I-471 / KY 8
Interchange Modification Project

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I-471 AT KY 8 INTERCHANGE MODIFICATION PROJECT

REVIEW OF THE DECISIONS ON THE FINAL ALTERNATIVES THAT WILL BE ADVANCED INTO THE NEXT STAGE OF PROJECT DEVELOPMENT

Below are links to the selected Conceptual Alternatives

Alternate 1
Alternate 2b
Alternate 5d
Cross Sections (1)
Cross Sections (2)

General Review

  • Sixteen (16)-Conceptual Alternatives have been considered to date: 1, 1a, 1b, 2, 2a, 2b 3,3a, 3b, 4, 4a, 5, 5a, 5b, 5d and 6. (This includes the three “hybrid” alternatives 2b, 3b and 5d, presented for the first time at the 9/19/07 IAC / S106CPs Meeting in Bellevue.) Of the pre-“hybrid” Alternatives, Stakeholders / Public favored 1, 2, 3, 4a and 5 while Design Team evaluations favored 2, 3, 5, 5a, 5b and 6.

    Of interest was the rating of Alternative 5b as one of the worst by Stakeholders and one of the favorites by the Design Team. The negative stakeholder reaction was largely due to severe impacts to the Bellevue commercial district and moderate impact to the Newport Island east of I-471.

  • A 9/19/07 ~ Interchange Advisory Committee / S106 Review Consulting Parties Rountable Discussion resulted in reaching consensus for advancing three Alternatives, 1, 2b and 5d.

Decision-Making Discussions

  • Traffic characteristics of the proposed southbound exit ramp “split” scenario were discussed. By keeping the exit open to Park Avenue and introducing a slip to Riviera via Providence Way, the southbound exit ramp terminal must be moved northward approximately 600’, well onto the Daniel Carter Beard Bridge approach structure. This shortens the available weaving distance on the Daniel Carter Beard Bridge (DCBB) and worsens the already hazardous weaving maneuver in the southbound lanes. For this reason, the Design Team decided to eliminate this “split” feature from future consideration. This resulted in the elimination of the following Conceptual Alternatives: 1b, 3, 4, 5, 5a, 5b and 6.

  • Alternatives 1a, 2, 3b and 4a maintain the existing weave length but will be eliminated for other reasons:

    • Alternative 1a; proposes the “Back-door into Bellevue”. The general public scored this Alternative 7th of 13 while the IAC and Design Team rated it 12th of 13. This concept was eliminated largely due to negative reaction related to adding traffic directly into neighborhoods of South Bellevue and Newport. Also, it adds traffic to Memorial Parkway Interchange.

    • Alternative 2; proposes a dual lane exit ramp terminal which prohibits the use of a continuous fourth lane due to lane balance issues. Also, the weaving distance on the DCBB is shortened somewhat by the dual lane terminal. Also, a single lane terminal has been determined to suffice with the given traffic.

    • Alternative 3b; closes the ramp to Park and puts all southbound exit traffic onto Riviera Drive. This overburdens Riviera Drive, in particular on the northbound approach to the intersection with KY 8. Access to the Party Source would be severely hampered.

    • Alternative 4a; closes the ramp to Park and puts all southbound exit traffic onto the northbound ramp intersection with KY 8 overburdening the intersection.

Final Alternatives Discussions

  • FHWA requires the inclusion of a “No-Build” Alternative. The purpose of the No-Build is to provide a baseline to which all build alternatives can be compared. Secondary impacts to adjacent interchange and street facilities can be quantified based on this comparison. A no-Build Alternative will be included in investigations where existing roadway network will be subjected to modeling with 2035 traffic forecast volumes.

  • The Design Team reached consensus on recommending the advancement of the following Conceptual Alternatives:

    • No-Build

    • Alternative No. 1: (Keeps the southbound exit to KY 8 via Park Avenue open)

    • Alternative 2b: (Closes the southbound exit to KY 8 via Park Avenue)

    • Alternative 5d: (Closes the southbound exit to KY 8 via Park Avenue).

  • The Design Team will conduct a refined traffic analysis involving VISSIM runs, for the following conditions:

    • No-build

    • No-build + fourth lane

    Both a continuous fourth lane and a fourth auxiliary lane condition will be modeled to determine which performs better. The outcome of the no-build condition will be applied to the three build scenarios.

    • Alternative 1 + fourth lane

    • Alternative 2b + fourth lane

    • Alternative 5d + fourth lane.

    Below are links to the selected Conceptual Alternatives

    Alternate 1
    Alternate 2b
    Alternate 5d
    Cross Sections (1)
    Cross Sections (2)

    If you have any questions, please feel free to email us at info@471project.org