Write Up:

MoDOT’s winter weather response is a key element in operating a reliable transportation system for the traveling public.  The diversity of Missouri, from a winter weather perspective as well as its population densities and vast highway system, makes winter weather management particularly challenging for MoDOT. To assist with these challenges, MoDOT uses a Winter Severity Index (WSI) tool to measure MoDOT’s response to winter weather and its impacts on the traveling public.  While most WSI systems focus solely on weather variables, the MoDOT WSI tool tells a broader story by providing a more comprehensive view of the weather’s impacts on the safety and mobility of the traveling public and the department’s operational costs.  

The tool collects traffic data, crash data and MoDOT operational data across all maintenance areas and then uses that data to calculate a safety and mobility cost for the traveling public and an operational cost for the department.  These costs are then normalized against historical averages to produce a WSI that can be used to accurately compare costs across all maintenance areas and district boundaries.  A WSI of one indicates costs are equal to historical averages, whereas a WSI greater than one or less than one indicates costs are greater than or less than average, respectively.  
To date, the 2024-2025 winter season is above average in terms of winter weather severity, with a WSI of 1.56, meaning the amount of accumulating precipitation received so far is approximately 60% greater than a yearly average.  The cost for winter weather related crashes has also increase for this point in the season with a WSI for crashes of 1.26, indicating a 26% increase in cost.  Although this shows an increase in the total cost, most of those costs have occurred over a few select areas, such as along the I-70 corridor.  When looking at crash cost per maintenance area the WSI for crashes is at 0.56, meaning crash cost across most maintenance areas has decreased by over 40%.  

On average, MoDOT's winter operations have cost about $49 million per year. As of January 31, 2025, MoDOT's cost for the 2024-2025 winter season is about $32 million, resulting in a WSI for operational cost of 0.6 to date.  However, Missouri typically experiences 8-10 winter events per season that impact multiple districts at the same time.  To date, Missouri has experienced just four multi-regional events this season.  When comparing costs per event and looking at where the season currently is, MoDOT’s WSI for operational costs is 2.69, meaning MoDOT is on pace to experience a total seasonal cost of nearly three times the average.  

Delay costs to the traveling public have also been impacted at this point in the 2024-2025 winter season. For the four multi-regional winter events that Missouri has experienced this season, the WSI for traffic delay cost is at 4.72, indicating a nearly five times increase in traffic delays. Although this increase is high, those costs have been influenced by peak costs experienced during ice events or extreme weather events.  When compared to an entire season the WSI for delays is at 0.98, meaning delay costs would be in line with typical seasonal costs.    

Purpose of the Measure:

This measure tracks the impacts winter weather has on the traveling public and MoDOT operations.  Knowing these impacts aids MoDOT in the review and analysis of each storm or a winter season and allows the department to better compare response practices and performance across the diverse regions of Missouri.

Measurement and Data Collection:

For determining the magnitude of the impacts a winter event has on the traveling public and MODOT, a Winter Severity Index is calculated based on data collected from multiple sources.  This data is centralized in a web-based integration and analytics platform that processes the data and provides interactive visualizations that enable users to identify trends.  

Data sources used for this tool include MoDOT TMS and MMS data, Regional Integrated Transportation Information System (RITIS), Road Weather Information System (RWIS), Missouri Automated Surface Observation System (ASOS), HERE Traffic Analytics, Missouri State Highway Patrol, and the National Weather Service.