Five years, millions of dollars later, Avimor underpass set to open this fall
The biggest residential development in Idaho has waited five years and committed millions of dollars to build a new underpass connecting its growing community on the east and west sides of Idaho 55. ITD describes the new feature as a milestone for the community and the surrounding area.
The underpass, about a mile north of Avimor Drive, is part of a larger mitigation agreement between Avimor and the Idaho Transportation Department. The agreement also includes a future realignment of Idaho 55 to the west of its current alignment, according to ITD.
Signed in 2023, the agreement requires the developer to pay ITD $5,000 for each residential lot developed over the life of the project — an estimated total of about $50 million — to help fund highway and related road improvements around Avimor along Idaho 55.
Avimor spans 23,000 acres, three counties, and is approved to build 10,000 homes. An ITD spokesperson said it is the largest residential development in Idaho’s history.
Construction of the underpass was delayed by an investigation from the U.S. Environmental Protection Agency and the U.S. Army Corps of Engineers into the classification of a stock pond near the site. The investigation concluded in January 2026, and the underpass is expected to open to the public by late September, according to lead developer Brad Pfannmuller.
The Avimor Community Infrastructure District’s development agreement states developers are allowed to take on debt up to $250 million in bonds over the life of the project for public infrastructure, including fire stations and pathways. Those funds can be used only for facilities that will ultimately be owned by public agencies, including ITD, the Ada County Highway District or the city of Eagle.
To date, the district has issued about $12 million in bonds, Pfannmuller said. That includes $10 million for the underpass and about $2 million for a traffic signal at Avimor Drive and several collector roads built during the project’s early phases.
About $7.5 million of the underpass funding is paying for construction of the structure itself, while the remaining $2.5 million is funding the connecting roads and improvements to the on- and off-ramps, Pfannmuller said.
“Avimor is the one paying for improvements to the greater transportation system, so this is growth paying for itself before it’s needed,” Pfannmuller told the Idaho Statesman. “It helps people get on and off the road without stopping traffic on Highway 55, and it improves safety for everyone passing through this community.”
In 2021, before annexing into Eagle, Boise County approved plans allowing Avimor developers to build 1,700 homes. As part of that approval, the county required the developers to build a separate underpass at Avimor Drive and Idaho 55 to safely connect the community as it continues being built on either side of the highway.
“I mean, the worst thing that can happen is we go and build 10,000 homes up here, and nobody can come and go from it,” Pfannmuller said.
Completion of the project is being hailed as a “major milestone” for Avimor by both ITD officials and Avimor CID. Agreements like this between developers, state agencies and local governments are common in Idaho and allow both ITD and developers to accelerate key transportation improvements, according to ITD.
“Often, we’re able to work certain improvements into our projects,” said Brian Duran, a development services manager with ITD. “Instead of the developer constructing an improvement and paying for it themselves, we can do the construction and be reimbursed for it.”
