38. No street laid out or altered by the Authority shall be of less width than-(a) forty feet, if the street be intended for vehicular traffic, or(b) twenty feet, if the street be intended for pedestrian traffic only:Provided as follows:-(i) the width of an existing street need not be increased to the minimum required by this section, if the Authority consider it impracticable to do so; and(ii) nothing in this section shall be deemed to prevent the Authority from laying out service passages for sanitary purposes of any width less than twenty feet.