Projects

US-20 South St. Anthony Interchange

Construction is now complete on Exit 343, a new full interchange on US-20 south of St. Anthony.

US-20 South St. Anthony Interchange

Construction is now complete on Exit 343, a new full interchange on US-20 south of St. Anthony.

Overview

A full interchange south of St. Anthony off US-20 improves safety and mobility along this very significant route through East Idaho. The interchange replaces multiple at-grade crossings.

Aerial view of US-20 south of St. Anthony taken in 2023 before construction of a new full interchange at this location.

Exit 343 is now complete south of St. Anthony along US-20

Construction was recently finished on U.S. Highway 20 of a tight diamond interchange south of St. Anthony, very similar to the interchanges constructed in years past at Thornton and Menan-Lorenzo. The project provides increased capacity, mobility, and safety for the traveling public.

Aerial view of US-20 south of St. Anthony taken in 2023 before construction of a new full interchange at this location.
Aerial view of US-20 south of St. Anthony taken in 2023 before construction.
Aerial view of US-20 Exit 343 South St. Anthony interchange with construction complete fall of 2025.
Aerial view of US-20 Exit 343 South St. Anthony interchange with construction complete.
Map detailing work being done on US-20 South St. Anthony interchange.

Background

An interchange at Exit 343 has been in the Idaho Transportation Department’s plans since the early 1980s, when US-20 was constructed in its current location and configuration. Right of way was purchased at that time and conceptual layouts for the interchange ramps were explored. About 10 years later, in 1991, a solo eastbound off ramp was constructed at this location.

In the years since then, growing and changing demands on this very significant eastern Idaho roadway mean this new interchange is needed. The project includes an overpass and on- and off-ramps for east and westbound US-20.

Traffic Impact

  • Two lanes of traffic are both running in both directions.
  • No additional work zones remain.
  • Traffic is currently running at the usual 70 mph speed of US-20.
Crews performing concrete work on the South St. Anthony interchange bridge.
Traffic control in place at South St. Anthony interchange construction zone on US-20.

Timeline

  • Summer 2022

    Technical information gathering, stakeholder coordination, develop line/grade for project

  • Fall 2022

    Public Open House; develop preliminary design

  • Late 2022- early 2023

    Refine and submit preliminary design

  • Spring 2023

    Finalize design; construction bidding

  • Late 2023

    Construction began

  • Late 2024

    Construction paused for winter

  • Summer- Winter 2025

    Finish work and construction finalized

Idaho Governor Brad Little Leading Idaho program logo. Blue Circle with white lines and stars within.

Funding for this project was assisted by Governor Little’s Leading Idaho Transportation Expansion and Congestion Mitigation (TECM) fund. The Leading Idaho initiative allows ITD to take a deliberate approach to invest in projects in corridors that will enhance safety, improve mobility, further strengthen Idaho’s economy, and positively impact communities across the state for years to come.

Contact

Project Manager Rob Smith, robert.smith@itd.idaho.gov or (208) 745-5663. 

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