Objective A of this research is to develop guidance on the operational analysis and traffic signal design and operation of DDIs and adjacent traffic signals. The guide should be useful to (1) a modeler working with designers to optimize the geometric design, (2) a signal designer implementing operational strategies, (3) a signal technician wiring the cabinet(s) and programming the controller(s), and (4) an operator fine-tuning the operation of the interchange and adjacent intersection in real-time throughout the day.
Objective B of this research is to identify, review, and evaluate the geometric design features and the associated safety and operational performance of in-service DDIs across the US. Two basic questions will be addressed: (1) What are the essential design characteristics of a DDI and how should an engineer utilize this information in the design of a DDI and (2) What are the safety and operational benefits of utilizing a DDI and how might the designer utilize this information in their design?
Objective C of this research is to develop and deliver a training and technology transfer program for the signal timing guidelines developed under Objective A. Ten workshops will be held at different transportation agencies that have a broad range of experience with DDIs.
Objective A is complete and Objectives B and C are underway. The guidance will cover both Objectives A and B and will also incorporate related research products. An outline for the guidance has been developed and two preliminary chapters dealing with traffic signals (Objective A) are available below.
Chapter 5, Conceptual Operations
Chapter 7, Final Design (only the signal portion)
Objective A: Operational Analysis and Traffic Signal Design and Operation
Task A.1. Review pertinent domestic and international literature on traffic signal design and operation at DDIs to identify best practices and lessons learned. This literature review should be kept current throughout the project since this design is new to the United States.
Task A.2. Identify leaders in the design, installation, maintenance, and operation of DDI signals. Use interviews or other techniques to gather information on best practices and lessons learned on traffic signals at DDIs, by themselves and in conjunction with adjacent intersections. Identify situations and typical failure modes that warrant the development of new control strategies to address them.
Task A.3. Describe new control strategy concepts that could address the problematic situations and failure modes identified in Task 2.
Task A.4. Calibrate and validate the microscopic simulation model that will be used in Task 6.
Task A.5. Within 9 months, submit an interim report documenting Tasks 1 through 4. The interim report shall also include a complete plan for conducting the simulation runs in Task 6 and a detailed outline of the guide.
Task A.6. Conduct microscopic simulation runs to explore issues such as (1) benefits of best and innovative control strategies that have been identified, (2) sensitivity of the operation to distances and speeds between signals, (3) impacts of different volumes and directional distributions, (4) sensitivity of the operation to timing parameters (e.g., offsets, cycle lengths, overlaps, phase sequence), (5) effectiveness of different detection schemes, (6) interactions between a DDI traffic signal and ramp meters, (7) optimal control for ramp traffic, (8) effective pedestrian strategies, (9) effective preemption and priority strategies, and (10) strategies to address phase starvation and queue spillback.
Task A.7. Insofar as practical, work with a transportation agency to field validate any new traffic signal control strategies developed.
Task A.8. Develop the guide on the operational analysis and traffic signal design and operation of DDIs and adjacent traffic signals that encapsulates best practices, lessons learned, and new strategies.
Task A.9. Submit a final report that documents the entire research effort and includes the Task 8 guide as a stand-alone document.
Objective B: Geometric Design and Safety Analysis
Task B.0. Prepare amplified work plan for the tasks associated with the second objective.
Task B.1. Perform an inventory of in-service DDIs. Task B.2. Meet with stakeholders to with first-hand experience in the design of DDIs.
Task B.3. Assess whether, and to what extent, the current design process reflects the explicit consideration of performance (e.g., pedestrian treatments, safety) and promotes efficient, if not optimal, combination of design elements to yield designs that are cost-effective when considering life-cycle benefits and costs.
Task B.4. Design a series of studies and experiments to fill gaps in the available knowledge of DDI design and safety performance. The studies are intended to answer very specific research questions and knowledge gaps based on the results of prior tasks.
Task B.5. Develop an interim report documenting the results of Tasks B.0 through B.4. Meet with the panel to finalize the experiment plan developed in Task B.4.
Task B.6. Execute the work plan following prioritization and approval from the panel.
Task B.6. Develop material on the geometric design and safety analysis of DDIs for inclusion in the NCHRP Project 03-113 guide. Provide any recommended text changes to the Green Book in an appendix.
Objective C: Training for Traffic Signal Timing Guidelines
Task C.1. Develop training materials based on the research results in NCHRP 03-113, tailored to a one-day course delivery. Course material will include PowerPoint slides and simulations of various DDI’s as case studies.
Task C.2. Determine appropriate venues for conducting the training including a) state and municipal agencies and b) national and regional meetings.
Task C.3. Acquire course certification from professional organizations (e.g., PDH credits, ITE), which will allow participants to acquire continuing education units.
Task C.4. Modify the training materials as necessary to meet the needs of each audience. Where possible, consider using local DDI’s for course discussion, such as in simulation software.
Task C.5. Conduct training on new DDI guidance specifically looking at the considerations at the immediate interchange influence area as well corridor impacts and potential treatments for remediation and anticipated benefits.
Task C.6. Submit a short final report documenting the entire training effort, survey responses following each course, recommendations for further enhancements to the course, and future training opportunities.