The Mayor of the District of Columbia is hereby authorized and directed to prepare a plan for the extension of a permanent system of highways over all that portion of said District not included within the limits of the Cities of Washington and Georgetown. Said system shall be made as nearly in conformity with the street plan of the City of Washington as the Council of the District of Columbia may deem advisable and practicable. The highways provided in such plans shall not in any case be less than 90 feet nor more than 160 feet wide, except in cases of existing highways, which may be established of any width not less than their existing width and not more than 160 feet in width.
