Source directory
Engineering and Reliability
Primary public sources for this domain, checked 2026-11-02. Delta Arc does not control these sources.
| Source | Can establish | Cannot establish | Updates |
|---|---|---|---|
| Tables of Frequently Requested NBI Information | How the Good, Fair and Poor summary terms are assigned from National Bridge Inventory component ratings, and what the published tables cover. | Whether any listed bridge can carry traffic safely, since the page defines classifications and links tables without assessing structures. | Data submitted annually; stated as final and archived by June 15 each calendar year, published shortly thereafter. |
| Bridge Condition by Highway System 2026 | National and state counts and deck area of bridges classified Good, Fair and Poor in the 2026 table. | The condition of a particular bridge, the cause of a classification, or any safety status. | Annual; this table is stamped 8/4/2026 and the page was updated 09/02/2026. |
| Bridge Condition by Posting Status (2025 workbook) | Counts of bridges by operating status, including open, closed and posted for load, cross-tabulated with Good, Fair and Poor as of 06/15/2025. | Why a bridge was closed or posted, or whether a bridge in an open category has adequate capacity. | Annual tables by year; the 2025 table is the latest posting table located as of 2026-11-02. |
| NBI ASCII files and terminology notes | That the term structurally deficient was retired with the 2018 data archive, and that 2025 was the last submittal in the Coding Guide format. | That older and newer ratings are directly comparable, or how an individual record was rated. | Datasets submitted each spring; stated as final and published by June 15 of each calendar year. |
| 23 CFR Part 650 Subpart C, National Bridge Inspection Standards (edition of 2025-04-01) | The federal minimum requirements for bridge inspection, load rating, load posting, closure criteria and critical findings. | Whether an owner met those requirements for a given bridge, or any amendment made after the edition date. | Annual CFR edition; this edition is dated 2025-04-01. |
| Questions and Answers on the National Bridge Inspection Standards, section 650.313 | FHWA's explanation of how inspection procedures, closure procedures and critical findings are meant to operate. | Binding law, since the page states that apart from cited statutes or regulations the contents do not have the force and effect of law. | Not stated; individual entries carry their own dates. |
| Specifications for the National Bridge Inventory (March 2022) | The current rating codes and descriptions for bridge components, including what code 4 denotes and what does not change a rating. | How an inspector applied a code to any bridge, or the operating capacity of a bridge. | Not stated; published March 2022 with errata listed separately by FHWA. |
| Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges (December 1995) | The general condition rating descriptions applied to historical inventory records under the earlier coding standard. | The current rating definitions, because FHWA states it has been superseded and will no longer be updated or maintained. | Not updated; superseded according to SRC-04. |
| Status of the Nation's Highways, Bridges, and Transit: Conditions and Performance, 25th Edition | The department's stated meaning of the poor classification and how it relates to closure, restriction and monitoring. | Current counts, since the edition describes 2008 to 2018 conditions, or the status of any bridge. | Described as biennial in the report's transmittal letter. |
| National Bridge Inspection Standards program page | The origin and purpose of the standards, and the regulatory and guidance documents that make up the program. | How the standards were carried out for any bridge or state. | Not stated; the page shows an update date of 05/27/2026. |
| Investigation HWY22MH003, Collapse of the Fern Hollow Bridge | The event date, status and summary findings of one federal investigation in which inspection quality and load rating were contributing factors. | The rate of inspection or rating error across the inventory, or the status of any other structure. | Not stated; the investigation is shown as completed. |
| Highway Investigation Report HIR-24-02 | How one recorded condition rating compared with the rating the investigation considered more accurate, and how element-level data differed from it. | That the same divergence occurs in other bridges, or how often it occurs. | Not stated; a single completed report. |
| Investigation HWY07MH024, Collapse of Interstate 35W Highway Bridge | The event date and the investigation's probable cause finding, which concerned load capacity arising in design. | A general relationship between condition ratings and failure risk, because the page does not discuss condition ratings. | Not stated; the investigation is shown as completed. |
| Disaster and Failure Studies Program | That a federal research program studies structural failures and names causes that include fires, earthquakes, wind, and errors in design, construction and materials. | Anything about National Bridge Inventory ratings or a particular bridge. | Not stated. |
Related
Evidence in this domain
Evidence Brief
What a Poor Bridge Rating Can Establish
A National Bridge Inventory Poor rating records component deterioration; it is not by itself a finding that a bridge is unsafe.
Decision Notes
Reopening Is Not Closure
An authority returning to normal does not tell you which recommendations were closed. Those are separate records.
Decision Notes
An Allotment Is Not a Replacement
A published funding allotment marks one step. It does not show a grant, a dollar spent or a pipe removed.
Decision Notes
A Cohort Rate Is Not a Conversion Factor
Thirteen percent of past queue requests reached operation. That does not mean 13 percent of today's queue will.
Source directory
Where the evidence lives
14 primary sources, with what each can and cannot establish.
How to cite this page. Delta Arc, LLC. “Source directory: Engineering and Reliability.” DA-SRC-engineering-reliability, version 1, as of 2026-11-02. https://thedeltaarc.com/sources/engineering-reliability/