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Human Factors and Driver Compliance at Unconventional Intersections


Several types of unconventional signalized intersections and interchanges have been in use or have recently emerged as effective solutions to ever growing urban congestion. These intersections and interchanges are innovatively created to provide the higher operational efficiency than conventional designs would be able to achieve. To name a few, unconventional signalized intersections include: Median U-Turn (also called Michigan Left), Bowtie, Superstreet, Jug-Handle, Quadrant Left, Continuous Flow, and Continuous Green T–Intersection. Two types of emerging interchanges are Displaced Left Turn Interchange (DLTI) and Diverging Diamond Interchange (DDI). Field studies have demonstrated great success of such intersection and interchange designs (e.g. 1), and some design guidance for these intersections and interchanges is available in a Federal Highway Administration (FHWA) report (2).

The current practice for analyzing the performance of such intersections and interchanges is primarily micro-simulation. Research on the safety and operations benefits of unconventional intersections is emerging, but limited information is available to assess driver compliance with these designs (e.g. determine types and frequency of illegal or unsafe movements by all road users- including bicycles and pedestrians). This research is needed to assist practitioners and researchers in improving these unconventional designs to provide expected safety and operational benefits. It is expected this research will provide guidance to improve typical unconventional intersection designs including, but not limited to, an improved geometric layout and enhanced use of traffic control devices, and these results may be included in future national reference material such as the American Association of State Highway and Transportation Officials (AASHTO) Green Book, Manual on Uniform Traffic Control Devices (UTCD), and Highway Capacity Manual (HCM).

In addition to driver compliance, other human factors that are barriers to implementation may also be evaluated such as public and political misconceptions of such alternative intersection designs.


The objectives of this research are: (1) to evaluate installed unconventional intersections (including, but not limited to DDI, CFI, and dual-lane roundabouts) to determine motorist compliance with the design and traffic control devices; (2) to evaluate compliance of pedestrians, bicyclists, or other modes; and (3) to improve unconventional intersection design guidance. This research is expected to determine compliance with such designs by evaluating illegal and/or unsafe movements such as wrong-way, failure to yield, stopping at a yield sign, failure to stay in lane, etc. Countermeasures will be developed to improve user compliance with these designs.


The quantity of unconventional intersections and interchanges being constructed is exponentially increasing in the United States as a result of safety and operational research. This proposal should further enhance this research by evaluating how road users react to these designs, and proposes countermeasures to increase user compliance hence facilitating expected safety and operational benefits. This research and resulting guidelines are needed as soon as possible to provide practitioners better information to enhance designs and best serve the traveling public. Implementation by State and local DOTs could be immediate once guidelines are provided.

Related Research:
  1. HDR Engineering and MODOT (2011). Diverging Diamond Interchange Performance Evaluation (I-44 & Route 13). Jefferson City, MO.

  2. FHWA (2010). Alternative Intersections/Interchanges: Informational Report (AIIR). McLean, VA: USDOT. FHWA-HRT-09-060.

  3. MODOT (2010). Missouri’s Experience with a Diverging Diamond Interchange - Lessons Learned. Jefferson City, MO: OR 10 - 021.


The major tasks of this research include, but are not limited to the following:

· Conduct a comprehensive literature review on practices and methodologies for analyzing unconventional intersections and interchanges,

· Conduct an agency survey to determine types and presence of unconventional intersections,

· Conduct field studies to determine types and frequency of user non-compliance with these designs,

· Develop and evaluate countermeasures to improve motorist and non-motorist compliance at unconventional intersections,

· Produce recommended designs and documents that can be incorporated into national references that propose to improve user compliance with unconventional intersections, and to help dispel any public misconceptions of these designs.


Implementation by State and local DOTs could be immediate once guidelines are provided.


The quantity of unconventional intersections and interchanges being constructed is exponentially increasing in the United States as a result of safety and operational research.

Sponsoring Committee:AKD10, Performance Effects on Geometric Design
Research Period:24 - 36 months
Research Priority:Medium
Source Info:Developed and submitted (September 2012) by Michael P. Reese and James H. Dunlop, North Carolina DOT.
Date Posted:11/16/2016
Date Modified:11/27/2016
Index Terms:Signalized intersections, Manual on Uniform Traffic Control Devices, Highway capacity, Highway Capacity Manual, Left turn lanes, Diamond interchanges, Traffic flow, Microsimulation, Geometric design, Driver performance,
Cosponsoring Committees: 
Operations and Traffic Management
Safety and Human Factors

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