Replacement of Idaho’s ‘most iconic’ bridge between Boise and McCall is taking shape

Idaho is embarking on replacing one of the state’s most iconic river spans after nearly a century.

The Rainbow Bridge, just north of Smiths Ferry and an hour outside of McCall, is approaching the end of its designed life as the state faces growing traffic demands on Idaho 55, according to the Idaho Transportation Department. ITD plans to preserve the concrete arched bridge built in 1933 and construct a new crossing alongside it, over the North Fork of the Payette River.

Listed in the National Register of Historic Places, the Rainbow Bridge would remain as a scenic overlook, BoiseDev reported.

ITD’s early estimates placed the construction cost of the new bridge at more than $54 million, with the federal and state governments funding the project in a roughly 60-40 split. The final price tag will depend on several factors, including the new bridge’s design, exact location and extent of associated roadwork, ITD regional spokesperson Sophia Miraglio told the Idaho Statesman.

State transportation officials aim to “design a long-term river crossing that will serve Idaho communities, travelers and commerce for the next 100 years,” she said in an email. “ITD is looking forward to working with the community on this project, as we will seek public input along the way.”

The state agency is doing environmental and geotechnical engineering work after it finished an initial review of options for a new bridge in 2021. Construction could begin as soon as 2027 and is expected to last up to two years, according to ITD’s most recent seven-year plan.

In December, ITD completed three years of roadwork on Idaho 55 about a half-mile south of the Rainbow Bridge. The mile-long safety improvement project in the sensitive mountain corridor widened and straightened the highway, adding shoulders and guardrails to help prevent vehicles from going off embankments into the Payette River.

But the project suffered repeated rock slides during construction that led to more than a year of delays. It also resulted in a doubling of the total cost — initially pegged at $30.8 million and closing at $62.8 million, according to ITD’s preliminary estimates.

Unique design one of three in Idaho

The Rainbow Bridge was built in just a year as part of President Franklin D. Roosevelt’s push for public works projects across the U.S. in the 1930s to help pull the nation out from the Great Depression. Paid for with federal emergency relief funds, the bridge cost just $74,000 to complete, according to the U.S. Forest Service.

The bridge’s distinctive look is owed to Charles A. Kyle, a native Canadian who was Idaho’s first chief bridge engineer, ITD said. He introduced the state to the open-spandrel design, an architectural form with open walls that was cheaper to build because it used less material. It was constructed by an Ogden, Utah-based firm and remains the largest single-span concrete arch structure in Idaho.

Kyle first used the design on the Salmon Bridge in Salmon in 1926 before moving on to downtown Boise’s Capitol Boulevard Bridge (then known as the Oregon Trail Memorial Bridge) that was finished in 1931. Two years later, he completed the Rainbow Bridge, which has acted as a critical link between the Treasure Valley and McCall.

It also has continued to amass appreciation from motorists — commuters and day-trippers — who traverse its scenic span. The Rainbow Bridge was recently voted Idaho’s most iconic overpass and ranked in the top 40 bridges across the U.S. in an online survey conducted by a South Florida Volkswagen dealership.

“This arch bridge is celebrated for its picturesque views of the surrounding mountains and (river), providing a stunning backdrop for travelers and photographers alike,” Gunther Volkswagen wrote. “The bridge’s design and location encapsulate the essence of Idaho’s outdoor appeal, offering a visual treat that complements the natural beauty of the area.”

The Perrine Bridge over the Snake River in Twin Falls and the Dent Bridge — the state’s highest bridge and one with the longest span — over the Dworshak Reservoir near Orofino also made the list of the U.S.’s top 100.

ITD said it hopes to approve a design for the Rainbow Bridge’s replacement this fall and a final design by fall 2026. Public meetings will be announced to receive community input throughout the process, Miraglio said.