Bridge Types and Materials: A Visual Guide

The material mix, nationwide

The NBI records a structure type and primary material for every bridge, concrete, prestressed concrete, steel, timber, masonry, and a handful of smaller categories. Concrete is the single largest family in the current file, 259,858 bridges. Concrete and steel together account for the overwhelming majority of the inventory; timber and masonry structures are a small, mostly older and rural share.

What material tells you, and what it doesn't

Material is a construction-era signal more than a condition signal. Steel and timber structures skew older on average, prestressed concrete became dominant in new construction from the 1960s onward, and a state's material mix often reflects when its highway network was built out, not how well it's maintained today. A well-maintained steel truss can outlast a neglected concrete slab.

Material alone doesn't determine the Good/Fair/Poor condition category, the 0-9 element rating scale does that, based on the actual inspected state of the deck, superstructure, and substructure. See which materials carry the most Poor-condition bridges in the takeaways below.

Culverts and other structure types

Not every NBI record is a classic open-deck bridge. Culverts, enclosed tube or box structures that carry a waterway or roadway underneath a fill, are recorded separately and receive a single culvert condition rating instead of the deck/superstructure/substructure split used for open-deck bridges. Movable bridges (bascule, swing, lift) and suspension/cable-stayed structures are also distinct structure-type codes, each a small share of the total.