Maintenance of a limited access highway shall include the removal of snow, the maintenance of curbs, shoulders, ditches and slope areas, the lighting of areas under elevated portions of limited access highways in urban areas, and may include the lighting of the highway or any part thereof, the maintenance of parking facilities under elevated portions of such highways, and the planting and trimming of trees, grasses, shrubs and vines on the right of way or slope areas.
36 P.S. § 2391.10