In late October of 2009, a major snowstorm tracked from the central Rockies across the Plains to Minnesota, dumping over 2 feet of snow in parts of Colorado. And yet major accident reports were few and far between for this event - in fact, not a single verifiable report of an icy road fatality accident came in from these regions. A fluke? Hardly - this is actually typical for a major snow event. Snowstorms are no strangers to icy road accidents, so why are the serious accident and fatality rates lower?
When a major snowstorm hits, communities are typically highly aware and prepared for the event prior to its impacts. Schools and workplaces close. Highways officials close many of the high-speed roads, including the interstates, that are the usual spots for fatal icy road accidents. When the storm is in progress, the sheer amount of snow prevents vehicles from easily reaching the speeds that are often associated with fatal accidents. Most accidents in snowstorms happen at the onset of the storm or on its fringes, where accumulations are lower.
Snow accounts for the most icy road fatalities during the winter, but it is the minor events - from a dusting to a couple of inches of accumulation - that cause the most serious snow-related accident outbreaks. That little dusting at morning rush hour - the one that never makes the news until after it's caused chaos - are the ones to watch out for. With minor snowfalls, people tend to be in 'business as usual' mode, not as aware of the hazards as they'd be for a big storm.
So, the key here is speed. Most fatal icy road accidents involve cars traveling highway speeds, usually above 45mph. During a big snowstorm, most drivers simply don't get their cars going that fast. During that little dusting of snow in the morning rush hour, drivers don't see the snow as much of a hazard, and don't adjust their speed as a result. And consequently, the accident rates reflect this.
So, to summarize, major snowstorms should be classified as one of the lowest-risk forms of icy road events. It's the smaller, 'sneakier' events that cause the most problems - the light overnight/morning snow and the light freezing rain event are the most insidious and dangerous weather events that people regularly face in this country.