If the commission finds that it is impracticable to construct an over-crossing or under-crossing on the established or proposed highway, and shall find that by deflecting the established or proposed highway a practicable and feasible over-crossing or under-crossing or a safer grade crossing can be provided, it shall continue the hearing and hold a supplemental hearing thereon. At least ten days' notice of the time and place of the supplemental hearing shall be given to all landowners that may be affected by the proposed change in location of the highways. At the supplemental hearing the commission shall inquire into the propriety and necessity of changing and deflecting the highway as proposed. If the proposed change in route of the highway involves the abandonment and vacation of a portion of an established highway, the owners of land contiguous to the portion of the highway to be vacated shall, in like manner, be notified of the time and place of the supplemental hearing. At the conclusion of the hearing, the commission shall enter its findings in writing, and shall determine the location of the crossing which may be constructed, and whether it shall be an under-crossing, over-crossing or grade crossing, and shall determine whether or not any proposed change in the route of an existing highway, or the abandonment of a portion thereof is advisable or necessary to secure an over-crossing, under-crossing, or safer grade crossing.