All drawbridges and approaches thereto in existence since March thirtieth, one thousand nine hundred and seventeen, and not less than six hundred feet long, forming part of a route described in chapter 6 of this title (s. 27:6-1 et seq.) and extending over a navigable waterway or part thereof, which forms the dividing line or part thereof between two municipalities in this state, shall become a part of the state highway system upon the taking over by the commissioner of the whole or a part of the route or routes of which the bridge and its approaches form a connecting or continuing part to the state highway system. The department shall thereupon immediately take over the improvement, betterment, reconstruction, resurfacing, maintenance, repair and regulation of the uses thereof.