$112 million I-15 Idaho project finishes eight bridge reconstruction after two years. Challenges included traffic management and unique dirt conditions but project continues with the Chubbuck Road rebuild. Part of a $400 million plan to modernize Idaho's infrastructure under TECHM.
Photo courtesy of Idaho Transportation Department
A Cat wheel loader works on the I-15 project.
A $112 million Pocatello, Idaho, interstate project under construction for more than two years reached a milestone this fall as crews opened all eight bridges in the rebuild.
"We're really excited to finally have all the I-15 traffic moved to the new mainlines," Idaho Department of Transportation (ITD) Project Engineer Greg Roberts said. "We can't express enough thanks to the community for their patience as we've worked through the logistics of such a large project."
Photo courtesy of Idaho Transportation Department
The ITD awarded the bid for the System Interchange project to the joint venture firm of Sundt-Cannon. The project includes the construction of eight new bridges, transitioning parts of Interstate 15 to collector-distributor lanes, the construction of 10 retaining walls, and the addition of a 1.3-mi. pedestrian and bike path. The bulk of that work is complete, but work will continue through the winter into next summer for the reconstruction of Chubbuck Road, which runs beneath the interstate.
The project addresses two issues, ITD spokesman Justin Smith said.
"The bridges were getting to be about 80 years old and at the end of their design life," he said. "At the same time, the design didn't meet modern standards or driver's expectation. The redesign takes away the merge from the left and makes everything merge from the right."
The biggest challenge was keeping traffic moving while work was under way.
"We have 30,000 to 50,000 vehicles a day in traffic volume so keeping traffic moving has been a large struggle for us," Smith said. "We were really lucky. We had another project called Northgate and that project was a new interchange just a couple of miles north of System. We were able to use that. In some cases, we closed ramps or we created temporary ramps.
"It was quite the dance to get everything built and still keep everybody moving around. We've had to do some innovation. We used a conveyor system to move dirt rather than trucks to make it safer so we don't have trucks coming on and off the Interstate as often."
But the dirt also posed a bit of a challenge at times. Crews call it "moon dust," Smith said. If the water content is too low, it becomes a fine powder, an extremely fine silt; if the water content is too high, it becomes slime.
"If it's just right, it compacts really nicely," Smith said. "We've got a water truck, and we've been putting down lots of water to keep the dust down around the construction site. The construction managers are continually monitoring it to see that we have the right amount of water."
Continuing work will include a new detour for traffic using the Pocatello Creek on-ramp to head west toward Chubbuck. Traffic will be routed through the Northgate Interchange while crews rebuild the old mainline roadway to match the grade of the new road. That work will continue into early spring. Chubbuck Road is scheduled to open partially to traffic in late December.
Photo courtesy of Idaho Transportation Department
The System Interchange project is part of about $400 million worth of projects in the I-15 corridor, the primary route from Idaho to Montana and originally built 80 years ago. The projects are funded under the Transportation Expansion and Congestion Mitigation Plan (TECHM) funded by the Idaho Legislature in 2017.
"The object was to get shovel-ready jobs running as quickly as possible," Smith said. "We were able to take jobs already on the shelf and get them going. Idaho is a place a lot of people would like to live. We've seen a lot of growth throughout the state, and with that comes a lot more traffic."
Some trivia about the new bridges from ITD:
- 24 steel girders (12 built in Montana, 12 built in Utah), 6 girders per bridge
- The girders traveled approximately 21,000 mi. to get to the job for all sections.
- Each girder is 7-ft. tall and 2-ft., 4-in. wide. The top and bottom flanges range from 1-in. thick to 2¾-in. thick with the "web" being 5/8-in. thick.
- Each girder weighs between 132,000 and 199,000 lbs. for the 414-ft. length.
- Three different sections per girder with the longest at 144 ft. and the heaviest section at 80,431 lbs.
- 414 ft. total length of girders
- Bridge width is 58 ft., 10 in.
- 16,896 7/8-in. bolts connecting the girders
- Total steel weight of approximately 4.32 million lbs., not including rebar.
Lori Tobias
Lori Tobias is a journalist of more years than she cares to count, most recently as a staff writer for The Oregonian and previously as a columnist and features writer for the Rocky Mountain News. She is the author of the memoir, Storm Beat - A Journalist Reports from the Oregon Coast, and the novel Wander, winner of the Nancy Pearl Literary Award in 2017. She has freelanced for numerous publications, including The New York Times, The Denver Post, Alaska Airlines in-flight, Natural Home, Spotlight Germany, Vegetarian Times and the Miami Herald. She is an avid reader, enjoys kayaking, traveling and exploring the Oregon Coast where she lives with her husband Chan and rescue pups, Gus and Lily.
Read more from Lori Tobias here.
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