sentences:  A southern extension to Steeles Avenue was later completed and the name Donald Cousens Parkway applied along the extension to Ninth Line.In addition to its role of funneling through-traffic around downtown Markham, the route serves as a boundary to residential development as land to the north and east are part of the protected Rouge National Urban Park and southwest limits of the planned Pickering Airport.Construction of the route began in 2002 north of 16th Avenue.