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Bridges & Structures

Subject: ACTION: Compliance with the National Bridge Inspection Standards - Background/Plan of Action for Scour Critical Bridges/Scour Focus States/Item 113 Coding Issues/Unknown Foundations/Tidal Bridges Date: March 23, 2006
From: /s/ Original signed by:
M. Myint Lwin, P.E., S.E
Director, Office of Bridge Technology
Reply to Attn. of: HIBT-20
To: Associate Administrator for RD&T
Directors of Field Services
Resource Center Director and Operations Managers
Division Administrators
Federal Lands Highway Division Engineers

The purpose of this memorandum is to provide clarification regarding State departments of transportation (DOTs) identified as "Scour Focus States" in the Federal Highway Administration's (FHWA) Strategic Implementation Plan. Also, we will be discussing issues pertaining to the national bridge scour evaluation program, specifically with regards to the coding of bridges for National Bridge Inventory (NBI) Item 113, bridges with unknown foundations, tidal bridges, and our request to receive a status report on the progress made by DOTs towards developing a plan of action (POA) for bridges identified as scour critical.


Since the initiation of the national bridge scour evaluation program in 1988, the FHWA has been tracking the progress made by DOTs towards completing scour screening and evaluation of approximately 484,500 bridges over waterways. We identified target dates for completing these phases of the program, March 1991 and January 1997, respectively. Also, we have reported that DOTs have made substantial progress towards completing these phases of the scour program - scour screening is 99.9 percent complete, and scour evaluations are over 93 percent complete. We have been monitoring the progress made by DOTs towards these phases of the national bridge scour evaluation program for the last 18 years, and would like to commend DOTs for all their efforts regarding their scour evaluations.

Plan of Action (POA) for Scour Critical Bridges:

While continuing to encourage DOTs to complete their scour screening and evaluations, we formally moved into the next phase of the scour program as documented in Mr. King W. Gee's July 24, 2003, memorandum, which encourages bridge owners to develop and implement a POA for each bridge coded scour critical as defined by NBI Item 113 of the FHWA's Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges. Please be advised that the updated National Bridge Inspection Standards (NBIS) regulation, 23 CFR 650.313.e.3, requires DOTs to prepare a POA to monitor known and potential deficiencies and to address critical findings for bridges identified as scour critical. We previously communicated to you by memorandum dated March 29, 2005, that the target date to comply with the updated regulation was January 13, 2006. The DOTs should have developed an implementation plan that defines their actions to reach full compliance with this requirement of the updated NBIS regulation as discussed in our Web site titled "Questions and Answers on the National Bridge Inspection Standards 23 CFR 650 subpart C," which can be found at https://www.fhwa.dot.gov/bridge/nbis/nbisqa.htm. Actions that should be presented in the plan include information pertaining to resources needed and a schedule for developing a POA for each bridge identified as scour critical. We request that you report to us on the status of the POA provisions of your corresponding DOT plan by May 5, 2006. In addition, we request a status report every April 15 and November 15 on your corresponding DOT progress towards developing POAs. This status report should continue until all bridges identified as scour critical bridges within your DOT have a POA. Please submit your initial status report by November 15, 2006.

We consider the completion of scour screening and evaluations of bridges over waterways and the development and implementation of POAs for scour critical bridges to be a high priority in the FHWA bridge program as we in FHWA, in partnership with DOTs, strive to ensure safety for the users of public surface transportation.

Scour Focus States:

A performance measure on reported bridges over water vulnerable to scour was implemented in Outcome 3, Highway Structures Provide a High Level of Safety and Service Under all Conditions, of the FHWA's Bridge Program Strategic Plan and adopted in the FHWA Strategic Implementation Plan. This performance measure represents the population of bridges, as reported by DOTs in the national bridge scour evaluation program, that: have not been screened for scour (approximately 150 bridges); have not been evaluated for scour (approximately 26,000); are scour critical (approximately 26,000); have been identified as tidal (approximately 900), and that have been identified as having unknown foundations (approximately 83,000). We established a goal of reducing this population of bridges (the sum of all of the above), which represents about 27.6 percent of all bridges over waterways (approximately 484,500) in calendar year (CY) 2004 to 10 percent by the end of CY 2010. We identified 10 potential DOTs in Spring 2005 that have demonstrated a steady progress towards conducting scour evaluations and/or making progress towards developing and implementing POAs to assist us in reaching the goal of reducing the percent of scour vulnerable bridges identified in our performance objective to 23.5 percent by the end of CY 2006. Ultimately, seven DOTs were identified as "Scour Focus States": CA, FL, MD, NY, OK, PR, and TX.

While we have identified these "Scour Focus States" to help us in reaching this short-term goal for CY 2006, we request that you continue encouraging your corresponding DOT management official to work towards the scour evaluation of the remaining bridges within their program, and to prepare POAs for their scour critical bridges as required by the updated NBIS regulation. Your assistance and that from your corresponding DOT will help us reach our long-term goal of reducing scour vulnerable bridges to 10 percent by the end of CY 2010.

Item 113 Coding Issues:

We would like to direct your attention to a couple of issues pertaining to the NBI Item 113 coding. While querying the NBI database for relatively new bridges (built within the last

10 years), we have identified that some of these bridges have been coded either "6" or "U" for the NBI's Item 113. This population of bridges should have undergone a scour analysis during design and their foundations should have been designed to be stable for the estimated scour depth. Also, DOTs should have "as-built" plans or other documentation available for its relatively new bridges with information about the type, depth and material so these bridges should not be coded "U." We suggest that your staff meet with his/her corresponding DOT management official to verify that new bridges over waterways are being designed for scour and that documentation regarding the bridge foundation is available (i.e., as-built plans) to ensure that new bridges are safe and will receive the appropriate code for Item 113.

Another issue pertains to Interstate bridges. We queried the NBI database for these bridges and have found that there are still Interstate bridges coded "6" for the NBI's Item 113. This leads us to believe that there are Interstate bridges that have not been evaluated for scour. We are including a copy of this query for the divisions with Interstate bridges coded "6" and request that they review this issue with their DOT management officials and encourage them to expeditiously evaluate these bridges and, if necessary, make the bridge safe for scour.

Also, we request that your staff check with his/her DOT management representatives (both State and local) to see if they have implemented the revisions made to the NBI's

Items 60 and 113, which we transmitted to our field offices by memorandum dated April 27, 2001, to ensure that bridges over waterways are coded according to the latest changes and guidance provided for these items.

Unknown Foundations:

We recognize that there is a need to develop better guidance to address bridges in the unknown foundations category of the national bridge scour evaluation program. We are taking action towards enhancing our current guidance on this important aspect of the program. For example, we are currently sponsoring a synthesis on unknown foundations, which should give us a better perspective of technologies, methods and managerial practices being used in this area. The synthesis report is expected by September 2006. Also, FHWA sponsored an unknown foundations summit in Lakewood, Colorado from November 15-16, 2005. This summit served to share knowledge on current technologies available through the industry and management strategies that have been used by DOTs to deal with bridges with unknown foundations.

We distributed the proceedings of this summit to our field offices on a CD-ROM by memorandum dated January 19, 2006. During a follow-up meeting to the summit, four teams were established to work on developing policy and guidance, and training and research needs on the subject of unknown foundations. We will be sharing with you the outcomes from these teams as soon as we complete the evaluation of their recommendations.

Also, we have previously communicated to you that unknown foundation bridges have been exempted from being evaluated for scour. While this still is our position (except for Interstate bridges), we would like to recommend, while we wait for the results of the synthesis and recommendations from the unknown foundation teams, that you encourage your corresponding DOT management officials to consider monitoring these bridges during and after a flood event as they may deem it necessary.

Tidal Bridges:

As previously mentioned, DOTs have reported over 900 bridges over tidally influenced waterways that have not been evaluated for scour. Please remind your corresponding DOT management official that these bridges are no longer exempted from being evaluated for scour.

Regarding updated guidance for tidally influenced bridges, we would like to inform you that we are finalizing interim guidance for design storm frequency and freeboard for the analysis and design of coastal bridges. We will be disseminating this guidance to our field offices as soon as its peer review is completed. Finally, we want to inform you that we are currently updating the FHWA publication Hydraulic Engineering Circular 25, "Tidal Hydrology, Hydraulics and Scour at Bridges" to expand and clarify guidance pertaining to procedures for estimating hydrologic and hydraulics parameters, among others, for estimating scour at bridges over tidally influenced waterways. The update is scheduled to be complete in Fall 2007.

Should you have any questions please do not hesitate to contact Mr. Jorge E. Pagán-Ortiz, Principal Bridge Engineer - Hydraulics and Leader of the FHWA National Hydraulics Team at (202) 366-4604.

Updated: 06/27/2017
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