41st Street Diverging Diamond Interchange

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The Diverging Diamond Interchange (DDI) is a simple design innovation that improves safety and mobility, often at a much lower cost, compared to conventional interchange designs. The key to what makes a DDI work so well is how left turns are handled. All left turns onto the freeway are free flow, meaning vehicles do not have to stop to access the ramp. The Federal Highway Administration developed this DDI Factsheet to help explain.

This project has been nearly ten years in the making as both SDDOT and the City of Sioux Falls move forward with constructing a new diverging diamond interchange to improve safety and enhance traffic operations. The diverging diamond was chosen because of safety features, greater capacity and efficiency that it provides for the traveling public, it reduces the conflict of left-hand turn movements and meets the needs of all road users to accommodate large trucks, pedestrians and bicyclists. In total, the project construction will take two years to complete with approximately $44 million in infrastructure improvements.

This is a priority corridor for the city and state for the following reasons:

  • I-29 and 41st Street are vital routes for commuters and local traffic.
  • 41st Street is the most heavily traveled street in Sioux Falls and the state of South Dakota. It provides access to all types of retail and employment centers.
  • The nearby Empire Mall consistently ranks among the state attractions that draws the most visitors

Watch this video to learn how to navigate a DDI.


The DDI will improve safety and traffic flow in the I-29 and 41st Street area. 41st Street will be widened to three lanes in each direction between Marion Road and I-29. Signal and sidewalk improvements at the 38th Street and Shirley Avenue intersection will also be completed as a part of this project.

Project benefits are:

  • Creating safer turns for entering and exiting the highway including safer left turn movements to reduce the number of collisions
  • Greater capacity and efficiency to move more vehicles through the intersection and decrease congestion and traffic delays
  • Drivers can make free flow right and left turns onto the freeway
  • Easy navigation to guide drivers with overhead signs, pavement marking, and traffic signals
  • Meeting the needs of all road users including large trucks and providing safe passage for pedestrians and bicyclists

Construction began in early 2022 and is anticipated to be completed in summer 2024. Visit our Traffic Alerts page to view maps, project timelines and current construction updates.

This project is a partnership between SDDOT and the City of Sioux Falls. SDDOT is leading project construction. D&G Concrete Construction is the primary contractor. Infrastructure Design Group, Inc. (InfrastructureDG) is the primary consultant for Construction Observation, Administration, and on-site Communications, with HDR serving as the Public Relations Specialist (PRS).

Funding for this project comes from a combination of SDDOT and City sources. The City is responsible for 81.95% of the actual cost of construction, while SDDOT will contribute 18.05%. Total project costs will be approximately $44 million.

While we always do our best to minimize impacts during construction, businesses and residents can expect:

  • Equipment, materials and construction crews located along the road and in the existing right-of-way.
  • Temporary, intermittent lane and road closures. Detours will be provided prior to closure.
  • Temporary gravel driveway access to businesses during lane and road closures. Access to businesses will remain open.

Property impacts. The contractor will notify property owners in advance.

West phase construction consists of installing sanitary sewer lines, water mains, and storm drainage. This work will include grading, temporary gravel/driveway access, concrete paving, other miscellaneous concrete work, and restoration.

41st Street will have one lane in each direction that remains open to traffic at all times.

Pedestrian access will be maintained at all times along 41st Street with signaled crossings at Valley View Road, Marion Avenue and Terry Road.

Shirley Avenue will remain open to traffic at all times.

I-29 will remain open to traffic at all times, with the exception of night closures during construction of the bridge.

IDG, Inc. will provide updates and notifications on a weekly/daily basis with property and business owners. Updates are provided via postcards and weekly updates through SDDOT and road closure notifications through City of Sioux Falls social media channels.

We are coordinating with utility providers to minimize temporary impacts. Notifications will be distributed prior to utility service interruptions.

All sidewalks and landscaping impacted by the project will be restored back to pre-construction condition. Although we aim to ensure restoration is complete one to two months after the final project is completed, restoration timelines depend heavily on weather conditions. If your property is directly impacted by construction, project staff will be in touch to provide specific details. If you have additional questions on restoration related to your property, please Contact Us