Interstate 90 is the main east-west transportation corridor in Washington State, connecting the large population and business centers of western Washington with the agricultural industries and recreational areas of eastern Washington.
On an average day, 28,000 vehicles travel over I-90; this number doubles on weekends and holidays. Due to heavy volume on I-90 in Snoqualmie Pass, which is expected to increase 2.1 percent annually until it reaches an average of more than 41,000 vehicles per day by 2030, the Washington State Department of Transportation determined that capacity needed to be added.
The condition of the existing roadway and surrounding environment indicated the need for safety improvements along the corridor. Travel along Snoqualmie Pass is not always reliable due to miles of stand-still traffic during busy summer weekends and closures in the winter due to avalanche control work.
Thus, WSDOT has launched the I-90 Snoqualmie Pass East project, a 15-mi. (24 km) safety improvement project from Hyak to Easton. The I-90 project will increase capacity and improve safety by building a new six lane highway, replace deteriorating concrete, reduce road closures due to avalanches, add and replace bridges and culverts, straighten sharp curves and stabilize rock slopes.
Moving People
and Wildlife
The uninterrupted movement of people, freight and business over I-90 Snoqualmie Pass is essential to the economic vitality of the state. Similarly, the uninterrupted movement of animals in the region is essential to the region’s environmental vitality.
One of the unique aspects of the project is the inclusion of overpasses and underpasses specifically designated for animals, reconnecting wildlife trying to move north-south (while improving transportation moving east-west) by creating underpasses and building bridges over the freeway for wildlife to allow the animals to move safely.
“Twenty-eight thousand vehicles per day bisect the Cascades,” said Jen Watkins, conservation associate with Conservation Northwest. “We can’t block their ability to move safely.”
“I-90 acts as a barrier to wildlife trying to migrate through the Central Cascades and is likely isolating wildlife populations,” said Megan Lott, who works in communications for the South Central Region of WSDOT. “As I-90 expands, it will make this barrier worse. As part of the I-90 project we are building bridges and installing culverts to correct fish passage and reconnect habitat along the Central Cascades and improve motorist safety by reducing dangerous collisions between wildlife and vehicles.”
The National Forest Service manages the land and has been pushing for this for years. So have state conservationists. The overpasses and underpasses will reunite wildlife populations divided by the highway, allowing animals to more easily find food, homes (especially when conditions change, such as a result of wild fires) and even new mates, which will add to the genetic diversity.
The 150-ft.- (45.7 m) wide overpass will be planted with native trees and shrubs to mimic the forests on either side so that the animals will think they’re still in the forest. The $6 million wildlife crossing is the first of more than 20 planned overpasses and underpasses spanning the landscape along Washington’s central Cascade Mountains.
“We are building approximately 20 wildlife crossings in areas where streams already cross under the highway and where monitoring data helped prioritize areas to invest in enhancing connectivity,” Lott added. “The wildlife overcrossing we started construction on in late May is the first crossing to be built over the roadway. During the planning phase of the I-90 project, this location was identified as a good location for potential connectivity due to diverse wildlife species. Wildlife naturally migrate through the Price Creek area and it’s a logical crossing for wildlife around the east end of Keechelus Lake.”
Four underpasses are already open. Game cameras have caught video of animals from river otters to deer crossing under the highway. The underpasses provide waterways, extra width for land animals and piles of rocks for small mammals to safely traverse the busy highway.
Preparing for the I-90 Snoqualmie Pass East project went well beyond the typical environmental impact study. It took five years of pre-construction baseline wildlife monitoring to identify different species and provide recommendations to guide the project design. These monitoring efforts included camera studies, snow tracking, movement data, public reporting, habitat studies, genetic sample collection and inventory of dead animals removed from the side of I-90.
Florida, Montana and a few other states have built similar animal crossings. Canada has constructed 44 of them along the Trans-Canada Highway. They have proved successful. The number of collisions with animals dropped by 80 percent by the time the Canadian project was finished. Banff National Park in Alberta, Canada, even has video of animals using these bridges.
There will be more in Washington too. Lott said preliminary designs of the remaining 8 mi. (12.9 km) of the I-90 project have incorporated one more overcrossing at Easton Hill. “Easton Hill provides a critical north-south migration for wildlife. An overcrossing at this location would provide the greatest opportunity for year-round use by the largest number of wildlife species, compared to other crossing structures like culverts or crossings under the roadway.”
Project Details
The I-90 project runs through the Central Cascades across Snoqualmie Pass to the town of Easton in Washington State. The 15-mi. project is broken into three different phases. The first phase consists of a 5-mi. (8 km) project from Hyak to Keechelus Dam. The second phase is a 4-mi. (6.4 km) project from Keechelus Dam to the Cabin Creek interchange. The third phase is 6 mi. (9.6 km) from the Cabin Creek interchange to the town of Easton.
The Washington State Department of Transportation received $551 million to design and construct the first 5 mi. of the I-90 project from Hyak to Keechelus Dam from the 2005 gas tax, Lott said. “Due to project savings from the five-mile project, WSDOT is using $107 million to build the next two miles from Keechelus Dam to the Stampede Pass interchange, which includes the wildlife overcrossing.” The remaining eight miles of the project are unfunded.
Construction on the 2-mi. (3.2 km) section that includes the wildlife overcrossing started May 2015 and is scheduled to be complete in fall 2019. The 5-mi. project started in spring 2010 and is scheduled to be complete in fall 2018.
“The benefit of this 2-mi. section of I-90 will improve capacity by adding a new six-lane highway, reducing rock falls by stabilizing rock slopes,” Lott continued.
Atkinson Construction is the general contractor and is in charge of building bridges and other structures. Sub-contractors include KLB for earthwork, Gary Merlino Construction for PCCP paving, Columbia Asphalt for HMA paving, Northeast Electric and M2 Industrial for the guardrail.
“All types of heavy construction equipment are required, including excavators, off-road haul vehicles, conventional dump trucks and front end loaders,” Lott said. Cranes also will be used to set precast panels and girders for the wildlife crossing and bridges.
Roadway excavation is anticipated to top 662,000 cu. yds. (506,135 cu m). Materials needed to complete the project include 114,000 tons (103,419 t) of crushed surfacing, 561,000 cu. yds. (428,915 cu m) of embankment, 41,000 cu. yds. (31,346.74 cu m) of cement concrete pavement, 59,000 tons (53,523.9 t) of hot mix asphalt and 4,400 cu. yds. (3,364 cu m) of concrete.
Phase 2 began in March. That work includes expanding the roadway to six lanes, doing highway improvements for 2 mi. and building the first wildlife overcrossing. Lott said it’s very similar to overpasses for vehicles. “The wildlife crossing is supported by footings. The load from the embankment above is transferred to the footing by the precast arch panels.”
The project remains on target to hit its deadline. “Crews haven’t run into any challenges yet on this section of the project,” Lott said.
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