Maybe you are thinking about the one that happened below one of the bridges on the Beltway to I-270 spur, in Bethesda? It torched that bridge very well.
My solution to D.C traffic (issues like this are happening almost daily) will be to sell everything and move as soon as possible.
When that one first happened, they said that it had the potential to shut down the Beltway and one of the two I-95 routes over the Potomac; fortunately the structural damage wasn't as bad as first feared.
The accident got talked about in Frederick because of the potential for trucks to be forced onto alternate routes, such as regular highways instead of the interstate.