Each company, after its line of road has been located, approved and established, may alter its grades and raise any highway bridges that pass over its tracks to such height as may be approved by the Commissioner of Transportation and may change the grade of the approaches to such bridges so as to conform to the change in the height of the bridges; but this section shall not authorize any company to raise its tracks so as to lessen the distance between an existing bridge and its tracks, without the approval of the commissioner. Damages accruing to any adjoining proprietor on account of any change of grade on the highways which are approaches to any such bridge, raised under the provisions of this section, shall be assessed and paid by such company in accordance with the provisions of sections 13b-270, 13b-274 and 13b-279.