The project included complete demolition and reconstruction of two bridges for both east and westbound lanes of I-84. Ramps were elongated and Blacks Creek Road was lowered underneath the new bridges. An eastbound auxiliary lane was constructed between the rest area and the interchange.
To reduce the impact of construction to motorists, ITD implemented a slide-in-place operation. Using this method, the majority of the new bridges were constructed adjacent to the existing bridges. Then, crews demolished the old structure and slid the new bridge into place.
“Moving these massive structures safely without damaging them is no small feat,” said ITD Project Manager Patrick Kelly. “We construct a rail system to guide the new bridge. Then, using Teflon mats and dish soap as lubricant, we slowly move the bridge into place. Once there, we get to work completing the approaches and can put live traffic on it in just a few weeks.”
This slide-in-place process reduced the impact to the traveling public from several months per bridge to only a few weeks. ITD moved the project up from its original construction timeline of 2023 due to rapid deterioration of the old bridge deck. The previous condition of both bridges created a hazard to the motoring public.
“This was a complicated project in a busy stretch of Interstate between Boise and Mountain Home,” said ITD Engineering Manager Jason Brinkman. “Our project managers, inspectors, and the contractor Knife River — the whole project team — really delivered a win for taxpayers with this project."
Construction began in November 2019. Crews will still be in the area to complete minor work, but no additional impacts to the public are anticipated. The estimated cost to plan, design, and construct this interchange is $15.7 million.