None of the provisions of this division shall apply to proceedings hereafter commenced for the construction of sidewalks when required for the safety of pupils attending the schools, or for the construction of improvements to or traffic safety facilities for railroad crossings when required for the safety of pupils attending schools or farmworkers or other workmen, within a city or county and the necessity for such requirement is found to exist by the legislative body of such city or county conducting said proceedings, expressed by resolution adopted by the affirmative vote of four-fifths of the members thereof. The findings and determinations made by the legislative body pursuant to this section shall be final and conclusive upon all persons in the absence of actual fraud.