A. Any municipality that proposes to widen an existing two-lane street to a width which would permit four or more lanes of traffic shall be liable for the entire costs of the improvement, except that portion of the costs that may be paid by the board of county commissioners, the State of Oklahoma, the United States of America, or the amount set forth in a petition for street improvements as assessable against property owners.

B. No assessments shall be collected nor shall any improvement bonds which are to be paid from assessment collections be sold or assigned after April 28, 1971, which relate to the financing or a widening project for which assessments are prohibited under subsection A of this section and unless the improvement has been completed as of April 28, 1971.