Developing a winter severity index: A critical review

Severe weather conditions, especially snow and ice during the winter season, threaten surface transportation nationwide and impact roadway safety and mobility. In particular, snow and ice decrease pavement friction and vehicle maneuverability, causing slower speeds, reducing roadway capacity, and increasing crash risk. These stressors make road maintenance during winter a pressing concern. The annual cost of winter highway maintenance in the United States is approximately $2.3 billion; however, evaluating the performance of such maintenance activities is difficult. To address this difficulty, the storm's severity should be standardized to measure performance against storm severity. Studies have been conducted to develop winter severity indices that can measure the difficulty in maintaining the targeted level of service due to storms in North America. Given the diverse approaches catalogued within these studies, there is a critical need for a comprehensive and organized literature synthesis to summarize existing approaches and to provide guidance for future winter severity index–development. To address this objective, this study investigated existing winter weather severity indices and classified the indices into different groups based on their development process and their similarities. In total, 19 winter severity indices were identified and sorted into seven groups. Subsequently, the key meteorological variables (i.e., temperature, snow, wind, and freezing rain) that have been used by other transportation agencies to develop winter severity indices were identified and explained in detail. Finally, the relevance of previous winter severity indices to future winter severity index–development was discussed and meteorological variables that can potentially be incorporated into the model were identified. This literature synthesis consolidates the current knowledge regarding winter severity indices and provides future guidance for developing an effective and reliable winter severity index.

恶劣的天气条件，尤其是冬季的冰雪，威胁着全国的地面交通，影响道路安全和通行能力。特别是，冰雪会降低路面摩擦力和车辆的操控性，导致车速减慢、道路通行能力下降以及碰撞风险增加。这些不利因素使得冬季道路养护成为一个紧迫的问题。美国每年冬季公路养护的费用约为23亿美元；然而，评估此类养护活动的效果却很困难。为了解决这一难题，应该对暴风雪的严重程度进行标准化，以便根据暴风雪的严重程度来衡量养护效果。已经开展了一些研究来制定冬季严重程度指数，以衡量在北美因暴风雪而维持目标服务水平的难度。鉴于这些研究中所采用的方法多种多样，迫切需要对文献进行全面而有条理的综合，以总结现有方法，并为未来冬季严重程度指数的制定提供指导。为了实现这一目标，本研究对现有的冬季天气严重程度指数进行了调查，并根据其制定过程和相似性将这些指数分为不同的类别。总共确定了19个冬季严重程度指数，并将它们分为7组。随后，确定并详细解释了其他交通部门在制定冬季严重程度指数时所使用的关键气象变量（即温度、降雪、风力和冻雨）。最后，讨论了以往冬季严重程度指数对未来冬季严重程度指数制定的相关性，并确定了可能纳入模型的气象变量。这篇文献综述整合了关于冬季严重程度指数的现有知识，并为制定有效且可靠的冬季严重程度指数提供了未来的指导。