Estimating Rear-End Accident Probabilities at Signalized Intersections: A Comparison Study of Intersections With and Without Green Signal Countdown Devices

Objective: Rear-end accidents are the most common accident type at signalized intersections, because the diversity of actions taken increases due to signal change. Green signal countdown devices (GSCDs), which have been widely installed in Asia, are thought to have the potential of improving capacity and reducing accidents, but some negative effects on intersection safety have been observed in practice; for example, an increase in rear-end accidents.Methods: A microscopic modeling approach was applied to estimate rear-end accident probability during the phase transition interval in the study. The rear-end accident probability is determined by the following probabilities: (1) a leading vehicle makes a “stop” decision, which was formulated by using a binary logistic model, and (2) the following vehicle fails to stop in the available stopping distance, which is closely related to the critical deceleration used by the leading vehicle. Based on the field observation carried out at 2 GSCD intersections and 2 NGSCD intersections (i.e., intersections without GSCD devices) along an arterial in Suzhou, the rear-end probabilities at GSCD and NGSCD intersections were calculated using Monte Carlo simulation.Results: The results suggested that, on the one hand, GSCDs caused significantly negative safety effects during the flashing green interval, especially for vehicles in a zone ranging from 15 to 70 m; on the other hand, GSCD devices were helpful in reducing rear-end accidents during the yellow interval, especially in a zone from 0 to 50 m.Conclusions: GSCDs helped shorten indecision zones and reduce rear-end collisions near the stop line during the yellow interval, but they easily resulted in risky car following behavior and much higher rear-end collision probabilities at indecision zones during both flashing green and yellow intervals. GSCDs are recommended to be cautiously installed and education on safe driving behavior should be available.研究目标：追尾事故是信号控制交叉口最常见的事故类型，原因在于信号切换时驾驶行为的多样性显著提升。绿色信号倒计时装置（Green Signal Countdown Devices，GSCDs）已在亚洲广泛布设，学界普遍认为其可提升通行能力并降低事故发生率，但实际应用中也观察到其对交叉口安全存在负面影响，例如追尾事故数量上升。 研究方法：本研究采用微观建模方法，估算相位过渡时段内的追尾事故概率。追尾事故概率由以下两类概率共同决定：(1) 前车做出“停车”决策，该决策通过二元逻辑回归模型构建；(2) 后车在可用停车距离内未能完成制动停车，这一情况与前车采用的临界减速度密切相关。基于对苏州某主干道沿线2个布设GSCDs的交叉口与2个未布设GSCDs的交叉口（即无绿色信号倒计时装置交叉口）开展的实地观测，本研究通过蒙特卡洛模拟计算了两类交叉口的追尾事故概率。 研究结果：结果表明，一方面，GSCDs在闪绿灯时段会对交通安全产生显著的负面影响，尤其对15至70米范围内的车辆；另一方面，GSCDs可在黄灯时段降低追尾事故发生率，尤其在0至50米的区域内。 研究结论：GSCDs可缩短犹豫区间，并在黄灯时段降低停车线附近的追尾碰撞风险，但在闪绿灯与黄灯时段，该装置易引发危险的跟车行为，使犹豫区间内的追尾碰撞概率显著升高。因此，建议谨慎布设GSCDs，并配套开展安全驾驶行为教育。