swing bridge

from The Century Dictionary.

• noun A bridge that may be moved aside by swinging (either as a whole or in sections), so as to afford passage for ships on a river or a canal, at the mouth of docks, or the like. See cuts under bridge and castle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A movable bridge that has as its primary structural support a vertical locating pin and support ring, usually at or near to its centre of gravity, about which the turning span can then pivot horizontally.