Whenever it is desired to establish or to change the previously established grade of any street, highway, boulevard, main thoroughfare, controlled-access facility, connecting link, major traffic street, alley, or part of such street, highway, boulevard, thoroughfare, facility, link, or alley, such establishment or change may be authorized by a city. Such authorization shall state the proposed grade by elevations or other definite data and shall refer to a plat with specifications fully detailing and showing the established grade or the amount of change in the grade line, which plat shall remain on file in the city offices. The authorization for and the order establishing or changing the previous grade may include the establishment of or the change of the previously established grade on any number of intersecting or connecting streets which may be reasonably appropriate and necessary to a proper adjustment of grade lines to the principal grade line proposed to be changed or to include the change of grade on cross streets so that traffic on such cross streets may pass under the street to the principal grade line to be changed by a subway or over the street to the principal grade line on a bridge, viaduct, or overpass.