This project will improve the seismic resiliency of U.S. Hwy. 97 so the highway can continue its role as a primary north-south lifeline route in the aftermath of a major earthquake. Scientists believe a 9.0 magnitude earthquake is likely when the next Cascadia subduction event, or “Big One" strikes the Pacific Northwest coast. Many geologists believe this not only possible, but overdue.
Most of the bridges in western Oregon are expected to suffer serious damage or destruction in a major earthquake. Since the expected ground-shaking in Central Oregon is expected to be lower than that which will be experienced in the Willamette Valley and Oregon coast, the state of Oregon will look to U.S. 97 to absorb the extra traffic pressure and function as a critical transportation corridor in the days and weeks following a major earthquake.
For these reasons, U.S. 97 is designated as a Tier 1 lifeline route. Tier 1 lifelines are the most critical highways in Oregon, because they are a backbone system to provide supplies to the parts of the state most vulnerable to the Cascadia subduction earthquake.
Although Central Oregon faces lower risks of catastrophic impacts from a Cascadia earthquake than the Willamette Valley and the Oregon coast, this area is not immune to earthquake damage.
In addition to the expected Cascadia subduction event, Klamath Falls is also subject to localized earthquake activity that poses additional risks for Klamath area bridges. The Klamath Falls area, for example, has a history of significant earthquake activity, most notably magnitude 5.6 and 5.9 earthquakes in 1993.
In order to ensure that U.S 97 remains a resilient north-south highway corridor, ODOT determined that seven bridges in the Klamath Falls area are highly vulnerable to earthquake damage. ODOT decided it is necessary to retrofit six bridges and replace one – the Pelican City Bridge.
Bridges in the Klamath Falls area have been carefully evaluated, and the following bridges have been identified as the most crucial where the project improvements will be performed.
The following bridges are included as part of this project:
US97 over UPRR (Lobert Bridge)
US97 over Lakeport Blvd & UPRR (Pelican City Bridge)
US97 over Nevada Ave
US97 over USBOR Canal
US97 over Link River (Link River Bridge)
US97 over OR140 (Greensprings Interchange)
US97 over Klamath River
The following is a summary of the work being done to each bridge.
U.S. 97 over Lakeport Blvd. and UPRR - During project development ODOT looked at retrofitting the current bridge but due to high repair costs and future maintenance costs, decided to replace the bridge. This will be accomplished by closing U.S. 97 for up to six weeks and using accelerated bridge construction to remove the existing bridge and build a new one in the same place. Typically replacing a bridge with conventional bridge replacement methods takes around six months (or longer). Accelerated bridge construction shortens the impact to the traveling public. For this bridge, much of the new structure will be constructed below the existing bridge. Once the new bridge is in place, the roadway leading up the bridge will be constructed and guardrail installed. Once all the safety elements are completed, the roadway will be reopened to traffic. While the highway is closed a detour for trucks and passenger vehicles will be in place.
U.S. 97 over Nevada Avenue - This bridge is just to the south of the U.S. 97 over Lakeport Blvd. and UPRR Bridge. This bridge will require two main retrofit elements. The first are drilled shafts behind the south end of the bridge. During drilled shaft construction, two lanes of traffic will be closed and traffic on U.S. 97 will be shifted to one side of the bridge to allow the construction contractor to work from the roadway to install the drilled shafts. The second retrofit element consists of enlarging the footings (under the ground) for interior bents on either side of Nevada Avenue. This will require traffic on Nevada Avenue be shifted to one side and then the other, to allow construction on the footings. During that time, the turn lane in the middle of the road will be closed. Staging will occur on Nevada Avenue under the bridge.
U.S.97 over the USBR Canal - This bridge is just to the south of the U.S. 97 over Nevada Avenue Bridge. This bridge will have two types of retrofits, those above the bridge on U.S. 97, and the other below the bridge. Within the U.S. 97 roadway, drilled shafts will be installed at the bridge ends. Similar to the Nevada Avenue Bridge, this will require closing two lanes temporarily and shifting traffic to one side of the bridge. Beneath the bridge, one support will be strengthened by installing micropiles through the existing footings. Additionally, various connections between the bridge deck and the supports will also be strengthened at all bridge supports.
U.S.97 over the Nevada Ave Bridge and USBR Canal Bridge are so close together that traffic control for both bridge will be coordinated into one stage/impact to the U.S. 97 traffic.
U.S. 97 over the Link River and Main Street - This is by far the most complex retrofit in this bridge bundle. Bridge replacement isn't an option with the current funding so the construction contractor will essentially be strengthening or completely replacing all of the bridges supports. In addition, connections between the bridge deck and supports will also be strengthened. On U.S. 97, drilled shafts will be installed behind each end of the bridge, including the southbound off-ramp. During this time, traffic will be restricted to one lane due to the narrowness of the bridge.
Traffic will be flagged through the bridge, one direction at a time. While installing the drilled shafts behind the southbound off-ramp, the ramp will be closed, with traffic detoured down to OR66/Green Springs Highway Interchange. Beneath the bridge, construction project work will be extensive, and will require Conger Avenue to be closed for about a year. Local access will still be allowed during this period. During the road closure, support strengthening will take place including installing micropiles through footings, enlarging and strengthening columns, and installing restrainer cables and keys to better connect the deck onto the supports.
Main Street will be narrowed to two lanes and shifted to the south to allow the adjacent road to be replaced completely. In addition, the western access road to Veterans Park will be temporarily closed to allow access to the five supports in the Link River that are being replaced entirely. Due to limitations on when work can occur within the Link River, construction is expected to take about four years.
Green Spring Interchange - This is the U.S. 97 Bridge over Highway OR66 Green Spring Highway. Retrofitting the bridge consists of strengthening the supports and the connections between the deck of the bridge and those supports. All work will be completed below the bridge, so no traffic impacts will occur on U.S.97. This will require closing a lane in each direction on OR66 to provide access to each support.
U.S. 97 over the Klamath River and BNSF railroad - This bridge has minimal retrofit work needed. Work will be completed from the highway at the north end of the bridge and from beneath the bridge at the south end. During construction, shoulders will be closed and traffic shifted to one side or the other on a daily basis. Traffic control measures will be installed daily, with the shoulders and roadway being opened at the end of each work shift.
A note for all bridges…
Many of the bridges will have existing guardrail replaced with new guardrail meeting current safety and crash standards. Also, three of the seven bridges are over railroads. All three of these bridges will have protective fencing installed to prevent objects, road debris and snow from falling onto the railroad tracks and trains.
The seven structures included in this project were prioritized as seismically vulnerable structures along U.S. 97 and require improvements in order to maintain safety standards.
This project will complete seismic resiliency of bridges along highway U.S. 97. If a major earthquake or other substantial event occurs in Oregon, U.S. 97 will be used as the major north/south lifeline for the state.