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Abstract：
Ramp metering relieves traffic congestion, reduces delay, and maintains the capacity flow on freeways. Due to its operational mechanism, ramp metering can also improve freeway safety. While the operational benefits of ramp metering have extensively been quantified, research on its safety effects is sparse. This study focused on evaluating the effects of ramp metering on the safety performance of the freeway mainline. It developed a crash risk prediction model for segments downstream of the entrance ramps when ramp metering is activated. The study was based on a corridor with system-wide ramp metering along I-95 in Miami, Florida. Real-time traffic, crash, and ramp metering operations data collected from 2016 to 2018 were used in the analysis. The study adopted a matched crash and non-crash case approach to evaluate the crash risk when ramp meters were activated and deactivated. A penalized logistic regression model was developed using a bootstrap resampling technique to estimate the effects of ramp metering activation and select important variables that could predict crash risk when ramp meters were activated. Results indicated that ramp metering improves safety along the freeway corridor by reducing the crash risk downstream of the entrance ramps. During ramp metering activation, the crash risk on segments downstream of the entrance ramps 5 min later can be predicted using the difference in the average lane speeds between upstream and downstream detectors, the average traffic volume in the lanes at the downstream and upstream detectors, and the coefficient of variation of speed between lanes in the upstream detectors. Also, the coefficient of variation of occupancy downstream could predict the crash risk 15 min later. The study results could be used by transportation agencies when evaluating the deployment of ramp meters. Moreover, the developed crash risk prediction model could be used in real-time to help agencies identify the increased crash risk and provide appropriate warning information to the upstream traffic.
摘要：
坡道计量缓解了交通拥堵，减少延迟,并保持高速公路的通行能力。由于其运行机制，坡道计量还可以提高高速公路的安全性。虽然斜坡计量的操作效益已被广泛量化，对其安全影响的研究较少。这项研究的重点是评估匝道计量对高速公路干线安全性能的影响。当激活坡道计量时，它为入口坡道下游的路段开发了碰撞风险预测模型。这项研究是基于迈阿密沿I-95的带有全系统坡道计量的走廊，佛罗里达实时流量,崩溃,和2016年至2018年收集的匝道计量操作数据用于分析。该研究采用了匹配的碰撞和非碰撞案例方法来评估启动和停用坡道仪表时的碰撞风险。使用Bootstrap重采样技术开发了惩罚逻辑回归模型，以估计坡道计量激活的影响，并选择可以预测坡道计量仪激活时碰撞风险的重要变量。结果表明，坡道计量通过降低入口坡道下游的撞车风险来提高高速公路走廊的安全性。在斜坡计量激活期间,可以使用上游和下游探测器之间的平均车道速度差来预测5分钟后入口坡道下游路段的碰撞风险。下游和上游探测器车道的平均交通量，以及上游探测器中车道之间的速度变化系数。此外，下游占用的变异系数可以预测15分钟后的撞车风险。研究结果可供运输机构在评估匝道表的部署时使用。此外，开发的碰撞风险预测模型可以实时用于帮助机构识别增加的碰撞风险，并向上游交通提供适当的警告信息。
