Subject to the provisions of Section 11-58-3, the corporate authorities of any municipality with a population of less than 500,000 have the power to levy and collect a tax to provide for the payment of the costs imposed by law upon the municipality for grade separations whenever, in the manner provided by law, (1) separation of the grade of the roadbed and tracks of any railroad from the grade of any public street or other public place has been found to be required for public safety, necessity, and convenience, and (2) a plan for a grade separation has been adopted and the proportion of the costs of the grade separation to be paid by the municipality has been prescribed.