Highway Bridges: Federal Highway Administration Could Better Assist States with Information on Corrosion Practices
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
Highlights
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
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.
Recommendations
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) | In 2021, U.S. bridges, including those on the National Highway System were estimated to need billions of dollars in repairs, including efforts to mitigate the effects of corrosion. The role corrosion plays in the deterioration of bridges is of particular concern, as about one-third of all bridges in the U.S. are made of steel, and other bridges may have steel components that are susceptible to corrosion. GAO selected five states-Florida, Illinois, Kansas, Rhode Island, and Wyoming-based on factors, such as bridge condition and geographic diversity. In 2021, GAO reported that state practices to prevent and manage corrosion vary based on environmental factors and bridge condition. 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 five selected states said limited information about specific corrosion practices' effectiveness is a challenge to implementing such 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. States reported that they need more information on the circumstances in which to use various practices to address corrosion on specific types of bridges in specific environments. GAO found that while FHWA helps states address corrosion through research and technical assistance, FHWA efforts have generally focused on overall bridge condition and may not have met states' needs to determine the circumstances in which to use specific practices. For example, FHWA's Bridge Preservation Guide identified practices that can be part of a bridge preservation approach but did not indicate under what circumstances they are most effective. FHWA officials said they can use activities, such as peer exchanges between states and case studies of state practices to share information about specific approaches to corrosion. Conducting these activities more regularly and with a specific focus on the challenges states face with regard to corrosion practices may be a way for FWHA to better assist states. Therefore, GAO recommended FHWA should ensure that its 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. In December 2023, GAO confirmed that FHWA conducted two regional peer exchanges that focused on state practices and materials used to mitigate bridge corrosion. In December 2022, FHWA held the first peer exchange in Minneapolis, MN for the Midwest States which have environments with arid conditions or that experience frequent freeze/thaw cycles and use de-icing chemicals on their highway bridges. In March 2023, FHWA held the second peer exchange in Orlando, FL for the Northeast, Southeast, and West States which have environments that experience freeze/thaw cycles or have highway bridges exposed to a saltwater environment. Through the peer exchanges that FHWA facilitated, state DOTs were able to share information about actions their states have taken to slowdown, reduce, and prevent corrosion from occurring to their existing bridges. State DOTs also shared the policy changes states have made to their design standards, details, and material specifications to eliminate the root causes of corrosion. In August 2023, FHWA also issued a report documenting the information presented in the peer exchanges. By holding these peer exchanges and publishing the findings, FHWA is providing the states better information about which corrosion practices are most effective for preserving their bridges.
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