Bridge Material Distribution Across the National Bridge Inventory
PlainBridges shows the distribution of bridge primary materials in the FHWA NBI. Rendered live from the bridges fact table grouped by material.
Research period:
Research question
What is the relative share of each primary construction material across the US national bridge inventory, and how does material relate to typical age and condition?
Methodology
This ranking reflects the data currently in our database, sourced from the agency referenced in the citation below and updated automatically as new filings are processed.
Coverage and exclusions: the source agency occasionally suppresses values for confidentiality, small sample size, or quality control, and suppressed rows are excluded from this ranking rather than shown as zero. If the agency later revises a figure, the revised value replaces the old one automatically the next time our data is refreshed.
Data provenance: we pull each release as it becomes available and normalize it into our database; a later release simply supersedes the one before it, so readers never see a mix of old and new figures on the same page.
Comparability across years: when the source agency revises its release schedule, definitions, or coverage, we note the affected years on the methodology page so readers can compare like-with-like rather than across a changed measurement.
Editorial governance: a named editor reviews every ranking page before publication (see the byline above). If an entity disputes a figure attributed to it, corrections are checked against the official source record before any change is made.
Every number on this page can be traced back to its source by following the entity links and the citation below, so independent verification never requires anything beyond the original public source.
See the methodology page for the complete ETL pipeline, source vintage, and column lineage.
Bridge Material Distribution Across the National Bridge Inventory
Live data: reflects the current dataset
The ranked top 10
Every row below reflects the current 10-record dataset. Reload the page after new data is processed to see the latest values.
| # | Primary material | Bridge count | Average year built |
|---|---|---|---|
| 1 | Concrete | 165,942 | 1,972 |
| 2 | Prestressed Concrete | 128,959 | 1,990 |
| 3 | Steel | 109,801 | 1,970 |
| 4 | Concrete Continuous | 73,141 | 1,974 |
| 5 | Steel Continuous | 44,418 | 1,975 |
| 6 | Prestressed Concrete Continuous | 27,970 | 1,993 |
| 7 | Wood or Timber | 13,960 | 1,967 |
| 8 | Aluminum/Iron | 2,169 | 1,994 |
| 9 | Masonry | 1,252 | 1,908 |
| 10 | Other | 342 | 1,985 |
Source: Federal Highway Administration (FHWA) - FHWA NBI item-43A material code documentation. Values reflect the current dataset, refreshed as new filings are processed. Federal Highway Administration (FHWA) - FHWA NBI item-43A material code documentation. Values reflect the current dataset, refreshed as new filings are processed.
Findings
Top entity in the ranking
The top-ranked record in this dataset is Concrete, with a value of 165,942 on the Bridge count column. The full top-10 set is rendered in the table above. Every value derives from the underlying bridges table; no number is hardcoded into this page. When the Federal Highway Administration (FHWA) publishes a revision and our ETL pipeline reingests, the ranking and the prose around it update on the next page load.
Distribution shape
The gap between the top-ranked record (165,942) and the 10th-ranked record (342) characterizes how concentrated the top of the distribution is. Where the top value is many multiples of the median value of the visible set, the population is highly concentrated, a small number of entities accumulate the bulk of the measured quantity. Where the top and bottom of the visible set are close together, the distribution is relatively flat across the top end. The full distribution beyond this top-10 cut is summarized in the aggregate context section below and explored in the linked entity profiles.
Aggregate context
Across the full bridges population, the aggregate query returns the following summary statistics. These anchors situate the top-10 ranking against the underlying population: how many records exist in total, what the sum of the ranking column is across all qualifying rows, and what the mean per-record value looks like. The methodology page documents the exact filter applied by the aggregate query (records with null or zero values on the ranking column are excluded). The aggregate row is computed by the same database engine that renders the ranking above, against the same snapshot.
Source provenance
The records in this ranking originate from Federal Highway Administration (FHWA), specifically the FHWA NBI item-43A material code documentation. PlainBridges compiles the agency's published vintage into our own database and rebuilds the site whenever the source refreshes, so these numbers stay current within hours of a new release rather than sitting frozen in a static export. The methodology page documents the source URL, the vintage date, and the transformation steps applied.
Why this ranking matters
Rankings like this one let a reader scan a population quickly and identify outliers, concentrations, and patterns that warrant deeper investigation. The detail pages linked from each entity in the table above give the full per-entity context: time-series history where available, related metrics from adjacent tables, and links onward to the underlying source records. The methodology page explains how an entity earns inclusion in the dataset and how the ranking column is computed at the source.
What this analysis cannot tell us
Material classification is taken from the NBI 'main span material' code (NBI item 43A) and reflects the primary load-bearing material of the main span. Many bridges combine materials (a steel-girder bridge with a concrete deck, for example) and the primary-material code does not capture the full structural composition. Average build year by material reflects historical construction patterns, steel was dominant in early- and mid-20th-century construction, prestressed concrete became dominant in the 1960s–1980s. Deficiency counts by material do not control for age or exposure, older steel bridges naturally show higher deficiency rates than newer prestressed concrete bridges because they have been in service longer and were designed to older standards.
Secondary cut from the same source
Structurally deficient bridges by primary material
Sources
- FHWA, National Bridge Inventory (NBI) - https://www.fhwa.dot.gov/bridge/nbi.cfm
- FHWA Recording and Coding Guide, Material codes (item 43A) - https://www.fhwa.dot.gov/bridge/mtguide.pdf
Every figure on PlainBridge is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.