Construction funding identified for widening of the St. Maries Dike

Narrow shoulders on ID-3

The Idaho Transportation Board has identified $18 million for widening of approximately three miles of Idaho Highway 3 north of St. Maries, with construction to start next fall.

Previously the board had approved $1.5 million for design, which began in April of 2020. Funding for construction comes from money that the department had held back last spring in anticipation of declining gas tax revenue during stay-at-home orders.

“Even with all the changes in 2020, we did not see a big drop in gas tax revenue, which is our primary source of funding,” Engineering Manager Marvin Fenn said. “Now we can use that money we held back to make our highways safer, as is the case with this widening project.”

Plans call for the highway to be widened by 11 feet to the east, making room for 11-foot travel lanes and 3-foot shoulders. To get this extra width, a lightweight, specialized product known as geofoam will be used.

Traditionally, highways are expanded by importing embankment material and building the base outwards, but ID-3 was built on soft soils. Extra weight would collapse the soft soils and cause settlement problems for the highway, and expanding outwards would affect nearby wetlands. The geofoam will allow expansion without adding weight or requiring land to be bought.

“Years ago we had tried to widen a longer section of the highway, but we couldn’t find a way to do it,” Fenn said.

Design plans are nearly complete. Benewah County Road and Bridge is in the process of preparing Goosehaven Road to serve as a detour during construction, which is expected to take several months next year.

“Although we’d like to see the project built this year, this extra time will allow for better bid prices, and we can start construction when the water table is at its lowest,” Fenn said. “The detour will also be ready, and the contractor will have more time to plan staging and get a head start on ordering specialized materials.”

Preliminary work this fall will relocate utilities and remove trees and vegetation.

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