Idaho’s Treasure Valley is in the western area of the state. It includes four of the state’s six largest cities, including the capital, Boise. Approximately 40 percent of the state population lives in the Treasure Valley, and three of its cities were among the 15 fastest growing in the U.S. in 2021. The area, however, is underserved in terms of infrastructure. The Idaho Transportation Department (ITD) is in the middle of a long-term project on SH 16 that aims to improve modality in the Treasure Valley.The Treasure Valley has only one true north/south state route (SH 55/Eagle Road) that travels through it. The route is heavily trafficked. The west side of the Treasure Valley has only local roads with lower speed limits serving north/south traffic.

SH 16 is a 16-mile route. The current phase of the project is adding 4.5 miles to the four-lane divided limited-access highway. The extension will result in SH 16 extending further south and connecting with I-84. I-84, which runs from Oregon to Utah, is the longest highway in the state and connects a few of Idaho’s largest cities.

The need to extend SH 16 has been on ITD’s radar for years. In 2011, ITD completed an environmental study to lengthen the Idaho 16 corridor. The current project is phase two as the first phase – which included building 2 miles of highway and a crossing over the Boise River – was completed in 2014. The final phase of the project, which will include adding multiple interchanges, is in the design phase and ITD is expecting to begin construction in a few years.

There are multiple tasks involved with building phase two of the extended roadway. Construction includes:

• 4.6 miles of highway
• A new I-84 interchange to access SH 16
• Signalized intersections at future interchange ramp terminals
• Reconstruction of the current signalized intersection at U.S. 20/26
• New overpasses over two roads
• Multiple bridges over irrigation canals and the railroad
• Minor adjustments to local roads near SH 16

“The overpasses will separate local traffic from SH 16 and maximize traffic flow for area drivers and those on the highway,” says Jeff Ryan, a Resident Engineer with ITD’s District 3 office. Ryan notes that phase two of the project was divided into three construction packages. “This was done due to the size of the project and the time frame needed to acquire right of way.” He adds that land acquisition for the project was challenging.

Near the project site are local farms that grow crops such as mint, onion, and wheat. There are also irrigation facilities in the area that serve these farms. “I had to learn the intricacies of how farmers irrigate,” Ryan says.

The irrigation facilities are via the multiple canals in the area. The new highway is crossing irrigation facilities, and irrigation has to remain active during the summer. It’s the only way to ensure the crops have water during the warm, dry summer months.

“We built temporary facilities to deliver the crops the water they needed,” Ryan says. “The farmers and contractors were in the field together going over the design of the new facilities.”  

Irrigation season runs from mid-March to October. After October, the irrigation system is turned off, so it’s not carrying water needed for crops. This part of the year is often when construction season winds down. However, the team had to handle some construction tasks during the late fall and winter months if they hoped to keep on schedule.

Another challenge the team dealt with was third-party utilities. There are utilities scattered throughout the area. “Coordinating with the private entities to relocate the utilities was one of our biggest challenges,” Ryan says.

The newly extended SH 16 will cross a railroad track. The Union Pacific line, which operates under Boise Valley Railroad, is in an area that is part of the next construction package. ITD worked hard to complete an agreement with the company to cross the railroad.

Phase two of the project has two companies serving as the general contractor – Knife River Corporation and Concrete Placing Company (CPC). Both contractors have worked with ITD many times over the years. “They both have a lot of experience with this type of work, are big, and have the resources to handle a project of this size,” Ryan says.

The budget for phase two is $225 million in construction contracts and another $17 million for administration services, such as testing and inspection. The project is being funded by the Governor’s Leading Idaho program, under which Transportation Expansion and Congestion Mitigation (TECM) funds are being used as debt service on bonds. The Leading Idaho program aims to expedite project timelines to address rapid growth and build critical infrastructure.

Local funds are also in the contract for items such as utility relocations, a partnership with the Ada County Highway District for improvements to a separated pathway adjacent to the project, and impact fees for increased traffic from a recently built Amazon distribution center. Currently, the project is on budget.

Phase two of the project began in the summer of 2022. It is expected to be complete in late fall 2025. Ryan says portions of the project are slightly behind due to irrigation challenges and third-party negotiations. The overall project, he adds, is right on schedule.

The SH 16 project is large by Idaho standards. It’s also critical to the rapidly growing Treasure Valley area. The route will give residents another way to access I-84. Greater access is expected to lead to further development in the area. With the extension of SH 16, drivers should experience congestion relief and improved commute times.