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Highway Bridges: Federal Highway Administration Could Better Assist States with Information on Corrosion Practices

GAO-21-104249 Published: Sep 28, 2021. Publicly Released: Sep 28, 2021.
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Fast Facts

People rely on the 146,000 bridges in the National Highway System. Most of the bridges are made of materials that are susceptible to corrosion—a leading cause of bridge failure. The percentage of bridges in "good" condition has declined since 2016.

The Federal Highway Administration researches factors that affect bridge condition (e.g., corrosion), and provides technical assistance to states. But state officials we talked to said they need more information about effective corrosion mitigation practices for specific environments and circumstances.

We recommended providing this information as part of FHWA's ongoing bridge preservation efforts.

Corrosion on a National Highway System bridge in Wyoming

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What GAO Found

According to the Federal Highway Administration's (FHWA) database of information on bridges' condition, the percentage of deck area, a measure that accounts for the size of a bridge, for National Highway System (NHS) bridges in poor condition has decreased since 2012. However, since 2016, the percentage of deck area for NHS bridges in good condition has also decreased, while the percentage of deck area for bridges in fair condition has increased. Although these data do not indicate the extent to which corrosion affects bridges' condition, studies GAO reviewed and stakeholders GAO spoke with—including FHWA, five selected states, and six associations—indicate a significant relationship between corrosion and bridge condition. (See figure.)

Examples of Bridge Corrosion

Examples of Bridge Corrosion

State practices to prevent and manage corrosion vary based on environmental factors and bridge condition. For example, states exposed to sea water and deicing chemicals may clean bridges to remove materials that could accelerate corrosion. Four of the five selected states prioritized rehabilitating and replacing poor condition bridges, while the fifth state said it took steps to address corrosion to preserve and maintain bridges in good and fair condition. States are transitioning to asset management practices that emphasize bridge preservation strategies. However, officials from the selected states said limited information about specific corrosion practices' effectiveness is a challenge to implementing asset management practices. For example, officials from some selected states said they use sealant on bridge decks to prevent corrosion while officials from another said they do not because they do not know how effective it is.

FHWA, within the Department of Transportation, helps states address corrosion through research and technical assistance. However, FHWA efforts have generally focused on overall bridge condition and may not meet states' needs to determine the circumstances in which to use specific practices. For example, FHWA's Bridge Preservation Guide identifies practices that can be part of a bridge preservation approach but does not indicate under what circumstances they are most effective. Although FHWA does not endorse specific practices, officials recognize their role in helping states make well-informed decisions regarding bridge corrosion. As states continue transitioning to an asset management approach, providing information about the circumstances under which different corrosion practices are most effective could help states make best use of their resources.

Why GAO Did This Study

In 2021, U.S. bridges, including those on the NHS, were estimated to need billions of dollars in repairs, including efforts to mitigate the effects of corrosion. House Report 116-106 included a provision for GAO to review the status of states' bridge corrosion-control planning. This report examines: (1) trends in the condition of bridges on the NHS and what is known about how corrosion affects bridge condition, (2) practices states use to address corrosion on NHS bridges and how selected states prioritize efforts to address corrosion, and (3) how FHWA assists states in addressing bridge corrosion.

GAO reviewed applicable statutes, regulations, guidance, and studies related to corrosion prevention and management, and analyzed data on NHS bridges. GAO selected five states—Florida, Illinois, Kansas, Rhode Island, and Wyoming—based on factors, such as the percentage of bridge deck area in good and poor condition and geographic diversity. Finally, GAO interviewed FHWA, state transportation, and various association officials and assessed FHWA's actions against internal controls for using quality information.

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GAO is recommending that FHWA's ongoing bridge preservation efforts include activities that focus on addressing the challenges states face with determining the circumstances under which specific corrosion practices and materials are most effective. DOT agreed with our recommendation and provided technical comments, which we incorporated as appropriate.

Recommendations for Executive Action

Agency Affected Recommendation Status
Federal Highway Administration The Administrator of FHWA should ensure that FHWA's ongoing bridge preservation efforts include activities, such as peer exchanges and case studies that focus on addressing the challenges states face with determining the circumstances under which specific corrosion practices and materials are most effective. (Recommendation 1)
FHWA concurred with the recommendation and indicated in its 180-day letter from January 2022, that it plans to conduct two regional peer exchanges related to corrosion, one for Midwest and Northeast states that experience frequent freeze-thaw cycles and use de-icing chemicals on their highway bridges and one for Southeast states that experience freeze-thaw cycles or have highway bridges exposed to saltwater. In February 2023, FHWA reported that it had conducted the first peer exchange with 7 Midwestern states from November 29, 2022 to December 1, 2022 in Minneapolis, MN. These states have environments with arid conditions or that experience freeze/thaw cycles and use de-icing chemicals on their highway bridges. FHWA plans to hold the second peer exchange with 9 states from south-east, north-east and west regions in February and March 2023. We will continue to monitor FHWA's efforts to implement the recommendation.

Full Report

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Asset managementBridge deckBridgesConservationCorrosion preventionInventoryNational highway systemPublic roads or highwaysConstructionTechnical assistance