Whenever any street of any city of the first class is partly inside the city and partly outside the city, and the land outside the city abutting on such street is an industrial tract or a school site, or the property of the state or any political subdivision thereof, such street may be included in any street improvement project of the city upon the written agreement thereto of the owner or owners of such land outside the city, which agreement shall subject such land to the assessment of costs of the benefits resulting from the improvement. Except as provided in this section, any such improvement shall be subject to the provisions of sections 16-609 to 16-655.