By Anthony Schoenecker, P.E., M.ASCE, SPRAT III, CBSI, and Mike Januszkiewicz, P.E., SPRAT III, CBSI
Bridge inspection and highway safety standards have drastically improved since the Federal Highway Administration’s national inspection safety standards became law in 1971. As the equipment and landscape continue to evolve, bridge engineers must adapt to more rigorous — but often helpful — industry requirements.
The natural environment is harsh and corrosive to bridges, regardless of the type of material, quality of construction, or means of erection. Our use of these structures further accelerates their deterioration. Civil engineers must conduct regular assessments of bridge elements to establish conditions and then address critical defects to preserve the safety and integrity of bridges. As the cost of new construction continues to rise, and with an increasing focus on the environmental and social impacts surrounding the construction of new structures, maintaining existing infrastructure is crucial.
Bridge safety programs are how civil engineers maintain infrastructure. These programs function as the first component of safety and are paramount to preservation. Additionally, bridge inspections are used to guide maintenance programs that protect the traveling public.
Over the decades, bridge inspections have evolved. This evolution showcases the challenges, innovations, and trends shaping the field, exemplifying the industry’s dedication to progress.
There are more than 623,000 highway bridges across the United States, according to the Federal Highway Administration’s Long-Term Bridge Performance Program. Many people drive over these structures daily without thinking about them or about the careful monitoring, cataloging, and maintenance involved in keeping them operational. This confidence stems from the fact that these structures are generally well-designed and maintained and are regularly inspected.
Federally mandated programs ensure bridges are carefully monitored, emphasizing the critical role that inspections play in safeguarding the traveling public and the nation’s infrastructure through routine assessments and cataloging defect types, locations, frequency, and severity. These data help bridge owners develop targeted preservation strategies, including maintenance plans, rehabilitation measures, and eventual replacement programs.
Inspections also provide critical insights into the rate and trajectory of deterioration, allowing owners to address issues proactively, and to forecast and budget for repairs.
Highway bridge standards
The basis of today’s bridge inspections began with the Federal-Aid Highway Act of 1968, which established the National Bridge Inspection Program, according to the Federal Highway Administration’s website. “All bridges constructed with federal funds, or which carried a federally funded road, were required to be inspected based on (Department of Transportation)-established standards for bridge safety.”
This act also put in place, in 1971, the National Bridge Inspection Standards. The NBIS became federal law under 23 CFR Part 650, Subpart C. The standards mandate that each state conduct bridge inspections at least once every two years and provide an inspection report of findings to the FHWA to incorporate into the National Bridge Inventory, among other actions. While the initial standards applied only to bridges on federal highways, their application expanded in 1979 to include all bridges on public roads.
The NBIS system has proven highly effective in identifying and addressing the vast majority of potential issues before they escalate, continuing to adapt as problem areas are discovered on particular bridge types or with specific bridge details. A major failure, defect, or material-specific vulnerability identified in the field often spurs investigation and review, and new solutions are developed and applied to identify similar defects before they lead to tragedy. This process ensures that bridge inspection remains a dynamic and evolving discipline.
Notable and recent examples include:
- The Mianus River Bridge failure in Greenwich, Connecticut, in 1983 led to a nationwide focus on fatigue and fracture in bridges and the introduction of the 1986 manual Inspection of Fracture Critical Bridge Members.
- The Schoharie Creek Bridge failure in Fort Hunter, New York, in 1987 led to mandates related to underwater inspection and scour analysis.
- The St. Anthony Falls, or I-35 W, Bridge collapse in Minneapolis in 2007 led to a nationwide review of truss bridges with gusset plates.
- During a 2021 inspection of the Hernando de Soto Bridge between Memphis, Tennessee, and West Memphis, Arkansas, crews found cracks in critical bridge members. These findings prompted ultrasonic testing of critical welds in T1 steel members across the U.S. starting later that year.
Railroad bridge standards
Railroads have long taken a more conservative approach to bridge construction, maintenance, and inspection. Since the early 1900s, railroad bridge owners have employed numerous variations of bridge inspections and continue to inspect their infrastructure based on their own guidelines. The Federal Railroad Administration adopted a formal program in 2009, under 49 CFR Part 214, requiring rail bridge owners to create a bridge management program for all rail-supporting bridge structures. These inspections are performed by in-house railroad teams and consulting engineering firms versed in railroad structures.
Bridge inspection challenges
One of the significant challenges in bridge inspection is safe access to critical areas. As part of any inspection, the ability to identify structural conditions requires near proximity to critical elements.
Prior to the implementation of modern Occupational Safety and Health Administration benchmarks for worker safety, standards were less stringent, with minimal or nonexistent requirements for safety harnesses or tie-off systems. Inspectors faced significant risks when working at heights or accessing hard-to-reach areas.
The design of any bridge significantly impacts the complexity of the access required to adequately complete its inspection. Suspension and cable-stayed bridges, for example, pose unique challenges with their tall towers and extensive cable systems. Older bridges often feature smaller, segmented members that are easier to climb and inspect. In contrast, modern structures tend to be less accessible, presenting fewer climbing opportunities. However, modern bridges may incorporate access aids like safety handlines, walkways, or platforms. When these aids are included in bridge design or retrofit plans, they greatly improve inspection efficiency and safety.
Specialized equipment (e.g., spider baskets, pick boards, and aerial platforms) was the first major innovation in bridge access, and this equipment is still a cornerstone of the inspection process. However, to address inspectors’ needs, engineers are turning to more sophisticated access methods.
Rope access revolution
One of the most significant shifts in recent decades is the adoption of rope access techniques. Modjeski and Masters launched its rope access program in 2000, making it one of only two major engineering firms with such a program at the time. These techniques mimic climbing methods used by rock and cave climbers.
While traditional methods like under-bridge inspection vehicles remain relevant, rope access can offer unmatched versatility and cost efficiency. In some cases, rope access minimizes the need for heavy equipment that disrupts traffic, allowing inspections to be completed with minimal impact on surrounding infrastructure.
Today, firms use a combination of traditional access equipment, modern rope access techniques, the latest inspection equipment, and nondestructive testing techniques. This seamless integration ensures comprehensive inspections of every part of a structure, regardless of complexity.
The evolution of defect identification
Once inspectors reach critical areas of bridges, they must know how to identify the condition of bridge members and what to do about it. Historically, inspectors were limited to only a handful of techniques, namely, visual observations and hand tools. Visual observation is the primary method of defect identification and condition assessment. However, these observations are limited to later-stage issues such as surface-breaking defects and deterioration.
But there is a critical need to address bridge defects at earlier stages of development. So to meet the increasing demands for precision and efficiency, inspectors are developing and implementing newer and better technological tools that can augment visual observations. Specialized testing and sensing capabilities, advanced instrumentation, and nondestructive testing can detect defects before visual signs appear.
A notable development is ultrasonic testing of bridge pins and welds. Nearly unheard of 40 years ago, ultrasonic testing is a recognized and necessary practice that is capable of sensing internal defects before they manifest visibly. Nondestructive tools like ultrasonic thickness gauges, liquid dye penetrant, and magnetic-particle testing are now included in a standard inspection tool kit.
Unmanned aerial vehicles have also been introduced to the field in the last decade. They are often equipped with high-resolution cameras and thermal imaging sensors that conduct assessments in places that would otherwise be difficult or dangerous to observe manually. Advanced innovations like these, as well as acoustic emission sensing, radiography, and ground-penetrating radar, are becoming commonplace. These technologies are excellent for identifying hidden defects.
Despite these advancements, traditional methods — like hammering steel to detect corrosion losses and sounding concrete — remain essential. The tactile feedback and auditory cues they provide are still unparalleled, highlighting the importance of hands-on expertise.
The future of bridge inspections
Another promising development is the implementation of artificial intelligence and machine learning. These technologies analyze large datasets, identify patterns, and predict maintenance needs, offering a proactive approach to bridge management. When paired with a digital twin of a bridge, engineers will obtain more unique data insights to forecast deterioration and maintenance scenarios.
These tools increasingly provide inspectors with non-invasive methods for assessing structural integrity. Like every other civil engineering discipline using AI, human expertise will remain indispensable for interpreting results and making informed decisions. Skilled inspectors will be essential for documenting and interpreting findings, ensuring accuracy, and making critical decisions.
A legacy of excellence
The evolution of inspection techniques over the past 50 years reflects the industry’s dedication to adapting and improving practices to meet higher standards and growing demands. Bridge inspections are not just a critical function for maintaining public safety; they are the foundation for preserving the infrastructure that connects our communities and powers our economies.
Looking ahead, the challenges and opportunities in bridge inspections will blend traditional expertise with technological innovation to ensure that infrastructure remains a safe, enduring foundation for the movement of goods and people. With every inspection, bridge engineers look to not only safeguard critical infrastructure, but also set a standard of excellence for the next generation of engineers and inspectors. In bridging the gap between tradition and innovation, the bridge inspection industry exemplifies what it means to adapt, innovate, and lead.
Anthony Schoenecker, P.E., M.ASCE, SPRAT III, CBSI, is a senior project manager and repair group leader at Modjeski and Masters. Mike Januszkiewicz, P.E., SPRAT III, CBSI, is a senior project manager and technical and rope access program coordinator at Modjeski and Masters.
This article first appeared in the March/April 2025 issue of Civil Engineering as “Revolutionizing Bridge Safety: The Changing Landscape of Bridge Inspections.”
