41,685 bridges are in poor condition. But this loading screen isn't one of them.
41,685 bridges are in poor condition. But this loading screen isn't one of them.
Bridges that open or move to allow ships to pass, including lift, bascule, and swing types.
Total in US
798
Poor Condition
21.8%
Avg Sufficiency
57.2
Average Age
66 yrs
Movable bridges are engineering marvels that can change position to allow boat and ship traffic to pass through. They are essential infrastructure along navigable waterways where the bridge deck cannot be built high enough to clear all marine traffic. The three main types of movable bridges are vertical lift bridges, bascule (drawbridge) bridges, and swing bridges, each with distinct mechanical systems.
Vertical lift bridges raise their entire span straight up between two towers, like an elevator. Bascule bridges pivot upward from one or both ends, much like a medieval drawbridge. Swing bridges rotate horizontally around a central pivot pier. Each type has advantages depending on the waterway width, required clearance, and span length.
Movable bridges are concentrated in coastal cities, along inland waterways, and in harbor areas. They present unique operational challenges because they require mechanical systems, power supplies, control systems, and operators. Many older movable bridges have been in service for nearly a century, and maintaining their complex mechanisms is a significant engineering challenge.
Each type of movable bridge uses different mechanical principles. Bascule bridges use a counterweight that balances the weight of the span, so only a small amount of energy is needed to open or close it. The span pivots on a trunnion (large axle), and the counterweight, located below the roadway or behind the abutment, rises as the span opens. Vertical lift bridges use counterweights hanging from cables that run over sheaves (pulleys) at the top of the towers. As the span rises, the counterweights descend, and large motors drive the system. Swing bridges rotate on a center pivot bearing. The bridge is carefully balanced on the pivot so that motors can rotate the entire span (or two spans) to create an opening. All types require precise counterbalancing so the motors need only overcome friction and wind resistance, not the full weight of the span.
Chicago has more movable bridges than any other city in the world, with over 40 bascule bridges spanning the Chicago River and its branches. The city developed its own distinctive double-leaf trunnion bascule design in the early 1900s, and raising the bridges has become a beloved spring and fall tradition.
Tower Bridge (London, bascule)
Arthur Kill Vertical Lift Bridge (New York/New Jersey)
Steel Bridge (Portland, OR, double-deck lift)
Michigan Avenue Bridge (Chicago, IL, bascule)
Cape Cod Canal Railroad Bridge (Massachusetts, vertical lift)
Duluth Aerial Lift Bridge (Minnesota)
| Rank | State | Count | % of Type |
|---|---|---|---|
| 1 | Louisiana | 139 | 17.4% |
| 2 | Florida | 137 | 17.2% |
| 3 | New York | 68 | 8.5% |
| 4 | Illinois | 55 | 6.9% |
| 5 | Washington |
There are 798 movable bridges in the United States.
Iconic bridges with a deck hung from cables draped over tall towers, capable of spanning enormous distances.
Modern bridges where cables run directly from towers to the deck, creating a dramatic fan or harp pattern.
One of the oldest bridge forms, using a curved structure to transfer loads outward to abutments at each end.
Bridges built from interconnected triangular elements, combining strength and material efficiency.
| 53 |
| 6.6% |
| 6 | New Jersey | 44 | 5.5% |
| 7 | Wisconsin | 37 | 4.6% |
| 8 | California | 36 | 4.5% |
| 9 | Massachusetts | 25 | 3.1% |
| 10 | Michigan | 25 | 3.1% |