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What the data show
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- Snow, rain and heavy fog are the average hours a month that each of the state's airports reported them, 2019 to 2022. Each report is capped at 24 hours.
- Fatal crashes are crashes on Interstates and U.S. routes in which at least one person died, 2019 to 2023 (NHTSA FARS). A crash counts only when it lies within 100 meters of the route, so counts are at least these numbers.
- Expected is modeled: the fatal crashes a typical road with the same traffic and design would have, from the model behind the main ranking, split by month with FHWA monthly travel data.
- The ratio compares states with themselves and with similar roads. The South is above 1 and the Northeast below 1 in nearly every month, snowy or not, so a state's color in one month does not show the effect of that month's weather. The findings above compare each state with itself, one week apart.
Sources: airport weather events (Wherobots data catalog), NOAA nClimDiv, NHTSA FARS, FHWA HPMS 2024 and Traffic Volume Trends. Analysis: Wherobots.