U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration

Bridges & Structures


Questions and Answers on the National Bridge Inspection Standards, 23 CFR Part 650, Subpart C

Except for any cited statutes or regulations, the contents of these Q&As do not have the force and effect of law and are not meant to bind the public in any way. These Q&As are intended only to provide information regarding existing requirements under the law or agency policies.

650.313 Inspection procedures

Q313-1 Can advanced technologies be used in bridge inspection? (New 3/01/2023)

A313-1 Yes, proven advanced technologies may be used to supplement but not supplant bridge inspection personnel and inspection methods (23 CFR 650.313(a)). These technologies are not a replacement for personnel performing inspections nor are they intended to replace visual and physical methods. Advanced technologies may be useful when visual and physical methods are not able to assess fully a bridge component or when their use enables an inspection to be done more efficiently without compromising the thoroughness and effectiveness of the inspection. The BIRM provides additional information.

Q313-2 Can unmanned aircraft systems (UAS) or drones, be used in a bridge inspection? (New 3/01/2023)

A313-2 UAS may be used by qualified Federal Aviation Authority (FAA) licensed personnel to supplement portions of a bridge inspection, but it cannot address all aspects of an inspection (i.e. live load response, auditory cues, sounding of members).  For example, UAS cannot currently perform physical (tactile) examination such as sounding or hammering on the surface of a bridge member. This type of examination is needed because it establishes the soundness of the material and if present, the dimensions of the defect for tracking deterioration over time and for determining strength or capacity when calculating a load rating. Use of UAS may also be subject to practical considerations such as lighting, the need for cleaning the portion inspected, and the potential for driver distraction.

When used effectively to supplement a bridge inspection, the use of UAS has the potential to provide efficiencies for some inspections such as limiting the amount of time access equipment is used and reducing the time working adjacent to live traffic. UAS may be used to supplement a bridge inspection when its capabilities are able to meet the requirements of a specific task in the bridge inspection. For example, a UAS may be an efficient tool for taking birds-eye view photography of a bridge site so that qualified personnel can observe and document changes in the channel since the last inspection. But even where UAS are used, if the photography shows concerning changes, the inspector must utilize physical (tactile) techniques to investigate further.

UAS operation is subject to all applicable FAA regulations. See https://www.faa.gov/uas for information.

Q313-3 What is an initial inspection? (New 3/01/2023)

A313-3 This term is defined in 23 CFR 650.305 “Initial inspection.”  The initial inspection is the entry point for the bridge in the NBI. The initial inspection is the first routine inspection and follows the same requirements as a routine inspection, see Section 4.2 of the AASHTO Manual for Bridge Evaluation (incorporated by reference, 23 CFR 650.317(a)) for more information.

Q313-4 What is meant by rehabilitation of a bridge as this prompts the need for an initial inspection? (New 3/01/2023)

A313-4 This term is defined in 23 CFR 650.305 “Rehabilitation.” Rehabilitation typically includes deck or superstructure replacement, structure widening, or major modification to substantial portions of the bridge. Performing maintenance, repairs, or preservation work does not prompt a need to perform an initial inspection.

Q313-5 How does the initial inspection requirement apply on an accelerated construction project? (New 3/01/2023)

A313-5 On projects with many phases or rapid progression through phases (e.g. nightly or weekend closures), it may not be feasible to complete an initial inspection every time a portion of a bridge opens to traffic. FHWA encourages owners to complete the initial inspection of bridges under construction as soon as practical, preferably before the bridge or portion of the bridge opens to traffic (23 CFR 650.313(b)). However, up to 3 months of construction work may occur and multiple phases might have elapsed before the initial inspection is required. See question Q303-5 “Does the NBIS apply to bridges partially open to traffic while under construction?” in the Applicability section for more information.

Q313-6 Does special equipment need to be used to perform a routine inspection? (New 3/01/2023)

A313-6 As stated in section 4.2 of the AASHTO Manual for Bridge Evaluation (incorporated by reference, 23 CFR 650.317(a)), special equipment, such as under-bridge inspection equipment, rigging, or staging, is necessary for routine inspection in circumstances where its use provides the only practical means of access necessary to identify the extent and severity of defects.

Q313-7 What are the objectives of a routine inspection? (New 3/01/2023)

A313-7 The objective of a routine inspection is it to observe and document the physical and functional condition of the elements of the bridge. The purpose is to identify any changes from the initial or previously recorded conditions and to ensure that the structure continues to satisfy present service conditions. These inspections are performed from the deck and ground or water level, or from permanent inspection structures. Access equipment, including ladders, bridge inspection cranes, rigging, and UAS, are utilized, as necessary, to view all areas of each bridge member in sufficient detail to identify the extent and severity of defects.

Q313-8 Is an underwater or NSTM inspection required on a rehabilitated bridge when the scope of rehabilitation work did not affect the underwater portions or the NSTMs on the bridge? (New 3/01/2023)

A313-8 No, a rehabilitated bridge only needs an underwater or NSTM inspection within 12 months if work was performed on portions of the bridge that are underwater (23 CFR 650.313(e)) or if the work was performed on a NSTM (23 CFR 650.313(f)). Any underwater portions or NSTMs that were not rehabilitated do not need an underwater or NSTM inspection within 12 months and can remain on their current underwater or NSTM inspection intervals, as applicable. See question Q313-10, for requirements in subsequent underwater and NSTM inspections.

Q313-9 For bridges which remain open to traffic while being rehabilitated, and the rehabilitation affects the underwater and/or NSTM portions of the bridge, does an underwater and/or NSTM inspection have to be performed within 12 months of completing the rehab work? (New 3/01/2023)

A313-9 Yes, for bridges with underwater portions or NSTMs that are being rehabilitated, those portions must receive an underwater or NSTM inspection within 12 months of rehabilitation work being completed (23 CFR 650 313(e) and (f)).

Q313-10 Once rehabilitation work is finished and the first underwater and NSTM inspection(s) is completed within 12 months or less, what needs to be inspected in subsequent underwater and NSTM inspections? (New 3/01/2023)

A313-10 Subsequent underwater and NSTM inspections must include all underwater portions (23 CFR 650.311(b)) or NSTMs on the bridge (23 CFR 650.311(c)) to ensure all elements that are the focus of these inspection types are regularly inspected at the same interval and timing on the bridge.

Q313-11 Can underwater imaging technology be used to supplement an underwater inspection? Can this technology supplant an underwater bridge inspection diver? (New 3/01/2023)

A313-11 Underwater imaging technology can supplement any underwater bridge inspection that is performed by an underwater bridge inspection diver(s). There may be situations when an underwater inspection cannot be performed safely using traditional diving methods. In these situations, underwater imaging technology may supplant an underwater bridge inspection diver(s) when there are documented procedures for using this technology on the bridge. The procedures must describe all requirements for performing underwater imaging on the bridge so that inspectors can appropriately prepare for, perform, and document a thorough underwater inspection using this technology (23 CFR 650.313(g)).

Q313-12 What is meant by a non-redundant steel tension member (NSTM) inspection? (Updated 3/01/2023)

A313-12 This term is defined in 23 CFR 650.305 “NSTM inspection.” A NSTM inspection must be at least a hands-on inspection of the NSTM or NSTM component (23 CFR 650.313(f)(2)).  The term “hands-on inspection” is also defined in 23 CFR 650.305. The intent of hands-on inspection is that the inspector is close enough to place their hands on the NSTM or NSTM component (tension area) being inspected.  The inspection may also include non-destructive evaluation or non-destructive testing methods.

Q313-13 Why is a hands-on inspection required for NSTMs? (New 3/01/2023)

A313-13 Bridges with NSTMs are at elevated risk of sudden collapse due to the inability of the system or member(s) to redistribute load and maintain stability in the event of full or partial fracture of the section. This, in turn, leads to a lower tolerance for cracking that can lead to fracture. Hands-on inspection mitigates this risk by identifying cracks in NSTMs at the early stages of growth so that they are addressed before propagating through, or fracturing, the section.

Q313-14 Do interior and exterior surfaces of NSTM box beams have to be inspected at arm’s length? (New 3/01/2023)

A313-14 Yes, surfaces of NSTMs must receive a hands-on inspection (23 CFR 650.313(f)(2)). Hands-on inspection is performed at arm’s length from a member’s surfaces to find fatigue cracks at the early stages of growth before they fracture the section. Fatigue cracks may initiate on any surface of a NSTM. Experience has shown that most fatigue cracks initiate near weld terminations of details, such as stiffeners which are often located on inside surfaces of box beams. Additionally, cracks initiate near material flaws or changes in member cross-section which are found on both inside and outside surfaces of box beams. As a result, interior surfaces where they are accessible and all exterior surfaces of NSTM box beams must receive a hands-on inspection to find fatigue cracks and other defects before serious problems develop. Finally, it is good practice to regularly check enclosed members for water intrusion so that problems are found early before serious corrosion defects and section loss develop.

There are NSTM box girders that do not have access hatches or are too small for inspectors to crawl through.  Borescopes, mirrors, and other remote inspection tools/devices should be used to access the interior if they can be inserted. There are also large NSTM box girders where the interior can be accessed, but additional equipment (e.g. ladder) is needed inside in order to perform hands-on inspection of the NSTM’s surfaces. Inspectors should carefully review the bridge’s NSTM inspection procedures to understand what access methods and equipment are needed to properly conduct the NSTM inspection. Often times, additional manpower and/or equipment are needed to safely access the interior of the structure which is often a confined space.

Q313-15 How do State transportation departments, Federal agencies or Tribal governments demonstrate that a bridge member has system or internal redundancy? (New 3/01/2023)

A313-15 FHWA published a memo outlining the criteria and process for State transportation departments, Federal agencies, and Tribal governments to follow if they choose to implement procedures to identify members with system or internal redundancy as described in 23 CFR 650.313(f)(1)(i). The memo can be obtained at: https://www.fhwa.dot.gov/bridge/pubs/MEMO-ATTACHMENT_Inspection-Interval-Implementation-FINAL_508v2.pdf

Q313-16 What is required in inspection procedures on bridges which require NSTM, underwater, in-depth, and complex feature inspections? (New 3/01/2023)

A313-16 Inspection procedures must include items described in Section 4.2 of the AASHTO Manual for Bridge Evaluation (incorporated by reference, 23 CFR 650.317(a)). Procedures for these inspection types should address these topics as applicable for the bridge:

  • Equipment needs
  • Personnel needs and qualifications
  • Access requirements
  • Scheduling considerations
  • Coordination with agencies and/or partners
  • Risk factors
  • Identify/describe those portions of the bridge to be inspected
  • Explain the inspection methods and techniques to be utilized
  • Description of the inspection interval
  • Documentation requirements
  • Reporting and follow-up processes

Each bridge that requires these inspection types must have written inspection procedures specific to that bridge that explain items unique to that bridge, so that inspectors can appropriately prepare for, perform, and document a thorough inspection (23 CFR 650.313(g)).

A State transportation department, Federal agency, or Tribal government may include general procedures in their procedures manual which address common aspects of these inspection types and are applicable to many bridges.  These general procedures can be referenced in bridge specific inspection procedures as described in the prior paragraph. However, general procedures alone do not meet the requirement of this subsection.

Q313-17 Do inspection procedures for a complex feature address the entire bridge? (New 3/01/2023)

A313-17 No, complex feature inspection procedures focus only on those parts of the bridge that warrant additional attention due to their inherent complexity, not the entire bridge.

Q313-18 Are inspection procedures required for special inspections? (New 3/01/2023)

A313-18 Yes, the purpose of a special inspection is to monitor a known or suspected deficiency, or to monitor special details or unusual characteristics of bridges that do not necessarily have defects. As a result, the scope of special inspections can vary widely between owners and bridges and the parameters for performing a special inspection must be defined by the owner and documented in special inspection procedures described in 23 CFR 650.313(h) and AASHTO, Manual for Bridge Evaluation (MBE) (incorporated by reference, 23 CFR 650.317(a)).

Procedures for special inspections are required so that inspectors can appropriately prepare for, perform, and document a thorough special inspection. Special inspection procedures should identify the area(s) to be inspected, methods to be used, and other pertinent information necessary to properly conduct the inspection.

Q313-19 For a bridge which requires a reduced interval inspection because of a localized deficiency, can a special inspection be performed on the member(s) instead of completing a routine or underwater inspection of the entire bridge? (New 3/01/2023)

A313-19 Yes, 23 CFR 650.311(a)(1)(ii) and 650.311(b)(1)(ii) allow a special inspection for monitoring localized deficiencies in lieu of performing a routine inspection or underwater inspection of the entire bridge when one or more condition ratings are coded three (3) or less due to localized deficiencies. The special inspection may only be utilized for the reduced inspection interval. A routine or underwater inspection of the entire bridge is still required for the regular interval (650.311(a)(1)(ii)(C) and (b)(1)(ii)(C).

Q313-20 What is the intent of a service inspection? (New 3/01/2023)

A313-20 This term is defined in 23 CFR 650.305 "Service Inspection." A service inspection determines if any major deficiencies or safety issues are present on a bridge. This inspection type can be performed by personnel with general knowledge of bridge maintenance or bridge inspection. It is intended to be less rigorous and costly as compared to a routine inspection. Only the inspection date and any follow up actions are required to be documented in the bridge file for this inspection type. The service inspection is only required when the routine inspection interval is greater than 48 months (23 CFR 650.313(i)). When this occurs, the service inspection interval is half of the routine inspection interval and is to be performed during the month midway between routine inspections (23 CFR 650.311(a)(3)).

Q313-21 Are there any bridge inspection types that can be performed without a Team Leader on site? (Updated 3/01/2023)

A313-21 Yes, the NBIS does not require a Team Leader for the damage and service inspection types.  Special inspections that do not meet the requirements of 23 CFR 650.313(h) also do not require a Team Leader. However, State transportation departments, Federal agencies, and Tribal governments are required to establish personnel qualifications for these inspection types and they may require a Team Leader and/or additional requirements (23 CFR 650.309(f)). It is important to have individuals with expertise in the special or damaged items being inspected.

Q313-22 When do bridges need to be re-rated for loads? (New 3/01/2023)

A313-22 There are many reasons a bridge would require re-rating for loads, such as but not limited to: a change in condition of a structural element; change in dead load; change in live load; or completion of construction, reconstruction, or rehabilitation (23 CFR 650.313(k)). The need to re-rate a bridge for loads is often in response to an inspection finding. However, there are other reasons a bridge may need to be re-rated for loads, such as new legal vehicles introduced or damage resulting from an unexpected event. The MBE and the BIRM provide additional information.

Q313-23 Are screening tools and other processes allowed to be used to process load permit requests that agencies routinely receive? (New 3/01/2023)

A313-23 Yes, screening tools and processes are acceptable methods of analyzing permit loads, provided they are founded upon actual modeling and analysis that envelope the hauling vehicle and load that is requesting a load permit.

Q313-24 Why do bridges which require a load posting have to be posted within 30 days or less? (New 3/01/2023)

A313-24 Load posting informs the travelling public of the maximum load that bridges can safely carry. For unrestricted legal loads, lack of load posting signs is a public safety issue, which some bridge owners consider to be a critical finding requiring immediate follow-up action. Due to the safety issue and other factors, owners must prioritize installation of load posting signs based upon the associated risks and need. In some situations, the urgency to implement a load posting is much less than 30 days. FHWA has established 30 days as the maximum time allowed to install or correct damaged, missing, or inaccurate load posting signs (23 CFR 650.313(l)(2)-(3)). This is consistent with the National Tunnel Inspection Standards.

Q313-25 What methods, other than posting, can be used to 'restrict' a bridge when it cannot carry permit or routine permit loading? (Posted from 6/21/05)

A313-25 When restricting permit or routine permit loads from crossing specific bridges, State transportation departments, Federal agencies, or Tribal governments may elect to issue restrictions to the permit holders to keep them from traveling specific routes with permit load capacity problems.

Q313-26 What does it mean to develop and document procedures for load posting a bridge? (New 3/01/2023)

A313-26 Document the process the bridge inspection organization uses to post a bridge. The process should describe the steps and timelines for posting a bridge. Procedures should identify the group(s) and position(s) that are responsible to complete the steps. There should be a process for escalating situations within the State transportation department, Federal agency, and Tribal government that do not meet timelines required in the process. Posting procedures should also address correcting damaged, missing, or inaccurate posting signs.

Q313-27 What does it mean to develop and document procedures for closing a bridge? (New 3/01/2023)

A313-27 Document general criteria for when a bridge must be closed, permanently or temporarily. All factors requiring bridge closure cannot be anticipated; therefore, criteria are expected to be general in nature and should be applicable to many bridges. Document the process the bridge inspection organization uses to close a bridge. The process should describe the steps and timelines for closing a bridge.  Procedures should identify the group(s) and position(s) that are responsible to complete the steps. There should be a process for escalating situations within the State transportation department, Federal agency, and Tribal government that do not meet timelines required in the process.

Q313-28 What information is required to be included in a bridge file? (New 3/01/2023)

A313-28 Section 2.2 of Chapter 2 of the AASHTO Manual for Bridge Evaluation (incorporated by reference, 23 CFR 650.317(a)) describes the required components of a bridge file. These components may exist in the bridge file electronically, on paper, or in locations outside the bridge file, as long as their location is appropriately referenced within the bridge file.

Other portions of Chapter 2 describe other excellent components that may be useful to an owner and could be contained in a bridge file. FHWA encourages maintaining these in the bridge files as well; however, those outside of Section 2.2 are not required as part of the NBIS.

Q313-29 How do the scour appraisal, scour evaluation, and the scour assessment processes work together? (New 3/01/2023)

A313-29 The scour appraisal is the overarching process that includes three methods for determining the worst case scour at a bridge; observed scour, scour evaluation, or scour assessment. These terms are defined in 23 CFR 650.305. The bridge owner must perform a scour appraisal for each bridge over water to determine if the bridge is scour critical (23 CFR 650.313(o)(1)). The scour appraisal for a bridge is based upon the least stable of observed scour, evaluated scour, or assessed scour.

Q313-30 Are Hydraulic Engineering Circulars (HECs) used for the scour appraisal determination? (New 3/01/2023)

A313-30 Yes. The scour appraisal procedure should be consistent with HEC 18 and 20 (23 CFR 650.313(o)(1)).  Additionally, scour appraisal includes scour evaluation and scour assessment processes. Scour evaluation should be consistent with HEC 18 and 20. Scour assessment should be consistent with HEC 20.

Q313-31 When is a scour plan of action (POA) required for a bridge? (New 3/01/2023)

A313-31 Any bridge that is determined to be scour critical through the scour appraisal process or has unknown foundations requires a scour POA (23 CFR 650.313(o)(2)). Scour POAs should be consistent with HEC 18 and 23 (23 CFR 650.313(o)(2)).

Q313-32 Can the same scour POA be used for more than one highway bridge? (Updated 3/01/2023)

A313-32 No, a scour POA must be developed for each scour critical bridge and for each bridge with an unknown foundation (23 CFR 650.313(o)(2)). However, some portions of scour POAs may be the same or very similar for some bridges. Examples of information in scour POAs that are unique for each bridge include: detailed information on the triggering event that initiates POA inspections, detailed instructions for decisions on closure, details to inspect, unique bridge inventory data, unique detour routing, and coordination with local public safety officials.

Q313-33 Does a scour POA need to describe installation of physical or hydraulic countermeasures or can it be based solely upon monitoring? (New 3/01/2023)

A313-33 For certain low risk bridges, a scour POA may be based solely on a monitoring program to manage risk associated with scour. As HEC 18 and 23 and other guidance documents explain, bridges with higher risk of scour-induced failure should have a scour POA that describes planned installation of physical or hydraulic countermeasures, or even replacement of the bridge, while also including a monitoring program that allows time to implement countermeasures or replace the bridge. It should be noted that implementing a POA based solely on monitoring does not remove the ‘scour critical’ status for that bridge.

Q313-34 Is a scour POA required for a bridge with designed and properly constructed scour countermeasures installed? (Updated 3/01/2023)

A313-34 A scour POA is not required for bridges whose foundations are protected by scour countermeasures that were properly designed and installed (in accordance with HEC-23) and are functioning. Countermeasures must be regularly inspected as part of routine and/or underwater inspections to ensure they perform as designed and scour problems do not reoccur (23 CFR 650.313(a)).

Q313-35 What is quality control and who performs it? (New 3/01/2023)

A313-35 This term is defined in 23 CFR 650.305 "Quality control." Someone knowledgeable in bridge inspection, such as the program manager or supervisor within the section shall review the report and inspection data for accuracy and completeness prior to finalizing the inspection (23 CFR 650.313(p)(2)). Quality control reviews also include checking calculations such as load ratings. Organizational structure can vary based on the owning entity performing or administering bridge inspections. If an inspection program is decentralized, the state program manager is still ultimately responsible for QC (23 CFR 650.307(f)), but the manner in which the program is carried out may differ according to each organization’s policy. The BIRM and the AASHTO MBE provides guidance for the implementation of appropriate quality control and quality assurance procedures.

Q313-36 What is quality assurance and who performs it? (New 3/01/2023)

A313-36 This term is defined in 23 CFR 650.305 "Quality assurance". Quality assurance is generally an independent review and is accomplished by the re-inspection of a sample of bridges by an independent inspection team and an independent check of calculations such as those in load ratings. QA reviews are to be performed by personnel other than the individual who completed the original inspection or calculations, such as, another inspection team, an independent team comprised of qualified personnel, or their agent (e.g., consultants) (23 CFR 650.313(p)(2)).  The BIRM and AASHTO MBE provides guidance for the implementation of appropriate quality control and quality assurance procedures.

Q313-37 What does it mean to “address” a Critical Finding? (New 3/01/2023)

A313-37 An owner has taken action to address public safety, such as closure, lane or load restriction, shoring, repair, or replacement of the bridge. Increased inspection intervals alone do not fully address a critical finding if the safety issue is not rectified.

Q313-38 What does it mean to “resolve” a Critical Finding? (New 3/01/2023)

A313-38 A permanent solution has been implemented to completely mitigate the deficiencies and protect public safety. This could involve permanent load restriction, repair, closure, or replacement of the bridge.

Q313-39 What type of notification is required for a critical finding on the NHS which results in a full or partial closure or an NSTM rated in serious or worse condition to FHWA? (New 3/01/2023)

A313-39 State transportation departments, Federal agencies, and Tribal governments must notify FHWA within 24 hours of discovery (23 CFR 650.313(q)(2)(i)). The notification does not require a written report. Notification can be quickly accomplished through a telephone conversation, email message, or other means. The method of notification should be agreed upon between the local FHWA division/FLH office and the State, Federal agency, or Tribal government and documented in the Critical Findings procedure.

Q313-40 What needs to be reported on critical findings to FHWA each month? (New 3/01/2023)

A313-40 State transportation departments, Federal agencies, and Tribal governments must provide at least monthly, a written status report for each critical finding until it is resolved (23 CFR 650.313(q)(2)(ii)). Each report must describe actions taken, underway, or planned to resolve the critical finding. The minimum information that is required in a status report is listed in 23 CFR 650.313(q)(2)(ii)(A)-(H). The minimum reporting requirement is once a month, unless there is a need for more frequent follow-up on a specific critical finding (23 CFR 650.313(q)(2)(ii)). The reporting process should be documented in the State transportation department, Federal agency, or Tribal government’s Critical Findings procedure.

Back to top

Updated: 03/14/2023
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000