Clear Roads II: Evaluation of SSI and WSI Variables

This new Clear Roads project will maintain its focus on advancing winter highway operations nationally through practical, practice-ready research related to materials, equipment and methods. State departments of transportation are aggressively pursuing new technologies, practices, tools, and programs to improve winter highway operations and safety while maintaining fiscal responsibility. In this research, Project Goals 1 and 2 are (1) to identify US and international agencies using Storm Severity Index (SSI) and Winter Severity Index (WSI), and (2) to determine the variables and measurement methods used to create the indices. In other words, an initial objective of this project is to gather the current state of practice on severity indices from agencies in the U.S. and around the world. Knowledge gathered from responding agencies will include: how they use their SSI/WSI, unique weather challenges they face, the weather variables chosen for the calculation, the instrumentation that collects the data, and the equation or software used to calculate the index. Clear Roads specifically requests that variables used to diagnose freezing rain be identified, as freezing rain is a particularly problematic type of weather for many transportation agencies. Project Goals 3 and 4 are (3) to gather statistical data resulting from analysis of each variable for consistency and variability, and (4) to recommend the most reliable variables, with the highest correlation to storm severity, for developing SSI/WSI. An effort to correlate each variable to severity will be necessary, as well, but this will also vary based on the differing weather regimes and quantity and quality of data present in each jurisdiction. In other words, a given variable may be weighted more heavily in some weather regimes versus others. In some cases, a variable will become more reliable, only when combined with another one or two. A given variable (or combination of variables) may also be deemed critical to the calculation, while being more difficult to measure. An example of this would be freezing rain. Ideally, freezing rain would be identified using observations up to 10,000 feet above surface of the earth (as the atmospheric temperature profile determines the melting and refreezing of precipitation as it falls), however, the temperature observations used across a road network are those taken close to the surface of the earth, and thus some inferences will need to be made or ancillary information included. Here, too, precipitation type must be identified as being rain while it falls onto a below-freezing road surface, yet many RWIS stations do not have a precipitation type identification device. These and similar considerations will be made when variables are analyzed for reliability. Project Goal 5 is to create a flexible spreadsheet tool that allows agencies to develop a state-specific SSI/WSI. What the Clear Roads states may desire is a tool that will perform a number of the more predominant calculations used by agencies or developed by research groups discovered in this project, once the necessary weather data elements are plugged in. This tool would likely be constrained in dimensions, as it would be challenging to simultaneously assimilate values that vary in both time and space in a spreadsheet context. Nevertheless, the tool could offer a basic or initial assessment of what might be required within each agency to perform a fully functional SSI/WSI that stands on its own.


  • English


  • Status: Completed
  • Funding: $74,940.02
  • Contract Numbers:


  • Sponsor Organizations:

    Clear Roads Pooled Fund

    St. Paul, MN  United States 
  • Managing Organizations:

    Minnesota Department of Transportation

    395 John Ireland Boulevard
    St Paul, MN  United States  55155
  • Performing Organizations:

    Narwhal Group

    554 West Capitol Street
    Salt Lake City, UT  United States  84103
  • Principal Investigators:

    Albrecht, Chris

  • Start Date: 20190502
  • Expected Completion Date: 20201231
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01704528
  • Record Type: Research project
  • Source Agency: Minnesota Department of Transportation
  • Contract Numbers: 1031543
  • Files: RIP, STATEDOT
  • Created Date: May 9 2019 12:58PM