During the past decade, Idaho has experienced rapid growth, so the state’s Transportation Department has embarked on a $300 million upgrade to Interstate 84, the most traveled highway in the state, with 31 million annual trips.

“This section of I-84 has seen a significant increase in traffic and crashes in the last decade,” says Jake Melder, Public Information Officer with the Idaho Transportation Department (ITD). “This project will improve safety and mobility not only within the Treasure Valley of Idaho but for the goods transported along the interstate from the ports of Seattle and Portland across the nation.”

This section of I-84 handles about 83,300 daily trips. Two thirds of the traffic on this interstate travels between Canyon and Ada counties. The road was originally constructed in the 1960s. The 7-mile long project will also support the economy for years to come.

“This project continues a vision of improving safety and mobility in Southwest Idaho, started years ago with adding lanes to I-84 in eastern parts of the Treasure Valley,” says Styles Salek, ITD Project Manager for Construction in Nampa. “This addresses growth and travel demand that has increased from the urban center of Boise on the east to Caldwell on the west.”

The federal Infrastructure for Rebuilding America program funded about $90.2 million of the project. The state also used user-fee based sources of state revenue. Grant Anticipation Revenue Vehicle (GARVEE) bonds were a primary funding mechanism for prior improvements east of this project.

ITD is preparing to continue the expansion of the interstate west. This summer, work will begin to reconstruct the aging original interstate infrastructure, and add a lane in each direction for approximately 4.7 miles. GARVEE bonds also will be used for this section of the project. The department has developed a comprehensive public awareness campaign for the project.

“To reach a diverse audience in the age of new media, ITD has conducted robust in-person meetings in conjunction with a project website,” Melder says. “The department also launched a podcast, ‘Drive Idaho,’ to highlight the work on I-84 with plans to expand the coverage to other highway projects in the region.”

Parametrix of Boise, Idaho, serves as the prime designer, and Horrocks Engineers of Pleasant Grove, Utah, was the prime for the environmental work.

“ITD had already gained Federal approval on the environmental study for this project, which expedited the delivery timeline and greatly enhanced our ability to begin construction in this corridor quickly,” Salek explains. “While design was under way between exit 33 and 36, ITD completed the environmental evaluation for the remaining urban segment of this corridor prior to commencing with the design and construction.”

The project entails adding a third traffic lane in each direction; expanding bridges; updating interchanges; adding auxiliary or slip lanes in each direction between interchanges; replacing a box culvert; and resolving other drainage issues.

At Exit 35, Northside Boulevard, ITD is replacing the traditional diamond interchange with a single point urban interchange.

“The reconstruction of the Northside interchange from a tight diamond to a single point urban interchange requires the longest steel girders in the state, at 221-and-a half-feet long, to clear span Northside Boulevard,” Salek reports.

Concrete Placing Co. (CPC) of Boise received the prime construction contract. The company began in 1962 and has successfully built many of Idaho’s largest highway projects, in addition to serving private markets in southwest Idaho, says Mike Burke, Vice President and Chief Financial Officer for CPC. The company works throughout the northwest, including Idaho, Montana, Nevada, Oregon, Utah, Washington, and Wyoming.

“CPC’s core work is structural concrete and concrete paving for highways and airports,” Burke adds.

Construction on this I-84 project began in the fall of 2019, with widening of the outside shoulders to accommodate two lanes of traffic in each direction during construction. Traffic currently flows on the outside lanes. Once CPC finishes the median construction, traffic will be placed on the inside lanes and crews will construct the outside lanes.

The department and contractor are keeping two lanes of traffic open on weekdays. That meant tight working conditions and phased construction, Salek says.

“Because of the limited right-of-way, initial phases of work take place in the median between the east- and west-bound interstate,” Burke says. “The median work leaves very limited access to the work zone.”

The stay-at-home COVID-19 pandemic response order resulted in a significant decrease in traffic, allowing some earlier lane closures on weekday nights.

CPC must provide 24-hour access to many businesses in the area, including a sugar beet processor, which sits on the northern edge of the project, as trucks haul sugar beets in and sugar out at all hours.

The contractor set up a concrete batch plant. Trucks bring the aggregate and cement to the plant. Crews are paving the highway with a 10.5-inch slab of concrete, more than 75,000 cubic yards, 7,500 truck loads, during this phase.

“A curing agent is applied to the concrete immediately after paving,” Salek explains. “Crews then proceed to cut stress relief lines in the concrete as soon as the concrete has hardened enough to permit. Both longitudinal and transverse joints are cut.” The concrete is projected to last more than 40 years.

“Much of the work is being built using electronic models and controlled by GPS or total stationing,” Burke says. “However, there still is a significant amount of traditional survey required.”

CPC is using typical construction equipment, including motor graders, rollers, wheel loaders, a variety of dump trucks, excavators of many sizes, aerial lifts and forklifts.

“There have been as many as six cranes on site at any one time, facilitating construction of two significant bridges, a sizable box culvert and MSE walls,” Burke adds. “The concrete and asphalt paving require its own set of equipment to make, deliver, place, and finish product.”

Burke says he is proud of “the commitment of our employees to build a highly technical project in the middle of a live interstate through the challenging seasons that Idaho has. The work is meticulously planned and executed by a talented group of people working night and day, including many of our subcontractors, most of whom we’ve worked with successfully in the past on other difficult projects.”

The current project is scheduled for completion in 2021. The next project to be let in the corridor is expected to continue into 2023.

“This is a project with strong community support,” Melder concludes. “The improvements are much needed, as this part of Idaho is one of the fastest growing parts of the U.S. This project is a high-profile example of ITD’s commitment to valuable public service.”