When it comes to snow-stunned traffic, it’s all about fall rates, bad timing and poor judgment

A January 2011 snowfall that would become known as Carmaggedon produced several inches of snow and sleet at the worst possible time. The storm itself wasn’t memorable, but the nightmarish rush hour traffic that formed during the heavy snow will live in infamy.

Every few years, D.C. area drivers relearn the hard way that a snowstorm’s societal impact cannot always be measured in inches.

The most disruptive snowstorms near the Beltway aren’t the big ones. Memorable winter storms like the record-breakers that produced more than two feet of snow in January 1996, February 2010 and January 2016 were well predicted. During major snowstorms, the forecast is clear and most travel is rightfully postponed or canceled.

The storms that can lead to traffic disasters are those that produce rapidly-accumulating snow during peak travel periods. For densely populated areas, the high snowfall rates and a poor collective reaction to the weather forecast can lead to extreme traffic disruptions.

Three inches of snow in one day is manageable. Three inches of snow in one hour can be disastrous.



Heavy snow and heavy traffic are a bad combination. When lanes become blocked by stalled and spun-out vehicles, traffic backs up quickly. Snow piles up between stopped vehicles. More traction is lost. More cars stall. Plows are delayed. Slow-moving traffic shifts to other bottlenecked roads. If this chain reaction continues, traffic flow will begin to seize on a regional scale.

When heavy traffic and heavy snow coincide, it is not just the weather that renders travel difficult to impossible; it is the number of people driving in the weather. All-wheel drive and high-performance winter tires are useless when roads are bottlenecked, blocked and filled to capacity.

The forecast of a major snowstorm keeps most would-be drivers off the roads. But the forecast of a modest snowfall has a lesser effect on total traffic volumes.

When the 2016 blizzard reached its peak intensity on January 23, local transportation department data show traffic volume on the Capital Beltway was reduced by more than 90 percent. On the day of Carmaggedon in 2011, volume on the Beltway was only slightly below the daily averages. Both storms came with advance warning but only one was taken seriously.

Since the January 2011 ordeal, similar self-inflicted fiascos occurred on the morning of Jan. 6, 2015 and the evening of Jan. 20, 2016; both were weekdays. Similar, more localized debacles have unfolded on weekends. On Saturday, Feb. 21, 2015, some drivers spent more than 6 hours stuck on a snow-covered Beltway.

Cold antecedent temperatures can hasten the effects of heavy snow during peak travel times but high snowfall rates can overcome initially warm road temperatures. Many of the D.C. region’s recent snow-stunned commutes were preceded by temperatures in the 50s.

Deducing the potential impacts from subtle weather systems and pinpointing narrow bands of heavy snow is challenging for forecasters. The movement and implications of major winter storms are more obvious. Much of the traffic impact during snowfall hinges on how seriously winter weather warnings are taken.

Increased telework, remote learning and more skilled forecasting lessen the amount of traffic during these quick-hitting weather events, freeing up some capacity for essential personnel and those with urgent travel needs.

Blockbuster snowstorms are impactful in different and often more predictable ways. To say that travel is severely impacted during these storms is a bit misleading because there simply isn’t much travel occurring on these days. More accurately, travel plans are severely impacted. It is the ill-timed and insidious snowfalls, coincident with the hustle and bustle of everyday life, that can leave deeper, lasting scars on unprepared commuters.

Dave Dildine

A native to the Washington area, Dave Dildine is no stranger to the region's complex traffic and weather patterns. Dave joined WTOP in 2010 when the station launched its very own in-house traffic service. You can hear him "on the 8s and when it breaks" from 2 p.m. to 7 p.m. on weekdays.

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