Overview
US-20 is the primary route to access the western entrance of Yellowstone National Park. It’s currently a four- lane divided highway from Idaho Falls to Chester. The Idaho Transportation Department is conducting an Environmental Assessment to be able to improve the section from Chester to Ashton to be four lanes as well.
Environmental Assessment
The Idaho Transportation Department and the Federal Highway Administration (FHWA) are conducting an Environmental Assessment (EA) to engage the public and evaluate impacts, benefits and costs associated with roadway improvements and reconstruction of US-20 between Chester and Ashton. US-20 is the main route to the western entrance of Yellowstone National Park. It’s currently a four-lane, divided highway from Idaho Falls to Chester, where it merges back to two lanes.
Purpose and Need
The purpose of the US-20 Chester to Ashton project is to enhance highway safety and operations by:
- Improving highway capacity and level of service
- Improving roadway condition
- Providing safe, efficient, and well-coordinated access to and from the highway
The need for these improvements is driven by the following:
The Chester to Ashton segment of US-20 was originally built in 1932. The current roadway does not provide sufficient traffic flow or passing opportunities to accommodate growing traffic volumes. The route has exceeded its service life and requires improvements to the roadway and drainage features as well as new pavement. Reconstruction will provide the opportunity to include design elements for reducing potential crashes.
Safety
Unconsolidated accesses along the corridor increase the risk of accidents due to increased turning movements and differences in traffic speeds. Between 2013 and 2017, more than 30 percent of crashes were same direction sideswipe, rear end, or angle related. As traffic volumes continue to increase, the risk of potential conflict points will also increase.
Highway Capacity and Mobility
The amount of traffic traveling the US-20 corridor from Chester to Ashton has grown significantly. The current configuration does not provide for sufficient traffic flow or passing opportunities to accommodate current and future traffic volumes.
Timeline
This Environmental Assessment began in 2018 and has undergone changes in administrative direction multiple times since. A determination on the assessment is now expected in 2026.
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2018
EA process began
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2019- early 2025
Environmental studies and determinations conducted
Early acquisition of property approved
Preliminary draft EA document reviewed and edited
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Late 2025- 2026
Goal to release Draft EA document
Public Meeting will be held following that release
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2030-31
Anticipated Construction
Frequently Asked Questions
The ITD recommended alternative would improve the existing US-20 two-lane roadway to a four-lane divided highway and interchanges. In addition, several local roadways are included to accommodate access changes resulting from the proposed project. Locations of these roads and interchanges are currently being evaluated in the EA.
*IMPORTANT NOTE: The Chester to Ashton Environmental Assessment is NOT part of the Planning and Environmental Linkage (PEL) study happening between Ashton and the SH-87 highway junction. This EA is independent of the PEL and following its own process and schedule.
ITD and FHWA have been coordinating with federal and state agencies as part of the environmental review process. Through this coordination and collaboration, the project team is refining project design to further reduce impacts on resources such as wetlands, businesses, residences and historic properties. ITD has begun early acquisition of property along mainline US-20 that supports the US-20 Chester to Ashton project and long-term planning efforts. ITD and FHWA have approved all property proposed for early acquisition as part of the US-20 Chester to Ashton Land Acquisition Project and will comply with the Uniform Relocation Assistance and Real Property Acquisition Policies Act of 1970 and Title VI of the Civil Rights Act of 1964.
Currently, ITD is unable to provide a specific date for the release of the draft Environmental Assessment (EA). Initially, ITD had anticipated having the draft EA available for public review by fall 2023. However, updates in federal guidance pertaining to wetland mitigation and environmental justice outreach extended the timeline in order to meet the revised requirements. It is now anticipated to be released in 2026.
Once the draft EA is released, there will be a formal 30-day period for the public to review and provide comments. Additionally, a public hearing will be conducted to present the environmental review findings, address any inquiries, and receive public input on the project. After the public comment period, FHWA will issue its final decision regarding the approval of the EA. The final design phase will then begin following approval, with construction anticipated in 2030-31.
Contact
If you have comments or questions regarding this project, reach out to Project Manager Eli Robinson: eli.robinson@itd.idaho.gov