Improvements to I-90 Snoqualmie Pass East Provide Safe Passage for Wildlife and Drivers
Safe Crossing for Drivers and Wildlife: Atkinson Construction’s Avalanche Bridges Among Cost Savings in First Phases of 20-Year I-90 Snoqualmie Pass Project
As the Washington State Department of Transportation (WSDOT) works with contractors through the 15-mile Interstate 90 Snoqualmie Pass East project between Hyak and Easton, Washington, drivers and wildlife are enjoying safer transit.
The corridor bisects an area the U.S. Forest Service considers critical for the north-south movement of wildlife in the Cascade Mountains. Previously, the corridor included no wildlife crossings, resulting in dangerous collisions and interrupted migration patterns.
The Snoqualmie Pass East project will add more than 20 crossings for fish and wildlife, including creek crossings, larger culverts, stretches of raised highway, and a couple of overcrossings above the roadway. The corridor’s first overcrossing, opened to traffic late last year, became Washington's first-ever wildlife bridge over a highway or freeway and the largest wildlife overcrossing in North America.
For drivers, the project expands the corridor from two to three lanes in each direction, increasing capacity for the growing number of vehicles traveling between the large population and business centers of Puget Sound and the agricultural industries and recreational activities of eastern Washington. The project also fixes the rough roadway with new concrete pavement, stabilizes slopes to reduce rock slides, minimizes avalanche closures, and increases safety by straightening curves and expanding chain-up areas.
Construction of the project’s $457 million, five-mile phase one, funded by Washington’s 2005 gas tax, began in 2009. Prime Contractor Max J. Kuney Construction of Spokane, Washington, completed the first three miles in 2015. In the remaining two miles, Prime Contractor Guy F. Atkinson Construction of Redmond, Washington, submitted a Cost Reduction Incentive Proposal to build two avalanche bridges instead of a new snowshed, resulting in significant long-term savings.
Overall savings from phase one allowed WSDOT to proceed with the project’s second phase, which extends two miles and includes the new wildlife overcrossing. Atkinson started construction of that $108 million contract in 2015. That segment, as well as their part of phase one, opened to traffic late last fall. With additional funding recently secured, planning and design for the final two phases of the project are underway.
Crossings Over and Under the Interstate
At the start, the project focused on replacing the corridor’s 64-year-old snowshed, which funneled snow over the westbound lanes of I-90. “Our legislature came to us and said ‘We want you to reduce road closures due to avalanches,’” said Brian White, Assistant Regional Administrator for Construction and Development in WSDOT’s South Central Region. “The existing snowshed only covered one side of the roadway and was too small to address all of the avalanches.”
In the project development process, “We determined additional needs, such as realigning the roadway, replacing the 50-year-old concrete, and pushing back the slopes to reduce rockfall,” White added.
In addition, the U.S. Forest Service had identified I-90 as a barrier to the movement of wildlife. “The section of I-90 we’re working on is in the National Forest, so we’re there by easement,” White explained. “In order to expand our roadway, we needed to get additional easement from the Forest Service, so we needed to make sure our project was in compliance with their management plan. To do that, we had to address wildlife connectivity.”
WSDOT collaborated with the Forest Service, Conservation Northwest, and other organizations to make the corridor more accessible to wildlife and their migration, while also increasing driver safety. To determine the best placement for wildlife crossings, WSDOT worked with Central Washington University in Ellensburg, Washington.
“Some of their master’s students came out to study the different species in the area, including deer, elk, fish, and pika,” White said. “They determined where the wildlife was moving and where the best habitats were so we could put our structures there.”
In many cases, “Our structures cross rivers and streams,” White said. “We needed to widen them for the additional lane, so we made sure those bridges were a little longer for wildlife to cross underneath the roadway.”
The overcrossing gives wildlife a more open alternative to travel between habitats on either side of the freeway. “We have six traffic lanes and a chain-up lane through the wildlife overcrossing, so the structure is pretty massive,” White said.
In fact, the overcrossing stretches 350 feet long and 150 feet wide. To build it, Atkinson’s crews set two concrete arch structures, each with 39 concrete segments, then backfilled with granular material. Last year they spread 115,000 cubic yards of soil over the structure. This year they’ll finish grading the top of the arch and add rocks and logs to mimic the forest ground.
“In two years, after it settles, the Restoration Services Team with the Forest Service will come back to plant some native trees and bushes we’ve been collecting and growing,” White said.
Cars now pass through the overcrossings’ two archways. Eight-foot walls on top block most of the traffic noise and prevent snow from falling on the roadway. WSDOT plans to add at least one more overcrossing in the later phases of the project.
Of course, animals weren’t the only thing coming down the mountain onto the roadway. To address the problem of avalanche closures, project plans originally included a longer, wider, and taller snowshed to replace the old one.
“We have a number of avalanche chutes in the area,” said Meagan Lott, Spokesperson for WSDOT’s South Central Region. “We wanted to build an extended snowshed that covered all the lanes and all those chutes so if they released naturally, the snow would go over the snowshed.”
Instead, Atkinson proposed building side-by-side viaducts and excavating the avalanche chutes to channel snow and rock between the piers and under the bridges toward Keechelus Lake.
“The change did two things for us,” White explained. “First, it reduced future maintenance and operations costs. The snowshed was so massive, we had to include fire suppression, lighting, and ventilation systems that would need yearly inspections and maintenance. Second, with the change to bridges, we turned it into a design-build job in the middle of this design-bid-build project. We handed the risk of construction to the contractor. We said, ‘This is your solution, so if something doesn’t align right or you run into a large boulder where we hadn’t planned on putting a shaft, that’s your responsibility to solve and pay for it.’”
Construction proceeded smoothly. Designed to accommodate 100-year avalanche events, the twin, 1,200-foot-long bridges virtually eliminate road closures due to avalanches.
According to Lott, “The avalanche bridges cost about the same as the snowshed to build, but saved $49 million over 75 years in maintenance and operations costs.”
Other cost savings allowed the work on I-90 to progress through phase two. “When we went out for advertising in phase one, we were fortunate to get good bids,” White explained. “That gave us enough dollars left over to fund the next phase with the wildlife overcrossing.”
Upon completion of all that work, “We had more savings from our contingency fund, so we let a new contract to install exclusionary fencing along the seven miles we completed,” White said. “That fencing will direct wildlife to the structures we built.”
Maintaining the Work
Throughout the project, Atkinson and Kuney Construction maintained two lanes of traffic in each direction during peak travel times. “That was one of the biggest challenges,” White said.
At night, “For almost three years in the summer, we did extensive blasting Monday through Thursday so we could stabilize the rock slope and make room for the additional lanes,” Lott said. “We closed the road for one to two hours for blasting and clean up, depending on how much debris came onto the roadway.”
Hundreds of thousands of cubic yards of the blasted rock were processed and reused in the project. Any trees taken down for the widening were also placed back in the corridor, used for purposes such as backwater solutions in streams or piles of logs for wildlife shelter.
For the last eight miles of the I-90 Snoqualmie Pass East project, WSDOT received $426 million from the Connecting Washington revenue package passed by the state legislature in 2015. The final two phases will continue widening the roadway, replacing deteriorated pavement, connecting wildlife habitats, and enhancing safety features. Phase three, covering six miles, is scheduled to start construction in 2021 and finish by fall 2025. The two-mile fourth phase is scheduled to start in 2026 and finish in 2029.