Developing a Research Roadmap for Highway Bridge Infrastructure Innovation: A Case Study

Abstract

Bridges are assets in every society, and their deterioration can have severe economic, social, and environmental consequences. Therefore, implementing effective asset management strategies is crucial to ensure bridge infrastructure’s long-term performance and safety. Roadmaps can serve as valuable tools for bridge asset managers, helping bridge engineers make informed decisions that enhance bridge safety while maintaining controlled life cycle costs. Although some bridge asset management roadmaps exist, such as the one published by the United States Federal Highway Administration (FHWA), there is a lack of structured research roadmaps that are both region-specific and adaptable as guiding frameworks for similar studies. For instance, the FHWA roadmap cannot be universally applied across diverse regional contexts. This study addresses this critical gap by developing a research roadmap tailored to Idaho, USA. The roadmap was developed using a three-phase methodological approach: (1) a comprehensive analysis of past and ongoing Department of Transportation (DOT)-funded research projects over the last five years, (2) a nationwide survey of DOT funding and research practices, and (3) a detailed assessment of Idaho Transportation Department (ITD) deficiently rated bridge inventory, including individual element condition states. In the first phase, three filtering stages were implemented to identify the top 25 state projects. A literature review was conducted for each project to provide ITD’s Technical Advisory Committee (TAC) members with insights into research undertaken by various state DOTs. Moreover, in the second phase, approximately six questionnaires were designed and distributed to other state DOTs. These questionnaires primarily covered topics related to bridge research priorities and funding allocation. In the final phase, a condition state analysis was conducted using data-driven methods. Key findings from this three-phase methodological approach highlight that ultra-high-performance concrete (UHPC), bridge deck preservation, and maintenance strategies are high-priority research areas across many DOTs. Furthermore, according to the DOT responses, funding is most commonly allocated to projects related to superstructure and deck elements. Finally, ITD found that the most deficient elements in Idaho bridges are reinforced concrete abutments, reinforced concrete pile caps and footings, reinforced concrete pier walls, and movable bearing systems. These findings were integrated with insights from ITD’s TAC to generate a prioritized list of 23 high-impact research topics aligned with Idaho’s specific needs and priorities. From this list, the top six topics were selected for further investigation. By adopting this strategic approach, ITD aims to enhance the efficiency and effectiveness of its bridge-related research efforts, ultimately contributing to safer and more resilient transportation infrastructure. This paper could be a helpful resource for other DOTs seeking a systematic approach to addressing their bridge research needs.

1. Introduction

Bridges are among the most crucial elements of infrastructure and are considered valuable assets for every country worldwide [1]. From their application in ancient times, such as in Ancient Rome, to their presence in modern societies across the globe, their vital role in connecting different regions is evident [2,3]. Bridges not only facilitate transportation and trade, directly impacting a country’s economy, but they also contribute to cultural exchange by linking diverse communities [3].

Bridges are such vital assets that overlooking their role in society can lead to severe and irreversible consequences. To shed light on this issue, the Tuojiang Bridge in Hunan, China, catastrophically failed in August 2007 before its official opening, resulting in about 65 fatalities, 23 injuries, and significant economic losses [1,2]. Similarly, the collapse of the Ponte Morandi Bridge in Genoa, Italy, in August 2018 was attributed to deficiencies in material and structural properties, as well as the failure to properly strengthen the bridge. This disaster claimed 43 lives and caused approximately USD 480 million in economic damages, with the commerce, industry, shipping, and transport sectors being the most severely affected [3,4,5]. More recently, on 26 March 2024, the Baltimore metropolitan area in Maryland, USA, experienced a devastating bridge collapse when a counter ship collided with the main pier of the Francis Scott Key Bridge. The impact caused the loss of support on one side of the main arch, leading to the deformation and eventual collapse of the bridge into the water [6]. This disaster disrupted port operations, resulting in an estimated USD 191 million per day in lost economic activity, including job and business losses [7].

These are just a few examples of bridge failures with significant societal impacts. However, the lessons learned from such disasters underscore the necessity of proper bridge asset management [8,9]. Effective management prevents significant losses by ensuring bridges continue to deliver financial, environmental, and social benefits, underscoring the importance of asset management for their safety and functionality.

In general terms, bridge asset management involves identifying the most effective strategies for optimizing the inspection, maintenance, rehabilitation, and replacement of bridges to ensure their safety and longevity, while also considering the life-cycle cost of the project [10,11,12]. Despite advancements in technologies (e.g., AI, digital twin, Unmanned Aerial Systems (UAS), and remote sensing) and the enhancement of their use in bridge structural health monitoring systems, asset management extends beyond merely implementing these technologies [13,14,15,16]. Balancing safety with various aspects of asset management, including the economic considerations of a project, can be challenging throughout the process. Nevertheless, asset managers and decision makers can address this challenge using a comprehensive roadmap that includes specific steps based on the existing gaps, resource allocation, timelines, and clearly defined responsibilities [17]. Despite their critical role in bridge management systems, significant gaps remain in the development of such roadmaps within the context of bridge engineering.

This research study was conducted to advance the application of roadmaps in bridge management systems. The following subsections first identify the gaps in the existing literature and then, based on these gaps, present the detailed objectives of the study.

1.1. Previous Studies

Despite its importance in bridge asset management, roadmaps have surprisingly rarely been provided in the literature, especially at national and international levels. One of the most recent and comprehensive roadmaps related to bridge infrastructure is the United States FHWA Bridge Preservation Research Roadmap, published in January 2024 [18]. This roadmap was developed to update the 2008 version, addressing advancements in bridge preservation practices, emerging technologies (e.g., AI, digital twins), and new challenges such as climate change and resilience. Specifically, it identifies research gaps and prioritizes topics to guide the FHWA and other agencies in funding and implementing effective preservation strategies. As a result of this roadmap, thirteen high-priority research topics were identified. These topics focus on (1) Quantifying the Effects of Bridge Preservation Activities, (2) Risk Assessment in Decision Making, (3) a Data Collection Framework for Bridge Maintenance, (4) Evaluation Methodology for Deck Preservation, (5) Life-Cycle Cost Analysis (LCCA) of New Materials/Technologies, (6) Non-Destructive Evaluation/Structural Monitoring for Deterioration Modeling, (7) Corrosion-Resistant Rebar Performance, (8) Corrosion Protection Techniques, (9) Live-Load Effects on Bridge Performance, (10) Preservation Techniques for Bridge Elements, (11) Element-Level Deterioration Models, (12) Sensing Data Integration (LiDAR, UAV, NDE/SM) into 3D/Digital Models, and (13) Bridge information Modeling and Digital Data Frameworks.

At the international level, few regions and countries have developed research roadmaps for bridge asset management. For instance, the European Road Transport Research Advisory Council (ERTRAC) released a research roadmap in 2021 aimed at providing safer roads in Europe. Despite its promising direction regarding infrastructure safety, the roadmap only addresses a few safety concerns related to bridge structures. Specifically, it highlights the importance of monitoring and maintenance in bridges as essential for ensuring infrastructure safety [19]. Similarly, the European Strategy Forum on Research Infrastructures (ESFRI) has published research roadmaps focused on infrastructure. Although it presents a substantial amount of information for each project, such as the coordinating country, estimated timeline, budget, headquarters, background, and description, it lacks sufficient research initiatives specifically related to bridge structures [20]. In addition, the European Commission published a report focused on research and innovation in bridge maintenance, inspection, and monitoring. Unlike the previous two examples, this report is specifically centered on bridge infrastructure. Firstly, it reviews European-level projects and introduces related research initiatives. Furthermore, it explicitly includes national-level research activities in countries such as Italy, Switzerland, Austria, Germany, France, Portugal, and Greece. While this report offers valuable insights into bridge infrastructure research, it does not detail the process of developing research roadmaps [21]. Last but not least, outside of Europe and North America, some regions have initiated early efforts to formalize bridge asset management approaches. For example, New Zealand introduced a roadmap in 2015 that emphasized data collection and the monitoring of road bridges [22]. While this initiative offers regional value, it does not constitute a comprehensive research roadmap specifically focused on the maintenance and preservation of road bridges.

While U.S. and international research roadmaps aim to guide infrastructure development and preservation, they differ significantly in their scope, specificity, and implementation strategies. The FHWA roadmap stands out for its clear prioritization of research topics, detailed methodological frameworks, and direct applicability to agency-level decision making. In contrast, many international documents, such as those by ERTRAC and ESFRI, tend to adopt a broader infrastructure or transportation lens, with limited emphasis on bridges as standalone research subjects. Furthermore, the U.S. roadmap demonstrates a more systematic approach to identifying research gaps and integrating emerging technologies (e.g., AI, digital twins), whereas international efforts often focus on policy-level guidance or project descriptions without providing detailed, actionable research pathways. Nevertheless, a common limitation across national and international roadmaps is that they tend to be either too general or insufficiently tailored to the specific research needs of the bridge sector. Accordingly, these documents may not adequately address the current needs of regions worldwide. In the United States, for example, a one-size-fits-all approach fails to account for the diverse conditions and localized challenges faced by individual states. This shortcoming is particularly evident when considering the varied climatic, economic, and infrastructural contexts that influence bridge maintenance and preservation strategies across different regions.

Among the U.S. states, Idaho, and specifically the Idaho Transportation Department (ITD), has been actively working on the plans for the purpose of the asset management of Idaho’s bridge infrastructure. Although the ITD Bridge Section has been a pioneer in advancing bridge materials, design, construction, preservation, and inspection in Idaho through sponsored research, it recognizes the need to transition from its previous ad hoc research requests to a more proactive and systematic approach. For this purpose and to fill the lack of sufficient research roadmaps in the literature for bridge infrastructure innovation, this study provides a strategic roadmap to prioritize research for the case of Idaho. Specifically, this study aims to align research efforts to ensure they complement and build upon one another.

1.2. Scope of the Research

The ultimate goal of this study is to develop a clear and prioritized roadmap that aligns with ITD’s mission of promoting safety, mobility, and economic opportunity. To achieve this, the following steps were taken:

• Conducting a comprehensive analysis of past and ongoing DOT-funded research projects from the past five years.
• Conducting a nationwide DOT funding and research survey.
• Performing a detailed assessment of ITD’s deficiently rated bridge inventory, including individual element condition states.

The findings from this process were integrated with the expertise of ITD’s technical advisory committee (TAC) to develop a refined list of high-impact research questions tailored to Idaho’s specific needs. This list was then systematically prioritized, with the top six research topics selected for further investigation.

Since there is no specific research roadmap or established methodology for developing such a roadmap in the context of bridge asset management, adopting the aforementioned novel approach to research requests allows for more effective identification and mitigation of potential risks and uncertainties, thereby reducing the likelihood of project delays or failures.

Figure 1 presents an overview of the proposed roadmap. As shown in the figure, a three-phase methodology is implemented to generate a research roadmap for ITD bridges, with a brief description for each phase. Each phase yields several findings, which serve as prerequisites for the ITD committee to make informed decisions on selecting suitable research projects for ITD bridges. Finally, the most important research projects needed for ITD bridges are identified, along with their descriptions, forming the core of the proposed research roadmap.

2. Methodology

The research team of this study consisted of three faculty members with experience in bridge engineering, two engineers from a U.S. national firm specializing in bridge design and inspection, and a graduate research assistant. The Technical Advisory Committee (TAC) included five members from ITD: three bridge engineers, one materials engineer who works closely with the bridge section, and a bridge engineer who is the Idaho representative for the Federal Highway Administration.

To rank and select the upcoming research initiatives, three phases were explored and presented to members of the Idaho Transportation Department’s TAC. These phases encompassed (1) evaluating and prioritizing recent state DOT-sponsored projects (both ongoing and completed) from the last five years, (2) conducting surveys with other state DOTs to pinpoint critical gaps in industry knowledge, and (3) assessing the structural integrity of Idaho’s deficient bridges. Following this presentation, the research team and TAC members collaboratively generated potential research concepts. These proposals were rigorously reviewed, debated, and prioritized to establish a concise list of six high-priority bridge research topics for Idaho.

Notably, in terms of application scope, the methodology initially considered all types of bridges, including both highway and railway bridges. However, the six high-priority research topics identified at the conclusion of this study are primarily applicable to highway bridges. This emphasis reflects the greater significance and larger number of deficient highway bridges in the state of Idaho, as the main focus of this study is on the bridge infrastructure of Idaho, U.S. The inclusion of railway bridges in the first stages of methodology was intended to enhance the generalizability of the study’s approach, allowing it to serve as a framework for future research. This is particularly relevant given the current lack of structured methodologies for developing a research roadmap in the bridge sector. The subsequent sections provide a comprehensive breakdown of the methodological process.

2.1. DOT Project Evaluation and Prioritization

To provide ITD TAC members with a thorough understanding of bridge-related research initiatives across the U.S., 857 active and recently completed DOT projects were identified through the Transportation Research Board’s Research in Progress (RIP) database [23]. These projects were categorized into the following key groups: construction materials, bridge management/preservation, inspection and monitoring, design and load rating, rehabilitation and repair, bridge decks, and miscellaneous (misc.).

These categories were developed by all members based on the relevance of keywords in the project titles and the topics addressed in the abstracts. For example, projects focused on mix design, novel concrete formulations, or other innovations in concrete properties were classified as “construction materials”. Projects addressing the performance, repair, or retrofitting of existing bridge components (such as girders or decks) were assigned to “rehabilitation and repair”. When the focus was specifically on bridge decks, such as overlays, condition evaluations, sealants, or durability testing, the project was placed in the “bridge decks” category. Furthermore, projects centered on inspection tools or strategies were classified under “inspection and monitoring”, while those involving structural analysis, capacity prediction, or the development of new design methods fell into the “design and load rating” group. Projects dealing with broader asset management or preservation practices were included in “bridge management/preservation”. Finally, if a project does not fit into any of these established groups (for example, those addressing hazardous material issues), it is classified as “miscellaneous”.

For instance, the projects titled “Reduce Concrete Cracking through Mix Design” and “Post-Fire Damage Inspection of Concrete Structures—Phase III—In-Situ Experimental Phase” were classified under the “construction materials” and “inspection and monitoring” categories, respectively. However, it is important to note that some projects naturally span multiple areas. In such cases, the categorization reflects the dominant focus, as interpreted from the project title and abstract. For example, projects involving bridge deck overlays could reasonably fit under either “bridge decks” or “rehabilitation and repair”; in this analysis, emphasis was placed on the deck-specific nature when applicable.

It is also worth mentioning that the projects were limited to those initiated within the last five years to ensure alignment with current industry advancements. Lastly, a rigorous three-stage filtering process was then applied to refine this dataset, resulting in a finalized list of 25 projects that closely align with ITD’s strategic priorities and research objectives. The subsequent section details the methodology behind this selection process.

2.1.1. First Filtering Stage

Given the substantial volume of data associated with 857 projects, this study focused exclusively on project titles and abstracts. Notably, since a large number of research projects were identified, both the research team and TAC members decided that the research team members would complete the first filtering, and the TAC members would complete the second filtering. Accordingly, in this phase, each member of the research team independently scored the projects on a scale of 0 (low relevance) to 5 (high relevance). This scoring scale was chosen because of its familiarity and ease of use, adequate granularity, avoidance of midpoint neutrality, ease of aggregation and interpretation, and alignment with project management practices. The criteria for assigning zero or lower scores to research projects in the first filtering included the following:

• Projects that were not relevant to highway bridge research. These projects were included in the list simply because some of the search keywords matched. Examples include railway bridges, highway sign structures, and pavement research.
• Projects that involved training.
• Projects that did not apply to Idaho bridges. For example, research on the effect of tsunamis on bridges does not apply to Idaho bridges, since Idaho is not a coastal state.

Individual scores were then averaged to generate an overall ranking for each project.

Table 1. Partial sample of the 857 recently completed and ongoing projects related to bridge structures, sourced from the Transportation Research Board’s Research in Progress database.

Project Number	Project Name	Ave. Ranking
1	Determination of Actual Derailment Loads on Transit Bridges	0.2
2	Practices to Enhance Resiliency of Existing Culverts	2.4
3	Evaluation of Coating Materials Using Accelerated Laboratory Weathering Test Protocol	1.0
4	Assessing the Need for Floodplain Culverts Based on Geomorphology	0.6
5	Performance Testing of GRS Test Piers Constructed with Florida Aggregates—Axial Load Deformation Relationships	0.6
$⋮$	$⋮$	$⋮$
854	Design Optimization and Monitoring of Joint-less Integral and Semi-Integral Abutment Bridges in Nebraska	3.2
855	Monitoring Transportation Structure Integrity Loss and Risk with Structure-From-Motion	1.4
856	New Seismic-Resisting Connections for Concrete-Filled Tube Components In High-Speed Rail Systems	1.6
857	Crushed Hydraulic Cement Concrete Adjacent to Underdrains	1.0
858	Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance	1.6

shows a representative sample of the ranked projects, highlighting the top five and bottom five entries alongside their respective scores.

Furthermore, Figure 2 summarizes the statistical distribution of these rankings. As illustrated in Figure 2a, the majority of projects (296) received scores between 1 and 2, with the remaining distribution as follows: 112 projects fell within [0–1], 241 within [2–3], 168 within [3–4], and 40 within [4–5]. Notably, Figure 2b reveals that approximately 75% of projects scored below 3, underscoring the selective criteria applied during evaluation. Finally, after analyzing the dataset, projects ranked below 3 were removed to refine the dataset. This left 208 projects, which then proceeded to the second stage of filtering.

2.1.2. Second Filtering Stage

The second filtering relied on the extensive practical experience of the TAC members. Two meetings were held in which the TAC members discussed the remaining 208 projects. Rather than employing individual rankings, the team evaluated project relevance through structured discussions focused on titles and abstracts. Decisions to retain or eliminate projects were made using a binary retention criterion (yes/no). The criteria for removing research projects in the second filtering included the following:

• Projects that were part of the pooled funded projects, many of which ITD has contributed to in the past.
• Projects that were similar to the ones that were funded by ITD in the past.
• Projects that did not apply to ITD bridges but were overlooked (i.e., not identified) by the research team members. For example, ITD does not use composite tub (CT) bridge girders. Therefore, research projects on repairing CT girders were removed.

This streamlined approach removed 129 projects, reducing the final list to 79 high-priority initiatives.

Table 2. Partial sample of the 208 selected projects from the first stage of this study.

Project Number	Project Name	Yes/No
7	Development of a Research Roadmap for ITD Bridge Section	Yes
36	Use of Fiber-Reinforced Polymer Composites for Bridge Repairs in Montana	Yes
44	Evaluate Bridge Deck Condition and Replacement Methods	Yes
67	Construction of Low-Cracking High-Performance Bridge Decks Incorporating New Technology	Yes
198	Rapid Post-Earthquake Displacement-Based Assessment Methodology for Bridges Phase I	No
241	Identification of Maintenance Practices to Impede Corrosion Impacts on Prestressed Concrete Box Beam Bridges	Yes
575	Durable Bridges Using Glass Fiber Reinforced Polymer and Hybrid Reinforced Concrete Columns	No
686	Development of Bridge Load Testing Program for Load Rating of Concrete Bridges	No
758	Assessment of Asbestos Containing Materials in Idaho Bridges	Yes
801	Repair Methods for Corrosion-Damaged Prestressed Concrete Girders	No

shows 10 samples of the dataset used in this stage.

2.1.3. Third Filtering Stage

Table 3. Number of projects in each category for 79 selected projects.

Category	Number of Projects
Construction Materials	18
Bridge Decks	19
Bridge Management/Preservation	4
Inspection and Monitoring	5
Design and Load Rating	16
Rehabilitation and Repair	16
Miscellaneous	1

presents the categories of the 79 selected projects, along with their corresponding numbers. As shown in the table, research topics related to bridge decks have the highest number of projects, followed by construction materials, design and loading rate, and rehabilitation and repair.

The final evaluation phase engaged all members of the ITD TAC alongside a retired research team member with prior expertise in ITD’s Bridge Section. Each of the 79 remaining projects was systematically scored on a 0–5 scale to assess two critical criteria and questions:

• Applicability to ITD’s Infrastructure: “Will the outcomes of the project directly benefit ITD’s bridge inventory?”
• The Need to Execute a Similar Project: “Is there a need for ITD to perform a similar project, given that the research is completed or in progress elsewhere?”

This collaborative scoring process ensured alignment with ITD’s operational needs. Furthermore, it recognized that while a project may be highly relevant to Idaho’s bridge infrastructure, repeating similar research may not be necessary if comparable efforts exist elsewhere. This distinction was considered essential for refining and selecting the most impactful research ideas. Figure 3 compares the average rankings of research categories for Criterion A (applicability to ITD’s inventory) and Criterion B (need for replication). As shown, the average scores for Criterion A consistently surpassed those for Criterion B. For Criterion A, the Bridge Decks category received the highest score, while Design and Load Rating ranked lowest. Similarly, for Criterion B, Bridge Decks again achieved the highest score, and Load Rating yielded the lowest values. Notably, since Criterion B is more relevant to future ITD research, projects were prioritized based on their Criterion B rankings. The top 25 projects, sorted by these scores, are detailed in the Results section of this study.

2.2. DOT Survey Questionnaire

A survey questionnaire was distributed by the ITD Research Program Manager to DOTs in all 49 other U.S. states to collect further information on research projects. While the review and ranking of DOT projects offer insight into specific agency interests and focus areas, the six survey questions were designed to provide a broader perspective on current and future research initiatives. Figure 4 illustrates a map of the U.S., where states that responded to the survey are highlighted in green, non-responding states in gray, and Idaho (the reference state for this study) is marked in orange. Additionally, the abbreviated name of each state is displayed within its respective region in the figure. As shown in the figure, responses were received from 21 states, primarily from the West, Midwest, parts of the South, and a few states in the Northeast. Specifically, the responding states included Arizona (AZ), Arkansas (AR), Colorado (CO), Delaware (DE), Iowa (IA), Kentucky (KY), Minnesota (MN), Mississippi (MS), Missouri (MO), Montana (MT), Nebraska (NE), New Jersey (NJ), North Carolina (NC), Oklahoma (OK), South Dakota (SD), Tennessee (TN), Texas (TX), Utah (UT), Vermont (VT), Washington (WA), and Wyoming (WY). However, some responses were incomplete or did not directly address the questions.

It is worth noting that while 21 of the 49 surveyed states (43% response rate) provided at least partial responses, the geographic distribution of respondents means that the findings may not fully capture the priorities of non-responding regions. Non-respondent DOTs may differ systematically in terms of bridge inventories, funding levels, climatic challenges, or organizational structures, factors that could influence their research needs and priorities. For example, states with older bridge infrastructure or more severe freeze–thaw cycles might place greater emphasis on durability and winter maintenance research than is reflected in the current respondent sample. In light of these limitations, the aggregated themes of this study were initially interpreted with caution by the experienced members of ITD and the research team.

Table 4. Details of the questions mentioned in the questionnaire.

Question (#)	Subject Area	Question
1	Bridge research priorities	What are the focus areas or priority topics for current and future bridge research at your DOT? Why are you focusing your efforts in these areas?
2	Recent impactful research on bridges	What research completed in the last 5 years has had the most impact on your state DOT’s bridge program? What was implemented and what benefits resulted from these projects?
3	Bridge research prioritization process	What process does your bridge program follow for identifying and prioritizing bridge research needs?
4	Bridge funding allocation	Please estimate the percentage of funding for current bridge research in your agency that is allocated to each of the main bridge component categories, including deck, superstructure, substructure, railing, and others.
5	Bridge funding allocation	Please estimate the percentage of funding for current bridge research in your agency that is allocated to each of the main bridge program activities, including design, construction, preservation, inspection, load rating, and others.
6	Bridge TPF funding	What percentage of the current bridge research funding in your agency supports bridge-related Transportation Pooled Fund (TPF) projects?

presents the survey questions along with their corresponding subject areas. As indicated in the table, three of the six questions focused on research prioritization, while the remaining three pertained to funding.

2.3. Bridge Element Condition State Analysis

The objective of this phase was to assess the current state of bridge elements and use these insights to inform ITD’s research priorities. Specifically, a condition state analysis was performed on bridge element data for structures with a condition rating of four or lower. In other words, the focus was on deficient bridges and culverts where key elements, such as the deck, superstructure, substructure, and culverts, had a condition rating of 4 or less.

To better understand condition states, this rating system assesses both the severity and extent of deterioration in bridge elements, ranging from 1 (good) to 4 (severe). While this system is useful for evaluating individual elements, it does not always directly correlate with overall bridge ratings for decks, superstructures, and substructures, except in extreme cases where an element is entirely in Condition State 4 [24]. The analysis considered all condition states but placed greater emphasis on Condition States 3 and 4, where deterioration is moderate to severe and may require structural investigations.

To carry out this analysis, data were collected from the FHWA website and ITD database. The study focused on isolating individual bridge elements from all qualifying bridges in Idaho, summing their respective condition states, and normalizing the data based on the number of elements and total quantities (e.g., area, length, or count). These steps ensured a comprehensive evaluation of bridge conditions, providing a foundation for determining research priorities.

Specifically, the analysis was conducted in three phases: data collection and construction, feature scaling, and the development of research topics for ITD. The following sections provide a detailed explanation of each phase.

2.3.1. Data Collection and Construction

Data collection in this phase involved gathering information on each bridge project in Idaho from two databases: FHWA and ITD. The dataset obtained from FHWA [25], published in 2023, was the most recent bridge element dataset available at the time of analysis, making it the logical choice for this study. This dataset contained seven key features, including the structure identification number (STRUCNUM), element number (EN); total element quantity (TOTALQTY); and condition state quantities for states 1, 2, 3, and 4 (CS1, CS2, CS3, CS4).

Table 5. Basic statistical information of the dataset gathered from FHWA.

	STRUCNUM	EN	TOTALQTY	CS1	CS2	CS3	CS4
Count	53	53	53	53	53	53	53
Mean	10,012.87	308.79	16,190.77	13,853.57	2040.40	72.51	224.30
SD	10.73	156.14	39,747.18	38,107.16	9925.55	339.64	1058.11
Min.	10,000.00	12.00	14.00	0.00	0.00	0.00	0.00
Q1	10,000.00	215.00	75.00	10.00	0.00	0.00	0.00
Q2	10,010.00	310.00	306.00	98.00	10.00	0.00	0.00
Q3	10,027.00	510.00	6063.00	2100.00	247.00	0.00	0.00
Max.	10,027.00	521.00	191,228.00	181,728.00	71,235.00	2000.00	7040.00

presents a summary of basic statistical information from the FHWA dataset, including the number of data points (Count), mean (Mean), standard deviation (SD), minimum (Min.), first quartile (Q1), second quartile (Q2), third quartile (Q3), and maximum value (Max.). The dataset included 53 records, with STRUCNUM values ranging from 10,000 to 10,027, EN values from 12 to 521, and TOTALQTY values ranging from 14 to 191,228. Additionally, the condition state quantities varied as follows: CS1 (0–181,728), CS2 (0–71,235), CS3 (0–2000), and CS4 (0–7040).

Although this dataset represents the most recent bridge element data reported to the FHWA, it is important to note that not all data points originate strictly from 2023. In Idaho, bridge inspections occur at intervals of up to two years, though more frequent assessments may be conducted for deteriorating structures. As a result, some of the data reported to the FHWA for Idaho may be up to two years old.

Alongside the dataset obtained from the FHWA website, the ITD provided an additional dataset containing detailed information on all bridges in Idaho. This dataset included features such as district (DISTRICT), material (MATERIAL), design (DESIGN), number of spans (SPANS), maximum span length (MAXSPANLEN), total length (LENGTH), year of construction (YEARBUILT), and condition ratings for the deck (DKRATING), superstructure (SUPRATING), substructure (SUBRATING), and culvert. The MATERIAL feature consisted of six distinct material types, each assigned a corresponding label: concrete (0), steel (1), prestressed concrete (2), concrete continuous (3), steel continuous (4), and wood or timber (5). Similarly, the DESIGN feature included various bridge design types, each labeled accordingly: stringer/girder (0), truss-thru (1), tee beam (2), single/spread box (3), channel beam (4), girder-floor beam (5), frame (6), arch-deck (7), slab (8), multiple box beam (9), and culvert (10).

The integration of ITD’s database alongside the FHWA database was intended to ensure that the data used in the analysis were comprehensive, accurate, and up to date.

Table 6. Basic bridge statistical information of the dataset gathered from ITD.

	DISTRICT	MATERIAL	DESIGN	SPANS	MAXSPANLEN	LENGTH	YEARBUILT	DKRATING	SUPRATING	SUBRATING
Count	181	181	181	181	181	181	181	181	181	181
Mean	3.55	1.70	1.26	2.18	51.20	114.97	1955.07	5.43	4.97	4.24
SD	1.74	1.45	2.08	1.96	43.38	127.82	21.52	1.21	1.10	1.22
Min	1.00	0.00	0.00	1.00	13.00	24.00	1908.00	0.00	0.00	0.00
Q1	2.00	1.00	0.00	1.00	26.00	34.00	1936.00	5.00	4.00	4.00
Q2	4.00	1.00	0.00	1.00	35.00	60.00	1960.00	6.00	5.00	4.00
Q3	5.00	2.00	2.00	3.00	58.00	152.00	1970.00	6.00	6.00	5.00
Max	6.00	5.00	9.00	12.00	250.00	689.00	2012.00	8.00	8.00	7.00

and

Table 7. Basic culvert statistical information of the dataset gathered from ITD.

	DISTRICT	MATERIAL	DESIGN	SPANS	MAXSPANLEN	LENGTH	YEARBUILT	CULVRATING
Count	5	5	5	5	5	5	5	5
Mean	3.00	0.80	10.00	2.60	27.60	45.00	1970.80	4.00
SD	1.22	0.45	0.00	1.52	37.59	28.52	22.13	0.00
Min	1.00	0.00	10.00	1.00	6.00	21.00	1940.00	4.00
Q1	3.00	1.00	10.00	1.00	7.00	30.00	1959.00	4.00
Q2	3.00	1.00	10.00	3.00	10.00	39.00	1973.00	4.00
Q3	4.00	1.00	10.00	4.00	21.00	41.00	1986.00	4.00
Max	4.00	1.00	10.00	4.00	94.00	94.00	1996.00	4.00

present the basic statistical information for bridges and culverts, respectively. As shown, the dataset includes 181 bridge records and 5 culvert records. The bridges were constructed between 1908 and 2012, while the culverts were built between 1940 and 1996. The most commonly used materials for bridges were concrete, steel, and prestressed concrete, whereas steel was the predominant material for culverts. Regarding bridge design, the dataset primarily focused on structures featuring stringer/girder, truss-thru, and tee beam designs.

2.3.2. Feature Scaling

The feature scaling process in this study involved two approaches: scaling by bridge element quantity and scaling by total element count. Scaling by element quantity ensures a fair comparison among bridge elements of varying sizes by normalizing their condition states based on their total quantities. Meanwhile, scaling by the number of elements adjusts condition state distributions according to the total count of bridge elements in use. This approach prevents outliers, such as elements with a high percentage of deficient condition states but low element counts, from disproportionately influencing the results. By applying feature scaling, both the distribution of element degradation and the total element quantities are effectively accounted for. The feature scaling method by element quantity is calculated by

$$D_{E,r}={\displaystyle \frac{{{\displaystyle \sum }}_{i=1}^N{d}_{E,r,i}}{T_q}}$$

(1)

where $D_{E,r}$ and $d_{E,r,i}$ represent the percentage distribution of element E among condition state r, across all deficient bridges (N) in Idaho, as well as the quantity distribution of element E among condition state r for bridge i, respectively. Moreover, $T_q$ denotes the total element quantity. Further, the weighted condition state distribution of an element (WCSD) can be calculated based on the total number of elements E among all deficient bridges within Idaho (N_E) as follows:

$${\left(D_{E,r}\right)}_{wa}=\left({\displaystyle \frac{N_E}{N}}\right)D_{E,r}$$

(2)

where ${\left(D_{E,r}\right)}_{wa}$ is the weighted average percentage distribution of element E.

2.3.3. Development of Research Topics for ITD

After calculating and visualizing the weighted condition state distribution for all deficient bridge elements, the results were compared. The analysis primarily focused on condition states 3 and 4 to identify elements that are most likely to require rehabilitation or replacement. To further highlight these critical elements, an additional graph was created to summarize and compare only the weighted condition state distributions for condition states 3 and 4. Based on the identified deficient elements, potential research topics related to their construction, replacement, or preservation were explored and introduced.

3. Results and Discussion

To develop a strategic research roadmap by identifying key research priorities for bridge innovations in the state of Idaho, this study followed a three-phase methodology, as outlined in Section 2. The phases included (1) evaluating and prioritizing recent state DOT-sponsored projects (both ongoing and completed) from the past five years, (2) conducting surveys with other state DOTs to identify critical gaps in industry knowledge, and (3) assessing the structural integrity of Idaho’s deficient bridges. The methodology section details the systematic approaches used in each phase. This section will analyze and discuss the results of each phase.

3.1. Phase I: DOT Project Evaluation and Prioritization

In this phase, the top 25 state projects were ranked, and a literature review was conducted for each project to provide ITD TAC members with insights into research undertaken by various state DOTs. In

Table 8. Summary of the top 25 state projects identified in phase 1.

Rank	Project Title	Sponsor	Overview
1	Reduce Concrete Cracking Through Mix Design	New Hampshire Department of Transportation (NHDOT)	The project aims to reduce early shrinkage cracking in concrete by optimizing the mix design. Since cracking during construction compromises long-term durability by allowing moisture and salts to penetrate, NHDOT seeks to develop a more resistant mix to minimize corrosion and deterioration. Success in this effort could make exposed decks and cost-effective construction methods more viable for bridge maintenance. To evaluate performance, NHDOT plans to test the new mix on standalone concrete structures, such as sidewalks and slabs [26].
2	Alkali-Silica Reaction (ASR) Mitigation in High Alkali Content Cements	Virginia Department of Transportation (VDOT)	This project aims to update VDOT’s alkali–silica reaction (ASR) guidelines for concrete, as the current standards rely on a withdrawn ASTM test method. VDOT plans to revise its ASR provisions to assess the alkali content of the entire concrete mix rather than just cement [27].
3	Evaluate Bridge Deck Condition and Replacement Methods	Texas Department of Transportation (TxDOT)	This project focuses on addressing aging bridge decks in Texas, where many have exceeded their service life and show soffit cracking. Since the superstructures and substructures remain in good condition, TxDOT aims to develop efficient deck assessment and replacement strategies to minimize costs [28].
4	Mitigation Strategies for Cracking in Concrete Bridge Decks	Maine Department of Transportation (MaineDOT)	This project aims to investigate and prevent concrete cracking as part of the MaineDOT’s previous research. To advance this goal, researchers studied cracking mitigation strategies [29].
5	Alkali-Silica Reaction Mitigation using Alternative Supplementary Cementitious Materials	New Mexico Department of Transportation (NMDOT)	Due to the increasing difficulty in sourcing class F fly ash, which is required in New Mexico to mitigate alkali–silica reactions (ASR), NMDOT has sponsored research at Louisiana State University to test alternative supplementary cementitious materials (SCMs). The focus is on two materials: natural pozzolan from within the state and metakaolin. These will be tested for workability, strength, and durability, with the goal of developing guidelines for their use to ensure effective ASR mitigation and extend the availability of these alternative SCMs [30].
6	Implementation of Bridge Preservation Actions	AAHSTO	This project aims to organize workshops for state DOTs and relevant local agencies to implement bridge preservation practices based on AASHTO publications. The project will involve several tasks: (1) drafting an outline for content, format, and delivery; (2) submitting a report for task 1; (3) compiling necessary materials; (4) testing a pilot instructor-led workshop at a state DOT; (5) gathering and applying feedback from the pilot workshop; (6) creating web-based modules; (7) determining the number and locations of workshops based on funding; (8) conducting the remaining workshops; and (9) submitting final deliverables [31].
7	Computer Vision Tools for Bridge Inspections and Reporting	Alaska Department of Transportation & Public Facilities (DOT&PF)	The project aims to develop AI-based tools that improve the accuracy, consistency, and speed of bridge evaluations. By using a simple photo and AI prediction, inspectors can identify and assess damage or defects [32].
8	Precast Pier System for Accelerated Bridge Construction in Idaho	Idaho Transportation Department (ITD)	This project tested a precast concrete pier system with new connection methods designed to support moments at column connections. The new connections, which use structural tubes filled with concrete at plastic hinge locations, aim to reduce construction time and improve seismic performance. Testing compared precast and cast-in-place cantilever pier columns, showing that precast columns performed better in seismic tests, with greater drift cycles, higher deflections, higher moment capacity, and better energy dissipation [33].
9	Durability and Volumetric Stability of Non-Proprietary Ultra High-Performance Concrete Mixes Batched with Locally Sourced Materials	North Dakota State University	North Dakota State University is researching the development of non-proprietary ultra-high-performance concrete to reduce costs, particularly for bridge closure pours, by using locally sourced materials. This approach will lower transportation and acquisition costs. To ensure the new NP UHPC maintains the performance of traditional UHPC, it will undergo various tests to assess its durability and volume stability [34].
10	Establishing Non-Destructive Evaluation (NDE) Protocols for Use in Early Age Bridge Deck Preservation Strategies	FHWA	This project aims to develop protocols for deck preservation strategies, with a focus on early-age vulnerability detection. The project is divided into two stages: Stage one involves collecting data on specified bridges using a specialized vehicle to measure cracks and deck permeability. The data will then be analyzed to prioritize maintenance needs. Stage two focuses on validating the data through inspection report comparisons and using the results to develop data-driven preservation strategies for bridge decks at various stages of their service life [35].
11	Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance	AASHTO	In 2016, the AASHTO technical committee introduced the Manual for Assessing Safety Hardware (MASH) to evaluate roadside safety features. Since many bridge rail systems were built before this update, there is a need to reassess these systems to meet MASH standards. This research aims to revise the AASHTO LRFD Bridge Design Manual and the AASHTO Roadside Design Guide to ensure MASH compliance [36].
12	Testing and evaluation of energy absorbing panels for over-height collision impact protection	FHWA	To address vehicle collisions, a major cause of bridge failure, seven states, including Arkansas, Georgia, Louisiana, New Jersey, New York, Oklahoma, and Virginia, have funded a project to test, install, and evaluate a new prototype system. This system aims to dissipate vehicle kinetic energy by crushing and deforming an internal honeycomb lattice mounted on an exterior girder face. After being tested through theoretical modeling, the system now requires physical testing before installation. The project focuses on determining the best installation methods, verifying the effectiveness of system, and validating the theoretical model with extensive testing [37].
13	Construction of Low-Cracking High-Performance Bridge Decks Incorporating New Technology	FHWA	This research explores the use of internal curing with supplementary cementitious materials and Low-Cracking High-Performance Concrete (LC-HPC) specifications to reduce cracking in bridge decks and extend their service life. The study identified and tested practical mixture proportioning procedures for LC-HPC and fine lightweight aggregate (FLWA) handling [38].
14	Significant Factors of Bridge Deterioration	Montana Department of Transportation (MDT)	This project aims to address challenges in developing Montana-specific bridge element deterioration curves. These challenges include identifying factors such as climate, traffic weight, construction, maintenance, and management practices, as well as issues with the bridge element rating scale and insufficient data for substandard ratings. Once solutions are identified, the results will be integrated into existing deterioration models to enhance forecasting accuracy [39].
15	Development of Deterioration Curves for Bridge Elements in Montana	Montana Department of Transportation (MDT)	This research was conducted to develop bridge element deterioration curves for integration with AASHTO’s bridge management software (BrM). The deterioration curves were created for six key bridge elements, including steel girders, concrete abutments, steel culverts, reinforced concrete decks, prestressed concrete girders, and concrete culverts, based on MDT maintenance priorities. The models were validated using input from MDT bridge engineers, and variations in deterioration patterns across five maintenance districts in Montana were also explored [40].
16	Feasibility of 3D Scanning Technology for Bridge Inspection and Management	Indiana Department of Transportation (INDOT)	The aim of this project is to create an automated framework that analyzes 3D scanned data to assess the condition and capacity of bridge components [41].
17	Vision-Based Detection of Bridge Damage Captured by Unmanned Aerial Vehicles	Rhode Island Department of Transportation (RIDOT)	The purpose of this research is to offer a more reliable method for bridge inspections using unmanned aerial vehicles (UAVs). These UAVs will gather data to generate 3D models of bridges, while AI will be used to detect and assess damage to bridge components [42].
18	Aerial Infrared Scanning of Bridge Decks for Detecting and Mapping Delamination	FHWA	Infrasense Inc. conducted research to evaluate the potential of using aerial imaging for deck condition assessments. Using aerial infrared thermography (aerial IF) and visual imaging data from a fixed-wing aircraft, Infrasense collected data on bridges along Alaska’s Parks Highway [43].
19	Improved Beam End Reinforcement Details for PCBTs with Debonded and/or Draped Strands	Virginia Department of Transportation (VDOT)	The research aims to enhance guidance on increasing stress limits for beam ends with debonded or draped strands based on a thorough literature review, DOT surveys, finite element modeling, and testing [44].
20	Internal Curing of Bridge Decks and Concrete Pavement to Reduce Cracking	Wisconsin Department of Transportation (WisDOT)	This research aims to develop tools, guidance, and specifications for implementing internal curing in concrete bridge decks. With the push for high-performance concrete over the past two decades, it was found that its low water-to-cement ratio makes it prone to early-age cracking. Internal curing, which provides moisture through aggregates, fibers, or polymers, was used to mitigate this issue. This study showed improved volumetric stability with a 0.36 water-to-cement ratio, with minimal effects at 0.45. The research concluded that internally cured concrete could extend bridge deck service life, and recommendations for WisDOT’s specifications were provided [45].
21	Data-Driven Decision-Making Framework for Inspection of Bridge Decks	Virginia Transportation Research Council (VTRC)	This project aims to enhance existing bridge inspections, as per the National Bridge Inspection Standards. The focus is on exploring alternative inspection methods using advanced technology, which will improve traditional inspections by providing consistent and additional data to inform maintenance decisions [46].
22	Low-Cement Concrete (LCC) Mixtures for Bridge Decks and Rails	Nebraska Department of Transportation (NDOT)	This project expands on research conducted by the University of Nebraska, which in 2021 developed a low-cement concrete mix for bridge decks and rails. The mix aimed to reduce cement content while maintaining similar properties to previous mixes but faced issues with workability, curing time, bleed rate, and air entrainment. This project seeks to resolve these problems and validate the mechanical and durability properties of mix by incorporating internal curing and liquid fly ash [47].
23	Accelerated Sulfate Attack Testing for Concrete	University Transportation Centers Program	The aim of this project is to develop a faster, more reliable method for testing sulfate attack on concrete. Currently, ASTM C1012 requires up to 18 months to assess sulfate resistance, so the project aims to shorten this time while achieving similar results. It begins with a literature review, studies the impact of supplementary cementitious materials on sulfate attacks, and explores alternative testing methods. The findings will be followed by experimental testing and validation [48].
24	Repair and Strengthening of Bridge Girders using Ultra-High-Performance Concrete (UHPC)	Nebraska Department of Transportation (NDOT)	The purpose of this project is to explore the use of Ultra-High-Performance Concrete for strengthening bridge girders. Building on two previous NDOT-sponsored studies focused on reducing UHPC costs and creating guidelines for cast-in-place (CIP) use, this research concludes that the superior performance of UHPC can also be applied to bridge girder repair and strengthening [49].
25	Influence of Nanomaterials-based Admixtures on the Entrained Air Void System and Freeze-Thaw (FT) Resistance of Concrete	Indiana Department of Transportation (INDOT)	This research focused on four objectives: (1) assessing the impact of nanosilica admixtures on the air-void properties of bridge concrete, (2) testing how air-void characteristics affect freeze–thaw resistance, (3) exploring how variations in production methods influence concrete durability, and (4) investigating the effects of non-traditional air entrainment products in concretes containing nanosilica admixtures [50].

, the top 25 state projects are ranked from 1 to 25, along with a brief overview of each project. According to the table, most projects focus on concrete materials as well as deck preservation strategies, highlighting their importance to evaluators in selecting the top projects. Additionally, as technology advances, the use of emerging technologies, especially AI, is evident in many of the listed projects. Given that bridge monitoring projects generate vast amounts of data and AI thrives on data, AI has the potential to be a game changer in modeling and analyzing such information, providing new insights into these projects.

It is also worth mentioning that, among most of the top 25 projects, the sponsors are DOTs, and the research is conducted by universities. This highlights the importance of collaboration between universities and DOTs in carrying out such projects.

3.2. Phase II: DOT Survey Questionnaire

In the second phase of this study, a survey questionnaire was distributed by the ITD to 49 DOTs across the U.S., with 21 DOTs responding. The questionnaire included six questions regarding the overview of current and future research projects, with details provided in Section 2.2 of this study. This section presents and analyzes the summary of responses to those questions. However, the details of the responses from each state to each question (especially questions 1 to 3) are included in Appendix A.

3.2.1. Response to Question 1

Although responses to this question varied significantly, they can be categorized into the following bridge-related topics: (1) design, (2) materials, (3) preservation and deterioration, (4) rail safety, (5) management, (6) repairs, (7) life-cycle cost, (8) digital information management (DIM) and digital delivery, (9) load rating, (10) deck overlays, (11) grease bearings, (12) concrete sealers, (13) culverts, (14) ice loading, (15) deck evaluation tools, (16) scour, and (17) construction speed. Notably, the two most frequently mentioned topics were (1) the use of Ultra High-Performance Concrete (UHPC) for bridge joints, repairs, and deck overlays; and (2) various bridge preservation concerns, including corrosion, concrete cracking, and evaluation techniques.

3.2.2. Response to Question 2

Table 9. Impactful research topics in each state.

State	Impactful Research Topic
Arizona	UHPC
Arkansas	Preservation, maintenance, and repair
Colorado	MASH rail
Delaware	Jointless bridges/overlay materials
Iowa	Accelerated bridge construction
Minnesota	UAS for bridge inspections
Mississippi	Prestressed beam camber
Montana	Non-proprietary UHPC
Nebraska	Non-proprietary UHPC
New Jersey	Structural management, including deterioration curves
North Carolina	Bridge repair
Oklahoma	Rebar corrosion
Utah	Polyester polymer concrete (PPC) for bridge deck overlays
Tennessee	Approach slab settlement
Texas	Bridge design
Washington	Prestressed concrete pile columns

summarizes the responses from each state regarding impactful research topics. Among the 21 respondent states, 5, including Kentucky, Vermont, Wyoming, South Dakota, and Missouri, did not provide sufficient information or fully answer the question. As a result, they are not included in Table 9, which indicates data from the remaining 16 respondent states. As shown in the table, UHPC and concrete materials, followed by bridge preservation, are the most impactful research topics overall.

3.2.3. Response to Question 3

Arizona, Delaware, Iowa, Minnesota, Nebraska, North Carolina, Oklahoma, Utah, Tennessee, Texas, and Washington collaborate with universities, internal committees, DOT staff, federal agencies, and industry professionals to identify and prioritize bridge research needs. Conversely, Arkansas, Colorado, Mississippi, Missouri, South Dakota, and Wyoming prioritize research based on departmental needs and current issues.

3.2.4. Response to Question 4

Figure 5 illustrates the average percentage of funding allocated to each bridge component category based on aggregated state responses. As shown, the majority of funding is assigned to the superstructure (32.2%), followed by the deck (27.2%), substructure (24.3%), other (12.2%), and railing (4.1%). This distribution underscores the prioritization of superstructure-related research and maintenance in current funding strategies. Notably, railing receives the lowest share, highlighting its comparatively minor focus in funding allocation. It should be noted that some incomplete survey responses were excluded from this analysis. While their omission means the figure may not fully represent funding patterns across all states, the dominance of superstructure, deck, and substructure funding (collectively comprising the majority of allocations) suggests that including additional data would likely not alter the overarching trends significantly. For instance, even if excluded responses were factored in, the disproportionately high percentages for superstructure and deck categories would likely remain unaffected due to their established priority. Nevertheless, the pronounced funding imbalance raises concerns about long-term infrastructure resilience. While prioritizing critical load-bearing components is rational, systematically underfunding other categories, such as railings, risks compromising holistic bridge safety and durability. To foster sustainable infrastructure, funding strategies should adopt a more equitable approach, maintaining robust investment in primary components while allocating adequate resources to secondary systems. Such a balance would ensure comprehensive research and maintenance, addressing vulnerabilities across all structural elements and enhancing systemic resilience.

3.2.5. Response to Question 5

In terms of funding allocation across bridge programs, as shown in Figure 6, most of the funds are allocated to the design program (31.1%), followed by construction (28.5%), preservation (26.2%), inspection (5.9%), load rating (5.3%), and other (3.0%). While the allocation to preservation is only slightly lower than design and construction programs, the observed underfunding of inspection, load rating, and other programs (collectively <15%) reveals a critical misalignment with asset management priorities. This pattern suggests a disproportionate focus on initial asset creation over sustaining long-term functionality. Although design and construction are essential for expanding or replacing infrastructure, the minimal funding for inspection and load rating, which are decisive factors for ensuring safety, compliance, and risk mitigation, brings about systemic vulnerabilities. For instance, inadequate inspections may fail to detect early signs of deterioration, leading to costly repairs or catastrophic failures downstream [51]. Similarly, the negligible other categories stifle innovation in areas such as climate adaptation, digital twins, or advanced analytics, which are increasingly critical for modernizing aging infrastructure [52,53]. Overall, asset management frameworks emphasize balanced investment across all life-cycle phases [54]. To build resilient infrastructure, the current funding percentages should be rebalanced to better align with these principles.

3.2.6. Response to Question 6

Figure 7 shows the percentage of research funding allocated to pooled fund projects, in which multiple states, federal agencies, and other stakeholders combine their resources to address shared transportation challenges based on the responses from DOTs. Notably, some states, such as Arizona and South Dakota, have not committed any funding to TPF projects supporting bridge efforts, showing 0% pooled fund participation. Accordingly, these two states are not illustrated in the figure. On the other hand, as can be seen in Figure 7, Delaware and Utah allocated 50% of their research funding to TPF projects. Moreover, it is worth mentioning that among those who provided specific percentages, the average allocation is approximately 15.7%. Therefore, funding contributions vary by state, as each state participates in TPF projects based on its interests and needs.

3.2.7. Summary of Key Findings Based on the Responses

The results of the questionnaire-based study reveal several critical insights into current bridge research priorities and funding patterns across U.S. DOTs. Bridge preservation, UHPC, and innovative materials consistently emerged as the most impactful and widely discussed topics. While some states prioritize research based on internal needs, others actively engage external stakeholders in the prioritization process, suggesting varying levels of institutional collaboration. Funding analysis indicates a strong emphasis on superstructure, deck, and substructure components, as well as a preference for design and construction programs over inspection and load rating. This imbalance raises concerns about long-term asset sustainability and resilience. Finally, pooled fund participation is inconsistent across states, with some contributing significantly while others report no involvement. Overall, the findings underscore both common themes and disparities in how bridge research is approached and funded, highlighting the need for more balanced and collaborative investment strategies nationwide.

3.3. Phase III: Bridge Element Condition State Analysis

In this section, the results of the weighted condition state for each element are presented and analyzed. It is important to note that the element data in this analysis were incorporated and identified using their element numbers (Element Identification System) according to the National Bridge Elements (NBE) [55]. Although there is no clear pattern linking the given numbers to their corresponding elements, some general rules can be applied. The three primary bridge structure categories (deck, superstructure, and substructure), along with two additional categories (bearing and railing elements), are divided into their respective elements. Each category falls within a designated range from 0 to 335 and is organized as follows:

• Deck elements (0–99);
• Superstructure elements (100–199);
• Substructure elements (200–299);
• Bridge Bearing Elements (310–316);
• Bridge Railing Elements (330–335).

Figure 8 illustrates the distribution of different bridge elements among deficient bridges in Idaho. Since the applied weights are determined by the number of elements, this figure helps explain how the weighted condition state percentage is calculated. To improve clarity, the weighted condition state percentages for individual elements were consolidated into Figure 9 and Figure 10. Notably, in these figures, the horizontal axes represent element IDs, formatted as “E+number”, where “E” denotes element and the number represents the unique ID. These IDs follow the classification criteria previously described. For instance, E12 refers to Element 12, and since its ID number is below 99, this identifies it as a deck element.

To identify the most deficient elements based on the data in Figure 8, Figure 9 and Figure 10,

Table 10. Descending element deficiency by element number weighted average.

Rank	Element ID	Element Name	No. of Bridges	Combined Weighted CS3 and CS4 (%)
1	E215	Reinforced Concrete Abutment	155	2.51
2	E220	Reinforced Concrete Pile Cap/Footing	51	1.28
3	E210	Reinforced Concrete Pier Wall	37	1.25
4	E311	Movable Bearing	40	1.10
5	E120	Steel Truss	23	0.73
6	E205	Reinforced Concrete Column	35	0.69

summarizes the top six deficient elements, along with their corresponding information.

Based on the findings of this phase, E215 (reinforced concrete abutment) is expected to rank highly on the final list due to its widespread use, with 155 bridges incorporating this element. In contrast, there are only 23 steel truss bridges, but the severity of their condition has placed them higher in the ranking. A more detailed analysis, incorporating a time component to investigate these specific elements, would be necessary to identify the underlying causes of their ranking. Another key consideration is that the element usage duration was not factored into the analysis. As a result, Figure 9 and Figure 10 do not account for instances where elements have been replaced or rehabilitated over a bridge’s lifespan. Consequently, bridge deck and bearing elements generally exhibit better condition and quality than elements that remain in use for longer periods and undergo less frequent replacement or rehabilitation. This trend is evident in Figure 10, where deck and bearing elements constitute a smaller portion of the total compared to superstructure and substructure elements.

To prevent misinterpretation, Figure 10 does not assess element longevity or effectiveness; it strictly represents the current condition and quantity of elements. Since time was not a factor in this analysis, a more precise interpretation would be that the elements displayed in Figure 10, and those ranked earlier in this section, are likely to require replacement soon. Given that funding will be allocated for the rehabilitation or replacement of these elements in the near future, research focused on optimizing this process could help reduce costs, save time, or enhance the performance of the newly rehabilitated elements.

In conclusion, this phase analyzed the weighted condition states of bridge elements in Idaho. Elements were categorized into five groups: deck, superstructure, substructure, bearings, and railings. The analysis revealed that substructure elements, particularly E215 (reinforced concrete abutment), were the most deficient, appearing in 155 bridges and exhibiting the highest combined weighted percentage in critical condition states (CS3 and CS4). Other notably deficient elements included reinforced concrete pile caps, pier walls, and steel trusses, each showing significant deterioration despite their varying levels of usage. Overall, the elements identified as most deficient are likely candidates for near-term rehabilitation or replacement. These findings highlight the need for targeted research into cost-effective repair strategies and performance-enhancing technologies to support long-term infrastructure sustainability.

4. Research Roadmap

Throughout this study, three distinct methodological phases were implemented to identify the most critical research projects for advancing bridge infrastructure innovation in Idaho, USA. The selection of the top research projects for Idaho was based on the state’s specific needs, interests, and gaps relative to other states. After the completion of the three methodological phases of the project, the principal investigator and the research assistant shared the following documents with the TAC and research team members: (1) summary of the DOT survey results, and (2) report on the condition state of deficient bridges in Idaho. Based on the examination of the summary reports and DOT projects that received high rankings, the members were asked to provide two or three bridge research ideas suitable for Idaho. In addition, they were asked to justify their proposed ideas. This process resulted in 23 project ideas. The generated list and the justifications were shared with all the members, and they were asked to rank each research idea from 0 to 10. The list of 23 research ideas was then ranked based on average scores received.

Table 11. Top twenty-three research topics suggested for research roadmap.

Rank	Topic
1	Evaluation of ITD’s Bridge Deck Preservation Strategies
2	Implementation of Internal Concrete Curing (ICC) to Enhance Concrete Performance
3	Development of More Reliable Camber Prediction for Prestressed Deck Bulb-T Girders
4	Evaluation of Alternative Thin Deck Overlay Materials for Newly Constructed Bridges with Deck Bulb-T Girders
5	Use of Non-Proprietary Ultra-High-Performance Concrete in Idaho Bridges
6	The Impacts of Type IL Cement on Bridge Structures
7	Bridge Deterioration Modeling
8	Increasing the Life of Concrete Bridge Components Using Protective Coatings
9	Load Ratings of Deteriorated Bridges
10	Creation of a Prioritization Program for all Deficiently Rated Bridges Within Idaho
11	Alternative Materials for Deck Reinforcement
12	Revaluation of Idaho’s Legal Vehicles
13	The use of Advanced Materials in Idaho Bridges
14	Utilization of Lightweight Concrete in Prestressed Beams
15	Utilization of FRP Rebars in Bridge Decks with Corrosive Environments
16	Evaluation of Steel Finger Joint Failure
17	Over-height Load Impacts
18	Utilization of MIRA for Assessing Bridge Deck Delamination
19	Development of a Program to Select the Optimal Repair and Preservation Methods
20	Scour Evaluation of Idaho Bridges
21	Optimizing Bridge Hydraulic Evaluations
22	Development of Eco-friendly Construction Materials for Idaho Bridges
23	Development of Prestressing Precast Concrete Stiffleg Bridges and Culverts

shows the list in ranked order. As seen in the table, many of the research areas overlap with the key research terms identified during each phase. For instance, the primary keywords derived from phases one through three, including concrete materials (especially UHPC), deck preservation strategies, and AI and data-driven methods, are prominently associated with the top projects. This demonstrates that a structured, multi-phase approach effectively established the foundation of the final research roadmap, providing a logical framework that guided the ITD TAC members in making logical project selections. Consequently, these phases can serve as a guideline for developing research roadmaps in the field of bridge infrastructure innovation.

To finalize the research roadmap and ensure it effectively aligns research projects with strategic objectives, each proposal should include a detailed project description and clearly defined expected outcomes. However, it is worth mentioning that a comprehensive literature review is a crucial part of every research roadmap. Since the purpose of this research study is to propose an overview of the top-ranked research priorities rather than provide a comprehensive literature review, a brief literature review is included in the project description section for each research topic.

Moreover, to investigate each project in greater detail, this study selected the top six projects from Table 11, which are expected to be conducted in the near future for ITD. It is worth mentioning that since the rank 1 and rank 4 projects in this table both address deck issues and significantly overlap, they were combined into a single project. As a result, the top six projects are (1) Evaluation of ITD’s Bridge Deck Preservation Strategies, (2) Implementation of Internal Concrete Curing (ICC) to Enhance Concrete Performance, (3) Development of More Reliable Camber Prediction for Prestressed Deck Bulb-T girders, (4) Use of Non-Proprietary Ultra-High-Performance Concrete in Idaho Bridges, (5) The Impacts of Type IL Cement on Bridge Structures, and (6) Bridge Deterioration Modeling. The following sections provide a more detailed discussion of these projects to enhance the comprehensiveness of the research roadmap.

4.1. Project A: Evaluation of ITD’s Bridge Deck Preservation Strategies

4.1.1. Description

Bridge deck preservation typically involves applying an epoxy seal shortly after construction, with reapplications every decade, while larger or high-traffic bridges receive a more substantial initial overlay. However, the effectiveness of this strategy in Idaho remains uncertain. For Deck Bulb-T girder bridges, ITD uses Polyester Polymer Concrete overlays, which perform well but are costly and require long waiting periods, conflicting with Accelerated Bridge Construction (ABC) principles. This raises the question of whether alternative overlays could offer a more efficient and cost-effective solution. Before addressing this question, valuable insights can be drawn from several studies, such as [56,57,58,59,60] on bridge deck overlay materials and [61,62] regarding bridge deck epoxy injection.

4.1.2. Outcomes

The outcomes of this research can include the following:

• Reducing costs and construction time for ITD’s bridge deck preservation efforts;
• Providing improved bridge deck surfaces for public use;
• Enhancing safety by extending the deck’s service life and minimizing the frequency of construction activities related to overlays or deck replacements.

4.2. Project B: Implementation of Internal Concrete Curing (ICC) to Enhance Concrete Performance

4.2.1. Description

Premature cracking of bridge decks has been a serious issue for many DOTs over the past decade, prompting engineers to experiment with various concrete mixtures, high-performance concrete (HPC), and admixtures to mitigate the problem. Once cracking begins, it worsens under service loads and environmental conditions, reducing the service life of roads and bridges and increasing maintenance costs. Although HPC is commonly used for its high strength and durability, its low water-to-cement ratio can limit its lifespan. ITD has adopted methods like crack sealing and thin polymer overlays, but these are costly and disrupt traffic due to the need for frequent applications. To address this, states like Illinois and Wisconsin have implemented internal curing (IC) techniques using presoaked aggregates (PA) to reduce drying shrinkage. This project aims to explore the effectiveness of PA in reducing shrinkage, particularly when combined with shrinkage-reducing admixtures (SRA), and to evaluate its impact on the alkali–silica reaction (ASR) in ITD concrete mixtures. Additional information about the mechanical properties of such materials, as well as their mechanisms and applications, can be found in several studies, including [63,64,65,66,67,68].

4.2.2. Outcomes

The internal curing process is expected to produce a higher-quality concrete product, enhancing durability, reducing maintenance costs, and extending its service life. This is achieved through the efficient hydration of the concrete, which minimizes shrinkage and thermal cracking. Additionally, the resulting concrete is less permeable, offering improved resistance to moisture and chloride penetration, factors that typically shorten the service life of bridge decks or concrete pavements. Notably, a longer service life leads to lower equivalent uniform annual maintenance costs for concrete structures. Internally cured concrete presents an economically and structurally viable solution for ITD, enabling the department to focus on maximizing return on investment, minimizing early-age cracking and traffic disruptions, reducing life cycle costs, and optimizing the performance and value of bridge materials.

4.3. Project C: Development of More Reliable Camber Prediction for Prestressed Deck Bulb-T Girders

4.3.1. Description

The current camber prediction system for prestressed concrete Bulb-T girders often inaccurately estimates long-term camber, leading to construction delays, increased costs, and quality control concerns. Even identical girders cast on the same bed can exhibit different cambers due to factors such as mix design, curing process, prestressing tolerances, and storage conditions. Additionally, material properties like aggregate type, cement, and admixtures influence concrete creep and shrinkage, further affecting camber behavior. Furthermore, in Idaho, Deck Bulb-T girders do not have reinforced concrete placed on top, and ITD’s existing camber calculation formulas typically underestimate, rather than overestimate, actual cambers. While no major flexural cracking has been observed, out-of-spec cambers require nonuniform overlay adjustments, increasing weight, cost, and complexity in maintaining a smooth bridge deck. This study aims to enhance camber control by identifying key parameters and refining predictive models to improve accuracy for Bulb-T girders commonly used in Idaho. The studies by Martin [69] and Brown [70] provide fundamental insights into camber estimation and prediction, which can offer valuable guidance for every project.

4.3.2. Outcomes

The deformation of concrete bridge superstructure elements, particularly those constructed sequentially, is significantly influenced by the time-dependent behavior of concrete, including its ability to creep and shrink over time. When actual deformations deviate from those predicted during the design phase, it can compromise the serviceability of concrete bridges, lead to increased costs, or extend construction timelines. Developing a procedure to accurately predict camber at each stage of Deck Bulb-T girders, from initial construction through the end of their service life, would enable ITD to address current construction challenges caused by inaccurate camber prediction models.

4.4. Project D: Use of Non-Proprietary Ultra-High-Performance Concrete in Idaho Bridges

4.4.1. Description

This project explores the use of non-proprietary ultra-high-performance concrete (UHPC) in various applications across Idaho bridges, including closure pours in new structures, thin deck overlays, and retrofit efforts such as column repairs. It includes a thorough review of existing non-proprietary UHPC mix designs developed in the U.S., with a focus on incorporating locally available materials and domestic products like steel fibers. To put it succinctly, in the U.S., the FHWA [71], Washington State DOT [72], Montana DOT [73], Michigan DOT [74], Nebraska DOT [75], and Idaho State University [76] have successfully conducted research in this area. Additionally, the project involves experimental testing to develop optimal mix designs, establish on-site mixing guidelines, and identify best practices for placing non-proprietary UHPC materials.

4.4.2. Outcomes

UHPC offers significant benefits in safety, economy, and innovation. In terms of safety, its use in Accelerated Bridge Construction (ABC) reduces exposure to construction activities for both workers and the traveling public, enhancing safety while minimizing traffic disruptions. UHPC’s exceptional durability and resistance to environmental factors result in longer-lasting structures, reducing maintenance needs and improving reliability through its high strength, bond strength, and toughness. Economically, non-proprietary UHPC lowers material and labor costs by eliminating the need for on-site engineers typically required by proprietary UHPC suppliers, as guidelines for field application can empower transportation department staff to manage projects effectively. Additionally, UHPC’s long lifespan and low maintenance requirements lead to substantial cost savings over a structure’s life cycle, while its resistance to deterioration extends service life, reducing replacement frequency. From an innovation perspective, UHPC enables customized mix designs tailored to specific project needs and supports advanced applications, such as slender, aesthetically pleasing components, fostering creativity and new techniques in infrastructure design and construction.

4.5. Project E: The Impacts of Type IL Cement on Bridge Structures

4.5.1. Description

The bridge industry is transitioning from traditional Type I/II cement to Portland-Limestone Cement (PLC), or Type IL, which has been widely used in Europe for over 30 years and marketed in the U.S. since 2012. Containing 5% to 15% inter-ground limestone fines, PLC meets ASTM and AASHTO standards and is recognized for its sustainability and performance benefits. This project aims to analyze the impact of PLC on bridge structures, focusing on durability, strength, environmental benefits, and long-term performance to assess its effectiveness in bridge construction. To better understand the mechanical properties of PLC, studies by [77,78,79] can be helpful.

4.5.2. Outcomes

The outcomes of this project will position ITD to adopt Type IL cement for bridges and concrete pavements. Implementing this type of cement will have a substantial environmental impact in Idaho by significantly reducing carbon emissions compared to traditional Type I/II cement. Additionally, the use of PLC will enhance the durability and extend the service life of Idaho’s bridges.

4.6. Project F: Bridge Deterioration Modeling

4.6.1. Description

This project aims to enhance bridge deterioration prediction by analyzing existing models and integrating Idaho-specific factors. It will involve reviewing current models, assessing Idaho’s bridge infrastructure, and developing a customized deterioration model that accounts for climate, traffic patterns, and regional materials. The goal is to improve predictive accuracy, enabling better maintenance planning and resource allocation. The final model will be integrated into ITD’s bridge management system, serving as a practical tool for optimizing maintenance strategies and ensuring the longevity and safety of Idaho’s bridges. This research will provide valuable insights for infrastructure management and support ITD in making data-driven decisions. Notably, in the literature, it can be seen that the Markov-based model, regression-based models, Poisson and negative binomial regression, binary model, Bayesian technique, and Weibull-based probability density functions are among the helpful tools for bridge deterioration modeling [80,81,82].

4.6.2. Outcomes

By integrating with ITD’s Bridge Management System (BMS), the newly developed bridge deterioration model will offer valuable insights into when and how maintenance should be performed, along with the confidence level of each prediction. These predictions can be utilized to determine the timing and type of required maintenance, identify potential safety concerns proactively, inform strategies for extending service life, and evaluate how different bridge properties influence deterioration rates.

5. Discussion

Asset management is a critical component of infrastructure systems, and bridges are no exception. A foundational aspect of bridge asset management is the development of research roadmaps. These roadmaps help prioritize the research necessary for maintaining and improving bridge infrastructure, and in turn, extend the lifespan of these critical assets. Despite the significance of research roadmaps in this context, there is a notable gap in the literature: no clear, structured methodology currently exists for developing research roadmaps specific to the bridge sector. This gap is evident when conducting a bibliometric analysis. Specifically, searches using the keywords “research roadmap” and “bridge” in article titles across Scopus and Google Scholar databases yield no results. To address this lack of research, this study proposes a novel three-phase methodology for creating a research roadmap tailored to bridge infrastructure. This methodology is designed to support technical advisory members of the Idaho Transportation Department in identifying and prioritizing research topics relevant to the state’s bridge infrastructure.

The first two phases of the methodology involve reviewing recent literature and examining ongoing and completed projects in other DOTs. These phases ensure that decision makers are equipped with up-to-date knowledge to inform the prioritization process.

The third phase focuses on analyzing the current condition of bridges in Idaho. Results indicate that structural deficiencies are primarily associated with superstructure components. This trend is likely influenced by environmental and natural hazard factors common to Idaho. The state of Idaho experiences significant temperature and precipitation variability, leading to freeze–thaw cycles, reinforcement corrosion, and chemical degradation [83,84,85]. Moreover, Idaho is situated in a seismically active region, further contributing to both substructure and superstructure damage [86,87]. When combined with other potential factors such as material degradation and human activity, these factors help explain the findings of the third phase.

Although the results from the third phase offer new insights into Idaho’s bridge infrastructure, engineers and researchers must act on these findings to mitigate future consequences. A well-structured research roadmap can guide these efforts by helping stakeholders make informed decisions about future projects. Some research institutions in Idaho, in collaboration with the Idaho Transportation Department, have already taken steps to address these issues. The research roadmap proposed in this study serves as a formal guide for these efforts and can act as a reference for similar regions.

As mentioned earlier, since there is no prior research specifically focused on proposing a research roadmap for bridge asset management, this study could serve as a benchmark for future research. It can assist asset managers in evaluating and improving the condition of bridges. Notably, although the research roadmap was developed based on Idaho’s bridge asset management needs and informed by the experience and knowledge of Idaho Transportation Department members, it is essential to enhance its applicability and usability for other DOTs and countries to make it more generalizable. The following paragraphs elaborate on key discussions related to this matter.

First and foremost, although the research roadmap concludes with six high-priority research projects specific to Idaho bridges, the three-phase methodology used to develop the roadmap can be applied globally. Specifically, each of the first two phases can be conducted through systematic research, enabling the identification of relevant trends and gaps in the field. The final phase of the methodology can also be accomplished through various methods, which will be discussed in detail later. Furthermore, the successful identification of high-priority research needs in this case demonstrates the viability of the three-phase methodology. In other words, since this methodology effectively supported Idaho Transportation Department members in developing the research roadmap, it helps to validate the process itself. Therefore, the proposed three-phase methodology can be applied in other regions by research institutions, universities, and transportation departments.

Regarding the high-priority research topics presented in the proposed research roadmap, these topics were carefully developed through the processes outlined in the first two phases of the methodology. The literature review and analysis of recent trends in other U.S. DOT projects helped decision makers identify and prioritize research areas aligned with national and international developments. Moreover, many U.S. DOTs, in addition to addressing their own specific needs, also undertake projects based on broader trends observed not only across the U.S. but also in regions with similar geographical conditions. For instance, UHPC, which has been identified as one of the six high-priority research topics for Idaho bridges, is a growing trend in both the construction industry and academia. According to the Scopus database, approximately 7260 articles have been published on UHPC, with about 6000 of those published between 2014 and 2024. The publication trend is steadily increasing, indicating sustained interest in this research area. More importantly, the database shows that China leads in UHPC research, with around 4000 published articles, followed by the USA with about 1000, Germany with 500, South Korea with 400, and Australia and Canada with roughly 300 each. This indicates that UHPC is not only a research trend in the U.S. but also a significant focus in other countries worldwide. Accordingly, the research roadmap proposed in this study can assist DOTs in other countries or regions by providing insight into current U.S. trends and, to some extent, global developments. The research topics, along with the detailed descriptions and expected outcomes, can offer valuable guidance to other DOTs, allowing them to customize and adapt the research to fit their specific needs. However, it is important to note that this roadmap was developed with Idaho’s unique conditions. Therefore, it is particularly applicable to regions with similar geographic characteristics, such as areas with variable temperatures, high rainfall or snowfall, and infrastructure susceptible to freeze–thaw cycles. Additionally, the roadmap may be especially relevant for regions located in areas of high seismic activity.

Furthermore, one of the most important components of the methodology designed for the research roadmap is the condition assessment of bridges and their elements. In this study, the analysis was conducted using a database provided by the Idaho Transportation Department and the U.S. FHWA based on routine inspections conducted at specific intervals. However, some regions or countries may lack such databases with sufficient data volume and quality. Consequently, conducting this phase may present challenges in those areas. Although the authors strongly recommend that such regions establish comprehensive databases for their bridge infrastructure, given the critical role bridges play in every transportation network, alternative approaches are suggested below. These recommendations, based on recent trends in the literature, aim to support implementation of the third phase, even in the absence of extensive data.

• Although this study utilized a database with a substantial number of features and target variables, the size of the database can be reduced through feature importance techniques. These techniques help identify and eliminate non-essential features. Notable methods include permutation feature importance [88], SHAP analysis [89], and Local Interpretable Model-Agnostic Explanations (LIME) [90]. After reducing the dataset, it can be customized to meet the specific needs of a DOT and refined with expert input.
• Collecting bridge condition ratings is often the most challenging task in data-scarce regions. However, advancements in technology and their increasing integration into the construction industry offer promising solutions. Modern structural health monitoring techniques such as deep learning–based image similarity analysis [91], AI-based Unmanned Aerial Systems (UASs) [15,92], and attention-enhanced co-interactive fusion networks (AECIF-Net) [93] can significantly aid in addressing these challenges.

To sum up, this study successfully developed a research roadmap for Idaho’s bridges using a three-phase methodology. While tailored to Idaho’s needs, the roadmap serves as a transferable framework for other DOTs, offering insights into recent advancements in bridge research and guiding the development of region-specific roadmaps. The proposed roadmap offers several practical benefits for asset managers, including structured decision making, resource optimization, scalability, stakeholder engagement, and continuous improvement.

Furthermore, compared to existing efforts by other agencies, such as those outlined in Section 1.1, this study presents a unique approach by combining a national literature review, peer agency practices, and local bridge condition assessments within a single, cohesive framework. This comprehensive strategy ensures that the identified research priorities are both evidence-based and tailored to local needs.

Lastly, beyond providing a replicable methodology, this work underscores the critical role of strategic research planning in addressing contemporary challenges. Ultimately, it aims to enhance bridge infrastructure resilience in an era marked by climate change and sustainability imperatives.

6. Summary and Conclusions

The Idaho Transportation Department (ITD) recognizes the importance of shifting from a reactive, ad hoc approach to research requests toward a more strategic and systematic framework. This transition aims to harmonize research initiatives, ensuring they are interconnected and mutually reinforcing to achieve more impactful results. To inform research recommendations that align with ITD’s priorities and address its needs, insights were drawn from two key tasks: (1) a review of best practices in bridge programs across other state Departments of Transportation (DOTs) and relevant literature and (2) the identification of critical knowledge gaps in the field.

To identify best practices in bridge programs, a comprehensive list of recent and ongoing research projects from state DOTs was gathered. This included 857 projects related to bridges and transportation structures sourced from the Transportation Research Board (TRB). To maintain relevance, only projects completed within the last five years were considered. These projects were then refined through a three-stage filtering and ranking process: (1) narrowing the list from 857 to 208, (2) further reducing it to 79, and (3) finalizing a shortlist of 25 projects.

The identification of critical knowledge gaps involved two primary activities: surveying out-of-state DOTs and analyzing the condition of deficiently rated bridges in Idaho. The DOT survey focused on bridge funding, research priorities, and the impacts of various initiatives. It revealed that bridge deck and superstructure funding were the highest priorities, with an average of sixteen percent of pooled funds allocated to these areas. Additionally, an analysis of deficiently rated bridge elements highlighted substructure components, such as reinforced concrete abutments, pier walls, and pile caps, as being in the most severe condition. The report suggested that frequent repairs or replacements of bridge decks, bearings, and rails could potentially prevent these elements from deteriorating further.

To develop research recommendations tailored to ITD’s priorities, project ideas were solicited from the research team and Technical Advisory Committee (TAC) members, guided by the findings from the two tasks above. This process generated twenty-three potential topics, which were then discussed and ranked. The top six projects were selected for further review and submission to ITD’s Research Advisory Committee (RAC). These projects include (1) Evaluating ITD’s Bridge Deck Preservation Strategies, (2) Implementing Internal Concrete Curing (ICC) to Enhance Concrete Performance, (3) Developing More Reliable Camber Predictions for Prestressed Deck Bulb-T Girders, (4) Utilizing Non-Proprietary Ultra-High-Performance Concrete in Idaho Bridges, (5) Assessing the Impacts of Type IL Cement on Bridge Structures, and (6) Modeling Bridge Deterioration. Overall, this study proposed a framework to develop a suitable research roadmap for bridge asset management applications, which is one of the most crucial components of infrastructure management.

Future research should extend the three-phase methodology developed in this study to establish strategic research roadmaps for other states, countries, or regions. Such efforts would not only promote the integration of research roadmaps into bridge engineering practice and advance bridge asset management systems globally but also empirically validate the generalizability of the proposed framework by this study. Concurrently, pilot studies of the highest-priority projects should be undertaken on representative Idaho bridge typologies to confirm the robustness of selected methodologies and to establish baseline performance metrics. These efforts may also help address limitations of the current study, particularly its specificity to Idaho and the practical applicability of the proposed research within the state.

Although this roadmap is calibrated to Idaho’s unique inventory and funding structures, its underlying framework (e.g., best-practice review, knowledge-gap analysis, stakeholder-driven topic selection, and ranked prioritization) can readily be adapted by other state or regional DOTs. By tailoring project-filtering criteria, survey instruments, and performance thresholds to local variables such as climate, bridge typology, and funding allocation, other agencies can implement an analogous, data-driven research program that aligns with their unique asset-management goals.