Research Approach

The research team identified and executed a research plan consisting of 13 tasks that were needed to accomplish the project objectives.

Task 1. Form an Advisory Group of a minimum of five knowledgeable professionals to work with the project panel in the evaluation of PPLT signal displays. Members of the advisory group will be well-respected, experienced traffic engineers knowledgeable in the PPLT issue. The research team will also interact with the Signals Technical Committee of the National Committee on Uniform Traffic Control Devices (NCUTCD) on a regular basis. The objective of these frequent meetings will be to provide a regular flow of information to the committee.

Task 2. Develop an evaluation matrix and conduct an engineering assessment of the different displays. The evaluation matrix will include safety, operations, implementation, human factors, and versatility. The engineering assessment will identify factual and judgmental information required to evaluate the proposed displays. Included in Task 2 is the administration of an agency survey. The objective of the agency survey is to identify and quantify the different types of protected/permitted left-turn signal displays used in the United States.

Task 3. Conduct photographic driver survey to determine driver understanding of the six basic PPLT displays using static and dynamic survey techniques. At a minimum, computer generated displays on static background photographs will be used to represent the dynamic aspects. A minimum of 300 responses will be obtained in each of eight regions where the different displays are used (2,400 responses total). Geographic locations to be surveyed are Seattle, Portland, Reno, Dallas, College Station, Orlando, Dover, and Detroit. Select survey candidates to be representative of the driving population.

Task 4. Conduct traffic operation studies to determine and compare traffic conflict rates for protected/permitted left-turn signal displays. The traffic observation studies will be completed in the eight survey areas to provide additional insights in driver behavior related to alternative PPLT displays. Eight hours of conflict data will be collected at three intersections within each geographic area. The research team will work with local traffic engineers to identify representative sites with PPLT displays and gather crash, traffic, geometry, and other relevant data to document conditions at each site.

Task 5. Conduct a review of crash data to determine and compare left-turn crash rates associated with various PPLT displays. Crash data will be obtained from the same sites evaluated for the traffic observation studies (Task 4), and from selected components of the crash database created in 1988 as part of a previous study by JHK & Associates, if possible. Crash data will also be requested from volunteer network established early in the project.

Task 6. Conduct a comprehensive analysis of the results obtained from the agency surveys, photographic driver surveys, conflict studies, and crash studies.

Task 7. Prepare a draft version of the video driver survey. The objective of this task is to develop a working prototype of the animated survey for panel review. The video driver survey will be used to assess driver understanding of alternative protected/permitted left-turn displays.