The common council may levy a tax annually which shall not exceed fifteen cents on each one hundred dollars of taxable property within the city for the purpose of a thoroughfare fund, which when collected shall be kept separate from the other funds of the city, and shall be a continuing fund to be drawn upon by the city board of public works and safety for work done under or in furtherance of or in carrying out a part of the official thoroughfare plan. (Prior code § 27-25)