• May 5th, 2018

The modern highway system has experienced considerable changes since the interstate system and other limited access highways were first designed and constructed in the mid-1900s. Population movement outside of cities and the increased movement of passenger and freight traffic have led to increased congestion and necessitated new approaches for maintaining mobility.

Mobility and capacity enhancements, including additional lanes, preferential lanes and ramps, and multilane exits have subsequently complicated the design and operation of interchanges. Drivers approaching an interchange must undertake the navigation task while workloads from the guidance and control tasks are particularly high. In addition to the task of selecting a lane appropriate to the desired route, which typically requires lane changes, drivers experience workload demands related to conflicting traffic from lane changes associated with entering and exiting maneuvers. The combined workload of guidance and control tasks related to collision avoidance and navigation is easily exacerbated by a reduction in available time to make a maneuver (due to speed or short distances between critical points) and factors associated with roadway geometric design, roadway cross section, and traffic volumes and density.

The purpose of this study was to develop recommendations for signing, delineation, and geometric design that will reduce workloads at critical points approaching interchanges that exhibit a high degree of complexity. In the development of these recommendations, the following activities were completed:

  • Identification of attributes influencing interchange complexity
  • Evaluation of current geometric design, signing, and marking practices
  • Simulator study investigating driver behavior at different interchange layouts
  • Field study investigating real-world driver behavior at complex interchanges

Chapter Topics

  • Chapter 1: Background information
  • Chapter 2: Contemporary literature and policies summary
  • Chapter 3: Development and categorization of attributes typical of complex interchanges
  • Chapter 4: Site evaluation and selection process, the basis for the field study, and input for the practices evaluation
  • Chapter 5: Practices evaluation, including information on a new method of evaluating traffic control devices (TCDs) alongside this project’s examination of contemporary practices throughout the United States and Canada
  • Chapters 6: Simulator study (methodologies, data collection, and analyses)
  • Chapter 7: Field study (methodologies, data collection, and analyses)
  • Chapter 8: Research results
  • Chapter 9: Recommendations