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Evaluation of Storm Severity Index (SWI) and Winter Severity Index (WSI) Variables

Started: May, 2019 Ended: April, 2020 Project ID #4W7797 Status: Completed

Results & Findings

As described in the final report, the reliability of variables used in the calculation of storm severity indices or winter severity indices (SSIs/WSIs) was evaluated via an expansive literature review, an international survey, and two rounds of interviews with data and device managers. A Recommendations Guide was created to help agencies who want to improve upon or build a new SSI/WSI; and included a thorough outline of reliable data, data sources, and SSI/WSI calculation methods. A spreadsheet tool was built that guides a user through the process of choosing variables and methods to address their predominant weather concerns.


The objective of this project is to identify agencies using SSI/WSI, determine the variables and measurement methods used to create the indices, and recommend variables to use and calculation methods.


Winter maintenance agencies can use a Storm Severity Index (SSI) or Winter Severity Index (WSI) as tools to help evaluate the performance of their maintenance crews and to plan for the efficient use of materials and other resources. In the last decade substantial work has been completed to develop nationwide  and statewide  SSI/WSI tools. From these past and ongoing projects the key variables, methods, and calculations can be used to aid in the development of a tool to help transportation agencies develop and use their own SSI/WSI. This project seeks to learn more about past efforts to create the SSI/WSI, to evaluate these past efforts on their reliability and correlation to severity, and to work toward creating a tool to guide jurisdictions when they develop their own SSI/WSI. Planned tasks include a literature review, a survey of practice, data collection and analysis, development or recommendations, and creation of a spreadsheet tool. WTI is providing project support to The Narwhal Group, which is the lead agency. The project is sponsored by the Clear Roads research program.


  • Laura Fay - PI

  • Chris Albrecht - Main External Contact

Files & Documents

Sponsors & Partners

  • Clear Roads Winter Highway Operation Pooled Fund Sponsor

Part of: Cold Climate Operations & Systems

Project Tagged In: winter maintenance, severe weather, weather index

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