“Shoulder” means that portion of the highway contiguous to the roadway generally extending the contour of the roadway, not designed for vehicular travel but maintained for the temporary accommodation of disabled or stopped vehicles otherwise permitted on the roadway.

   “Ditch slope” is that portion of the highway adjacent to the shoulder if one exists or adjacent to the roadway on roads without shoulders, extending to the bottom of the roadside ditch and is not constructed or maintained for the use of any vehicles except those engaged in construction or maintenance.