Traffic is up on this I-84 interchange west of Boise. More construction is coming

Rachel Spacek
·3 min read
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Nampa residents and Canyon County commuters know how congested Karcher Road can get between the Interstate 84 off ramp and Caldwell Boulevard.

The Idaho Transportation Department hopes its latest construction project on Karcher Road will help ease traffic that often backs up onto the interstate.

If roadwork on the Karcher interchange sounds familiar, that’s because it has been done multiple times before. ITD expanded the interchange just five years ago to increase capacity on Karcher Road. In 2017, with support from the city of Nampa, ITD removed the single-direction westbound off-ramp. A year later, ITD added a lane to the westbound loop off-ramp to reduce I-84 backups.

ITD now says that by 2025 it will:

  • Add a lane for westbound off-ramp traffic on the Karcher Road bridge.

  • Add a third westbound lane and a right-turn lane at the intersection of Karcher Road and Caldwell Boulevard.

  • Repave Karcher from I-84 to Middleton Road. The estimated cost of the project is $20 million to $25 million.

Built in 2006, the Karcher Interchange, shown here, has undergone many construction updates to try to mitigate congestion on both the interstate and Karcher Road. The Idaho Transportation Department plans to begin work on the latest iteration in February.
Built in 2006, the Karcher Interchange, shown here, has undergone many construction updates to try to mitigate congestion on both the interstate and Karcher Road. The Idaho Transportation Department plans to begin work on the latest iteration in February.

Why more construction?

ITD projections didn’t foresee the population increases that Nampa has experienced since the interchange was built in 2006.

The Karcher Interchange was built in 2006 to provide access from the interstate to State Highway 55 toward Marsing. When it opened for traffic, it provided opened access to undeveloped land north of I-84 and to the growing commercial area near the Karcher Mall. Since then, the daily traffic counts on the Karcher Interchange have nearly doubled since, according to ITD.

Last year the Idaho Statesman reported that Karcher Road, or ID 55, was one of three stretches of Treasure Valley roads that had the most significant growth in traffic volumes over the last five years.

Since 2019, when ITD completed the most recent Karcher Interchange updates, Nampa’s population has increased by over 12%, according to the Community Planning Association of Southwest Idaho. The traffic volume on Karcher Road has also increased.

“Growth in the area has exceeded anticipated traffic volumes that the interchange was designed for,” said the transportation department in its online project outline.

The interchange was originally designed in 2006 to handle 48,400 cars per day by 2026. In 2023, ITD said the interchange saw nearly 52,000 vehicles per day. ITD expects that by 2045 at least 71,000 vehicles will pass through the interchange daily.

ITD began “evaluating the Karcher Interchange in 2017 and began designing improvements in 2021,” said Sophia Miraglio, spokesperson for ITD, in an email. She said the department is beginning improvements two years before the end of the “design life” of the interchange.

Miraglio said in 2006 the Karcher Interchange was designed to encourage commercial growth in an area that was mostly farmland.

The 2006 map shows the area where ITD built the Karcher Interchange. In a 2006 Idaho Statesman article, the newspaper reported that the interchange “raises hopes for new stores.”
The 2006 map shows the area where ITD built the Karcher Interchange. In a 2006 Idaho Statesman article, the newspaper reported that the interchange “raises hopes for new stores.”

“That is exactly what this interchange did,” she said.

The department plans to finish construction on the interchange by fall of 2025.

All lanes on Karcher will be open during the daytime with all major roadwork taking place from 10 p.m. to 5 a.m. At night one lane will be open in each direction on Karcher. ITD said online that there will be overnight lane closures on I-84, bike lanes and sidewalks will have detours, and speed limits will be reduced.

Other Karcher Road projects

Further west down Karcher Road, ITD has begun to study ways to improve traffic flow on Karcher Road between Pearl Lane and Middleton Road. The department plans to widen the highway from two lanes to five lanes.

Online ITD said that the area around Idaho 55 “is growing rapidly, causing traffic volumes to increase beyond what SH-55 was designed to handle.” Average daily traffic volume along ID 55 between Pearl and Middleton Road is around 30,000 vehicles, according to the ITD website.

“In many areas, the highway has not been widened since it was constructed in the 1930s,” ITD said on its website.

Construction has not begun. ITD plans to puchase the property for expansion in 2025 and 2026.

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