The Idaho Transportation Department (ITD) is replacing the Division and Elizabeth Park overpasses on Interstate 90 in the northern part of the state, near Kellogg, to improve safety.

“The aging bridges were past their service life and were scheduled for replacement,” says Joey Sprague, Project Manager for ITD. “We are replacing the existing bridges with wider ones to meet current standards for shoulder width.”

These I-90 bridges over the two local streets carry about 15,000 vehicles daily, a busy highway in this part of the country. The area surrounding these bridges is mainly commercial, with some residential.

These bridges were built in the 1960s and are about a mile and a half from each other. Idaho currently has more than 900 bridges that are 50 years or older, and by 2027 more than 1,000 will be a half century old or older. Steps for addressing them are part of Idaho’s Statewide Transportation Improvement Program. As of 2021, 79 percent of the state’s bridges were deemed in good condition.

In addition to completely replacing the two two-lane bridges from the foundations up to the deck, the project includes adding shoulders and extending the eastbound on ramp at Division Street to bring it up to current design standards. That ramp work was completed in 2022.

“It did not have enough length for traffic to accelerate to highway speed before merging,” Sprague says. “The lengthening of the ramp is a big safety improvement.”

The project includes repaving Division and Elizabeth Park streets, which will address any damage to the pavement caused by the construction.

ITD engineers designed the project in house. HDR Engineering, headquarters in Omaha, Nebraska, is managing the construction project. Sprague reports HDR has worked hard to keep the project on track and moving forward.

The communications team used 511 to provide the public with updates, crashes, detours, weather, width restrictions for truckers and other information. In 2023, ITD released an updated website and 511 app with even more features.

Concrete Placing Company of Boise, Idaho, received the $17.4 million construction contract. The company was founded in 1962 by Earl Ferguson and remains family owned and operated, with John B. Ferguson, Earl’s son, at the helm. During his leadership, the company grew to be a major force in concrete construction in the Northwest.

Work began in March 2022. Wet weather interfered with construction plans in the spring, but the contractor was able to make up that lost time. Crews did not work during the winter and had to stop in November of last year, because cold temperatures and heavy snow prohibited construction activities.

“I give a lot of credit to Concrete Placing Company for how well they ran the project and how efficient they were with what they did,” Sprague says. “We had good teamwork.”

During the first construction season in 2022, Concrete Placing completed construction of the eastbound overpasses and widened the eastbound on ramp at Division Street. However, crews paved over the unfinished decks with asphalt when time ran out to place a polyester polymer concrete (PPC) overlay. The PPC provides waterproofing to help protect the road from salts used to de-ice during the winter. Later this year, the asphalt will be removed and the PPC poured.

“We use salts to keep our highways safe during the winter, and since concrete is porous, that salt can gradually leach into a bridge deck and corrode the reinforcing steel inside it,” Sprague says. “A PPC overlay helps prevent that from happening, resulting in a longer lifespan for the bridge.”

Work resumed in the spring on the westbound bridges. The bridges are supported by a spread footing and steel H-pile foundation, with concrete columns. The beams are precast, prestressed concrete voided slabs. With this method of construction, excess concrete is removed from the slab and replaced by rigid plastic forms containing air, creating a lighter slab. The forms are arranged in a grid formation.

Crews took precautions to ensure no construction debris entered into the nearby Coeur d’Alene River, which runs alongside I-90 in this area. The bridges over the river were not replaced.

One travel lane in each direction on I-90 will be closed during construction. Crews built crossovers in the median to enable the traffic to flow in both directions on the same set of lanes. The crossover continues through both job sites. However, the crossover design did not include provisions for drainage of stormwater on the flat grades, leading to water remaining on the road and ponding. The team will add catch basins and culverts to drain the water and solve the problem.

At Division Street, drivers will experience periodic closures and no on-street parking or sidewalks. Being in a downtown area, the detour is short when closures are needed. At Elizabeth Park Road, one lane will remain open with one-way, alternating traffic, except for nighttime closures when the beams are lifted into place.

“We try to close Elizabeth Park as little as possible, because there is more of a detour involved with closing that street,” Sprague says. “There is only one alternate route out of there, on a gravel road.”

Later this year, crews will place the final PPC overlay on all of the bridge decks. Work on the bridges was scheduled to resume in March 2023. The project is scheduled for completion in fall 2023.

“I’m most proud we were able to get as much done last year as we did despite all the delays we faced early in the project,” Sprague concludes. “Opening all of the traffic lanes before winter 2022-2023 was crucial.”

Photos courtesy Idaho Transportation Department