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SH-3 widening

Increasing the width of the shoulders on the dike will improve safety.

Roughly three miles of SH-3, also known as the St. Maries dike, will be widened by 11 feet between both intersections of Goosehaven Road.


To finish construction sooner and reduce costs, SH-3 will be closed, and Goosehaven Road will serve as the detour for approximately three months. The project is anticipated to be complete in August 2022.

Impacts start in April

Design details

The highway will be widened approximately 11 feet to the east, and guardrail will be installed. After construction, lanes will be 11 feet wide and shoulders will be 3 feet wide.

To get this extra width, crews will use a specialized, lightweight product known as geofoam.

Environmental challenges

Previous projects that planned to widen a longer section of highway stalled due to environmental challenges. SH-3 serves a dike that separates the St. Joe River from lowland farming grounds and is constructed on soft soils.

Traditionally, highways are expanded by importing embankment material, but in this case, the extra weight would collapse the soft soils and cause settlement problems for the highway. It would also require the department to buy more property and likely cause significant wetland and cultural impacts.

Using the ultra-light geofoam will allow expansion without adding weight. It also won’t require more land to be bought, minimize utility moves and avoid wetland/culture impacts.

Details on geofoam


Funding for design of the latest project was approved by the Idaho Transportation Board in April of 2020 for the amount of $1.5 million. No money was identified for construction at the time.

In May of 2021, the board allocated $18 million for construction. The funds come from money ITD held back in spring of 2020 in anticipation of reduced gas tax revenue during the COVID-19 pandemic.

The bid was awarded to Knife River for $13 million in October 2021.

construction funding announcement
April 2022

Construction begins

Work will take three months, with traffic detoured to Goosehaven Road to expedite construction.

Read more


Night work during May will eliminate conflicts between trucks delivering materials to the site and trucks hauling away materials. Residents on Goosehaven Road should expect increased traffic and noise at night. Read more.

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