Working alongside the Idaho Transportation Department (ITD), Sundt is enhancing mobility and modernizing key sections of I-15 and I-86. Through innovative construction methods and close collaboration with ITD, the team accelerated the construction schedule, optimized project phasing and reduced costs while delivering safer, more efficient transportation infrastructure.

 

Modernizing miles in Idaho

The construction of the I-86 and I-15 System interchange, known as the “Flying Y,” and the I-15 Widening Northgate to South Hall updated critical transportation infrastructure, improving mobility throughout Idaho. Both sections of highway are heavily trafficked by locals, visitors headed north to Yellowstone and commercial vehicles delivering essential goods through the Intermountain region. Updating bridges, ramps, traffic separation infrastructure and improving overall highway geometry helps create a safer drive for all motorists as well as reduce congestion, especially prevalent during the summer months.

Together, these projects provide more reliable freight movement, improved access for residents, and infrastructure that will support Idaho’s growing economy for years to come.

 

Bridging the gap for a 60-year-old stretch of highway

 

The I-86 and I-15 System Interchange in Pocatello, Idaho connects two major north-south and east-west corridors through Idaho, allowing travelers to move seamlessly between the two highways. It’s nicknamed the “Flying Y” for the Y shape created when you look at the two large highways from above. Originally constructed in the mid-1960s, bridges on the I-86 and I-15 System Interchange needed upgrading to help address congestion that compromised driver safety and ease of traffic. Sundt’s upgrades to the project marked the largest ITD project in recent years.

These upgrades included the construction of eight new bridges, six of which were within the I-15 and I-86 interchange and the other two located at I-15 and Chubbuck Road. Additionally, teams transformed parts of the existing I-15 northbound to new collector-distributor lanes to lessen traffic on the Pocatello on-ramp. Sundt also built 10 retaining walls, requiring one million cubic yards of earthwork excavation, several ramps and highway realignments.

“The goal of the Flying Y project was to improve accessibility,” said Ben Becker, area manager. “We built a collector system to be able to feed the road to improve movement around town and improve capacity for the freeway going north.”

Sundt partnered with ITD to optimize the phasing plan to maximize the material used. The teams came up with a plan to reuse onsite material to reduce waste, lower costs, and improve phasing. By the project’s completion, the team successfully reduced the import quantity for earthwork by roughly 200,000 cubic yards and the export/waste by 350,000 cubic yards using these phasing methods.

“As part of the large ITD I-15/I-86 Interstate System Interchange project, Sundt has been working with the City of Chubbuck for the portion that involves the reconstruction of Chubbuck Road. Sundt has done a great job of keeping the City informed and included in decisions. I appreciate their professionalism and would not hesitate to work with them again in the future,” said Bridger Morrison, P.E., City Engineer & Public Works Director, City of Chubbuck, Idaho.

The project completed in the fall of 2025.

 

Accelerating construction with slip-form techniques

 

On the I-15 Widening from Northgate to South Hall our team is widening a 3.9-mile stretch of I-15 to three lanes in each direction. This project marks the first time a concrete median barrier has been slip-formed on an ITD project. Slip-forming the concrete median barrier instead of using the traditional hand-forming technique accelerated construction by enabling continuous placement while reducing labor and equipment needs. This technique paired with a refined phasing schedule shaved six months off the original construction schedule.

This project is part of a multi-year program to widen and improve 51 miles of I-15 between Pocatello and Idaho Falls with new interchange ramps, replaced bridges, machine underpasses, and increased vertical clearance for overpasses.

Many Sundt employee-owners from the “Flying Y” carried over to the I-15 widening project. The continuity of the project team streamlined project start up, strengthened the client relationship and fostered trust through proven performance. This smooth transition led to open communication and a seamless construction process. Building on these established relationships allowed the team to communicate effectively, respond quickly to challenges and deliver the project efficiently.

Planned completion for the widening is the end of 2026.

Learn more about our approach to building critical infrastructure here.