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US 20: Chester to Ashton Environmental Assessment

The Idaho Transportation Department (ITD) 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.

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Study Update

What improvements are being proposed?

The ITD recommended alternative would replace the existing US-20 two-lane roadway with a four-lane divided roadway and interchanges. In addition, several local roadways are included to accommodate changes to access 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.

What has ITD been doing?

ITD has completed wetland delineations, conducted presence/absence surveys for sensitive plants and animals, and identified historic resources within the Study Area. FHWA and ITD are also coordinating with the U.S. Army Corps of Engineers (wetlands), U.S. Fish and Wildlife Service (threatened and endangered), Idaho Fish and Game (sensitive state species), and the Idaho State Historic Preservation Office (historical resources) to ensure the necessary approvals and permits needed to begin construction can be efficiently obtained. Agency coordination and reviews are an important part of the EA process. Much time has gone into this coordination in an effort to minimize risk to the project in the future, and ensure successful permitting and completion of the project once construction begins. This project utilizes federal funding, so FHWA is a cooperating agency on this EA and must provide reviews and approvals of all documents and reports.

When will the EA be completed?

It is anticipated that the EA will be completed in late 2022 during the holiday season. In an effort to avoide schedule conflicts during the holidays and maximize the public’s and agency availability to review the document and provide comments, the EA document will be made available for public review in early 2023. At that time, a public meeting and formal 30-day public review and comment period will take place. Following the public comment period, FHWA will issue a decision document. Final design will likely be completed in 2023, with construction anticipated to begin in 2025.

Purpose & Need

The purpose of the U.S. 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 U.S. 20 was originally built in 1932. The current roadway does not provide sufficient traffic flow or passing opportunities to accommodate growing traffic volumes. The roadway 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.

Roadway Condition

The original road was built in 1932 and various projects have been completed to maintain its usability. However, the roadway has exceeded its design life and current conditions are rated as poor to very poor. Issues such as frost heaves, cracking, and rutting are commonplace along the corridor.


Unconsolidated accesses along the corridor increase the risk of accidents due to increased turning movements and differences in traffic speeds. Between 2013 and 2017, over 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 & Mobility

The amount of traffic traveling the U.S. 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.

Public Involvement

•  ITD has evaluated current and future traffic volumes, safety data, and other conditions in the area to develop improvements that address the purpose and need of the project.

•  A key part of ITD’s evaluation is the identification of issues and concerns important to the public. Throughout project development, ITD will solicit feedback from the public on needs along the corridor.

•  Alternatives developed will also be presented to the public and documented through the National Environmental Policy Act (NEPA) process.

30% design to technical specialists;. agency reviews of technical reports; SHPO and consulting parties review of Memorandum of Agreement.
FALL 2021/EARLY 2022
Refine design to better identify impacts to properties; develop concise ROW plans of the impacted properties.
Coordination with agencies, reviews, and finalization of draft EA; Meet with property owners; refine ROW plans for impacted properties
EARLY 2023
Draft EA approved by FHWA for public distribution and host public meeting; public comment period; signed decision document
Stake and appraise properties to be acquired; property acquistion
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