Interstate 29/20th Street South Interchange

20th Street South looking east from 22nd Avenue South

The I-29/20th Street South interchange opened to traffic on July 30, 2023 and has had even more traffic than expected. Now the City and SDDOT will expand the corners of the 20th Street South and 22nd Avenue South intersection to better serve large trucks.

August 4, 2025

Project Update

The project Finding of No Significant Impact (FONSI) has been approved and signed by the Federal Highway Administration and SDDOT. View the FONSI.

FONSI approval indicates that the project will not have a significant impact on the human or natural environment and that all comments and/or concerns about the project have been satisfactorily addressed. It also allows the project to move forward to an anticipated September 2025 bid letting.

Comments and responses on the Supplemental Environmental Assessment can be viewed on pages 50 and 51 of the FONSI.

Project Overview

The east side intersection widening at the 20th Street South and 22nd Avenue South is being completed to better accommodate large vehicle traffic. The project is using unanticipated remaining BUILD Grant funds from the 2022/2023 I-29/20th Street South Interchange project.

Project Features

  • Widen intersection corners for large vehicles at the NE and SE corners of the 20th Street South and 22nd Avenue South intersection.
  • Reconstruct and raise approximately 140 feet of the Allyn Frerichs Trail to match the widened intersection corner and meet ADA guidelines.
  • Relocate Interstate Telecommunications Coop (ITC) utility building.

Closures

  • Traffic will be maintained during construction.
  • The recreational trail will be closed. A pedestrian detour will be provided.
Map showing corner widening at 20th Street and 22nd Ave S intersection.

Click image to enlarge.

Project Timeline

Project timeline

Why the project now?

The I-29 Exit 130 Interchange project was driven by the critical timeline imposed by the BUILD grant. The grant required that the interchange's environmental assessment, design, right-of-way acquisition, and bidding be completed within a compressed 18-month period to avoid forfeiting the allocated funds. Typically, a minimum of 4 years would be necessary to complete those steps.

To improve this intersection, right-of-way from Edgebrook Golf Course (EGC) must be acquired. However, as EGC is designated as a 6(f) Land and Water Conservation Act property, it cannot be repurposed for non-recreational use unless an equivalent replacement property of equal value and utility is secured.

The extensive approval process required for this conversion posed a significant risk to the overall project's bidding deadline of November 2021. In addition, no adequate replacement property was available to mitigate any impacts to/conversions of the EGC property. Therefore, the steps to convert the EGC property, acquire it, and construct the intersection to accommodate large vehicles were not completed as part of the 2022/2023 interchange project.

The 2022/2023 interchange project was completed under budget, allowing the remaining BUILD grant funds to be allocated. This allowed the City of Brookings to optimize the grant's terms, ensuring that the maximum number of eligible improvements (including widening the intersection corners) can be completed within the overall project's scope.

As part of the interchange project, SDDOT purchased private property that meets the replacement requirements for the impacted/converted EGC property at the intersection corner. The replacement property is in the southeast corner of EGC. Watch the presentation in the documents section for more information.

Documents

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Intersection Expansion Finding of No Significant Impact

July 2025
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Intersection Expansion Presentation

June 2025
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Supplemental Environmental Assessment

May 2025
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Interchange Finding of No Significant Impact

January 2021
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Interchange Environmental Assessment

October 2020

Project Partners