weeks, when this earthquake occurs.
"There's going to be widespread interruption to the transportation system," Johnson said.
Pullen likens Portland's bridges to patients in a hospital. Each one has different issues and vulnerabilities when it comes to earthquakes.
"The one that's on life support is the Sellwood Bridge," Pullen said.
A historic landslide is pushing the Sellwood Bridge east. That has already caused the columns to crack and twist. Engineers say an earthquake would likely take out the whole west end of the existing Sellwood Bridge. A new Sellwood Bridge is under construction and county officials say it will to survive a 500-year earthquake. It's scheduled to open for traffic in 2015.
Just north of the Sellwood Bridge is the Ross Island Bridge, which faces problems of its own.
"The Ross Island is a very vulnerable bridge," Johnson said.
Johnson's main concern is that the sandy soil surrounding the bridge supports would almost liquefy.
"There's a potential for some banks moving around and sliding into the river and not providing adequate support," Johnson said.
A PSU simulation of a 9.0 earthquake predicts "moderate damage" to the Ross Island Bridge. That simulation ranked four downtown bridges on a damage scale of "none" to "complete" collapse.
Peter Dusicka -- an associate professor at PSU’s Department of Civil & Environmental Engineering, which headed up this study -- explained the scale to KOIN in an email:
“The designation of 'collapse' can mean the bridge falls down, though more likely it'll mean that the bridge is so damaged that it is unusable,” Dusicka wrote. “It may still be standing in some form.”
Johnson says the safest downtown bridge is the Marquam. PSU's simulation predicts only minor damage here, thanks to retrofitting that should keep the bridge deck on its columns.
"We've pretty much taken care of Marquam," Johnson said.
That's not the case with the Hawthorne Bridge.
"Worst-case scenario, it could dance off the columns," Pullen said.
Pullen says there's also concern the 880,000-pound counterweights could crash onto the bridge deck.
"You can see how high up they are, and how top heavy," Pullen said.
Concerns with the Morrison Bridge are similar, except the counterweights are below the bridge. It has not been retrofitted.
Just downstream, the Burnside Bridge is more prepared for an earthquake. It has been deemed a lifeline emergency route by the county, prompting upgrades in 2002. County officials say that work will ensure that the bridge deck will stay connected with the columns.
"We've put our limited resources into making sure the Burnside is going to do well," Pullen said.
The Steel Bridge, which is the only link between east and west for MAX mass-transit train riders, is very vulnerable. PSU's simulation predicts complete collapse. There's concern about shaking, and the bridge deck also has those massive counterweights.
"Those big weights don't behave well during a seismic event," Johnson said.
The Broadway Bridge may not have counterweights above it, but it is vulnerable. It was built in 1913 and has not been retrofitted. Neither has the Fremont Bridge, where the main span isn't the state engineer's biggest worry. Instead, the biggest worry is its double deck approaches.
"It's hard to say whether it would collapse or not," Johnson said. "But there would definitely be some movement and some damage and the bridge would not be useful after quake."
PSU's study predicts moderate damage here. Both the county and the state say more needs to be done to prepare Portland's bridges.
"We are trying to wave our arms and get the message out there," Johnson said.
According to ODOT, state and federal funding for bridges has been cut by almost $35 million since 2009. Almost all of the funding is being used for bridge maintenance; last year, less than two percent went towards seismic upgrades.
"What people should realize is that we do know how to retrofit bridges," Johnson said. "And if there were funding available, we could preclude some of the damage."
For those like Mike Pullen, the message is clear.
"We're not ready; stories like this help remind people of that."