Flail mowers are used by municipalities and highway departments, attached to large tractors and usually seen driving slowly down the highway, mowing the roadway and ditch.
They cut the grass with a series of short chains spinning along an axle. Flail mowers don't really cut the grass so much as they thrash or hack at it at very high speeds. The toughness of a flail mower is useful for cutting tall thick grasses and woody weeds that grow along the highway.
