McMillan and Black Cat Roundabout

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The Ada County Highway District (ACHD) is designing a future roundabout for the McMillan and Black Cat intersection. The purpose of the project is to improve traffic flow and increase safety for all users.

Proposed Improvements

  • Construct a multi-lane roundabout at the McMillan and Black Cat intersection
  • Add curb, gutter and a detached 10-foot-wide multi-use pathway
  • Construct crosswalks at each leg of the intersection with two-stage pedestrian crossings
  • Install rectangular rapid flashing beacons (RRFBs) at each pedestrian crossing
  • Add a truck apron for larger vehicles to use if necessary and intersection lighting


The Ada County Highway District (ACHD) is designing a future roundabout for the McMillan and Black Cat intersection. The purpose of the project is to improve traffic flow and increase safety for all users.

Proposed Improvements

  • Construct a multi-lane roundabout at the McMillan and Black Cat intersection
  • Add curb, gutter and a detached 10-foot-wide multi-use pathway
  • Construct crosswalks at each leg of the intersection with two-stage pedestrian crossings
  • Install rectangular rapid flashing beacons (RRFBs) at each pedestrian crossing
  • Add a truck apron for larger vehicles to use if necessary and intersection lighting


  • Interim Signal Installation

    Share Interim Signal Installation on Facebook Share Interim Signal Installation on X (formerly Twitter) Share Interim Signal Installation on Linkedin Email Interim Signal Installation link
    supporting image
    An interim signal has been installed at Black Cat and McMillan to assist with alleviating increased congestion in the area as a result from the Ustick Road widening project and the Idaho 16 construction. This signal includes two poles and four mast arms and will eventually be replaced by a multilane roundabout currently scheduled for 2029, as a part of the Five-Year Plan.

    More info: https://www.facebook.com/share/1H7NwbPUit/


    An interim signal has been installed at Black Cat and McMillan to assist with alleviating increased congestion in the area as a result from the Ustick Road widening project and the Idaho 16 construction. This signal includes two poles and four mast arms and will eventually be replaced by a multilane roundabout currently scheduled for 2029, as a part of the Five-Year Plan.

    More info: https://www.facebook.com/share/1H7NwbPUit/


  • Check out the design!

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    Please review the information below to learn more about the project and provide comments. While your comments are always welcome, the comment period closed on July 26, 2023

    Please review the information below to learn more about the project and provide comments. While your comments are always welcome, the comment period closed on July 26, 2023

Page last updated: 09 Mar 2026, 01:39 PM