The construction of concrete alley crossings on the line of the sidewalks shall be governed in all respects by the requirements for alley paving; except, that the contractor will be required to bevel off the edges of the paving in a manner that has been followed for several years, and that the drop on the property line of the street from the curb or sidewalk line to the center of the alley may be more than two inches, running out to zero at the gutter lines. The finished surface shall be a warped surface and shall be so made as to in each individual alley best serve drainage, sidewalk and alley travel. In cases of unusual character of elevations in sidewalk, curb and gutter and alley ground surface, the contractor must receive his instructions as to grade and surface, the contractor must receive his instructions as to grade and surface to be used from the city engineer. The wearing surface of all alley crossings must be crossed and rolled with a corrugated roller or otherwise roughened to the approval of the city engineer. (Prior code § 27-49)