Characterize Dynamic Dilemma Zone and Minimize its Effect at Signalized Intersections

摘要

Dilemma zone at signalized intersection has been recognized as a major potential causing rearend crashes, and has been widely studied by researches since it was initially proposed as the GHM model in 1960. However, concepts conventionally defined to represent yellow phase dilemma lack integrity. This research conducts a comprehensive literature review with attempt to clarify the interrelationship among dilemma zone, option zone, and indecision (decision) zone, and to develop a heuristic framework to present the contributing factors in dilemma zone modeling. A new method for modelling the locations and lengths of the dilemma zone using video-capture techniques and vehicle trajectory data is presented in this report. First, dilemma zone is mathematically modeled based on the literature review. Then, field-observed trajectory data extracted by the video-capturing-based approach are used to calibrate the contributing factors involved in the dilemma zone models. The high accuracy of the time-based trajectory data has significantly enhanced the accuracy of the calibrated dilemma zone models. Two sets of trajectories are explored for calibrating the dilemma zone contributing factors. One is concerned with maximum yellow-onset safe passing distance and minimum yellow-onset stopping distance. The other is concerned with 10Xth percentile yellow-onset passing distance and stopping distance for the prevailing travel behaviors. The latter alternative actually precludes too conservative and too aggressive behaviors in response to yellow indications. One critically important result is the dilemma zone look-up charts that are developed based on the calibrated dilemma zone models. Such charts provide a convenient tool to identify locations and lengths of dilemma zones for any speed and yellow duration conditions. Additionally, impact of arrival type and vehicle types are also explored. Results reveal that traffic in a good progression (Arrival Type . 4) has a further option zone. It is also discovered that the length of option zone decreases as vehicle size increases, while the downstream boundary of option zone is further from the stop line as vehicle size increases. In overall, the project provides primary study results and solid basis for future study of the optimum signal detection placement and related dilemma zone protection problems with consideration of multispeed protection.