A moveable bridge, or movable bridge, is a bridge that moves to allow passage for boats or barges. In American English, the term is synonymous with, and the latter is the common term, but drawbridge can be limited to the narrower, historical definition used in some other forms of English, in which drawbridge refers only to a specific type of moveable bridge. An advantage of making bridges moveable is the lower cost, due to the absence of high piers and long approaches. The principal disadvantage is that the traffic on the bridge must be halted when it is opened for passage of traffic on the waterway. For seldom-used railroad bridges over busy channels, the bridge may be left open and then closed for train passages. For small bridges, bridge movement may be enabled without the need for an engine. Some bridges are operated by the users, especially those with a boat, others by a bridgeman ; a few are remotely controlled using video-cameras and loudspeakers. Generally, the bridges are powered by electric motors, whether operating winches, gearing, or hydraulic pistons. While moveable bridges in their entirety may be quite long, the length of the moveable portion is restricted by engineering and cost considerations to a few hundred feet. There are often traffic lights for the road and water traffic, and moving barriers for the road traffic. In the United States, regulations governing the operation of moveable bridges – for example, hours of operation and how much advance notice must be given by water traffic – are listed in Title 33 of the Code of Federal Regulations; temporary deviations are published in the Coast Guard'sLocal Notice to Mariners.
Bascule bridge – a drawbridge hinged on pins with a counterweight to facilitate raising ; road or rail
*Rolling bascule bridge – an unhinged drawbridge lifted by the rolling of a large gear segment along a horizontal rack
Folding bridge – a drawbridge with multiple sections that collapse together horizontally
Curling bridge – a drawbridge with transverse divisions between multiple sections that curl vertically
Fan Bridge - a drawbridge with longitudinal divisions between multiple bascule sections that rise to various angles of elevation, forming a fan arrangement.
Vertical-lift bridge – the bridge deck is lifted by counterweighted cables mounted on towers ; road or rail
Table bridge – a lift bridge with the lifting mechanism mounted underneath it
Retractable bridge – the bridge deck is retracted to one side
Submersible bridge – also called a ducking bridge, the bridge deck is lowered into the water
Tilt bridge – the bridge deck, which is curved and pivoted at each end, is lifted at an angle
Swing bridge – the bridge deck rotates around a fixed point, usually at the centre, but may resemble a gate in its operation ; road or rail
Transporter bridge – a structure high above carries a suspended, ferry-like structure
Jet bridge – a passenger bridge to an airplane. One end is mobile with height, yaw, and tilt adjustments on the outboard end
Locks are implicitly bridges as well allowing ship traffic to flow when open and at least foot traffic on top when closed
Visual index
Accidents
April 23, 1853 – Rancocas Creek, New Jersey: Engineer of the Camden & Amboy's 2 p.m. train out of Camden, New Jerseymissed stop signals and ran his train off an open drawspan at Rancocas Creek. There were 27 fatalities.
September 22, 1993 – Mobile, Alabama, US: In heavy fog and low visibility, a disoriented towboat pilot made a wrong turn and entered a non-navigable waterway. Due to inexperience and improper radar training, the pilot did not realize he was off-course and struck an unfinished swing bridge over the Big Bayou Canot around 2:45AM, knocking it out of alignment by approximately three feet, although his initial supposition in the low visibility was that one of the barges had run aground. The rails kinked but did not break, so no fault was indicated for approaching trains. Approximately 8 minutes later, an Amtrak train carrying 220 passengers derailed at the kinked portion of the rails, killing 47 and injuring 103 more.
November 23, 1996 – Kearny, New Jersey, US: An Amtrak passenger and mail train derailed while crossing the Portal Bridge over the Hackensack River, sideswiping another passenger train in the process. Thirty-four people were injured. A broken rail joint on one pair of the bridge's movable rails at each end of the span caused a track misalignment, while still making electrical contact with the landward rails; thus signals were clear, derails closed, and a fault indication was not displayed.
