North Ada County is getting a new $55M interchange. What it’ll cost drivers
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- ITD begins $55M interchange work at Idaho 16 and State Street, disrupting traffic.
- New bridge and loop ramp aim to improve traffic flow and safety by 2027.
- Project supports long-term growth, with traffic forecast to rise 73% by 2045.
Changes are coming to a busy intersection in growing North Ada County — and, for the time being, so are some traffic headaches.
As of Sunday, drivers can observe a new traffic pattern at the intersection of Idaho 16 and Idaho 44, also known as State Street, on the border of Eagle and Star. The shifts, which include lane closures and speed reductions, come as crews for the Idaho Transportation Department work to revamp the crossing into a full-blown interchange.
Construction of the interchange began in August and, is scheduled to move into a new phase this week, according to a news release from the department. During this phase, ITD will:
- Reduce Idaho 16 to one lane in each direction between the Boise River Bridge and Idaho 44.
- Shift northbound Idaho 16 traffic onto the highway’s southbound lanes.
- Reduce speed limits to 55 miles per hour in the work zone around the intersection.
- Open all lanes of Idaho 16 directly abutting the intersection, with normal traffic operations.
“These traffic changes will allow crews to prepare and place concrete for (Idaho) 16 and build the northbound off-ramp for the new interchange,” said ITD spokesperson Jill Youmans in the release.
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$55 million ‘partial cloverleaf’ interchange
When the interchange opens in 2027, it will feature a bridge allowing Idaho 16 to cross over State Street, on- and off-ramps enabling travel between the two highways, and a “loop” ramp that will eliminate a “high-volume” left-turn from westbound State Street to southbound Idaho 16, according to an ITD project page. The loop ramp gives the interchange a “partial cloverleaf” design, similar to the interchange at the I-184 on-ramp at Franklin Road in Boise.
ITD also plans to widen State to three lanes in both directions immediately around the intersection, from Moyle Avenue to Short Road. That work will include adding a lane along the highway’s south, according to an email alert from the department. The department will also construct a pathway on the south side of State.
The interchange comes at a $55 million cost. It was improved as part of the first phase of ITD’s work on the Idaho 16 corridor, when the state extended the highway south from State Street to Chinden Boulevard in 2014. In 2022, the department announced it would start work on the second phase of the corridor, extending it further south from Chinden to Interstate 84 and building a series of interchanges and overpasses.
The last of the interchanges on that docket is the one at State Street — though ITD is now considering interchange work further north.
Once the corridor between I-84 and State Street opens, estimated in 2027, ITD anticipates that drivers will be able to make the roughly 7-mile trek in seven to 10 minutes. In roughly 20 minutes, they could get from I-84 to Emmett.
The new freeway is the Treasure Valley’s first in at least 40 years.
ITD warns drivers of ongoing construction
The adjusted configuration that started this week is anticipated to be in place until November, according to the email alert, though additional construction will continue from there. It also indicated that State Street would be reduced to one lane heading east from the intersection during construction.
According to ITD, throughout construction on the interchange, drivers can expect:
- At least one lane of travel in each direction on Idaho 16 and Idaho 44 will remain open.
- Most construction will occur during the day, but some night work will be necessary, prompting “occasional nighttime noise.”
- Access to local cross streets east and west of the intersection have or will change, including at Moyle Avenue, Hamlin Avenue, Short Road and Crystal Springs Lane. The Moyle intersection has been signalized; Crystal Springs and Hamlin have been changed to right-in, right-out only. A left turn from Short will be eliminated.
ITD warns that flaggers will be present, and motorists are asked to use caution. Delays and occasional detours on both highways should be anticipated.
“This is a challenging work zone, and we are actively looking at ways to improve traffic flow through the area,” said Styles Salek, an ITD design and construction engineer, in a statement included in ITD’s news release on Friday, Sept. 26.
Interchange hoped to help accommodate growth
The new interchange is expected to accommodate a growth in traffic in the coming two decades, as well as allow for faster, more free-flowing north-south travel, according to ITD.
In 2014, roughly 15,000 vehicles used the intersection per hour during the afternoon rush, from 4 p.m. to 6 p.m. By 2045, that’s anticipated to jump to 26,000 vehicles. That’s a 73% increase.
As growth in the Treasure Valley continues to push north, ITD’s plans for Idaho 16 don’t stop at State Street. The department recently unveiled new plans for the roughly 14-mile stretch of highway from State to Idaho 52 in Emmett. Those, not yet finalized, will include more interchanges and overpasses — and come with their own nearly $500 million price tag.
This story was originally published September 29, 2025 at 3:59 PM.
