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I-90 Idaho 41 Interchange

Traffic volumes on Interstate 90 and Idaho Highway 41 continue to grow, prompting the redesign of the interchange to safely accommodate more drivers.

The interchange will be redesigned to enhance safety and capacity. Depending on the new design, that could involve replacing bridges, realigning on- and off-ramps, providing continued access for cyclists and pedestrians, and constructing capacity for planned and possible expansion. As the project develops with public input, other considerations--such as the existing at-grade railroad crossing, synchronization of signals, barriers between lanes, the proximity of the Huetter rest area, and the grade of the interstate--may be addressed as well.

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Evaluation of Proposed Alternatives

As part of a value planning process that brought multiple stakeholders together to develop and explore possible modifications to the interchange, nine alternatives were proposed and evaluated. All alternatives were designed to enhance safety, improve mobility and be compatible with future expansion. The group developed and applied criteria to rank the proposed alternatives; more information on that criteria can be found under the downloads and resources section.

Of the nine alternatives, two were selected by the team to present to the public for comment. Both alternatives meet the base needs defined by local stakeholders and have similar impacts to Seltice Avenue, but the designs differ in cost and planned improvements to the westbound I-90 off-ramp.

Please continue reading to learn more about each alternative before giving comment.

View displays from the public meeting.

Half-Diamond Interchange

With the half-diamond interchange design, the five-leg intersection at Seltice Way and ID-41 would be replaced with a four-leg intersection. The loop ramp for drivers exiting westbound I-90 would remain, though safety improvements—such as adjusting the radius of the curve and adding a deceleration lane prior to exiting the freeway—would be constructed. Two signals would be required to direct traffic from ID-41 onto I-90.

Seltice Way would be elevated over ID-41, requiring a new bridge. Pending further traffic modeling, signals or roundabouts would be required to connect Seltice Way, ID-41 and other local roads. They would provide access to the residential area south of I-90 and serve all traffic to and from Seltice Way to either I-90 or ID-41.

This design is estimated to cost $31 million.

View the half-diamond design.

SPUI Interchange

Most interchanges direct traffic with two signals coordinated with each other. With this alternative, a single-point urban interchange (SPUI, pronounced "spooey") would be used to control movements to and from I-90 and ID-41 with just one signal. SPUIs tend to be more efficient and decrease travel times at busy intersections.

To construct the SPUI, ID-41 would move to the west and dive under I-90 and Seltice Way. The old portion of ID-41 would be removed, and the Centennial Trail would be extended along that alignment to connect with the planned path to be constructed with the expansion of ID-41 in 2020-21. Because movements at all I-90 ramps would be handled by one signal, the signal at the I-90 westbound off ramp/Seltice Way/Herborn Place would be eliminated.

Pending further traffic modeling, signals or roundabouts would be required to connect Seltice Way, ID-41 and other local roads. They would provide access to the residential area south of I-90 and serve all traffic to and from Seltice Way to either I-90 or ID-41.

This design is estimated to cost $65 million.

View the SPUI design.
Spring 2018
Early design
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Fall 2018
Value planning with local stakeholders, and a public meeting to collect input on alternatives
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Winter 2018
Preferred alternative selected
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2019-2020
Design finalized and right of way acquired
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Spring 2023
Anticipated start construction, though if funding becomes available the project could be constructed earlier
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Fall 2024
End of construction (depending on selected design)
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Spring 2018

Early design

Engineers began collecting data to assess the needs of the project, ranging from traffic volumes to stakeholder identification, to develop various interchange designs.

Project
Updates

Value Planning

ITD met with the city, planners and engineering firms to assess the needs of the project before creatively and collaboratively identifying solutions. Nine alternatives were explored by the group, and the department has selected two alternatives to present to the public at the meeting in early November.

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