A swing bridge is a type of movable bridge whose deck rotates about a vertical axis, usually located in the middle of the waterway, so that openings appear on either side of the central pier for vessels to pass through. It is one of the oldest mechanical bridge types and is still used on waterways where vertical clearance is limited.
How a swing bridge works
The bridge deck rests on a central turning pier with large ball or roller bearings. When the bridge needs to open, the deck is rotated electrically or hydraulically:
- Traffic and pedestrians are stopped and barriers are lowered
- End locks are released
- The bridge rotates 90 degrees, ending up parallel to the waterway
- Vessels can pass on either side of the central pier
- After the passage the bridge rotates back and is locked again
Types of swing bridges
- Symmetrical swing bridge — two equal arms rotating around the centre
- Asymmetrical swing bridge — one long and one short arm, often counter-weighted
- Bowstring swing bridge — an arched span that swings as a unit, typical for 19th-century railway bridges
Applications
Swing bridges are found at:
- Narrow waterways — where there is little room for a lift or bascule bridge
- Low-lying terrain — where a drawbridge would take too much room
- Historic structures — many monumental 19th-century swing bridges are preserved
- Industrial estates — easy-to-operate swing bridges in harbours and canals
Pros and cons
Advantages:
- Compact structure without tall superstructure
- Unlimited vertical clearance when open
Disadvantages:
- A pier in the waterway obstructs wide vessels
- Road traffic waits a long time during openings
- Maintenance of the turning mechanism is costly
Related terms
- Bridge
- Bascule bridge
- Lift bridge
- Drawbridge
- Pontoon bridge
- Folding bridge
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