In the issuance of permits authorized by the Common Council for the erection or alteration of structures and other improvements, the proposed street and thoroughfare rights-of-way as set forth by this plan shall be protected and no such permit or permits shall be issued if the work proposed thereunder would encroach upon the existing or proposed sites or existing or proposed rights-of-way indicated on the Thoroughfare Plan adopted by this subchapter.
('75 Code, § 73.6)