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This map of 30 years of car crashes should persuade you not to drive in snow

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Winter is a dangerous time to drive.

Examining fatal car crash data from 1975 to 2011, University of Georgia researchers Alan Black and Thomas Mote have identified more than 30,000 automobile fatalities that were related to wintry weather conditions. Cook County, Illinois, had the most winter-weather-related fatalities of any county, with 462 recorded during the 36-year period.

We already know that winter storms are far and away the leading cause of weather-related car crash deaths, causing more than hurricanes, tornadoes, and floods combined.

What this map adds is a geography of some of the most dangerous places to drive in a winter storm — one that doesn't fully align with the places that get the most snow.

You can see in the map above that most of the winter-related car crash deaths happen in the Great Lakes region and then snake up north through Pennsylvania and New York. But there are also a few surprising places in the Southwest — like Coconino County, Arizona, and McKinley County, New Mexico — where accidents are also higher than average, suggesting an unfamiliarity with driving in winter weather.

The overwhelming majority, or 96 percent of the counties included in the study, had 50 or fewer winter-weather-related automobile fatalities. Only 17 counties had 100 or more fatalities. The average number of fatalities per county was 12, and only counties with at least one winter-related fatality were included in the study.

Winter weather conditions cause a 19 percent increase in traffic crash

In a separate study of 13 major cities, Black and Mote found a 19 percent increase in traffic crashes and a 13 percent increase in injuries during wintry conditions. The type of winter precipitation (snowfall versus freezing rain, ice pellets, or sleet) had no bearing on the increased likelihood of an accident, but evening hours experienced a greater rate of accidents than other times of day.

Winter precipitation did not increase the odds of being in a fatal crash, however. Black said this was "presumably because people slow down," and at reduced travel speeds the risk of being in a fatal car crash does not increase.

Lots of winter storm deaths "don't get counted"

The National Weather Service collects information on weather-related fatalities in its storm events database, with data available from 1950 to 2015, but Black told me that the NWS database is incomplete, especially when it comes to counting fatal car crashes related to wintry conditions.

"The NWS records what we call 'direct fatalities,' or where the weather directly causes the death like a death in a tornado," said Black. "But a lot of these winter precipitated automobile crashes don’t get counted because the weather was not a direct cause of death."

In the NWS data, only about 30 to 40 deaths are linked to wintry weather conditions annually. Black's research found as many as 842 deaths caused by winter-related automobile accidents from 2002 to 2011.

Before Black and Mote undertook their study, there was no data that measured the number of car crash fatalities related to winter weather conditions. So Black had no idea how pervasive an issue it was. But now he says he wants the public to listen when meteorologists or police issue travel warnings. "It's no different than taking shelter from the tornado; staying home might save your life," said Black.

Black and Mote gathered the data for their study from the National Highway Traffic Safety Administration's Fatality Analysis Reporting System (FARS) for the years 1975 to 2011 and isolated fatalities related to winter precipitation.

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