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SDDOT I-29 Exit 71 Online Meeting

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I-29 Exit 71

Public Meeting and Open House

Welcome to the I-29 Exit 71 Interchange Modification Study virtual engagement!
This is the second of two public meetings for the study. Since the first public meeting, the Exit 71 interchange and I-29 mainline alternatives have been revised and further evaluated to develop preliminary recommendations. We are looking for your feedback on these revisions, preliminary recommendations, and other considerations for the design team later in the project.

The purpose of the meeting is to:

  • Present revised alternatives and preliminary recommendations
  • Gather feedback on interchange alternatives and proposed access modifications
  • Gather feedback on potential impacts during construction (vehicle width and access requirements, potential alternate routes, timelines, etc.)

Project Area Map

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This map indicates the areas along I-29 that are included in the study area.  Focus areas include the I-29 Exit 71 interchange and I-29 mainline from Exit 68 through Exit 73.

Presentation Overview Video

Video Thumbnail
4:16

Video transcript can be found here.


Study Schedule

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The study schedule shows the anticipated pace of the project. Data collection and analysis will take place from February 2021 to August 2021 with Public Meeting #1 taking place on Monday, August 23, 2021. The interchange alternatives will be refined and evaluated from August 2021 to September 2021 with Public Meeting #2 taking place shortly after this process is completed. The IMJR will be developed, reviewed, and revised in October through December of 2021. The final IMJR will be submitted in January 2022. An environmental scan will be conducted from February 2021 to January 2022 and the subsequent environmental an environmental study from January to October 2022.

Draft Purpose and Project Need



Draft Purpose and Need

The project team drafted the following preliminary purpose statement that can be further developed as the project study progresses. The intent of this statement is to:

  1. Solicit your input to help the project team better understand corridor and intersection issues

  2. Use the input to refine the final purpose and need statements to comply with the National Environmental Policy Act (NEPA)

Project Purpose

To preserve transportation assets, provide for the reliability and efficiency of the transportation system, and provide consistency with transportation planning along I-29 mainline from Exit 73 to Exit 68 and on CH110 through the Exit 71 interchange.

Primary Needs

The primary "drivers" of the project and reflect the fundamental reasons why the project is being pursued.

Traffic operations: Forecasted traffic volumes indicate capacity needs on I-29 mainline and at the Exit 71 interchange through the 2050 Planning Horizon. The identified need from the planning process is a capacity deficiency, requiring that I-29 mainline and the Exit 71 interchange operate at least at a LOS “C” in urban areas and “B” in rural areas. The expected 2050 traffic volumes will cause segments of I-29 to operate at LOS “D” in urban areas and LOS “C” in rural areas and Exit 71 interchange ramp terminal intersections to operate at LOS “F”.

Road surface conditions: Based on the pavement condition survey of I-29 through the study area, the SDDOT Pavement Management System indicates a need to bring I-29 pavement condition rating to an acceptable level to accommodate the current and projected travel load.

Secondary Needs

Additional needs that are desirable, but not the core “drivers” of the projec.

Safety: Crash trends supporting a need for improvement include the Exit 71 southbound ramp crash rate exceeding the critical crash rate and multiple injury crashes, including one fatality, at the Exit 71 southbound ramp terminal. Along I-29, the proportion of rear-end crashes through the study area is approximately two times the percentage of rear-end crashes throughout all of I-29 in South Dakota.

Current design standards: Existing Exit 71 geometric elements, including intersection and stopping sight distance, shoulder width, vertical curve geometry, slopes, and ramp junction taper rates, support improvement to meet current SDDOT Road Design Manual guidelines.

Goals

Desired project outcomes beyond the transportation issues identified in the Purpose & Need and balance environmental & transportation values.

Goal 1: Accommodate Sioux Falls MPO Multi-Use Trail Study and local municipality bike plans

Goal 2: Regulatory compliance

Goal 3: Avoidance and minimization of environmental impacts, or enhancement opportunities

Study Area Data



Study Traffic Volumes

Daily and peak hour (morning and afternoon commute periods) traffic volumes were developed for three analysis scenarios:

  • Existing conditions (2021 traffic counts)
  • 2028 Year of Project Completion
  • 2050 Planning Horizon

The two future-year scenarios account for expected increases in traffic volumes passing through the study area and anticipated development.

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The Traffic Volumes Study graphic shows existing and forecasted traffic volumes along I-29 mainline, within Exit 68, 71, and 73, and along the 271st Street, 27rd Street, and 276th Street corridors.  Forecasted traffic volumes reflect estimated traffic growth to Years 2028 and 2050.

Study Area Traffic Operations Analysis


Using the existing and forecasted traffic volumes, study area intersections and roadway segments were analyzed to identify future capacity improvement needs in terms of Level of Service (LOS).

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The Traffic Operation Analysis graphic shows morning and afternoon (AM and PM) Level of Service (LOS) measures for traffic operations along I-29 mainline and at the Exit 68, 71, and 73 interchanges.  Operational measures include freeway operations, interchange ramp merge and diverge operations, and ramp terminal intersections.  LOS was determined for existing traffic volumes and forecasted 2028 and 2050 traffic volumes.

LOS Definitions

Level of service (LOS) is a quantitative stratification of performance measures representing quality of service, or how well a transportation facility operates from a traveler’s perspective.

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The Level of Service table shows the ratings of density of multi-lane highways and freeways. Ratings are also provided for intersection control delays in unsignalized and signalized intersections.

Study Area Crash History (2016 – 2020)


I-29 Exit 71 Southbound Ramp Terminal Intersection: 4 crashes
  • One fatality and one serious injury
  • 3 of 4 crashes were angle type crashes
  • Sight distance limitations supports future interchange improvements

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The Crash History graphic shows points of crashes within the study area from 2016 to 2020. Types of crashes indicated on this diagram include fatal injury, incapacitating, non-incapacitating, possible, no injury and wind animal hits.
I-29 Mainline:
134 crashes
  • 0 fatal crashes and 1 serious injury crash
  • 25% of I-29 crashes were rear-end crashes
  • 2x the percentage of rear-end crashes for I-29 statewide (12% of crashes were rear-end)

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The Severe Injury Crash History graphic shows points of crashes within the study area from 2016 to 2020. Types of crashes indicated on this diagram include fatal injury and incapacitating injury.

Environmental Resources

This map shows some of the known resources adjacent to the I-29/Exit 71 Interchange project area. In the upcoming months, the project team will be conducting more detailed field studies to analyze and minimize impacts to biological, cultural, and socioeconomic resources such as:

  • Historic Properties
  • Farmland
  • Wetlands and Streams
  • Threatened and Endangered Species
  • Visual Resources
  • Noise
  • Floodplain
  • Land Use

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The Environmental Considerations graphic shows the locations of environmental aspects that could prohibit or be impacted by future projects in the study area. Details on the diagram include airport property, rivers and streams, Lincoln County drainage districts, wetlands, FEMA flood hazards, spill reports and storage tanks, and land zoning.

CDI Alternatives

Compressed Diamond Interchange Alternatives

Interchange Overview

The I-29 Exit 71 compressed diamond interchange alternatives consist of:

  • Similar interchange type and footprint to what is out there today
  • Full reconstruction of interchange (ramps, 273rd Street, and bridge)
  • Two options: I-29 under and I-29 over 273rd Street
  • Intersections could open as stop-control (stop signs on the ramps) and then signalized when warranted by traffic volumes
  • 273rd Street expanded to 3-lane section with turn lanes and access management

Interchange Alternatives

Compressed Diamond Interchange – I-29 Under

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This image shows the conceptual layout of a Compressed Diamond Interchange, and what the road under it would look like. Details on the diagram include proposed roadway, raised median, sidewalk, bridge construction, access control, FEMA floodplain, NWI wetlands, existing Right of Ways and property lines, existing control of access points, additional control of access points needed, retaining walls, grading limits, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.
  • Year 2050 Level of Service (LOS)
    • Interchange: LOS A
    • Ramp Terminal Intersections: LOS B or better
    • Least vehicular delay of the three interchange types
  • Construction and ROW cost: $20.5 million
    • Least cost of all interchange alternatives
  • Opportunity to maintain traffic on 273rd Street across I-29 during construction

Compressed Diamond Interchange – I-29 Over

Click to enlarge.

This image shows the conceptual layout of a Compressed Diamond Interchange, and what the road over it would look like. Details on the diagram include proposed roadway, raised median, sidewalk, bridge construction, access control, FEMA floodplain, NWI wetlands, existing Right of Ways and property lines, existing control of access points, additional control of access points needed, retaining walls, grading limits, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.
  • Year 2050 Level of Service (LOS)
    • Interchange: LOS A
    • Ramp Terminal Intersections: LOS B or better
    • Least delay of the three interchange types
  • Construction and ROW cost: $25 million
  • Potential impacts to WAPA transmission lines (which would increase cost)
  • 273rd Street closed across I-29 during construction

SPI Alternatives

Single Point Interchange Alternatives

Interchange Overview

The I-29 Exit 71 SPI alternatives consist of:

  • Single, signalized interchange intersection
  • Full reconstruction of interchange (ramps, 273rd Street, and bridge)
  • Two options: I-29 under and I-29 over 273rd Street
  • 273rd Street expanded to 3-lane section with turn lanes and access management

Interchange Alternatives

SPI – I-29 Under

Click to enlarge.

This image shows the conceptual layout of a Single Point Interchange, and what the road under it would look like. Details on the diagram include proposed roadway, raised median, sidewalk, bridge construction, access control, FEMA floodplain, NWI wetlands, existing Right of Ways and property lines, existing control of access points, additional control of access points needed, retaining walls, grading limits, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.
  • Year 2050 Level of Service (LOS)
    • Interchange: LOS B
    • Ramp Terminal Intersection: LOS C or better
    • Greatest vehicular delay of the three interchange types
  • Construction and ROW cost: $33 million
    • Greatest cost of all interchange alternatives
  • Opportunity to maintain traffic on 273rd Street across I-29 during construction
  • Greatest separation between interchange and next adjacent local intersections

SPI – I-29 Over

Click to enlarge.

This image shows the conceptual layout of a Single Point Interchange, and what the road over it would look like. Details on the diagram include proposed roadway, raised median, sidewalk, bridge construction, access control, FEMA floodplain, NWI wetlands, existing Right of Ways and property lines, existing control of access points, additional control of access points needed, retaining walls, grading limits, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.
  • Year 2050 Level of Service (LOS)
    • Interchange: LOS B
    • Ramp Terminal Intersection: LOS C or better
    • Greatest vehicular delay of the three interchange types
  • Construction and ROW cost: $29.5 million
  • Potential impacts to WAPA transmission lines (which would increase cost)
  • 273rd Street closed across I-29 during construction
  • Greatest separation between interchange and next adjacent local intersections

DDI Alternatives

Diverging Diamond Interchange Alternatives

Interchange Overview

The I-29 Exit 71 DDI alternatives consist of:

  • Two signalized crossover intersections at each of the ramp terminals that cross over traffic to the opposite side of the roadway through the interchange
  • Full reconstruction of interchange (ramps, 273rd Street, and bridge)
  • Two options: I-29 under and I-29 over 273rd Street
  • Layouts reflect 273rd Street expansion to a 4-lane section (two through lanes in each direction), but interchange could open with a single through lane in each direction plus turn lanes

Interchange Alternatives

DDI – I-29 Under

Click to enlarge.

This image shows the conceptual layout of a Diverging Diamond Interchange, and what the road under it would look like. Details on the diagram include proposed roadway, raised median, sidewalk, bridge construction, access control, FEMA floodplain, NWI wetlands, existing Right of Ways and property lines, existing control of access points, additional control of access points needed, retaining walls, grading limits, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.
  • Year 2050 Level of Service (LOS)
    • Interchange: LOS B
    • Ramp Terminal Intersection: LOS B
  • Construction and ROW cost: $25.5 million
  • Opportunity to maintain traffic on 273rd Street across I-29 during construction

DDI – I-29 Over

Click to enlarge.

This image shows the conceptual layout of a Diverging Diamond Interchange, and what the road over it would look like. Details on the diagram include proposed roadway, raised median, sidewalk, bridge construction, access control, FEMA floodplain, NWI wetlands, existing Right of Ways and property lines, existing control of access points, additional control of access points needed, retaining walls, grading limits, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.
  • Year 2050 Level of Service (LOS)
    • Interchange: LOS B
    • Ramp Terminal Intersection: LOS B
  • Construction and ROW cost: $30 million
  • Potential impacts to WAPA transmission lines (which would increase cost)
  • 273rd Street closed across I-29 during construction

Interchange Alignment Options

The 273rd Street corridor was further evaluated with varying degrees of southward alignment shift through the interchange to address the following goals:

  1. Construct new 273rd Street bridge off alignment to maintain traffic on existing bridge during construction
  2. Increase separation between 273rd Street and a potential frontage road at Kenworth Place to provide for:
    1. Rocky Mountain Double truck turning movements: eastbound frontage road to westbound 273rd Street
    2. Southbound Kenworth Place queue storage: greater separation provides reduced risk of southbound Kenworth Place queues blocking northbound Kenworth Place (turning from 273rd Street) access to the frontage road

The following options were developed for the Compressed Diamond interchange (I-29 under) alternative but have elements applicable to all interchange type.

Note: With each of these options, there would be varying levels of risk of southbound Kenworth Place queues blocking access to the frontage road intersection. If a rearage road connection is feasible to the north between Irownworks Avenue and Kenworth Place, a frontage road would likely not be required. A rearage connection would address the increased separation goal (Goal 2) by providing ample distance between intersections.

Option 1: 6’ Offset
New bridge constructed 6’ south of existing bridge

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This shows the first alignment option that would offset the bridge 6 feet to the south.

Benefits

  • Least right-of-way impact and cost
  • Traffic maintained on existing bridge during construction of new bridge (Goal 1)

Drawbacks

  • Does not accommodates all ‘Rock Mountain Double’ turn movements (Goal 2a)
  • 71’ separation between frontage road and 273rd Street presents greatest risk of blocking frontage road (Goal 2b)
    • 1 semi-truck would fill available queue storage area

Option 2: 55’ Offset
New bridge constructed 55’ south of existing bridge

Click to enlarge.

This shows the first alignment option that would offset the bridge 55 feet to the south.

Benefits

  • Moderate right-of-way impact and cost
  • Traffic maintained on existing bridge during construction of new bridge (Goal 1)
  • Accommodates all ‘Rock Mountain Double’ turn movements (Goal 2a)
  • 124’ separation between frontage road and 273rd Street reduces risk of blocking the frontage road (Goal 2b)
    • Accommodates 1 Rocky Mountain Double within available queue storage area

Drawbacks

  • 124’ separation still exhibits some risk to potential blocking of frontage road (Goal 2b)
    • 2 semi-trucks would extend beyond available queue storage area

Option 3: 80’ Offset
New bridge constructed 80’ south of existing bridge

Click to enlarge.

This shows the first alignment option that would offset the bridge 80 feet to the south.

Benefits

  • Traffic maintained on existing bridge during construction of new bridge (Goal 1)
  • Accommodates all ‘Rock Mountain Double’ turn movements (Goal 2a)
  • 150’ separation between frontage road and 273rd Street provides:
    • Greatest extent queue storage between intersections
      • Accommodates 2 semi-trucks or 1 Rocky Mountain Double truck + passenger vehicle within available queue storage area
    • Meets SDDOT minimum spacing guidelines (150’ between frontage road and highway)

Drawbacks

  • 124’ separation still exhibits some risk to potential blocking of frontage road (Goal 2b)
    • 2 semi-trucks would extend beyond available queue storage area

Interchange Alternative Evaluation

Interchange Alternative Preliminary Recommendation

I-29 Mainline Alternatives



SDDOT is planning to reconstruct I-29 through the study area as part of the I-29 Exit 71 interchange project. Preliminary plans include:

  • Expanding I-29 to 6 lanes (3 lanes in each direction) from I-29 Exit 71 northward
  • Reconstructing I-29 with 4 lanes (2 lanes in each direction) from I-29 Exit 71 southward to Exit 68
    • Grading would include space for a future 3rd lane in each direction
    • The 3rd lane in each direction would likely be added by Year 2050

One of this study’s goals is to determine whether I-29 through and south of Exit 71 needs to include all 6 lanes with the interchange project or whether the preliminary plan of paving 4 lanes now and adding the 3rd lane in each direction when needed will meet future needs.

Click the images below to enlarge.

Exit 68 to Exit 71 (4-lane)

This image shows the conceptual layout of a 4-lane section with grading for a future third lane in each direction from Exits 68 to 71. Details on the diagram include the proposed roadway, the widening transition, bridge construction, FEMA floodplain, NWI Wetlands, existing right of way and property lines, retaining walls and anticipated right of way impacts.

Exit 68 to Exit 71 (6-lane)

This image shows the conceptual layout of a 6-lane construction from exits 68 to 71. Details on the diagram include the proposed roadway, the widening transition, bridge construction, FEMA floodplain, NWI Wetlands, existing right of way and property lines, retaining walls and anticipated right of way impacts.

Exit 71 to Exit 73 (6-lane to 4-lane transition)

This image shows the conceptual layout of a 4-lane section with grading for a future third lane in each direction from exits 71 to 73. Details on the diagram include the proposed roadway, the widening transition, bridge construction, FEMA floodplain, NWI Wetlands, existing right of way and property lines, retaining walls and anticipated right of way impacts.

Exit 71 to Exit 73 (6 lane)

This image shows the conceptual layout of a 6-lane construction from exits 71 to 73. Details on the diagram include the proposed roadway, the widening transition, bridge construction, FEMA floodplain, NWI Wetlands, existing right of way and property lines, retaining walls and anticipated right of way impacts.

Exit 73 to Exit 74 (6 lane)

This image shows the conceptual layout of a 6-lane construction from exits 73 to 74. Details on the diagram include the proposed roadway, the widening transition, bridge construction, FEMA floodplain, NWI Wetlands, existing right of way and property lines, retaining walls and anticipated right of way impacts.


Airport Runway Protection Zone Avoidance Options

Option 1
Reconstructs I-29 on the existing alignment with the new 3rd lane in each direction added to the inside median. New median width is 36’.

Click to enlarge.

Image dipects widening 1-29 to 6 lanes in each direction.

Option 2
Realign I-29 outside of the RPZ to the east. Exhibits a 36’ median width to match I-29 to the north

Click to enlarge.

Image dipects relocating I-29 lanes Outside of Airport Runway Protection Zone.

Option 3
Realign I-29 outside of the RPZ to the east. Exhibits a 60’ median width to match I-29 to the south.

Click to enlarge.

Image dipects relocating I-29 lanes Outside of Airport Runway Protection Zone.

I-29 Mainline Evaluation and Preliminary Recommendations

273rd Street Concepts



The 273rd Street (Lincoln County Highway 110) conceptual layouts reflect potential future improvements to illustrate what the future corridor might look like in conjunction with the planned SDDOT I-29 Exit 71 reconstruction. While these improvements are based on identified transportation needs through this study’s 2050 Planning Horizon, they are considered conceptual with regard to extent of modifications on 273rd Street and implementation timeframe.

Click to enlarge.

This image shows a conceptual layout for County Highway 10/273rd Street. Details on the diagram include proposed roadway, roadway concept, raised median, sidewalk, removed access, existing right of way/property lines, anticipated right of way impacts, signalized intersections, stop condition intersections and yield condition intersections.

Potential ITS Elements



Preliminary ITS elements being considered as part of this study are shown in the figure. Recommendations from this study will be used as a guide to implement technologies as part of the planned I-29 Exit 71 interchange and I-29 mainline reconstruction project, other future corridor projects and/or SDDOT statewide ITS programs.

Potential ITS Map

Preliminary Intelligent Transportation Systems (ITS) elements being considered as part of this study are shown in the figure. Recommendations from this study will be used as a guide to implement technologies as part of the planned I-29 Exit 71 interchange and I-29 mainline reconstruction project, other future corridor projects and/or SDDOT statewide ITS programs.

Proposed Variable Speed Limit (VSL) sign locations south of I-29 Exit 71 would be part of a larger I-29 corridor VSL implementation. The full extent of this implementation beyond the study area and specific VSL sign locations will be identified outside of this study. This figure illustrates how those elements could would fit within the planned SDDOT I-29 Exit 71 interchange and I-29 mainline reconstruction project.

Click to enlarge.

This image shows potential Intelligent Transportation System (ITS) elements within the study area.  Both existing and proposed elements are shown, including closed-circuit television cameras (CCTV), variable speed limit (VSL) sign locations, dynamic message signs (DMS), ramp and interstate closure gates, flashing beacon signs, environmental sensing station (ESS) towers, fiber optic lines, and traffic data collection type and locations.

Stay Connected

Thank you for your participation!

Leave a Comment

Today, please provide feedback on the revised I-29 Exit 71 interchange and I-29 mainline alternatives, evaluation, preliminary considerations for construction to help develop final recommendations for the study. Comments will be accepted until December 17, 2021.


Make a comment

The comment period for this meeting has ended. If you would like to leave a general comment, please use the comment form on the project website.


Mark Your Calendar

This will be the final public meeting of the Interchange Modification Study if the National Environmental Policy Act (NEPA) classification is determined to be a Categorical Exclusion (CE). If an Environmental Assessment (EA) is required, a third public meeting will be held during the summer/fall 2022.


Project Contacts

Questions for the project team?

Jon Wiegand, P.E., PTOE, Consultant Project Manager
jonathan.wiegand@hdrinc.com | 605-782-8105

Steve Gramm, P.E., SDDOT Project Manager
steve.gramm@state.sd.us | 605-773-3281

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The comment period for this meeting has ended. If you would like to leave a comment, please use the comment form on the project website.