Sentence:  On highways such as I190 and I290 a <WSD>conga line</WSD> lets plows make a clean sweep from curbline to curbline on one pass he said. 
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.