§ 249. Investigation by the department of transportation. The department of transportation shall upon the receipt of such resolution or concurrent resolution, investigate and determine whether the bridge so sought to be abolished is of sufficient public importance to come within the provisions of this article, taking into account the use, location and value of such toll bridge for the purpose of common traffic and travel and shall also investigate as to the value of such toll bridge and from the estimate and data transmitted by the board or boards of supervisors, or from such other information as the department of transportation may secure, prepare an estimate of the probable cost of acquiring such toll bridge. After such investigation such department of transportation shall certify its approval or disapproval of such resolution. If it shall disapprove such resolution, it shall certify its reasons therefor to such board or boards of supervisors. If it shall approve such resolution it shall certify its approval thereof to the attorney general, and shall transmit to him the estimate made by the department of transportation of the probable cost of acquiring such toll bridge, together with any data the department of transportation may have in its possession in relation to the value thereof.