Ashland and Oregon Department of Transportation (ODOT) officials Monday struggled to launch a “seismic triage” of bridges that are vulnerable in the inevitable Cascadia earthquake, deciding which can be detoured around, which can’t be detoured and would suffer major damage and those that get minor damage and could be fixed in a few months.

The study of bridges on major highways and local streets is vital because of the likely situation where food and water supplies are wiped out and must be driven in.

The discussion at the City Council's regular study session included recitation of the certainty that there would be major injuries, deaths and collapsed housing and buildings, requiring a range of supplies, shelter and personnel. Fixing the highway problem before the quake will be enormously expensive, with statewide costs going over $5 billion, said Arthur Anderson, area manager for ODOT.

The troublesome Cascadia Subduction Zone runs from the Bay Area into British Columbia, and is caused by the offshore San Juan de Fuca plate worming its way under the North American plate. The last major snapping of the seismic rubber band in Oregon in 1700 dropped the earth 6 feet and triggered a huge tsunami across the Pacific.

“We are at the potential horizon” of a repeat of the quake, Anderson said, referring to the typical 400- to 600-year period between major temblors. “It’s a matter of when, not if … a lot of communities will be isolated if something isn’t done in advance.”

Because there are so many bridges on I-5, ODOT is focusing on Highway 97 on the eastern side of the Cascades as the state’s main north-south route, says Anderson. It runs from Klamath Falls to I-84 near The Dalles and can serve Portland. To serve the Willamette Valley, Highway 58 from Highway 97 across the Cascades to Eugene would be the main path.

Where major bridges on I-5 have collapsed, Anderson said ODOT would bulldoze debris out of the way, if possible — or detour on old Highway 99, which survives for many stretches, including Ashland and Medford.

Several area projects are in "Triage #2," which means they face heavy damage with no good detour, so work should be done soon. They are:

—Highway 140, running from Medford to Klamath Falls and allowing access to Highway 97, the main north-south route and to points east. It has four bridges in Triage #2. This would cost $5 million.

—Interstate 5 north of the north Medford interchange is Triage #2 with 13 bridges, costing $20 million. This comes in phase 2 and would allow “reasonable access” to major population and economic centers to the north.

—Interstate 5 south of the north Medford interchange is better off. Because of recent bridge construction there are no bridges that would be hit hard. However, it has three unstable slopes. This is phase 3 in the valley and will cost $10 million.

“The Rogue Valley has adequate detour routes,” said Anderson.

Oregon would shift to Redmond as the state’s main airport — and the point from which supplies are trucked.

In Ashland, Public Works Director Mike Faught says, the essential routes will be Main-Siskiyou-Lithia Way, Ashland Street, Oak-Eagle Mill, and Mountain-Hersey. They all feed to I-5.

Mayor John Stromberg said the city is doing its own triage on bridges and is working in tandem with ODOT, which, if done soon, makes it easier to tap into state funding as they go. Federal funds are normally available, he said, but “given what’s going on in Washington,” that’s not for sure.

Faught proposed a two-year, $31,000 seismic evaluation on bridges on main routes, along with getting estimated costs for retrofitting, followed by grant applications. As part of this, the council will decide on the controversial bike-pedestrian bridge on East Nevada Street.

The town has 34 bridges and a railroad trestle. Six and the trestle are triaged as essential and on the critical routes, Faught reported. Included are the Lithia Way and East Main bridges in busy downtown Ashland. “They would most likely fail” (in their present state), he said.

The owner’s association at Mountain Meadows asked for retrofit of the adjacent North Mountain overpass of the freeway, since they could be isolated if the low bridge over Bear Creek also fails. ODOT said the overpass is seismically vulnerable and would fail, but doesn’t make the triage list. It also would cost up to $600,000. Staff said the best course is to build the 12-foot wide Nevada Street bridge.

The state plan is in five phases over 50 years. Phase 1, the coming 15 years, would cost $936 million. It calls for replacing seven bridges and retrofitting 122. It includes work on Highway 58, from Eugene to Highway 97.

Phase 2 goes out to 30 years and costs $904 million. It includes I-5 from Eugene to the California border, going through the Rogue Valley.

Phase 3 is $1.02 billion and includes Highway 140 from I-5 to Klamath Falls. Phase 4 is $766 million and includes Highway 199 to the California border. Phase 5 is $1.4 billion and includes replacement of the Medford viaduct at $374 million.

Bridge replacement costs are based on 2013 dollars. Retrofit is based on a very damaging 9.0 magnitude scenario. The report says the I-5 bridge between Oregon and Washington is vulnerable and would come down in the “big one.”

The seismic upgrade for the state would prevent the loss of $84 billion to the Oregon economy, Anderson reported. The work would have to be done anyway, over the long term, the report said, and even if the quake doesn’t happen it would have “significant benefits” to the economy.

As for the slide-prone Highway 101 on the coast, Stromberg said, “A lot of it’s going to get killed.” Projects on the coast are scheduled toward phase 4 and 5.

Stromberg said such advance planning is making him feel more confident, where, just a few years ago, “I felt hopeless and isolated. It was very sobering to imagine ourselves in that situation.”

The council asked that Faught’s proposals be brought back soon for a vote.

—John Darling is an Ashland freelance writer. Reach him at jdarling@jeffnet.org.