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US-12 and 21st Street

This project will realign the busiest intersection in Central Idaho to improve safety and traffic flow.

After construction, the design will resemble that of standard intersections and be made of concrete, which resists wear from heavier traffic better than traditional pavement.

Construction phases
Impacts will be consistent.
See the local detour.
Planned improvements
Preview changes.
Project updates
Completed traffic study
Asset 5
Winter 2016
Gathered public comments
Asset 5
Spring 2017
Completed preliminary design
Asset 5
Fall 2017
Finalized design
Asset 5
March 2019
Anticipated beginning of construction
Asset 5
October 2019
Anticipated end of construction
Asset 5

Downloads & Resources

HandoutsAsset 4
Asset 5
July 8

Idaho Street closure

Starting July 8, Idaho Street will be reduced to one lane for approximately three weeks, and drivers heading south will be directed to take 18th Street and then 11th Street. The intersection of 21st and Idaho streets will be closed for a portion of that time.

Asset 5
April 2019

Truck detour

Detours are in place and will be for the next five months. Truck traffic traveling on 21st Street is advised to use 11th Avenue and 18th Street rather than the detour from Idaho Street to 21st Street to avoid a sharp curve.

Asset 5
April 4

Detours start

Detours planned to be in place Monday, April 8.

April 4 update
Asset 5
March 2019

Nighttime work begins

Utility work is ongoing, nighttime work is expected to start April 1, and daytime work will follow soon after that. Once daytime work starts, detours will be in place.

March 2019 update
Asset 5
February 2019

Public meeting

Construction is anticipated to begin in March, with an open house held in late February for the public to ask questions.



The first stage of construction is complete, with stormwater improvements in place, G Street changes made and much of the heart of the intersection rebuilt. The next stage includes all of the concrete pavement for westbound US-12 and the proposed signal. It also finishes the intersection work at Idaho Street and 21st Street.

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