The Idaho segment of Interstate 84 (I-84) is a major traffic corridor that crosses the state from the Oregon state line on the west to the Utah state line on the southeast. Designated as the Vietnam Veterans Memorial Highway, I-84 is one of the busiest highways in Idaho.

The route generally follows the path of the Snake River and passes through the Idaho cities of Boise, Nampa, and Mountain Home in the region known as Treasure Valley, which includes five counties that make up the Boise metropolitan area. The valley is a significant Idaho economic hub for technology, agriculture, health care, and manufacturing.

I-84 is an important freight and commerce corridor, connecting western ports to inland destinations like Salt Lake City, Utah, and Denver, Colorado. Locally, it serves Treasure Valley as the main east-west thoroughfare. At its busiest location, daily traffic is approximately 160,000 vehicles, which is nearly double the volume of traffic 20 years ago.

Canyon County, one of the Treasure Valley counties, is the second-most populous county in Idaho. As part of its ongoing work to improve I-84 in Canyon County, the Idaho Transportation Department (ITD) is constructing improvements to I-84 between the Centennial Way and Franklin Road interchanges in Caldwell, the Canyon County seat. This multi-year project began construction in November 2023 and is scheduled for completion in 2027.

“The greater Boise area has seen significant growth on par with the fastest growing areas within the United States,” said David Barrett, ITD District 3 Staff Engineer. “The growth shows no sign of slowing down, and the older four-lane divided highway is no longer able to keep up with the demand.

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“The Idaho Transportation Department has been widening Interstate 84 through the Treasure Valley systematically over the last 20 years with federal- and state-funded bonding programs. In Canyon County, much of it is has been updated to a modern six-lane roadway [three in each direction] with auxiliary lanes between ramps. This latest widening will greatly relieve stress in the Nampa and Caldwell area.

“As population growth on the west end of the valley continues, this section of highway will be important to ensure that Idaho’s safety, mobility, and economic prosperity continue for many decades to come.”

The Centennial Way/Franklin Road project includes:

• Widening I-84 to three lanes in each direction with auxiliary lanes between interchanges
• Replacing the 10th Avenue bridge
• Removing one westbound on-ramp at the 10th Avenue Interchange
• Updating the pedestrian overpass
• Building a sound wall along Hannibal Street
• Adding a traffic signal at the westbound ramps at the Centennial Way Interchange

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“The project widens I-84 between milepost 27 and milepost 29 to three lanes in each direction,” Barrett said. “Auxiliary lanes between ramps allow safer weaving and merges. Because the 10th Avenue bridge structure in Caldwell could not accommodate the additional lanes, it is being rebuilt. The existing pedestrian bridge just east of the 10th Avenue bridge is receiving upgraded fencing and repairs to ensure a long life.

“The older storm sewer system — which combined both City of Caldwell and ITD runoff and dumped directly into the nearby Boise River — is being reconstructed and separated into two systems treating the water before leaving the site. Additionally, a section of sound wall will be constructed on the north side between the Centennial Way and 10th Avenue interchanges.”

The general contractor for the $93.4 million ITD project is Concrete Placing Company of Boise. The designer is Horrocks Engineers Inc. of Meridian, Idaho.

The Idaho Transportation Department has made a significant investment in modernizing and expanding the interstate through southern Idaho. Planning for improvements in the Treasure Valley began in the early 2000s. The federal-aid Grant Anticipation Revenue Vehicle (GARVEE) bonding program provided the initial revenue necessary to accelerate improvements in the Boise area in the early 2000s. ITD has proceeded to make necessary improvements west toward Canyon County.

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Funding for the Centennial Way/Franklin Road project is provided by Idaho’s Transportation Expansion and Congestion Mitigation (TECM) program.

“The TECM program was created by the Idaho Legislature in 2017,” Barrett said. “Lawmakers added the ability to also use TECM funding to bond for projects in 2019 and in 2021, guaranteeing $80 million annually to be used as debt service for bonds that would fund acceleration of critical improvements statewide.

“The combination of bond sale proceeds with the addition of other funding sources has surpassed $2 billion to address the highest priority mobility and safety improvements, to allow continued modernization of Idaho’s transportation infrastructure and to support the state’s economic growth and quality of life. In 2025, as part of Governor Brad Little’s Leading Idaho initiative, the legislature approved another $60 million in TECM funds over three years to continue statewide progress.

“Using the TECM fund for bonding has accelerated the development and construction of critical transportation infrastructure that would otherwise take decades to build. ITD secures TECM bonds with a pledge of future state sales tax transfer, and the Idaho Housing and Finance Association issues bonds on ITD’s behalf on an as-needed basis. This ensures that funds are available for the duration of the projects while limiting interest costs.”

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According to Amy Schroeder, TECM Division Administrator, additional investments in I-84 include 5 miles of modernization and widening east of Boise, between the south Jerome Interchange and the Twin Falls interchange, and new interchanges at south Jerome, Burley, and Heyburn.

“ITD is currently studying continued improvements to I-84 west of the Centennial Way/Franklin Road project,” Schroeder said. “The department will receive environmental approval for the I-84, SH-44 to Centennial Way project in 2025. While ITD hasn’t identified funding to construct the entirety of this project, the most critical component, reconstruction of the interchange at SH-44 [exit 25], is programmed for construction in 2031. ITD is also beginning a study to expand I-84 at the east end of the Treasure Valley toward Mountain Home, Idaho.”

The project is currently in Stage 2 of five planned stages, according to Barrett.

“The north half of the 10th Avenue bridge has been reconstructed,” Barrett said. “Approximately 40 percent of the concrete pavement has been placed, and the sound wall on the north has been constructed. New fencing has been placed on the pedestrian bridge. Currently the contractor is working in the center of the roadway, constructing the median barrier and main storm sewer trunkline.”

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During construction on such a major undertaking as the Centennial Way/Franklin Road project, along a busy primary thoroughfare, a top priority is maintenance of traffic. Barrett said that ITD has phased the construction to reduce traffic impacts to the highest practical extent.

“The work impacts not only the main line interstate traffic but also that on adjacent city streets with businesses and residences,” he said. “The interstate splits the city of Caldwell in half, with 10th Avenue being the major north-south route under I-84.

“Traffic volumes required that the existing four lanes remain open throughout construction. Select lane closures have been necessary but have been restricted to non-peak hours [overnight and early morning]. The existing four-lane highway has been maintained by initially constructing temporary asphalt along the southern side and then shifting traffic south, to reconstruct the northern third of the roadway and half of the 10th Avenue bridge.

“Just as important is the passage of pedestrians. The nearby pedestrian bridge serves foot and bike traffic. Initially, designers planned to route all pedestrian traffic to 10th Avenue while the pedestrian bridge was under an eight-month closure. However, demolition of the 10th Avenue bridge, as well as placement of girders, necessitated simultaneous closure. ITD and the contractor worked to come up with a workable solution. Routing pedestrians to the next closest exit was not reasonable due to the distance. The solution was to charter a local bus company to operate during daylight hours while 10th Avenue was closed.”

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Currently, westbound traffic has been shifted to the newly constructed pavement to allow for work within the median. Once this is constructed, eastbound traffic will be shifted to the fully completed north half of the roadway, to allow completion of construction of the 10th Avenue bridge and the eastbound interstate lanes.

Several temporary ramps have been constructed to maintain access to the three interchanges within the project limits. Some extended ramp closures are part of the plan, requiring traffic to be diverted to the nearby entrances.

“Fortunately, there are multiple exits within a mile of each other, limiting the required detour route,” Barrett said.

In addition to the pedestrian and vehicle issues, other project challenges have included encountering unknown utilities that required adjustment, according to Barrett.

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“Arguably, the greatest example of overcoming these challenges to the project has been the amazing attitude of teamwork between ITD, the contractor, the design consultant, the CE&I [Consultant Engineering and Inspection] groups, the public engagement team, and the City of Caldwell. Early on, ITD implemented formal partnering to encourage a teamwork attitude. This has led groups which are often at odds with each other to consider themselves to be part of a larger group all working together to accomplish the project.

“Davey Jensen, ITD’s Consultant CE&I Project Manager, helps the team anticipate critical issues early and works collaboratively to identify solutions, ensuring challenges are addressed before they escalate. Brent Lotridge, the contractor’s Project Manager, focuses on the solutions to problems such as addressing a pothole in the bridge while it is small rather than ignoring it, which would lead to a much larger problem. The contractor’s surveyor group, comprised of Christina Nemec and Marcus Beagley, has been working closely with Will Rice and the design support team, to ensure that the roadway surface will drain properly and that slopes aren’t too steep. Kate Wallace, ITD’s Consultant Outreach Coordinator, regularly makes checks to nearby businesses to ensure work is not overly impacting their access or keeping hotel clients awake at odd hours.”

“In my 10-plus years of working with ITD, I’ve never seen a team work as closely and constructively to produce a quality project in a safe and timely manner,” said Styles Salek, ITD Resident Engineer. “Everyone chips in to be a part of the solution, and I can say we’re all true partners.”

According to Salek, the teamwork has been paying off.

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“To date, the project has had 30 change orders totaling $835,000 — far less than many similar projects at this stage — bringing the total project cost to $93.4 million, an increase of 0.8 percent, which is well within the department’s average contingency,” he said. “Additionally, the project is expected to be completed almost seven months early.”

• Owner: Idaho Transportation Department, District 3
• General Contractor: Concrete Placing Company, Boise, Idaho
• Designer/CE&I: Horrocks Engineers Inc., Meridian, Idaho
• Public Outreach: RBCI, Boise, Idaho
• Other Contractors: NXB Geo, Quality Electric, Specialty Construction Supply, Boise River Fence, Curtis Clean Sweep, Knife River, Precision Communications Holdings LLC, Integrity Inspection Solutions Inc., Center Creek Construction, North American Construction, Nucor Harris Rebar Boise, Qualitree Inc., Earth Energy Inc., Northwest Landscape LLC, PMB Cellular & Specialty Grouting, Dr Pipeline LLC, Harris Rebar Placing LLC, A-Core Concrete Cutting Inc., Railco LLC, Syman LLC, Earth Energy Inc., H & S Company LLC, National Coatings Inc., Antigo Construction Inc., Peak Concrete Construction LLC, Dennis Phipps Well Drilling Inc., G2B Company Inc., ProTech Coatings Inc.
Photos courtesy of Idaho Department of Transportation