30-09-2017, 04:54 PM
A movable bridge is a bridge that moves to allow passage (usually) for boats or barges. In American English, the mobile bridge and the drawbridge are synonyms, and the latter is the common term, but the drawbridge can be limited to the narrower historical definition used in some other forms of English, in which the drawbridge refers only to a specific type of mobile bridge.
One advantage of making mobile bridges is the lower cost, due to the absence of high docks and long approaches. The main disadvantage is that traffic on the bridge should be stopped when it opens for passages. For railway bridges rarely used on occupied canals, the bridge can be left open and then closed for train passages. For small bridges, bridge movement can be activated without the need for a motor. Some bridges are operated by users, especially those with a boat, others by an (or bridge) tender; some remotely using camcorders and speakers. Bridges are usually driven by electric motors, whether operating winches, gears, or hydraulic pistons. While the mobile bridges as a whole can be quite long, the length of the moving portion is constrained by engineering considerations and cost to a few hundred feet.
There are often traffic lights for road and water traffic, and mobile barriers for road traffic. In the United States, regulations governing the operation of movable bridges (such as drawbridges) - for example, hours of operation and how much notice must be given for water traffic - are listed in Title 33 of the Code of Federal Regulations , temporary deviations are published in the Local Notice to Coast Guard Mariners.
One advantage of making mobile bridges is the lower cost, due to the absence of high docks and long approaches. The main disadvantage is that traffic on the bridge should be stopped when it opens for passages. For railway bridges rarely used on occupied canals, the bridge can be left open and then closed for train passages. For small bridges, bridge movement can be activated without the need for a motor. Some bridges are operated by users, especially those with a boat, others by an (or bridge) tender; some remotely using camcorders and speakers. Bridges are usually driven by electric motors, whether operating winches, gears, or hydraulic pistons. While the mobile bridges as a whole can be quite long, the length of the moving portion is constrained by engineering considerations and cost to a few hundred feet.
There are often traffic lights for road and water traffic, and mobile barriers for road traffic. In the United States, regulations governing the operation of movable bridges (such as drawbridges) - for example, hours of operation and how much notice must be given for water traffic - are listed in Title 33 of the Code of Federal Regulations , temporary deviations are published in the Local Notice to Coast Guard Mariners.