SH-55 Rainbow Bridge

Nearly a century after its construction, the current Rainbow Bridge no longer meets ITD standards for state highway bridges. Despite regular maintenance and major repairs, the structure is deteriorating to the point where ITD will no longer be able to maintain it for highway traffic. Other issues include narrow lane and shoulder widths, tight curves on both sides of the bridge, and limited sight distance for drivers.

An evaluation in 2025 confirmed the level of corrosive elements in the concrete and rebar is extensive. ITD has recommended removing the bridge due to safety risks, future costs, and a lack of options to keep and use the bridge efficiently. The Federal Highway Administration and ITD will make a final decision later this year once the environmental process is complete. ITD shares regular updates at public meetings.

ITD is working with technical and environmental experts, agencies, and community members to design a new bridge. This process includes: 

• Completing environmental studies regarding wetlands, endangered species, cultural resources, viewshed and socioeconomic resources, the Clean Water Act, and other issues.
• Completing technical studies such as geotechnical and hydraulics work.
• Evaluating a range of alternatives for a new bridge.
• Determining the future of the existing bridge.
• Developing design and construction plans for the bridge and roadway.
• Working with local agencies and the public throughout the process.

Construction could begin as early as 2028, depending on funding.

The new bridge will be located slightly northwest and upstream of the existing bridge. The alignment will eliminate sharp curves on both sides of the bridge. The design will include two 12-foot lanes and wider shoulders.

New retaining walls near the bridge will stabilize the canyon slopes and give crews room to keep the existing bridge open during construction.

The bridge will have a “steel thru-arch” design. This design was chosen based on engineering considerations and public input. ITD will continue technical work on the design over the next few months. This work will help ITD make decisions about the angle and color of the arches, as well as the barrier railing and retaining wall design.

ITD is approaching decisions about the Rainbow Bridge with a high level of transparency, education and community involvement. The community input process will be a key component of the final recommendation for the new bridge and the existing bridge. 

ITD is hosting a series of community open houses and small-group meetings during this project: 

• Community open houses will be scheduled at key points of the design process. The first set was held in July 2024 in McCall, Horseshoe Bend and online. The second set was held in July and August 2025 in Cascade and online. ITD also hosted a booth at the Valley County Fair. A third public meeting was held on May 21, 2026 in Cascade.
• A Bridge Involvement Group will meet prior to each community open house. The first meeting was held in July 2024 in Cascade. The second meeting was held in July 2025 in McCall. The third meeting was held in May 2026 in McCall. Meetings are open to community leaders, stakeholders and members of the community who are willing to invest a higher level of time and engagement.

Click to watch a video of ITD’s responses to questions from the 2025 public meetings.

Design is underway. Construction could begin as early as 2028, depending on funding.