6.8% Poor Spans, 168.6M ADT: Structurally Deficient Bridges Versus Daily Traffic

Ask how many U.S. highway bridges are “structurally deficient” and you will get a vocabulary fight before you get a number. The Federal Highway Administration retired that label after the 2017 Pavement and Bridge Condition Performance Measures rule. Beginning with the 2018 National Bridge Inventory (NBI) archive, the summary condition is Good, Fair, or Poor. Poor means any of deck, superstructure, substructure, or culvert is rated 4 or lower on the NBI condition scale. News desks and state DOTs still say structurally deficient in plain language; this desk treats Poor as the operational successor and keeps both phrases in view so readers are not lost in the rename.

The 2024 final inventory is unambiguous on the count. Of 623,218 public highway bridges, 42,080 are Poor — 6.8% of the stock. That is the share of spans. The harder question in the brief is traffic: how much average daily traffic (ADT) still crosses those spans? Summing FHWA’s Bridge Condition by Functional Classification ADT tables for 2024 puts 168.6 million ADT on Poor bridges — about 3.4% of the inventory’s ADT total near 4.94 billion. The mismatch is the story. Poor bridges are a larger slice of the count than of traffic, yet the residual ADT is still enormous in absolute terms: more than a hundred million vehicle-days of exposure every day on structures the inventory itself flags as Poor.

The interactive dashboard above keeps that pairing open. Count vs ADT stacks Poor against Good+Fair for bridge count, inventory ADT, and deck area. Condition mix shows the national Good/Fair/Poor donut and splits Poor ADT into rural versus urban. Functional class ranks Interstate-to-local intensity with toggles for setting and metric. Decade path traces Poor count share down from roughly 9.8% in 2010 toward 6.8% in 2024 alongside a softer ADT-share line. NHS vs non-NHS contrasts the National Highway System’s 3.0% Poor share with 7.9% off the NHS. State scatter plots Poor share against ADT still riding Poor spans.

Poor is not closed — and ADT is not unique trips

A Poor rating is not an automatic closure order. When officials determine a bridge is unsafe, they close it or post weight limits; CRS notes that roughly 43,600 bridges carried a weight restriction in a recent national cut, a related but separate ledger from the Poor count. Most Poor bridges remain open. ADT in the NBI is the average daily traffic on that structure, not a national unique-trip census. Summing ADT across bridges double-counts vehicles that cross multiple spans in a day. That is exactly how FHWA and BTS publish the tables, and it is the right unit for an inventory exposure question: how much traffic loading sits on Poor decks.

The national ADT sum on all bridges is about 4.94 billion. The Poor subset is 168.6 million, or 3.4%. Deck area tells a middle story: Poor bridges account for about 4.9% of inventory deck area (19.8 million of 407 million square meters). Count share (6.8%) exceeds deck share, which exceeds ADT share — consistent with a stock where many Poor bridges are smaller, lower-volume rural structures, while a minority of larger urban Poor bridges pull traffic and area upward.

The decade path: fewer Poor spans, stubborn residual traffic

CRS highway-bridge briefs that cite the NBI put the national Poor share near 9.8% in 2010, 9.4% in 2012 (57,049 Poor bridges), 8.3% in 2015, 7.5% in 2019, and 6.7% in the 2025 print (41,685 Poor). The 2024 FHWA final used here sits at 6.8% with 42,080 Poor bridges. The count has fallen by roughly 15,000 Poor spans since 2012 even as the total inventory grew. That is real progress on the rehabilitation and replacement ledger.

It is not the same as eliminating traffic exposure. Desk-bridged ADT shares that track published count shares fall from roughly 5% of inventory ADT early in the 2010s toward the 3.4% FHWA 2024 print. The slope is down; the floor is not zero. Every percentage point of national ADT still represents tens of millions of vehicle-days on Poor structures. Policymakers who celebrate the count decline without watching the ADT residual are reading only half the meter.

NHS corridors look cleaner; local systems carry the count

On the National Highway System — the backbone Congress and FHWA watch for freight and interstate mobility — 4,389 of 147,439 bridges are Poor (3.0%). Off the NHS, 37,691 of 475,779 bridges are Poor (7.9%). Almost 90% of Poor bridges by count sit outside the NHS. That split explains why national headlines can sound alarming while Interstate travelers see fewer posted distress signals: the inventory’s worst count concentration is on lower-order roads.

Traffic cuts the other way on absolute volume. Urban Poor ADT is about 135.5 million; rural Poor ADT is about 33.1 million. Roughly 80% of ADT on Poor bridges is urban even though CRS and FHWA repeatedly note that about 80% of Poor bridges are rural. Rural America owns the count problem; metro corridors own most of the traffic still rolling on Poor decks. Replacement dollars follow that asymmetry — urban Poor spans are larger, more expensive, and more disruptive to stage — which is why deck-area and ADT metrics matter alongside simple bridge counts.

Functional class: collectors punch above Interstates on Poor intensity

BTS’s Transportation Statistics Annual Report figure on bridges in Poor condition versus ADT (built from FHWA functional-classification tables) makes the class ladder visible. Rural major collectors show Poor count shares near 10.5%, with Poor ADT shares near 5.6%. Rural Interstates sit near 2.6% Poor by count and about 2.3% by ADT. Urban Interstates are similar on ADT share (~2.9%) even though their absolute Poor ADT — 53.0 million — dominates every other class because urban Interstate volumes are enormous.

Toggle the dashboard’s functional-class panel to Poor ADT volume and urban Interstates leap to the top. Toggle to Poor count share and rural collectors and locals climb. That is not a contradiction; it is two valid prioritization lenses. A state DOT chasing how many Poor bridges it owns will land in rural collector country. A freight desk chasing how much traffic still loads Poor decks will land on urban Interstate and principal arterial spans.

States: Iowa leads share; California leads Poor ADT

State panels rearrange the ranking again. Iowa prints 4,544 Poor bridges on a 23,719-bridge inventory — a 19.2% Poor share, among the highest in the 2024 table — yet its summed Poor ADT is only about 1.2 million. California’s Poor share is a comparatively modest 5.9% (1,527 of 25,848), but Poor ADT sums to about 28.7 million, the largest volume in the illustrative state set. New York, Illinois, Pennsylvania, and Massachusetts also combine mid-to-high Poor shares with multi-million Poor ADT totals. Texas and Georgia show the opposite corner: large inventories with Poor shares near 1–2% and moderate Poor ADT.

West Virginia (18.6% Poor share) and Rhode Island (15.2%) illustrate small-inventory, high-share systems where almost one in five or one in six spans is Poor. Puerto Rico prints a 13.9% Poor share with about 4.4 million Poor ADT — a territory-scale reminder that the inventory is not only a 50-state story. The scatter panel encodes the trade: horizontal axis is Poor share, vertical is Poor ADT in millions, bubble size tracks Poor bridge count.

What the meters do not say

Poor is a condition summary, not a failure prediction. Two bridges rated 4 can differ sharply in load posting, fracture-critical details, scour risk, and inspection frequency. ADT is an average; peak-hour and truck shares are not in these national rollups. The 2018 definitional cut from “structurally deficient” to “Poor” is close but not identical to the pre-2018 SD flag — long time series should be read as a family of related meters, not a single unbroken series. Mid-decade ADT shares in the trend table are desk bridges where FHWA did not republish a matched ADT-on-Poor national percentage; the 2024 ADT share is the hard FHWA print.

Funding is another ledger. IIJA and state programs move billions into bridge repair, but obligation rates, local match capacity, and design-bid-build timelines mean the inventory turns slowly. A falling Poor count with a stubborn ADT residual is exactly what a system looks like when the easiest rural replacements clear first and the high-traffic urban Poor spans take longer to stage.

Reading the 2026 desk in one line

6.8% of NBI spans are Poor — the modern “structurally deficient” stock. They still carry 168.6 million ADT, 3.4% of inventory traffic and 4.9% of deck area. NHS corridors are cleaner on count share (3.0%) than non-NHS roads (7.9%). Urban decks absorb most of the remaining traffic exposure. The national count is better than a decade ago; the residual vehicle loading on Poor structures is still a daily operations and capital-planning fact, not a historical footnote.

Sources

• [FHWABridge Condition by Highway System 2024](https://www.fhwa.dot.gov/bridge/nbi/no10/condition24.cfm)
• [FHWABridge Condition by Functional Classification ADT 2024](https://www.fhwa.dot.gov/bridge/nbi/no10/fcadt24.cfm)
• [FHWATables of Frequently Requested NBI Information](https://www.fhwa.dot.gov/bridge/britab.cfm)
• [BTSBridges in Poor Condition and Avg Daily Traffic on Bridges 2024](https://www.bts.gov/browse-statistical-products-and-data/info-gallery/bridges-poor-condition-and-avg-daily-traffic-0)
• [CRSHighway Bridges: Conditions, Funding Programs, and Issues (R47194)](https://www.everycrsreport.com/reports/R47194.html)