OPERATIONAL ANALYSIS OF ADVANCE WARNING FLASHERS Sudeeksha Murari, MSc Virginia Tech, murari@vt.edu , MSc Virginia Tech, milosm@vt.edu Montasir M. Abbas, PhD Virginia Tech, abbas@vt.edu Review paper Abstract: Advance Warning Flashers have been used across United States and Canada for warning the motorists approaching a high-speed signalized intersection to either slow down or prepare to stop. These systems are in close correlation to geometry of the intersection and dilemma zone protection. Conventional warning systems usually work in fixed- time or with a trailing overlap at the end of green, leading to increased red light running as users adapt to the system. Recently developed systems tried to integrate separate computer devices to add the ability to predict the end of green phase. Those systems faced issues with false activations and lengthy lead flash times. This paper provides a comprehensive review of the developed advance warning systems. Furthermore, paper elaborates on the drawbacks that these systems face and proposes an advance warning system integrated in the controller logic. Keywords: Advance warning flashing, dilemma zone protection, human factors, traffic signal controller OPERATIVNA ANALIZA SIGNALNIH TREP Sudeeksha Murari, MSc Virginia Tech, murari@vt.edu Virginia Tech, milosm@vt.edu Montasir M. Abbas, PhD Virginia Tech, abbas@vt.edu Pregledni rad Rezime: zaustavljanjem. Ovi sistemi su u direktnoj vezi sa geometrijskim karakteristikama raskrsnice i potrebom upozorenja ob dovodi do po signalnu indikaciju, s obzirom da se korisnici navikavaju na sistem. Sistemi koji su razvijeni u skorije vreme se baziraju na dodatnom kompjuteru, koji pored zelenog signalno rad predstavlja sveobuhvatni pregled trenutne prakse i Dalje, ovaj rad ukazuje na konkretne problem unutar logike rada kontrolera za upravljanje radom svetlosnog signala. : e kontroler za upravljanje radom svetlosnog signala 1. BACKGROUND The introduction of traffic signals usually tries to resolve two conflicting interests of the intersection operation: the interest for safety and the interest for efficiency. In the case when signalized intersection is located on a high-speed road where speed is greater than 45 mph, the emphasis on intersection safety is of greater importance. The emphasis on safety is mainly due to the larger collisions consequences. Although traffic signal on a high-speed road can serve its primary safety function of separating conflicting flows of vehicles, additional safety issues might appear. The issues are usually with sight or stopping distance and can relate to unawareness of intersection, dilemma zone, or other issues [1]. Limited sight distance issues can result in unawareness of intersection and are mainly due to the geometric constraints. The issues usually originate from vertical or horizontal curvature, or sight obstruction objects. Stopping distance issues are under significant influence of dilemma in the diver decision process. This dilemma appears in the case of onset of yellow change interval. This is in the area at a definite distance from the intersection where driver is in the dilemma zone, i.e., a driver is unsure whether the distance from the stop bar is short enough to proceed through intersection or it is too long and he has to slow down and stop [2]. In the cases of wrong driver decision in dilemma zone, an abrupt stop may lead to rear-end collision, while proceeding and running on red may lead to right-angle crashes. Factors such as vehicle type or downhill grade contribute to increasing the size of dilemma zone [3, 4]. Figure 1 summarizes the factors affecting driver behavior approaching an intersection. Figure 1. Factors that affect the driver behavior approaching a signalized intersection Limited sight distance Isolated intersection Unawareness of intersection Speed limit Downhill grade Percentage of heavy vehices Stopping distance