That's not really it. We get snowstorms of this size once every 2 or 3 years, sometimes more. The problem is that somehow they didn't keep up with plowing and salting on that stretch of I-95, and that led to back-ups, and once that happened, there was no way to prevent ice from forming on the road. An exacerbating factor was that it was raining before the snow event, so they weren't able to pre-salt/brine the roads.
Notice that the major traffic jam was on I-95 South outside of the beltway, it wasn't on the outer loop, inside DC, or in Maryland even though the storm blanketed the area.