BOISE, Idaho — The Idaho Transportation Department (ITD) has announced its plans to begin soil testing underneath the historic Rainbow Bridge on Highway 55, to collect data for future construction plans for a new bridge.

According to ITD, the bridge has been standing since 1933 and no longer meets current highway safety standards. Environmental and design planning began last spring, but ITD will begin drilling in 18 locations around the existing bridge this June to collect samples.

“Prior to the drilling, ITD will remove trees and vegetation near each drilling location to allow a helicopter to safely lower equipment,” officials said. “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 Idaho Transportation Department said the project would also decide the future of the existing bridge, adding ITD wanted the process to be as transparent as possible.

“Public input will be a key consideration in the final recommendation for the new bridge and the existing bridge,” ITD’s Dan Gorley said.

Sampling will last throughout June, and ITD said drivers should expect 15-minute delays as officials will be drilling. However, work will stop for the weekend at 12 p.m. each Friday.

Construction of the new bridge is expected to start in 2027 or 2028, ITD stated.