The commission may authorize the department to acquire or construct tubes, tunnels, subways, underpasses, or overpasses either in connection with bridges or as separate highway crossings whenever the department deems such acquisition or construction advisable. All of the provisions of this chapter shall be fully applicable to the tubes, tunnels, subways, underpasses, or overpasses, the acquisition and construction of which is so authorized, and they shall be included within the word “bridge.”