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Why can an arch bridge use less material than a beam bridge of the same span?

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bridge The multiple-span Seto Great Bridge over the Inland Sea, linking Kojima, Honshu, with Sakaide, Shikoku, Japan.

An arch bridge is generally more material-efficient than a beam bridge of the same span because of how it manages structural forces.12

While a beam bridge must resist bending stresses across its entire length, an arch bridge carries loads primarily through compression. In an arch, downward pressure forces the structural elements (such as the wedge-shaped voussoirs in masonry) together, which enhances the bridge's load-carrying capacity. By utilizing this compressive strength, the arch design allows for a more efficient distribution of forces, requiring less material to maintain stability over a given span compared to the bending-resistant requirements of a beam.32

As spans increase, minimizing this "dead load" (the weight of the structure itself) becomes a critical engineering priority, leading designers to favor forms like the arch that provide greater strength with less material.4