Sentence:  Plows, snowblowers and dump trucks have formed their winter <WSD>conga lines</WSD>, and most Montreal Island cities say they'll have streets and sidewalks cleared of snow by Thursday. 
Meaning of the word marked with <WSD> tags:  A moving formation of snowplows and/or similar equipment, arranged in a diagonal line across a multilane highway, airport runway, or other roadway, such that the snow from the first vehicle is passed to the second, and then from the second to third, and so on, thereby clearing much or all of the route's width in a single pass.