Developing a Winter Severity Index to Improve Safety and Mobility

Adverse weather conditions are responsible for millions of vehicular crashes, thousands of deaths and billions of dollars in economic and congestion costs. Local, state, and federal agencies face increasing pressure to efficiently allocate resources in order to maintain accessibility to area roadways during adverse weather events and must balance safety with stringent budget accountability. Many of these agencies utilize some type of performance or mobility metric to assess how well they are maintaining road access; however, such metrics often do not consider the overall severity of weather conditions, thus making it difficult to accurately assess success and failure for the agency. Some agencies that do consider weather severity in their performance metrics do not have an explicit index for weather conditions alone nor are the weather data used robust enough to elucidate the complex variability of most weather events. This research focuses on the development of an independent winter weather severity index for the state of Nebraska (NeWINS). NeWINS is an event-driven index that was derived for the Nebraska Department of Transportation (NDOT) districts across the state. The unique features of this index will include varying levels of complexity in order to more accurately capture atmospheric conditions, while simultaneously allowing for simplicity-dependent entirely on the needs of the end‑user. The index will also bring in a climatological aspect that has not been incorporated in many current indices.

A ten-year (2006-2016) winter database of meteorological variables (e.g., air temperature, wind speed, snowfall amount) for the state of Nebraska was obtained from the National Centers for Environmental Information (NCEI). Specific data sources include Automated Surface Observing System (ASOS) stations, the National Weather Service (NWS) Cooperative Observer Program (COOP) network and Community Collaborative Rain, Hail and Snow Network (CoCoRAHS) sites. Meteorological parameters were grouped into categories that subsequently provided a storm intensity classification for the index. The index applied statistical analyses along with the Delphi method, a structured communication protocol, to the collected database and developed a mathematical formula that can be used to measure winter severity for each district. To validate the developed winter severity index, real‑time case studies were conducted.

It is expected that developing a winter severity index for the state of Nebraska would help both local and state transportation agencies to efficiently allocate resources during adverse weather events, while balancing safety, mobility, and available budget. Furthermore, the theoretical and practical contributions provided by NeWINS can be used by other local, state, and federal agencies to improve their performance measurement practices.