Test drilling on SH-55 near Rainbow Bridge in Valley County

The Rainbow Bridge on SH-55 north of Smiths Ferry.

The Idaho Transportation Department (ITD) will begin soil and rock sampling this June for a project to build a new bridge over the North Fork of the Payette River in Valley County. The project will address plans for the nearby Rainbow Bridge that has served Idaho travelers for nearly 100 years.

The sampling will require test drilling in 18 locations around the existing bridge. Preparations are expected to begin next week. Drivers can expect up to 15-minute delays on weekdays in June for the drilling and associated preparations. Work will stop for the weekend each Friday at noon.

Prior to the drilling, ITD will remove trees and vegetation near each drilling location to allow a helicopter to safely lower equipment. The ground will be re-seeded after drilling. Results will be used for designing the bridge foundation, supports and retaining walls along State Highway 55.

The current Rainbow Bridge was constructed in 1933 and no longer meets standards for state highway bridges. ITD began environmental and design work this spring for a new bridge adjacent to the current bridge. The project will include a decision about the future of the existing bridge.

“We intend to approach this project with a high level of transparency, sensitivity and community involvement,” ITD Resident Engineer Dan Gorley said. “Public input will be a key consideration in the final recommendation for the new bridge and the existing bridge.”

ITD will host community open houses and a stakeholder working group this July. Additional community involvement opportunities will be scheduled later this year. To request an invitation to future meetings, please email info@sh55rainbowbridge.com or visit https://itdprojects.idaho.gov/pages/rainbowbridge.

The project is planned for construction in 2027 or 2028.