Four months, 125 days. Not much time –barely more than a season. It's also how long it took the Idaho Transportation Department (ITD) to replace an overpass. The key to completing the bridge in such a timely manner was as simple as ABC or Accelerated Bridge Construction.

The Wolf Lodge Interchange, just east of Coeur d'Alene and in the northern panhandle of the state, connects a scenic lake byway called Idaho Highway 97 to Interstate 90. It marks the end of the highway and is used by motorists to gain access to attractive scenery.

The bridge needed structural work, and there were also issues with the clearances. John Vaudreuil is a Transportation Staff Engineer for the Idaho Transportation Department who served as the Project Manager and Design Engineer for the project.

"We made the decision to replace rather than repair and preserve,” said Vaudreuil.“The extent of the repair work that would have been required was not worth the cost compared to the amount for the life cycle of a new bridge." The old interchange, which was built in 1960, had a number of spalls and cracks, and exposed rebar in the abutment and pier, plus substandard vertical clearance and shoulder widths.

Designing the Bridge

ITD District 1 and the District’s Bridge sectiondesigned the new bridge structure. HMH of Hayden,Idaho,did the construction oversight, and Concrete Placing Company Inc. of Boise, Idaho,was the construction contractor. Vaudreuil credits his late colleague, Ken Clausen as the mastermind behind the expedited bridge design.

The new overpass is taller, wider, and longer. With the increased vertical clearance, larger trucks are able to use the road. Ultimately, the project improved safety for all motorists by removing guardrails, widening shoulders, and increasing vertical clearance.

To expedite the construction, the team went with the ABC method,which cut down on the construction duration from 10 months to just four months. This significantly reduced traffic impacts for the thousands of vehicles (about 20 percentof which are commercial trucks) thattravel under and across the interchange each day.

The team worked in a non-linear process to accelerate the project. Vaudreuil said, "In order to utilize ABC, you have to come up with an effective staging plan." This allows for concentration on activities that can be done simultaneously, and if thoroughly monitored during construction, can maximize efficiency.

Constructing Safely

One of ITD’s main goals was to minimize the traffic impacts during construction on the four-lane interstate without compromising safety. "We had to run I-90 traffic up the interchange ramps while doing the overhead work to maintain mobility," saidVaudreuil.

The bridge design used precast elements for the substructure and a minimum amount of cast-in-place concrete. "We were able to realign the overpass while commuters were using the existing facilities, which minimized inconveniences," saidVaudreuil. Althoughuse of precast members speeds up the process, it can be challenging. "It's critical to have a precise survey and be accurate in your fabrication of the parts so the pieces fit exactly as they are conceived in the plan," saidVaudreuil.

Another factor inthe speed of the project was Ultra High-Performance Concrete (UHPC), a material not widely used in the United States. The team used UHPC for the closure pour of deck bulb tee girders.  The UHPC provided strong, durable, and maintenance-free connections between the deck bulb tee girders. 

"Using these girders with UHPC helped the construction duration because we were able to fabricate components at the same time preconstruction work was underway and before mobilizing to the project and initiating traffic control restrictions,” said Vaudreuil.“There was no need to watch concrete cure, and we did not have to wait. Done conventionally the project would not havebeen completed in one season.” He adds that the UHPC is 20,000 psi concrete, which is extremelystrong.

Vaudreuil noted that an extra inch of thickness was added to the depth of the girders to allow for profile grinding. "Once the adjacent girders with slightly varying camber were connected together, surface grinding was done in order to create a truefinish deck.” Afterwards a polyester concrete overlay was placed on the deck to provide a highly durable, skid resistant wearing surface that also seals the deck and extends the lifecycle.

Lighting and Noise Concerns

The ITD made use of adaptive lighting on the interchange to protect the area’s completely black night sky by limiting light pollution. "The adaptive lighting will allow ITD to have the ability to make the light more intense as needed," saidVaudreuil. He anticipates the lights being raised gradually till a proper balance is found as those in the area adjust, easing the transition toward increased safety.

Noise was also a concern when constructing the overpass. To cut down on the noise, ITD avoided using apile driver. Instead, the design specified drilling into the underlying rock and then setting piling into the rock sockets and filling voids with concrete. Vaudreuil said, “This allowed us to precisely position the piles for abutments and pier construction without creating much noise.”

Clearly, the Wolf Lodge Interchange project was impressive for its speed. However, another impressive feat was the cost. The entire project cost $4.7 million,which is less than what was originally budgeted. Vaudreuil, whonotedthe project was featured at a recent Western Bridge Conference, described it as a successful undertaking for the state. He credits the ABC method for keeping costs down as the reduced time reigned in costs for the state and the contractor.

"We received a great deal of support and people are very pleased," saidVaudreuil. And so are the commuters and tourists who use the Wolf Lodge Interchange.