Each year, the American Road and Transportation Builders Association (ARTBA) releases its annual Bridge Report, offering a detailed snapshot of the nation’s bridge infrastructure. The 2019 edition of this report revealed that 7.7 percent of all bridges in the United States are classified as structurally deficient. While this figure represents a modest improvement over previous years, the pace of repairs remains a significant concern for engineers, policymakers, and the traveling public. Understanding what these numbers actually mean requires looking beyond the headline percentage. For engineers and construction professionals involved in bridge work, foundational knowledge about construction of culverts and minor bridges siting and investigation provides important context for how these structures are planned and assessed before they ever enter the national inventory.
Understanding Structural Deficiency in Bridges
The term structurally deficient does not mean a bridge is in imminent danger of collapse. Rather, it indicates that one or more structural components of the bridge require attention. These components may include the deck, superstructure, substructure, or culverts. When any of these elements receives a low rating during inspection, the bridge is flagged and scheduled for monitoring, load restrictions, or repairs. The ARTBA report documented 47,052 structurally deficient bridges out of a total of 616,087 in the national inventory. This was a reduction from 54,249 the previous year, but a significant portion of that decline came from a definition change that took effect on January 1, 2018, which removed 6,533 bridges from the structurally deficient category. The actual reduction attributable to completed repairs was only 567 bridges.
Understanding the different types of bridges helps explain why certain designs are more prone to specific kinds of structural deficiency. Beam bridges, truss bridges, arch bridges, suspension bridges, and cable-stayed bridges each have unique load paths and failure modes that inspectors must evaluate. The inspection process follows federal standards under the National Bridge Inspection Standards program, which mandates that every bridge over 20 feet in length be inspected at least once every 24 months. Bridges that fail to meet these standards are assigned a priority rating that determines how quickly repairs must be carried out.
The Scope of the National Repair Challenge
Beyond the 47,052 structurally deficient bridges, the ARTBA report identified over 235,000 bridges nationwide that need some form of repair. This represents roughly 38 percent of the total bridge fleet. The scale of this challenge is enormous, requiring coordinated efforts across federal, state, and local agencies. The rate of repair work in 2018 was at its slowest point in five years. Over the previous five-year period, the average annual reduction in structurally deficient bridges was 1,700, making the 2018 reduction of 567 bridges a notable slowdown. When comparing different structural systems, each presents unique repair considerations. For example, cable stayed bridges offer advantages over suspension bridges for spans under 1000 meters, including reduced cable vibration and easier deck replacement. These engineering considerations directly affect how maintenance and repair programs are designed for different bridge types across the national inventory.
The financial implications are staggering. Bringing all structurally deficient bridges up to standard would require an investment well into the tens of billions of dollars. However, the economic cost of inaction is even higher when factoring in traffic delays, vehicle damage from poor road surfaces, reduced freight efficiency, and the risk of emergency bridge closures that can reroute traffic for months at a time. Every dollar spent on bridge rehabilitation yields multiple dollars in economic benefit over the life of the structure.
Regional Disparities in Bridge Conditions
Bridge conditions vary dramatically from state to state. The states with the highest absolute numbers of structurally deficient bridges include Iowa with 4,675, Pennsylvania with 3,770, Oklahoma with 2,540, Illinois with 2,273, and Missouri with 2,116. These five states alone account for more than 30 percent of all structurally deficient bridges in the country. When measured as a percentage of each state’s total bridge inventory, the picture looks different:
| State | Structurally Deficient Bridges | Percentage of State Inventory |
|---|---|---|
| Rhode Island | 1,682 | 23.0% |
| West Virginia | 1,593 | 19.8% |
| Iowa | 4,675 | 19.3% |
| South Dakota | 1,124 | 16.7% |
| Pennsylvania | 3,770 | 16.5% |
Rhode Island led the nation with 23 percent of its bridges classified as structurally deficient. These regional disparities reflect differences in climate, traffic volumes, construction history, and state-level investment in infrastructure maintenance. States with older bridge inventories and more extreme weather cycles tend to show higher deficiency rates, as do states with significant rural road networks where lower traffic volumes may delay repair prioritization. Engineers working on bridge rehabilitation projects must evaluate local conditions carefully. Understanding how plate girder bridges perform under different loading and environmental conditions is essential when planning state-level maintenance programs for aging steel bridges in colder climates.
Key Factors Driving Bridge Deterioration
Several factors contribute to the deterioration of America’s bridge infrastructure. Age is one of the most significant variables. The average age of a bridge in the United States is over 45 years, and many bridges were designed for lower traffic volumes and lighter vehicles than what they carry today. Beyond age, the following factors accelerate structural decline:
- Exposure to deicing salts and freeze-thaw cycles that corrode reinforcing steel and spall concrete decks, reducing load capacity over time
- Increasing traffic volumes and heavier legal load limits than originally designed for, causing fatigue accumulation in steel and concrete members
- Deferred maintenance caused by funding shortfalls at the state and local levels, allowing small problems to grow into major defects
- Scour around bridge foundations from hydraulic forces during flood events, which can undermine the stability of piers and abutments
- Fatigue cracking in steel members from repeated stress cycles over decades of service, particularly in older truss and girder bridges
Specialized bridge types present their own maintenance profiles. For instance, movable bridges have mechanical and electrical systems that require additional inspection protocols beyond the standard structural evaluation. Bascule bridges, lift bridges, and swing bridges each have unique operating mechanisms that can fail independently of the structural components, adding complexity to state maintenance programs and requiring specialized training for inspection crews.
Repair Approaches, Investment Strategies, and the Path Forward
Addressing the 235,000 bridges in need of repair requires a multilayered strategy spanning from short-term load postings to full replacement programs. Engineers, construction firms, and transportation agencies are pursuing several approaches to accelerate the repair process:
- Accelerated bridge construction techniques that use prefabricated elements to reduce on-site construction time from months to weeks
- High-performance materials such as ultra-high performance concrete and corrosion-resistant alloys that extend service life beyond traditional designs
- Advanced inspection technologies including drones, ground-penetrating radar, and acoustic monitoring to detect structural defects earlier
- Innovative contracting methods like design-build and public-private partnerships that streamline project delivery and share risk
- Asset management systems that prioritize projects based on risk scoring, condition ratings, and network criticality
For bridges with longer spans, selecting the right structural system is critical to long-term performance. Engineers must understand the tradeoffs between different designs. For example, cantilever bridge types and their advantages and disadvantages provide useful comparison points when planning new crossings or major rehabilitations. Cantilever bridges can be constructed without falsework, making them suitable for deep valleys or wide river crossings where temporary support structures are impractical.
Funding for bridge repair comes from multiple sources, including federal programs like the Highway Trust Fund, state transportation budgets, local bond measures, and toll revenue. Key challenges in bridge funding include the federal gas tax not being increased since 1993, reducing its purchasing power by over 40 percent; state-level bond programs constrained by debt limits; local governments lacking technical capacity to manage complex projects; and rising construction costs outpacing inflation. The engineering of bridge towers and cable systems plays a crucial role in long-term durability. Understanding the design of towers of suspension and cable stayed bridges is essential knowledge for engineers involved in large-scale bridge repair programs, as these components are among the most expensive and difficult to replace or strengthen in the field.
The ARTBA 2019 report delivered a mixed message. The decline in the percentage of structurally deficient bridges from 8.9 percent to 7.7 percent shows that repair programs are producing results, but the slowing pace of work signals that current efforts are insufficient to address the full scope of the problem. With 38 percent of the nation’s bridges needing some form of repair, the challenge demands sustained investment, innovation in construction methods, and a trained workforce capable of executing complex rehabilitation projects. Every structurally deficient bridge that is repaired represents not just an improved safety outcome but also a restored connection for communities. Examining awe inspiring bridges around the world reminds us of what civil engineering can achieve when resources and expertise are aligned behind ambitious infrastructure goals.