SH-3 traffic detour starts late February to prepare for spring construction

Narrow shoulders on ID-3

The Idaho Transportation Department will partially close State Highway 3 north of St. Maries to prepare for spring construction. Unless winter weather causes a delay, the closure will start on Monday, Feb. 28, and continue for two weeks.

“If the forecast changes, we’ll have to push our closure to the following week,” Project Manager Matt Heinichen said. “Drivers should pay attention to signs in the area and for exact timing.”

The plan is to close at least one lane of the highway from milepost 89.9 to milepost 92.5, with traffic detoured onto Goosehaven Road. During the closure, crews will remove vegetation along three miles of highway to make room for widening this spring.

“We may close both lanes on SH-3 and detour all traffic for up to five days in this two-week window so we can test the detour we expect to have in place for when we start the widening effort,” Heinichen said. “We want to determine if the county road will be able to support two-way traffic during construction.”

Widening is scheduled to begin in late April and take three months to complete. Closing the highway completely and using Goosehaven Road as a detour will expedite the 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. No additional lanes will be added. 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 SH-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.

Learn more at