page_title: Swing bridge
section_title: Advantages
hierarchical_section_title: Swing bridge / Advantages
caption_attribution_description: English: The BNSF Railway Bridge 9.6 is a swing-span railroad bridge across the Columbia River, connecting Portland, Oregon with Vancouver, Washington, United States. It was opened in 1908. This photo was taken from near the bridge's northern end, in Vancouver, showing the swing-span section turning (in the process of closing).
context_page_description: A swing bridge is a movable bridge that has as its primary structural support a vertical locating pin and support ring, usually at or near to its center of gravity, about which the turning span can then pivot horizontally as shown in the animated illustration to the right. Small swing bridges as found over canals may be pivoted only at one end, opening as would a gate, but require substantial underground structure to support the pivot.
  In its closed position, a swing bridge carrying a road or railway over a river or canal, for example, allows traffic to cross. When a water vessel needs to pass the bridge, road traffic is stopped, and then motors rotate the bridge horizontally about its pivot point. The typical swing bridge will rotate approximately 90 degrees, or one-quarter turn; however, a bridge which intersects the navigation channel at an oblique angle may be built to rotate only 45 degrees, or one-eighth turn, in order to clear the channel.
context_section_description: As this type requires no counterweights, the complete weight is significantly reduced as compared to other moveable bridges.
  Where the channel is wide enough for separate 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 moveable span, as the construction will not impede traffic.
caption: BNSF Railway bridge across the Columbia River in Portland, Oregon, showing the swing-span section turning.
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