Published June 30, 2025
Types of Bridges Explained: Beam, Arch, Suspension, and More
The National Bridge Inventory categorizes America's 624,000+ bridges by structural type, and each type has distinct strengths, vulnerabilities, and maintenance requirements that affect its condition rating over time. From simple beam bridges on rural roads to iconic suspension bridges spanning major waterways, understanding bridge types helps explain why some structures age better than others.
Beam and Girder Bridges
Beam bridges are the workhorses of American infrastructure, accounting for roughly 60% of all bridges in the NBI. They consist of horizontal beams (steel, concrete, or prestressed concrete) supported at each end by piers or abutments. Simple, economical, and quick to build, they are the default choice for spans up to about 250 feet.
In the NBI data, beam bridges show a wide range of condition ratings. Newer prestressed concrete beams tend to rate well, while older steel beam bridges in northern states suffer from corrosion and freeze-thaw damage. Beam bridges are generally the easiest and least expensive to repair or replace.
Truss Bridges
Truss bridges use a framework of triangular elements to distribute loads efficiently, allowing longer spans than simple beams with less material. They were the dominant bridge type in the 19th and early 20th centuries and many remain in service today.
Many truss bridges are classified as fracture-critical because their design offers limited redundancy — a single failed member can lead to disproportionate collapse. The I-35W bridge collapse in Minneapolis involved a steel deck truss. Truss bridges require careful inspection of connections, gusset plates, and individual members for fatigue cracking and section loss.
Arch Bridges
Arch bridges transfer loads primarily through compression in the curved arch, making them inherently strong and durable. Stone and concrete arches can last centuries — some Roman arches are still standing after 2,000 years. In the NBI, arch bridges consistently show some of the best average condition ratings.
Modern concrete arch bridges remain an excellent choice for medium to long spans, particularly in valleys and over deep gorges. Their main vulnerability is foundation movement: if the abutments shift, the arch loses its geometry and can crack. Scour at arch foundations is a particular concern for bridges over water.
Suspension Bridges
Suspension bridges use main cables draped between tall towers to support the deck through vertical hangers. They can span the longest distances of any bridge type — the Verrazzano-Narrows Bridge spans 4,260 feet. America's most iconic bridges (Golden Gate, Brooklyn, George Washington) are suspension designs.
Suspension bridges require specialized maintenance of cables, hangers, towers, and anchorages. Main cable corrosion is a major concern that can be difficult to detect and expensive to remediate. Despite these challenges, major suspension bridges generally maintain good condition ratings because they receive substantial maintenance budgets as critical infrastructure.
Cable-Stayed Bridges
Cable-stayed bridges use cables running directly from towers to the deck, offering an economical alternative to suspension bridges for medium-long spans of 500-3,000 feet. They have become increasingly popular since the 1970s and represent many of the newest major bridges in the US.
Because most cable-stayed bridges in America are relatively new, they generally have excellent condition ratings. However, cable corrosion and fatigue are emerging concerns as the first generation of these bridges ages. The FHWA cable inspection guidelines address these maintenance needs.
Culverts
Though often overlooked, culverts account for a significant portion of NBI structures. A culvert is a buried structure (pipe, box, or arch) that allows water to flow under a road. Structures over 20 feet are included in the NBI and must be inspected like other bridges. Culverts are particularly susceptible to scour, sediment blockage, and corrosion of metal components.
Movable Bridges
Movable bridges — including bascule (drawbridge), vertical lift, and swing span designs — open to allow vessel passage. America has over 1,000 movable bridges, concentrated along coastal waterways and navigable rivers. Their mechanical systems add maintenance complexity and cost beyond that of fixed bridges, and many are among the oldest structures in the NBI.
How Type Affects Condition
Bridge type significantly influences how a structure ages and what maintenance it needs. The NBI data shows that newer prestressed concrete beam bridges and arch bridges tend to maintain the best condition ratings over time, while older steel truss bridges and movable bridges show the highest rates of deterioration. When exploring bridge data on BridgeSafety, the structural type is one of the most important factors in understanding why a particular bridge received its condition grade.
Frequently Asked Questions
Beam/girder bridges are by far the most common, representing approximately 60% of all bridges in the National Bridge Inventory. They are the simplest and most economical design for short to medium spans.
Arch bridges tend to have the longest lifespans. Many stone and concrete arch bridges built over a century ago are still in service with good condition ratings. Their form naturally distributes loads through compression, which is inherently efficient.
Suspension and cable-stayed bridges can span the longest distances, but truss bridges are often the strongest relative to their material usage for medium spans. The strongest type depends on the span length, load requirements, and site conditions.
The NBI classifies bridges into seven primary structural types: beam/girder, truss, arch, suspension, cable-stayed, culvert, and movable (including drawbridge and lift bridge). Each type has multiple subtypes based on materials and design details.
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