The board of supervisors or other governing body aforesaid or the Commissioner of Highways may, however, within thirty days from the date of the submission of such plans, specifications and descriptions, reject the same, and may apply to the Commission to inquire into the necessity for such crossing, and the propriety of the proposed location, and all matters pertaining to its construction and operation; and, thereupon the Commission, in its discretion, may, after notice served upon the public service corporation, the board of supervisors or other governing body aforesaid, and the Commissioner of Highways, suspend work on such crossing for such reasonable time prescribed in such notice as it may deem necessary to make such inquiry. The Commission may, in its discretion, employ expert engineers, at a cost not to exceed $500, to be paid by the public service corporation desiring the crossing, who shall, with the Commission, or some member thereof, or such person as the Commission may designate, (1) examine the location, plans, specifications and descriptions of appliances and methods proposed to be employed, (2) hear any objection, and consider any modification that the board of supervisors or other governing body aforesaid, or the Commissioner of Highways, may desire to offer, and, (3) within such time as the Commission may fix, reject, approve, or modify such plans, specifications and descriptions. The final order of the Commission shall, unless an appeal be taken to the Supreme Court by any party to the proceeding within thirty days of the date of such final order, be final and binding on the public service corporation and the board of supervisors or other governing body aforesaid, and the Commissioner of Highways.