Reducing the risk of rear-end collisions with infrastructure-to-vehicle (I2V) integration of variable speed limit control and adaptive cruise control system

Objective: Adaptive cruise control (ACC) has been investigated recently to explore ways to increase traffic capacity, stabilize traffic flow, and improve traffic safety. However, researchers seldom have studied the integration of ACC and roadside control methods such as the variable speed limit (VSL) to improve safety. The primary objective of this study was to develop an infrastructure-to-vehicle (I2V) integrated system that incorporated both ACC and VSL to reduce rear-end collision risks on freeways. Methods: The intelligent driver model was firstly modified to simulate ACC behavior and then the VSL strategy used in this article was introduced. Next, the I2V system was proposed to integrate the 2 advanced techniques, ACC and VSL. Four scenarios of no control, VSL only, ACC only, and the I2V system were tested in simulation experiments. Time exposed time to collision (TET) and time integrated time to collision (TIT), 2 surrogate safety measures derived from time to collision (TTC), were used to evaluate safety issues associated with rear-end collisions. The total travel times of each scenario were also compared. Results: The simulation results indicated that both the VSL-only and ACC-only methods had a positive impact on reducing the TET and TIT values (reduced by 53.0 and 58.6% and 59.0 and 65.3%, respectively). The I2V system combined the advantages of both ACC and VSL to achieve the most safety benefits (reduced by 71.5 and 77.3%, respectively). Sensitivity analysis of the TTC threshold also showed that the I2V system obtained the largest safety benefits with all of the TTC threshold values. The impact of different market penetration rates of ACC vehicles in I2V system indicated that safety benefits increase with an increase in ACC proportions. Conclusions: Compared to VSL-only and ACC-only scenarios, this integrated I2V system is more effective in reducing rear-end collision risks. The findings of this study provide useful information for traffic agencies to implement novel techniques to improve safety on freeways.

Objective: 自适应巡航控制（Adaptive Cruise Control，ACC）近年来被广泛研究，以探索提升道路通行能力、稳定交通流及改善交通安全的路径。然而现有研究鲜有探讨将ACC与可变限速（Variable Speed Limit，VSL）这类路边管控手段相结合以提升交通安全的方案。本研究的核心目标是构建一套车路协同（Infrastructure-to-Vehicle，I2V）集成系统，将ACC与VSL二者结合，以降低高速公路上的追尾碰撞风险。
Methods: 首先修正智能驾驶模型（intelligent driver model）以模拟ACC行为，随后介绍本文采用的VSL管控策略。在此基础上，提出集成ACC与VSL这两项先进技术的I2V系统。仿真实验共设置四种场景：无管控、仅采用VSL、仅采用ACC以及I2V集成系统。采用基于碰撞时间（Time to Collision，TTC）衍生的两项替代安全评价指标——暴露碰撞时间（Time Exposed Time to Collision，TET）与积分碰撞时间（Time Integrated Time to Collision，TIT），来评估与追尾碰撞相关的交通安全问题，同时对比各场景的总出行时长。
Results: 仿真结果表明，仅采用VSL与仅采用ACC两种方案均能有效降低TET与TIT值（降幅分别为53.0%、58.6%与59.0%、65.3%）。I2V集成系统结合了ACC与VSL的双重优势，取得了最优的安全效益（降幅分别达71.5%与77.3%）。针对TTC阈值的敏感性分析同样显示，在所有TTC阈值下，I2V系统均能实现最大的安全收益。此外，针对I2V系统中ACC车辆的不同市场渗透率的分析表明，安全效益随ACC车辆占比提升而显著增加。
Conclusions: 相较于仅采用VSL或仅采用ACC的场景，本研究提出的I2V集成系统在降低高速公路追尾碰撞风险方面更为高效。本研究结论可为交通管理部门实施新型交通安全提升技术提供参考依据。