Addressing extreme weather in transportation asset management plans: a US perspective

Within the past two decades, transportation agencies throughout the US have suffered increased loss due to extreme weather and climate change–related events, hereafter referred to as ‘extreme weather events’. In 2024 alone, the US reported 27 separate billion-dollar weather and climate events, incurring an annual cost of $182.7 billion (NOAA and NCEI, 2025). The damage caused by extreme weather events, such as flooding and drought, impacts the lives and livelihoods of the affected communities, which are often disproportionally disadvantaged populations (GCA, 2019). These events also affect the long-term function (e.g. increased travel costs due to disruption) (Tirasirichai and Enke, 2007) and performance (e.g. increased scour and erosion damage) (U.S. DOT, 2014; Padgett et al., 2012, 2008) of the transportation networks these communities rely on.

Due to the threat of extreme weather events, the US Department of Transportation (DOT) has made it a strategic objective to address extreme weather by improving infrastructure resilience (U.S. DOT, 2022). In this context, resilience is defined as ‘the ability to anticipate, prepare for, and adapt to changing conditions and withstand, respond to, and recover rapidly from disruptions’ (FHWA, 2014). For some US transportation agencies, infrastructure resilience is also considered in terms of mitigating risk or reducing vulnerability, which can lead to increased resilience (Flannery et al., 2018). Risk can be defined as ‘the potential for adverse effects from the occurrence of a particular hazardous event, which is derived from the combination of physical hazards, the exposure, and vulnerabilities’ (National Academy of Sciences, 2012), whereas vulnerability is the susceptibility to failure based on factors such as the condition and age of the asset being considered (Flannery et al., 2018). Because of the relationship between these terms, resilience, risk, and vulnerability are often used interchangeably by transportation agencies, especially US DOTs (Pena et al., 2023a). This paper defines resilience in the broadest sense and considers all resilience, risk, and vulnerability practices when discussing resilience despite their distinct definitions.

The shift within the US towards resilience-thinking was codified with the passage of the 2021 Bipartisan Infrastructure Law (BIL). BIL provides federal regulation and funding that incentivises transportation agencies, like state DOTs, to assess and document resilience practices within their agencies. Specifically, BIL has led to the development of the Promoting Resilient Operations for Transformative, Efficient, and Cost-Saving Transportation (PROTECT) programme and changes to transportation asset management (TAM) regulations. PROTECT is a federal cost-sharing programme in which agencies that develop a Resilience Improvement Plan (RIP) are eligible for additional funding for resilience activities. While RIP development remains flexible, agencies are recommended to take a systematic, risk-based approach to resilience planning and investments (FHWA, 2022). BIL also requires state DOTs to consider and document resilience practices within federally mandated transportation asset management plans (TAMPs). These risk-based plans require states to report on inventory and condition for National Highway System pavements and bridges, including performance measures and goals, financial information, lifecycle cost and risk management practices, projected performance gaps, investment strategies, and, following BIL, practices used to address resilience and extreme weather (Kalla, 2022).

In 2022–2023, state DOTs published updated TAMPs in accordance with BIL requirements. These updated TAMPs provide an opportunity for DOTs to learn from and leverage resilience practices their counterparts have adopted, especially as many states are developing RIPs. Therefore, the aim of this paper is to conduct a comprehensive review of the resilience practices discussed in state TAMPs. While similar reviews have been conducted (Pena et al., 2023a; Pena et al., 2023b; Liu and McNeil, 2020), previous efforts did not focus on the most recent iteration of state TAMPs. As such, this paper will provide an up-to-date synthesis of resilience practices across regions as documented in state TAMPs. The objectives of this paper are to identify: (1) commonly used resilience practices and (2) existing gaps in resilience planning at the state level. This paper will serve as a resource for agencies who are developing or looking to improve their RIPs or resilience practices generally.

The paper is organised into four sections. ‘Review methodology’ describes the approach used to assess state TAMP resilience practices. ‘Review findings’ summarises the types of events discussed in the TAMPs as well as key resilience practices identified during the review. ‘Resilience planning gap analysis’ identifies resilience planning gaps, based on the TAMPs reviewed, when compared with resilience best practices. Conclusions and future direction are provided in ‘Conclusions’.

To better understand how state DOTs are incorporating resilience into transportation planning, a meta-analysis of state TAMPs, like the one by Liu and McNeil (2020), was conducted. Key steps (Figure 1) included: (1) general review and summary of TAMPs, (2) identification of common resilience themes and activities, and (3) a gap analysis.

Forty-five publicly available and Federal Highway Administration (FHWA)–certified TAMPs were reviewed (Figure 2); abbreviations for states discussed are provided in  Appendix. The review of each TAMP centred on understanding specific practices states use to address ‘extreme weather events and resilience’. Due to the size of the TAMPs, the review was limited to sections containing the key words ‘resilien’, (i.e. capturing resilience, resiliency, and resilient) ‘extreme weather’, and ‘climate’ as each reflect the language used in the BIL. The TAMP sections on risk management and life cycle planning were also reviewed in their entirety as FHWA recommended states ‘explain the processes used to develop the extreme weather and resilience’ in these sections specifically (Kalla, 2022).

After an initial review, resilience practices discussed in the TAMPs were assigned to one of six categories: leadership and agency structure, capacity and competency, collaboration and communication, resource requirements, risk and resilience assessment, and business processes. These six categories correspond to the key building blocks (Table 1) for effective incorporation of resilience into transportation planning identified in National Cooperative Highway Research Program (NCHRP) Report 1052 (Pena et al., 2023b). In the report, Pena et al. (2023b) conduct a comprehensive review of best practices from case studies and define key building blocks, a roadmap, and proposed action items for agencies to incorporate resilience into transportation planning. Based on the description of each resilience category provided in the NCHRP report, subcategories or general practice themes for each resilience category were identified to help further categorise resilience activities within the TAMPs (see italicised text in Table 1).

All distinct resilience activities being utilised by states currently (i.e. rather than proposed or aspirational activities) identified within the TAMPs were documented. Activities were categorised into the resilience categories and subcategories described above based on their alignment with the descriptions provided in the NCHRP report. It is important to note that two subcategories – understanding asset RnR and standardising the integration of resilience into business processes – were redefined to be more specific, given the number of TAMP resilience activities that aligned with each. The redefined subcategories correspond to the bold text in Table 1. Another important caveat to note is that while the resilience activities described in more detail in the next section are aligned with the descriptions provided for resilience categories, the resource requirements focus on the collection and delivery of reliable data and acquisition of appropriate information and technology is instead covered in the discussion of business processes. This is because the resilience activities within the TAMPs related to the use of data and technology were discussed within the context of integrating resilience into existing business practices.

The final step in conducting the meta-analysis was to compare the identified resilience activities adopted by state DOTs with best practices. The 27 action items for improving resilience transportation planning identified by Pena et al. (2023b), each of which corresponds to one or more resilience category, were used as a benchmark for which TAMP resilience activities could be compared. Each of the action items was assigned to one or more resilience activity that fell within the resilience category defined for that action item. For each action item, the number of TAMPs that discussed at least one of the corresponding resilience activities was assessed and used to identify areas that state DOTs should collectively spend more time and funding on.

This meta-analysis exclusively focused on practices to address extreme weather and climate change documented within the TAMPs; therefore, the key activities and gaps identified as part of this review may not be exhaustive.

The TAMPs reviewed provide broad representation of geographical regions, system sizes, and extreme weather experienced throughout the US. In total, the TAMPs discussed practices to address 12 event categories as depicted in Table 2. While some of the events described, such as earthquakes and tsunamis, are not related to climate change, these events were included in this assessment as they were discussed in sections focused on resilience within the TAMPs. Of these, flooding, winter weather, earthquakes, landslides, and extreme temperatures (e.g. extreme heat and extreme cold) were the most common.

In the following sections, specific resilience activities addressing these event types are summarised. As mentioned in ‘Review Methodology’, findings are categorised into the six resilience categories. Figure 3 provides an overall summary of the number of resilience categories addressed by each state agency.

The first resilience category assessed was leadership and agency structure. Within the reviewed TAMPs, resilience activities aligned with this category focused on establishing a vision and strategy for resilience. Table 3 and Figure 4 summarise the leadership and agency structure resilience activities described and the number of TAMPs in which these activities were discussed.

The most employed resilience activity within this subcategory (40% of TAMPs reviewed) is the development of a committee or governing body to oversee and implement resilience-related activities. For DOTs, this type of governing body exists within the TAM governance framework (District Department of Transportation, 2022), as an independent, intra-agency committee (Virginia Department of Transportation, 2021; Texas Department of Transportation, 2022; Pennsylvania Department of Transportation, 2022; Iowa Department of Transportation, 2023; Washington State Department of Transportation, 2022; New Jersey Department of Transportation, 2022; Colorado Department of Transportation, 2022; Connecticut Department of Transportation, 2022), as an interagency committee (South Carolina Department of Transportation, 2022; New Mexico DOT, 2022; New Jersey Department of Transportation, 2022; Massachusetts Department of Transportation, 2023; Louisiana Department of Transportation and Development, 2022; Georgia Department of Transportation, 2022; Florida Department of Transportation, 2022; Minnesota DOT, 2022), and/or as a standalone office/division (Oregon Department of Transportation, 2022; Delaware Department of Transportation, 2022; South Carolina Department of Transportation, 2022; Florida Department of Transportation, 2022). While the location and function of these committees vary, these groups are an essential part of identifying system risks to extreme weather and ensuring that resources are available for resilience-related activities. In some states, these groups have furthered the development of resilience practices beyond the direct scope of state-maintained assets. States like Texas and Florida, for example, have formed resilience coalitions that include representatives at the metropolitan planning organisation and regional levels (Texas Department of Transportation, 2022; Florida Department of Transportation, 2022). Cross-agency governing bodies and, in the case of Florida, a Chief Resiliency Officer are enabling the development of action plans and policies.

State TAMPs also describe establishing policies (22% of reviewed TAMPs) to ensure resilience is being considered at the agency level. This approach is useful in creating momentum for asset-level resilience implementation (Colorado Department of Transportation, 2022; Connecticut Department of Transportation, 2022; Florida Department of Transportation, 2022; Michigan Department of Transportation, 2022; New Jersey Department of Transportation, 2022; Hawaii Department of Transportation, 2022; California Department of Transportation, 2022; North Carolina Department of Transportation, 2022; South Carolina Department of Transportation, 2022; New Mexico Department of Transportation, 2022). In some instances, these policies and directives have led to the development of governance bodies (South Carolina Department of Transportation, 2022; New Mexico Department of Transportation, 2022; Colorado Department of Transportation, 2022), while in other cases it has mandated the incorporation resilience in project planning, design, and maintenance (North Carolina Department of Transportation, 2022; New Jersey Department of Transportation, 2022; Hawaii Department of Transportation, 2022; Florida Department of Transportation, 2022). When states already have established policies, states have a more compelling business case as to why different planning and design choices should be made and funded. States also describe (22% of reviewed TAMPs) strategic objectives focused on improving resilience; this includes both TAM-focused resilience goals (Colorado Department of Transportation, 2022; Florida Department of Transportation, 2022; Illinois Department of Transportation, 2023; Massachusetts Department of Transportation, 2023; New Jersey Department of Transportation, 2022; Puerto Rico Highways and Transportation Authority, 2022; Rhode Island Department of Transportation, 2022) as well as agency or state level commitments (California Department of Transportation, 2022; New Mexico Department of Transportation, 2022; Washington State Department of Transportation, 2022). Most states have not formally defined resilience in their TAMPs (11% of reviewed TAMPs); states that have are typically adopting definitions similar to those established by national transportation organisations (Connecticut Department of Transportation, 2022; Florida Department of Transportation, 2022; Louisiana Department of Transportation and Development, 2022; Michigan Department of Transportation, 2022; Colorado Department of Transportation, 2022).

Very few states discussed resilience activities that aligned with the second resilience category reviewed – capacity and competency. Those states that did consider the role of capacity and competency described the need for training on resilience policies, procedures, and tools (Georgia Department of Transportation, 2022; Idaho Transportation Department, 2022; New Mexico Department of Transportation, 2022; Vermont Agency of Transportation, 2022; Minnesota Department of Transportation, 2022; California Department of Transportation, 2022; Nevada DOT, 2022) or knowledge management (Tennessee Department of Transportation, 2023). However, each of these TAMPs states that these activities were either aspirational or were to be developed following the completion of an agency project. Because there are no existing resilience practices related to capacity and competency discussed in the reviewed TAMPs, no specific practices are quantified.

Collaboration and communication on resilience efforts, the third resilience category assessed, is implied in all TAMPs reviewed. As described previously, many states have formed governing bodies, including those with external stakeholders, for the purposes of guiding agency resilience efforts. State TAMPs also describe the creation of resilience plans or the prioritisation of resilience in existing transportation plans, which implicitly require collaboration and communication. As these resilience efforts overlap with activities ascribed to other resilience categories reviewed, these practices are quantified and described more fully in the sections on leadership and agency structure and business processes.

The fourth resilience category assessed was resource requirements. Resilience activities associated with this category focused on funding. Table 4 and Figure 5 summarise which states discussed the allocation of funding for resilience, while the section to follow provides additional discussion on the specific methods of implementation.

Currently, very few states (16% of TAMPs reviewed) are addressing resilience through investment strategies. Of the states that have, approaches vary, with some targeting specific state or federal commitments earmarked specifically to address asset resilience (e.g. investing $100 million over 10 years to improve stormwater systems (Rhode Island Department of Transportation, 2022)). Other states described future programming that includes a resilience consideration that is not focused solely on building resilience (e.g. Oregon’s Fix-It programme (Oregon Department of Transportation, 2022)) or designating a percentage of projects to be resilience-focused (Ohio Department of Transportation, 2022).

The fifth resilience category assessed was RnR assessments. As TAMPs are risk-based plans, most of the resilience efforts discussed in the state TAMPs fell within this category. Key subcategories described in the TAMPs that aligned with RnR assessments include risk registers, risk assessments, and scenario planning. Table 5 and Figure 6 summarise the resilience activities falling within each subcategory and the number of states in which these activities were discussed.

A risk register is a commonly used element, often presented as a table listing key agency risks, a plan to address these risks, and the risk owner (FHWA, 2017). While not explicitly a resilience practice, states are able to define the most important extreme weather threats to the transportation network and describe potential mitigation actions the agency is currently taking or plans to take to mitigate the risk, which may include improving asset resilience. All reviewed TAMPs use a risk register, with the majority identifying extreme weather as a key risk to the agency’s pavements and bridges.

Most state DOTs utilise methodologies (60% of TAMPs reviewed) and tools (44% of TAMPs reviewed) to perform risk assessments, employing detailed data-driven approaches to assess risk that aligns with the development of RIPs. State TAMPs describe using internal risk scoring to evaluate asset vulnerability and consequential impacts of extreme weather events. However, how risk and/or resilience is defined within the context of resilience assessments varies. Definitions included the product threat, consequence, and vulnerability (Colorado Department of Transportation, 2022; Wisconsin Department of Transportation, 2023); criticality, exposure, and sensitivity (Illinois Department of Transportation, 2023); frequently flooded roadways and criticality (Delaware Department of Transportation, 2022); robustness, redundancy, and criticality (Iowa Department of Transportation, 2023); and exposure, sensitivity, and adaptive capacity (Ohio Department of Transportation, 2022). Similarly, analysis approaches vary, with some states using publicly available tools (e.g. Federal Emergency Management Agency Risk Assessment, Vulnerability Assessment Scoring Tool, etc.) (Alaska Department of Transportation, 2022; Ohio Department of Transportation, 2022), while others developed methodologies internally that target threats of specific concern to the agency. The calculation of risk and resilience includes quantitative risk indices as well as more qualitative descriptions of risk found in the Extreme Weather Vulnerability Assessments as part of FHWA Climate Resilience Pilots. Quantitative risk indices often rely on external data sources, such as future projections for climatic conditions and sea level rise (Florida Department of Transportation, 2022; Wisconsin Department of Transportation, 2023; Pennsylvania Department of Transportation, 2022; Texas Department of Transportation, 2022; Connecticut Department of Transportation, 2022). In some cases, the final risk or resilience index developed is stored and integrated into the agency’s asset management system for future decision making (California Department of Transportation, 2022; Illinois Department of Transportation, 2023).

Some states (20% of TAMPs reviewed) defined critical assets as part of their RnR assessments, where criticality is defined as the importance of the asset to the overall function of the network. However, how states measure criticality varies depending on available data and agency objectives. Criticality metrics consider asset attributes such as function (e.g. number of lanes, annual average daily traffic, % truck, and geometrics) (Arizona Department of Transportation, 2021), classification (e.g. route type and significance) (Arizona Department of Transportation, 2021; Delaware Department of Transportation, 2022; Hawaii Department of Transportation, 2022; Iowa Department of Transportation, 2023), economic value (Vermont Agency of Transportation, 2022), condition (Delaware Department of Transportation, 2022), social value (Delaware Department of Transportation, 2022; Hawaii Department of Transportation, 2022; Iowa Department of Transportation, 2023; Vermont Agency of Transportation, 2022), redundancy (e.g. detour length) (Arizona Department of Transportation, 2021; Delaware Department of Transportation, 2022; Utah Department of Transportation, 2023), network connectivity (Texas Department of Transportation, 2022), interdependence (Texas Department of Transportation, 2022), and robustness (Utah Department of Transportation, 2023). Criticality and risk metrics are often combined to arrive at a total score for future investment prioritisation (22% of TAMPs reviewed). This approach enables DOTs to develop ranked project lists for use in project scoping (Wisconsin Department of Transportation, 2023; Ohio Department of Transportation, 2022), life cycle planning, and general decision making. Some state DOTs are moving beyond prioritisation based on risk alone and are considering methodologies focused on monetising risk (California Department of Transportation, 2022; Colorado Department of Transportation, 2022). This enables risks posed by different extreme weather threats to be more directly compared based on expected cost.

Finally, state TAMPs also discuss where and how risk assessments and prioritisation methodologies are documented and made available. Many states utilise mapping tools (Alaska Department of Transportation, 2022; Arizona Department of Transportation, 2021; Colorado Department of Transportation, 2022; Delaware Department of Transportation, 2022; Illinois Department of Transportation, 2023; North Carolina Department of Transportation, 2022; Rhode Island Department of Transportation, 2022; Utah Department of Transportation, 2023), prioritised project lists (New Mexico Department of Transportation, 2022; Ohio Department of Transportation, 2022), and scorecards or matrices (Texas Department of Transportation, 2022; Delaware Department of Transportation, 2022) to present information about RnR. These tools enable visualisation of high-priority asset locations and help facilitate discussions on system resilience issues. Many of these tools have been developed by state DOTs and therefore are customised to meet the specific goals of the agency, including the possibility of deploying the tool to prioritise investments recommended in RIPs.

In most states, scenario planning is performed by predicting future system performance based on current condition, treatment costs and triggers, rate of deterioration, and funding availability (AASHTO, 2020). However, some states (7% of TAMPs reviewed) are beginning to consider additional life cycle planning scenarios that address system resilience (Hawaii Department of Transportation, 2022; Oregon Department of Transportation, 2022; Indiana DOT, 2022). One such example is Indiana DOT who developed a resiliency life cycle planning scenario. The analysis focused on assessing the overall performance of its pavements and bridges under increased extreme weather threats. This scenario assumes the agency will experience increased flood events, leading to a 20% increase in bridge replacement and structural pavement repair costs (Indiana Department of Transportation, 2022). As a result, the agency discovered that, given current and expected investment, there will be a performance gap between desired and predicted by 2037.

The final resilience category assessed was resilience business processes. Within the TAMPs reviewed, resilience business processes fell into four subcategories: materials and design, treatment selection, plans, and performance management. Table 6 and Figure 7 summarise the key resilience activities and the number of states in which each was discussed.

A key practice appearing in many TAMPs is the proper design and construction of assets to ensure resilience to extreme weather. Most state DOTs (60% of TAMPs reviewed) described existing or new design guidance to address changing extreme weather conditions that impact pavement and bridge performance. Design guidance for pavements aims to address and mitigate failure related to permafrost (Alaska Department of Transportation, 2022), flooding (Oklahoma Department of Transportation, 2022; Wisconsin Department of Transportation, 2023; Florida Department of Transportation, 2022), or extreme weather more generally (Pennsylvania Department of Transportation, 2022; Iowa Department of Transportation, 2023; Idaho Transportation Department, 2022; Alaska Department of Transportation, 2022; Connecticut Department of Transportation, 2022; Delaware Department of Transportation, 2022; Florida Department of Transportation, 2022; Hawaii Department of Transportation, 2022; Rhode Island DOT, 2022). For bridges, design guidance predominantly considers seismic or scour potential (Wyoming Department of Transportation, 2022; Washington State Department of Transportation, 2022; Utah Department of Transportation, 2023; Tennessee Department of Transportation, 2023; Arkansas DOT, 2022; Illinois Department of Transportation, 2023; Mississippi Department of Transportation, 2022; Puerto Rico Highways and Transportation Authority, 2022) using ductility-based and probabilistic-based solutions (Alaska Department of Transportation, 2022) and load and resistance factor design (Mississippi Department of Transportation, 2022; Arkansas DOT, 2022). Common design solutions include raising structures (Alaska Department of Transportation, 2022; South Carolina Department of Transportation, 2022; New Hampshire Department of Transportation, 2022; North Dakota Department of Transportation, 2022) and armouring slopes (Minnesota Department of Transportation, 2022) to mitigate potential flooding and sea level rise.

Beyond design, material choice is another common consideration (29% of TAMPs reviewed). For pavements, states rely on material selection that enables pavements to be more resilient to changes in moisture or temperature. This includes permeable pavements, pavers, or open-graded friction course (District Department of Transportation, 2022; Georgia Department of Transportation, 2022; Massachusetts Department of Transportation, 2023; Rhode Island Department of Transportation, 2022) for improved drainage and high-performance pavement, interlayers, or modified binders (Connecticut Department of Transportation, 2022; Massachusetts Department of Transportation, 2023; Wyoming Department of Transportation, 2022; New Jersey Department of Transportation, 2022) for extreme heat. For bridges, elastomeric bearings, epoxy, and galvanised steel are used to ensure bridges can withstand climatic conditions (New Jersey Department of Transportation, 2022; Tennessee Department of Transportation, 2023; Iowa Department of Transportation, 2023). For states in which wildfires and extreme variation in heat and moisture are common, the use of fire-resistant materials (California Department of Transportation, 2022) or materials less susceptible to extreme conditions such as asphalt aging and antistripping agents (Minnesota Department of Transportation, 2022; Tennessee Department of Transportation, 2023) is also a common practice.

Another common practice is to use forecasted data and tools to better inform the design and material selection process (11% of TAMPs reviewed). For pavements, data from Modern-Era Retrospective Analysis for Research and Applications and Long-Term Pavement Performance (LTPP) programme (Wyoming Department of Transportation, 2022) enables states to assess the expected impact of climate change on performance, while tools such as Pavement ME and LTPPBind help states determine the optimal binder grade to combat extreme temperatures. To assist in the proper design and treatment of bridges and culverts, state DOTs described using sea level rise and other projection data (Hawaii Department of Transportation, 2022; Florida Department of Transportation, 2022; Alaska Department of Transportation, 2022), such as Coupled Model Intercomparison Project data and drainage and hydraulic data rather than historical datasets alone.

Nature-based solutions and construction standards are two less common (16% and 9% of TAMPs reviewed, respectively) strategies. In some states, nature-based design guidelines and policies, focused on vegetation management, are introduced to improve drainage, reduce erosion, and mitigate wildfire spread (Arizona Department of Transportation, 2021; California Department of Transportation, 2022; Colorado Department of Transportation, 2022). Additional nature-based solutions include wetland and natural shoreline buffer identification (Delaware Department of Transportation, 2022; Florida Department of Transportation, 2022) and the consideration of green infrastructure solutions throughout the design process (District Department of Transportation, 2022; New Mexico Department of Transportation, 2022). Construction standards are also considered an important tool for ensuring resilient design and construction. States discuss carefully reviewing and updating construction standards and specifications to ensure infrastructure is built to withstand risk (Alaska Department of Transportation, 2022; Idaho Transportation Department, 2022), incentivising contractors to meet specifications related to resilience (South Dakota DOT, 2022) and allowing schedule flexibility to ensure construction is completed per specifications (Tennessee Department of Transportation, 2023).

The first practice discussed was the consideration of resilience in the treatment selection process or the process by which an agency decides what type of treatment is most appropriate for a given asset. For this paper, treatments include maintenance, rehabilitation, and reconstruction activities (i.e. interventions that range from minor surface repairs to major replacements of the assets). Selecting the proper treatment, in terms of cost and benefits, to harden the asset against extreme weather can reduce the loss of service and performance associated with these events. The most common practice (47% of TAMPs reviewed) is to utilise historical extreme weather risks to inform treatment selection. In many TAMPs, state DOTs described using information on whether an asset was previously damaged or was in an area vulnerable to extreme weather to assess when and where to treat assets (Alaska Department of Transportation, 2022; Georgia Department of Transportation, 2022; Idaho Transportation Department, 2022; Indiana Department of Transportation, 2022; Iowa Department of Transportation, 2023; New Hampshire Department of Transportation, 2022; Ohio Department of Transportation, 2022; Oklahoma Department of Transportation, 2022; Oregon Department of Transportation, 2022; Puerto Rico Highways and Transportation Authority, 2022). In doing so, agencies can decide whether alternative treatments would help harden the asset to those risks. Similarly, agencies also consider seismic or scour risk ratings in treatment selection and prioritisation (Alaska Department of Transportation, 2022; Arkansas DOT, 2022; California Department of Transportation, 2022; Georgia Department of Transportation, 2022; Illinois Department of Transportation, 2023; Michigan Department of Transportation, 2022; Montana Department of Transportation, 2022; Pennsylvania Department of Transportation, 2022; Rhode Island Department of Transportation, 2022; Washington State Department of Transportation, 2022; Tennessee Department of Transportation, 2023; Texas Department of Transportation, 2022).

Another practice described in 24% of TAMPs reviewed is to rely on increased maintenance to preserve assets in a state of good repair for longer. While not directly related to treatment selection, increased maintenance helps prolong the need for more time and cost-intensive treatment activities and may harden the asset against reduced performance due to extreme weather events. Many states discussed increased management of roadside vegetation and landscaping (Arizona Department of Transportation, 2021), improved maintenance of drainage structures (Louisiana Department of Transportation and Development, 2022; Montana Department of Transportation, 2022; New Hampshire Department of Transportation, 2022), and the development of de-icing standards (Massachusetts Department of Transportation, 2023) to mitigate risk related to wildfires, flooding, and winter weather, respectively. Others describe implementing increased asset-specific treatments, such as crack sealing for pavements, to prevent increased deterioration from moisture and freeze-thaw (Minnesota Department of Transportation, 2022; New Jersey Department of Transportation, 2022; Tennessee Department of Transportation, 2023).

Less commonly, state DOTs are incorporating resilience into deterioration modelling, considering future risk to extreme weather in treatment selection and developing decision trees (13%, 2%, and 4% of TAMPs reviewed, respectively). States with more advanced data collection and research activities use additional data to update asset management performance models and decision-making tools (Alaska Department of Transportation, 2022). This includes the incorporation of seismic, hydraulic, and/or other extreme weather risk data into asset management systems, enabling state agencies to predict performance based on changing climatic conditions more easily. Some states update existing deterioration models by recalibrating performance models (Georgia Department of Transportation, 2022), while others continuously review existing deterioration models to ensure they accurately reflect current and future conditions (Indiana Department of Transportation, 2022; Minnesota Department of Transportation, 2022; Nevada DOT, 2022; New Jersey Department of Transportation, 2022). Like state DOTs using historical risk to inform treatment selection, some states utilise projected risk to identify the best long-term treatments. This includes using sea level rise projections to identify the best treatment types for bridges (Hawaii Department of Transportation, 2022). Finally, other state DOTs are integrating climatic variables into their decision trees. A decision tree is a decision-making tool that systematises how agencies select treatments based on characteristics of the asset considered (e.g. functional class, condition of the asset, and so on).

Strategic-level plans, such as Long Range Transportation Plans or Statewide Transportation Improvement Programme plans, define agency-level programmatic goals used in project prioritisation (FHWA, 2023). They represent an opportunity for agencies to support and promote system resilience for all assets. Some state DOTs (42% of TAMPs reviewed) are incorporating resilience in their strategic planning process by identifying resilience as a key focus of the agency (Washington State Department of Transportation, 2022; Puerto Rico Highways and Transportation Authority, 2022; Pennsylvania Department of Transportation, 2022; Missouri Department of Transportation, 2022). The inclusion of resilience as a strategic objective is important for supporting and funding resilience projects over time. As an agency’s resilience practice matures, strategic plans can call out specific activities that warrant resources such as capability development for resilience programmes (e.g. training or staffing) (New Mexico Department of Transportation, 2022), vulnerability assessments (Michigan Department of Transportation, 2022), or practices that more broadly address extreme weather (e.g. development of a climate action plan) (Pennsylvania Department of Transportation, 2022; District Department of Transportation, 2022; Delaware Department of Transportation, 2022; California Department of Transportation, 2022). Some DOTs are also incorporating resilience as part of multi-modal strategic planning such as in Freight Resilience Plans (Nevada DOT, 2022; Texas Department of Transportation, 2022; Wyoming Department of Transportation, 2022). A less common practice (18% of TAMPs reviewed) is to develop a resilience action plan, focused on specific tasks or activities the agency is working on to improve resilience at various planning levels; many agencies consider their RIP as an action plan.

In 31% of TAMPs reviewed, state DOTs described using increased monitoring and data collection to better assess the impact climatic conditions have on asset performance. This is creating the ability to better update deterioration models and decision-making processes. Most states focus on tracking or collecting asset damage data following extreme weather events. Data collected on the asset condition is used to inform project prioritisation and evaluate treatment effectiveness (Colorado Department of Transportation, 2022; Hawaii Department of Transportation, 2022; Massachusetts Department of Transportation, 2023; Minnesota Department of Transportation, 2022). Other state DOTs track maintenance types, costs, and actions taken to restore assets following an extreme weather event (Alaska Department of Transportation, 2022; Arkansas DOT, 2022; South Dakota DOT, 2022).

Less common performance management resilience activities include real-time monitoring (16% of TAMPs reviewed) and the development of asset-level resilience metrics (9% of TAMPs reviewed). Real-time monitoring applications (e.g. BridgeWatch, StreamStats, and ShakeMap) are used to collect information on meteorological, hydrologic, and oceanographic conditions (Georgia Department of Transportation, 2022; Idaho Transportation Department, 2022; North Carolina Department of Transportation, 2022; Oklahoma Department of Transportation, 2022; Puerto Rico Highways and Transportation Authority, 2022; Tennessee Department of Transportation, 2023), enabling agencies to track the impact extreme weather events have on specific assets and assess when emergency response may be necessary. Some state TAMPs also describe the development of asset-level performance metrics for resilience. This includes hazard indices, like the subgrade stability index, to objectively assess an asset’s risk to extreme weather threats (Alaska Department of Transportation, 2022) and performance metrics and objectives focused on adaptation (that is sea level rise adaptation) (California Department of Transportation, 2022). Proxy metrics are also used to assess resilience (Minnesota Department of Transportation, 2022; South Dakota DOT, 2022). For the Minnesota DOT, proxy metrics for resilience included existing measures of weather-related damage and proposed metrics such as pavement performance during extreme heat (Minnesota Department of Transportation, 2022). In South Dakota, existing performance data and age information was merged to develop a pavement virtual age metric (South Dakota DOT, 2022), defined as the expected age on a pavement performance curve relative to the actual age of the asset (year since construction). This resilience proxy metric was used to determine whether treatments were effective given existing climatic conditions and performance deterioration models need to be adjusted to account for changes in these conditions.

As discussed in the methodology, a gap analysis was also conducted. A summary of the gap analysis findings, including each action item, its associated resilience categories, TAMP-defined activities aligned with the action item, and the number of TAMPs in which the action item is addressed appears in Table 7. There were two cases where no resilience activities directly aligned with the action items, making them resilience planning gaps in their own right: (1) participate in training to increase staff competencies, and (2) develop an effective knowledge management programme to preserve and disseminate institutional knowledge.

Of the remaining action items, nine actions are well addressed by practices described within the TAMPs (i.e. addressed in over 50% of TAMPs). Notably, many states have already identified and selected resilience improvement strategies. The remaining action items represent existing gaps or areas of opportunity for states moving forward. In addition to the two action items for which no resilience activities could be assigned, four action items were discussed in less than 15% of the TAMPs. However, action item 22 may be underestimated, due to a lack of information as to whether RnR assessments were qualitative or quantitative. The remaining three action items represent areas in most need of improvement:

• Conduct scenario planning to advance transportation system resilience. As described herein, few states employ scenario planning with consideration to resilience in their TAMPs. This is likely related to a lack of data, technology, or investment needed to forecast future conditions or funding for infrastructure resilience at the network level. However, as many states begin to develop RIPs and resilience action plans, it is important for them to consider how resilience investment, or a lack thereof, impacts the performance and function of their network. In doing so, states can better determine which strategies and investments are most needed and make more informed decisions on how to harden their networks for the future (Pena et al., 2023b). The implementation of resilience scenario planning can be supported by existing research conducted by FHWA (Dix et al., 2023, 2018).

• Develop/adopt RnR performance measures. At present, TAMPs describe limited metrics being used to assess the resilience of an asset. Instead, agencies describe using other metrics, such as condition and financial information, as proxies for asset resilience (Minnesota Department of Transportation, 2022; South Dakota DOT, 2022). The importance of explicit resilience performance metrics is twofold: (1) agencies with performance metrics can better assess progress in improving resilience over time, and (2) having standardised performance metrics can enable agencies to share resources and tools for resilience planning. In assessing resilience over time using these metrics, agencies can better predict future asset needs through practices like scenario planning and more easily prioritise resilience investment. Moreover, standardised resilience metrics would enable state DOTs with varying resource levels to seamlessly utilise tools and planning practices developed by peer agencies or federal partners. The lack of and need for resilience metrics has been supported in various research reports in recent years (Dix et al., 2018; Flannery et al., 2018).

• Develop/adopt definitions for RnR. There is a lack of standardised definitions for key risk and resilience terms. As described previously, vulnerability, risk, and resilience are terms used interchangeably by state agencies. A lack of clear definitions makes it difficult for agencies to create buy-in internally or share frameworks or practices developed by other agencies. It is recommended that definitions be consolidated and standardised at the state level as suggested in NCHRP Research Report 1014 (Pena et al., 2023b).

In this paper, a meta-analysis was conducted on existing resilience practices as described in BIL-compliant TAMPs. Forty-five TAMPs were reviewed, and common practices for addressing resilience were categorised into NCHRP Research Report 1052 resilience categories. This research also identified gaps in resilience planning at the state level by comparing practices described in state TAMPs with best practices identified in that same report. Among the areas that would benefit from additional research and development, three stood out: (1) conduct scenario planning to advance transportation system resilience, (2) develop/adopt RnR performance measures, and (3) develop/adopt definitions for RnR.

While this research provides valuable insight into existing practices being performed by state DOTs to address resilience, the scope of the synthesis was solely focused on practices discussed in TAMP documents and therefore is not exhaustive. A further review of state DOT planning documents, especially RIPs, could help improve our understanding of the state of the practice within the US, especially with regard to TAM. In doing so, agencies, within the US and abroad, will be able to learn from and adopt the best practices of peer agencies and in turn be better suited to address increased threats posed by extreme weather events moving forward.