US-20 Idaho Falls to Arco

This project will develop preliminary design plans for reconstructing the aging US-20 roadway and determining how future passing lanes may be implemented to enhance safety along the route.

This area of the US-20 corridor is located in Butte, Bingham, and Bonneville counties and is an important route for local Idahoans, commuters, recreationalists, farmers, and other motorists. It also serves as the primary route to access the INL and the city of Arco, and is a popular east/west route between Mountain Home and Idaho Falls.

The existing roadway, originally constructed in 1950, has surpassed its service life. In addition, the roadway foundation is failing, and routine maintenance treatments are becoming less effective. Reconstructing this part of US-20 is needed to ensure it can continue serving as a safe route for motorists.

US-20 sees many diverse users, including snowplows, farming equipment, buses, motorhomes, trailers, and more. This project will evaluate turning US-20 into a four-lane highway. Adding passing lanes will increase safety by improving traffic flow and providing safe passing opportunities.

Community involvement is important to ITD and to the success of this project. ITD is coordinating with many local city and county officials, and several local agencies about the project, including the INL, Department of Energy (DOE), Department of Defense (DOD), and Bureau of Land Management (BLM).

In addition, ITD will communicate with the public through a variety of channels and provide opportunities for community members to give input on the project. ITD hosted a public meeting for community members to learn about the project in September 2025: