Map 4 (Mandatory Sidewalk Widenings) in Appendix A of this Chapter specifies locations of mandatory sidewalk widenings. The depth of such sidewalk widenings shall be as indicated on Map 4 in Appendix A and shall be measured perpendicular to the street line. All sidewalk widenings shall be improved as sidewalks to Department of Transportation standards, at the same level as the adjoining public sidewalks, and shall be accessible to the public at all times.