Daniel b . Fambro Student Paper award : modeling Dynamic Dilemma Zones using observed Yellow - onset Trajectories

iNTRODUCTiON Intersection crashes constitute a significant portion of total crashes nationwide. The report " National Agenda for Intersection Safety " quotes that in the year 2000, more than 2.8 million intersection-related crashes occurred, which amounts to 44 percent of all reported crashes. 1 Among all possible factors contributing to the intersection-signal-related crashes, yellow phase dilemma is one of the major problems that has not been fully solved. A dilemma zone (DZ) is a roadway segment within which a vehicle approaching an intersection during the yellow interval can neither safely clear the intersection nor stop comfortably at the stop line. 2 It is formed due to the minimum safe stopping distance (X c) being longer than the maximum yellow clearance distance (X 0), as illustrated by Figure 1a. This definition along with its mathematical model, the GHM model, is further applied in the ITE handbooks as a guideline for determining the yellow change and all-red clearance intervals. 3,4 Based on the ITE yellow interval formula and the assumed parameter values (i.e., driver's perception-reaction time as 1.0 second[s], and vehicle's deceleration rate as 16 ft./s 2), the calculated yellow interval theoretically guarantees that X 0 is longer than X c. Thus, it would be ensured for an approaching vehicle to either safely stop or clear the intersection during the yellow interval. At this point, the defined yellow dilemma is supposed not to exist. However, in reality this dilemma is hard to eliminate because of two primary reasons: (1) drivers' driving behaviors vary with their different aggressiveness, and the assumed parameter values may not be compatible with all the drivers' driving features. In other words, DZ is dynamically featured