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Bridge inspection policy has recently been updated to reflect the Federal Highway Administration’s Specifications for the National Bridge Inventory, commonly called SNBI. The SNBI replaces the older 1995 Recording and Coding Guide and brings the National Bridge Inspection Standards (NBIS) into closer alignment with modern inspection practice and statutory requirements. One of the most substantive changes concerns Nonredundant Steel Tension Members, now referred to in the regulations by the acronym NSTM.
An NSTM is a primary steel member fully or partially in tension that lacks load-path, system, or internal redundancy; the failure of such a member may cause a portion of or the entire bridge to collapse. Because of that risk, the SNBI and updated NBIS impose specific training, inspection, documentation, and reporting requirements for NSTM inspections.
The updates include three interlocking elements that agencies must address: 1) who may lead and perform NSTM inspections and the required training, 2) how inspection intervals for NSTMs are determined under a risk-based approach, and 3) how NSTMs are identified, inspected, documented, and reported in the new SNBI schema. These changes are accompanied by firm transition dates and compliance metrics that agencies must follow.
FHWA issued guidance clarifying the NSTM training requirement on February 23, 2024. Under 23 CFR 650.309(c), team leaders performing NSTM inspections on or after June 6, 2024, must have successfully completed FHWA-approved training on proper NSTM inspection procedures.
The FHWA-approved course is Bridge Inspection Techniques for Nonredundant Steel Tension Members (FHWA-NHI-130078), taught by the National Highway Institute. The FHWA memo explicitly states that team leaders who have already completed an earlier version of FHWA-NHI-130078 are considered to have satisfied the requirement. FHWA strongly encourages those certified under earlier versions to attend the updated course, and it also recommends or makes available a free online refresher titled Bridge Inspection Techniques for Nonredundant Steel Tension Members Refresher (FHWA-NHI-130078A).
FHWA is sponsoring multiple in-person sessions of FHWA-NHI-130078 and will fund at least three individuals from each State to attend one of these sessions. NHI is coordinating additional concurrent sessions so states have better access; the FHWA memo anticipated this increased availability by late March (per the memo language). The Division Offices are instructed to work with States to ensure the training requirements are understood and met.
If a State anticipates difficulty meeting the training requirement for team leaders before they must perform NSTM inspections, the Division Office should coordinate with the State to develop and document a risk-based plan that maintains bridge safety until the team leaders receive training. FHWA staff, including the Bridge Safety Engineer, are available to support such coordination.
Additional training-related regulatory points that were incorporated into NBIS include required refresher training hours for program managers and team leaders, end-of-course assessments requiring a passing score (70% or higher), and recognition of alternate training approved prior to the May 2022 regulation update where applicable. The 70% passing score ensures quality by emphasizing verified knowledge over mere task completion, promoting competence, accuracy, and higher performance standards.
The updated NBIS moves inspection interval policy toward a risk-based framework consistent with the MAP-21 requirements and the SNBI. The regulation provides flexibility and also sets limits specific to NSTMs.
Agencies may use simplified or more rigorous risk-based methods to set inspection intervals:
This approach allows agencies to adopt policy-based intervals, with a maximum NSTM inspection interval of 48 months. Implementation requires FHWA notification of the agency’s policy. This option is intended to provide predictable scheduling while enabling agencies to manage resources.
Under the more rigorous method, an agency assembles a Risk Assessment Panel. The Risk Assessment Panel must include at least four members, of which two must be licensed Professional Engineers, and must have the demonstrated expertise to evaluate fatigue, fracture risk, materials behavior, redundancy, and related conditions.
Using this method, agencies may evaluate and justify longer intervals for certain inspection types in some cases, but importantly, NSTM inspections cannot exceed 48 months under the general direction of NBIS text; any extension must be supported by the panel’s analysis and coordinated with FHWA. When an interval greater than 48 months is considered, mid-interval checks, or other monitoring are required to verify the condition assumptions that justified the extension. Formal FHWA approval is required for rigorous-method interval determinations where approvals are mandated by the regulation.
The regulation also provides reasonable tolerance windows. For example, when unavoidable delays occur, a tolerance period of up to three months may be allowed.
Taken together, the intent of the risk-based approach is to let agencies optimize limited resources while ensuring that higher-risk elements receive more frequent attention. Agencies must choose the approach that aligns with their technical capacity, resources, and tolerance for risk, and they must document and maintain the analyses and approvals for their chosen methods.
Transitioning to the SNBI is far more than simply submitting data in a new format. It is a full-scale data mapping, cleansing, and migration effort. Agencies must align legacy data with SNBI standards, resolve discrepancies, and adopt new coding rules. Success requires tight coordination between engineering, IT, and data management teams.
The SNBI implementation timeline establishes specific dates agencies must meet when transitioning from the legacy 1995 Coding Guide to the SNBI schema:
Because NSTMs are explicitly identified and coded in SNBI, agencies must ensure their inventory and reporting systems capture the required NSTM fields and related inspection data before these milestones. Updating data systems and validating submissions in advance reduces the risk of noncompliance when the SNBI submission window opens.
NSTMs are fracture-critical by definition. The lack of redundancy in load paths means that a single undetected or unaddressed defect may result in a portion of or an entire bridge collapsing. The updates in NBIS and SNBI address this heightened risk with clearer expectations for inspection competence, inspection procedure rigor, and consistent national reporting.
Consider a steel highway bridge in which a small crack develops in a fracture-critical tension member. Under sustained loading, this seemingly minor defect can propagate rapidly, precipitating a sudden and catastrophic structural failure. This scenario underscores the real-world risks of unmonitored critical components. NSTM regulations are specifically designed to mitigate such hazards, ensuring that every essential element is thoroughly inspected, accurately documented, and proactively monitored before it poses a significant safety threat.
The regulatory changes accomplish three practical aims:
These elements work together to reduce the likelihood of a missed NSTM defect and to provide a consistent, auditable record of how agencies identify and manage fracture-critical members.
A formal, documented procedure for redundancy goes beyond generic guidelines, it lays out a step-by-step methodology that can withstand FHWA review. For example, an agency might document a comprehensive fatigue analysis using finite element modeling to evaluate load paths and identify critical members. The procedure would specify modeling assumptions, load combinations, inspection intervals, and criteria for flagging potential failures, creating a rigorous, auditable record that serves both as a compliance tool and a blueprint for consistent decision-making.
NBIS Section 650.313 and Metric #16 (Inspection Procedures - NSTM) set expectations for how NSTM inspections must be planned, documented, and executed. The FHWA guidance and Metric #16 criteria require the following for bridges with NSTMs:
Metric #16 also provides compliance assessment guidance. For Population 1 (bridges with NSTMs open to traffic), the metric requires that sampled bridges meet the documented-procedure and inspection requirements to be considered in compliance. For Population 2 (bridges claimed to have internal or system redundancy), documentation and approvals must be available and adequate or the metric may be assessed as noncompliant.
Risk factors that must be considered within procedures and during inspections include fatigue-prone details, problematic materials, poor welding techniques, out-of-plane distortion, prior cracking or repairs, cold service temperatures, load posting conditions, low superstructure condition codes, high truck traffic, debris build-up, older service life, and impact or overload susceptibility.
To comply with NBIS and SNBI for NSTM management, agencies should take the following concrete actions immediately:
The SNBI and NBIS updates place renewed emphasis on identifying, inspecting, and reporting on Nonredundant Steel Tension Members. These requirements are precise: team leaders must be trained; inspection procedures must be documented and require hands-on inspection unless redundancy is demonstrated and FHWA-approved; NSTMs must be identified and reported in the SNBI schema; inspection intervals are to be determined using a risk-based framework and, with respect to NSTMs, kept within the regulatory boundaries described above; and agencies must meet the SNBI reporting milestones.
Agencies that take these requirements seriously and act promptly, confirming training, documenting procedures and NSTM locations, selecting and documenting their inspection interval approach, coordinating with FHWA, and updating data systems will be in the best position to manage fracture-critical members safely and comply with the SNBI transition timeline.
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