No street laid out or altered by the Board shall be of less width than -(a)forty feet, if the street be intended for carriage traffic, or(b)twenty feet, if the street be intended for foot 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 Board consider it impracticable to do so;(ii)nothing in this section shall be deemed to prevent the Board from laying our service passages for sanitary purposes of any width less than twenty feet.
