Investigating the effectiveness of safety countermeasures at highway-rail at-grade crossings using a competing risk model

Introduction: Highway-rail at-grade crossings (HRGCs) are critical locations where a railway and a roadway intersect with one another. Crashes at those locations often result in fatalities and economic and social damages due to the impacts on both road and rail users. The main purpose of countermeasures at HRGCs is to permit safe and efficient rail and highway operations. Method: Countermeasures at highway-rail grade crossings (HRGCs) considered in this study include all traffic control devices and other warning and barrier devices at or on approaches to crossings. In general, active devices are commonly accepted as more effective countermeasures than passive devices. However, many of the previous effectiveness studies are either at the project level or were conducted without considering the before-improvement condition. This study focuses on the network-level marginal effectiveness of countermeasures on crash rate and severity levels during the 29-year study period from 1990 to 2018 by fully considering before-improvement control levels. A competing risk model (CRM) is able to accommodate the competing nature of crash severities as multiple outcomes from the same event of interest, which is crash occurrence in this study. Subsequently, CRM is used in this study as an integrated one-step estimation approach that investigates both crash frequency and severity likelihood over time. Results: The study findings indicate that adding audible devices to crossings already equipped with gates will result in a considerable annual decline in crash occurrence likelihood (0.25%). The same device installed at crossings already controlled by gates and flashing lights results in less reduction in crash occurrence likelihood of 0.14%. Moreover, adding a stop sign to the active crossing controls of gates, standard flashing lights, and audible devices will lead to a decrease in the probability of crash occurrence and severe crashes (injury and fatal). However, adding stop signs to crossings equipped only with crossbucks will increase the crash occurrence.     

SO2污染防治对策

概述了国内外ＳＯ２污染防治现状。指出了上海市大气中ＳＯ２污染严重状况，提出了近期与远期相结合；引进消化吸收国外先进技术与组织国内科技攻关相结合；经济手段与法制手段相结合；解决呼吸带与高空污染相结合的ＳＯ２污染防治对策与建议。重点建议，目前需集中力量控制中、小型锅炉的ＳＯ２排放量；走国际合作道路，加快研制开发大型电厂的脱硫装置，从根本上解决大气中的ＳＯ２污染；国家与地方迅速制订对排入大气中的ＳＯ２污     

水体有毒有机污染研究

对有毒有机污染物的主要种类,实际的检出水平,健康影响评价、污染处理技术进行了简要介绍,在此基础上对管理对策进行了探讨。