• Design Consistency on Corridors

    NCDOT Research Project Number: 2020-31

 Executive Summary

  • ​Alternative Intersection and Interchange (AII) designs are those which provide an innovative approach to the geometric or control features which may improve operations and/or safety for drivers. NCDOT is a national leader in AII implementation which provides safe, efficient, and cost-effective travel solutions for North Carolina drivers. As corridor construction or improvement projects continue to utilize AII designs, a key concern of driver confusion is identified when different AII designs are adjacent in a corridor. Due to the range of design and operational differences in these AII designs, there is concern that drivers will be confused on how to safely navigate a corridor when adjacent intersections may handle movements in different ways – especially left turns.

    This project aims to collect measurable data on driver behavior and understanding of AII designs and how drivers react to successive unique AII combinations. As an example, a driver anticipating a left turn at the second cross street ahead may first pass through a Continuous Flow Intersection (CFI), where you must take an early left turn bay to cross over before the cross street. After seeing this left turn style, there may be significant confusion if a Median U-Turn immediately follows where drivers must drive past the cross street and make a u-turn then right turn maneuver. Drivers need time and space to observe design differences, identify the correct movement to accommodate their route, then change lanes and merge or diverge as needed.

    The results of this project will be a predictive model for recommended spacing between adjacent AII designs of different types. The research team has extensive experience in driver behavioral studies, AII design and operations, as well as human subject research. Design combinations will be reviewed by the StIC to ensure they are realistic design scenarios that NCDOT may consider. This model will then be incorporated into a worksheet or computational engine as well as a guidance document which will be available for NCDOT and their consultants to use in future corridor designs. These products will ensure NCDOT continues to lead the country in AII innovation while remaining focused on driver understanding and safety.

R. Thomas Chase
R. Thomas Chase; Christopher Cunningham; David B. Kaber
Doumit Ishak
Stephanie C. Bolyard
NC State University - ITRE
University of Florida

 Related Documents

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 Report Period

  • August 1, 2019 – January 31, 2022


  • In Progress


  • Traffic, Mobility, Safety and Roadway Design

 Sub Category

  • Facility Design

 Related Links

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