Swingbridges of Southeast Texas

A swing bridge is a bridge that has as its primary structural support a vertical locating pin and support ring at or near to its center, about which it can then pivot horizontally as shown in the animated illustration below.

In its closed position, a swing bridge carrying a road over a river or canal, for example, allows road traffic to cross. When a water vessel needs to pass the bridge, road traffic is stopped (usually by traffic signals and barriers), and then motors rotate the bridge approximately 90 degrees horizontally about its pivot point.*

Advantages*

As this type requires no counterweights the complete weight is significantly reduced as compared to other moveable bridges.
Where sufficient channel is available to have individual traffic directions on each side the likelihood of vessel-to-vessel collisions is reduced.
The central support is often mounted upon a berm along the axis of the watercourse, intended to protect the bridge from watercraft collisions when it is opened. This artificial island forms an excellent construction area for building the movable span as the construction will not impede channel traffic.

Disadvantages*

The central pier forms a hazard to navigation.
Where a wide channel is not available a large portion of the bridge may be over an area that would be easily spanned by other means.
A wide channel will be reduced by the center pivot and foundation.
When open, the bridge will have to maintain its own weight as a balanced double cantilever, while when closed and in use for traffic the live loads will be distributed as in a pair of conventional truss bridges, which may require additional stiffness in some members whose loading will be alternately in compression or tension.
If struck from the water near the edge of the span, it may rotate enough to cause safety problems (cf. Big Bayou Conot train disaster).

*From Wikipedia, the free encyclopedia

Swingbridges

TX12 Swingbridge over the Sabine River east of Deweyville

TX82 Swingbridge at Sabine Pass

TX87/73 Swingbridge between Bridge City and Orange

Round Bunch Road Swingbridge in Bridge City