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    <title>Transport Research International Documentation (TRID)</title>
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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
    <image>
      <title>Transport Research International Documentation (TRID)</title>
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      <link>https://trid.trb.org/</link>
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    <item>
      <title>Micro-mechanical characterization of polymer-modified asphalt mixtures using discrete element modelling with soft-bond and linear contact bond models</title>
      <link>https://trid.trb.org/View/2624780</link>
      <description><![CDATA[Polymer-modified asphalt (PMA) mixtures offer improved performance compared with conventional binders, particularly in terms of crack resistance and durability under increasing traffic and environmental loading. However, capturing their micromechanical behavior and failure mechanisms remains challenging owing to their internal heterogeneity and particle-scale interactions. This study utilized the Discrete Element Method (DEM), implemented via the Particle Flow Code (PFC), to simulate Uniaxial Compressive Strength (UCS) and Indirect Tensile Strength (ITS) tests on PMA mixtures with varying specimen sizes and aggregate gradations. Two contact models, Linear Contact Bond (LCB) and Soft Bond (SB), were evaluated to represent tensile fracture and progressive bond degradation. The numerical models were calibrated and validated against the experimental results, which showed a deviation of less than 1.5 % in the compressive strength and modulus across the nine PMA formulations. A strength-size effect was observed and modeled, enabling the conversion of non-standard field core strengths to laboratory-equivalent values. Additionally, a high-resolution image dataset of asphalt surface distress (cracks, potholes, and marking degradation) was developed to support computer vision–based pavement monitoring. The integrated simulation and imaging framework presented in this study offers new insights into microscale failure behavior, supports more accurate field data interpretation, and contributes to intelligent maintenance strategies for resilient pavement infrastructure.]]></description>
      <pubDate>Wed, 07 Jan 2026 09:09:18 GMT</pubDate>
      <guid>https://trid.trb.org/View/2624780</guid>
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    <item>
      <title>Incentivizing U.S. Airport Privatization</title>
      <link>https://trid.trb.org/View/2589143</link>
      <description><![CDATA[All but one of the commercial airports in the U.S. are government owned. This paper looks at why airports in the U.S. have failed to become privatized or leased as public-private partnerships (P3s), the benefits of privatization, and possible tax reforms that could encourage privatization. The tax law changes discussed relate to the payment of outstanding tax-exempt airport bonds when there is a change in control, and the inclusion of airports in surface transportation tax-exempt private activity bonds (PABs). The paper outlines how long-term P3s might improve U.S. airport performance, how airport privatization could impact financial proceeds, and what the impact would be on federal tax revenue.]]></description>
      <pubDate>Thu, 18 Dec 2025 11:53:45 GMT</pubDate>
      <guid>https://trid.trb.org/View/2589143</guid>
    </item>
    <item>
      <title>Bond Vs. Pay-Go</title>
      <link>https://trid.trb.org/View/2606746</link>
      <description><![CDATA[This research examines the value of financing infrastructure improvements through bonding versus a program of pay-go improvements. Postponed construction becomes more costly in nominal terms because inflation raises the cost of construction over a longer period before construction begins. However, postponements can also create a variety of other situations. For example, postponements add to the level of damage that must be repaired when projects are subsequently let to contract. Both methods of finance encounter factors such as availability of funds and fiscal stability, inflation, population growth, as well as congestion growth rates, to name a few. While there is no one-size fits all answer, understanding how these factors influence the outcomes and when they may be applicable, allows policy makers to make more informed decisions for the future.]]></description>
      <pubDate>Thu, 16 Oct 2025 17:02:36 GMT</pubDate>
      <guid>https://trid.trb.org/View/2606746</guid>
    </item>
    <item>
      <title>Mechanical Model and Experimental Verification of Horizontally Layered Rock Beams for a Tunnel Roof with Different Bonding Strengths between the Layers</title>
      <link>https://trid.trb.org/View/2573055</link>
      <description><![CDATA[The interlayer plane denotes the relatively weak layer within the stratified rock mass, which significantly impacts the overall rigidity, strength, and stability of the tunnel roof. In this paper, based on the failure modes of tunnel roofs in a horizontally layered rock mass with varying interlayer bonding strengths, the equivalent section method was employed to derive two kinds of mechanical calculation models for the bending failure of multilayered rock beams characterized by high and low interlayer bonding strengths, respectively. Additionally, a calculation formula for the relative slipping deformation between layered rock beams with low bond strengths was developed. According to the similarity principle, horizontal multilayered rock beams composed of rocklike materials and similar interlayer bonding materials were prepared for indoor three-point bending tests to monitor the deformation and stress characteristics of the multilayered rock beams with different bonding strengths under external loads. The research results indicated the following: (1) There are significant differences in the internal forces and deformations of the rock beam during bending and failure under the two models. When the interlayer bond strength is high, each layer of the rock beam works together, and the stress conforms to the stress distribution law of the standard beam section; with the increase of external force, vertical cracks are developed, and there are no obvious separation and slip cracks. When the interlayer bond strength is low, the stress of each layer of the rock beam near the failure point is larger than that of the corresponding position of the high-bond-strength rock beam, there are concentrated interlaminar shear cracks and multiple vertical cracks, and obvious relative slip occurs between layers. (2) When high-bond-strength rock beams operate in unison, a decrease in interlayer bonding strength leads to a gradual reduction in flexure rigidity, while the peak load progressively increases. Conversely, when low-bond-strength rock beams work independently, there is a significant decline in both their peak load and flexure rigidity. (3) The three-point bending tests of multilayered rock beams validate the mechanical calculation models of the composite rock beam with high bonding strength and the laminated rock beam with low bonding strength, which elucidates the working mechanism of multilayered rock beams under varying interlayer bonding strengths. This research objectively reflected the internal force and deformation characteristics of rock beams during bending, providing a valuable theoretical reference for tunnel roof stability analysis.]]></description>
      <pubDate>Mon, 08 Sep 2025 14:54:04 GMT</pubDate>
      <guid>https://trid.trb.org/View/2573055</guid>
    </item>
    <item>
      <title>Bond Performance for Corroded and Epoxy-Coated Steel and Glass Fiber Reinforced Polymer Dowel Bars</title>
      <link>https://trid.trb.org/View/2562017</link>
      <description><![CDATA[Installing dowel bars at rigid pavement joints provides load transfer to adjacent slabs, and the bond between the dowel bars and the surrounding concrete plays an important role. However, the abrasion incurred in the transportation of bars before installation and the development of dowel bar corrosion due to deicing agents can reduce the effectiveness of the load transfer mechanism. Consequently, the reduced performance of the dowel bars can lead to accelerated pavement deterioration. The goal of this study is to quantify the effects of corrosion on the bond strength between the dowel bar and concrete using pullout testing. The study uses three dowel bar materials: uncoated carbon steel, epoxy-coated carbon steel, and glass-fiber reinforced polymer (GFRP). The uncoated steel dowel bars were subjected to accelerated corrosion at different levels, reflecting varying in-field deterioration states. The pullout strength and variation between the pullout force and dowel bar displacement were obtained for the various materials following the AASHTO T 253 procedure. Through the findings of this study, the long-term bonding behavior of steel dowel bars in rigid pavement can be accurately represented in the corroded state and compared with non-metallic options.]]></description>
      <pubDate>Mon, 30 Jun 2025 09:17:39 GMT</pubDate>
      <guid>https://trid.trb.org/View/2562017</guid>
    </item>
    <item>
      <title>Construction Contracting in the Zero Emission Transportation Sector: Evidence from Underrepresented Businesses</title>
      <link>https://trid.trb.org/View/2445215</link>
      <description><![CDATA[This study investigates the degree to which underrepresented construction contractors face challenges in California's zero-emission transportation sector to devise a simpler and more efficient bonding structure. Using a survey dispersed over underrepresented businesses across the state, the study provides several suggestions for a statewide bonding program that caters to the needs of contractors. Both qualitative and quantitative methods are used in the study. The survey data are evaluated using econometric tools to analyze whether there are any statistically significant associations between contractors' characteristics and their industry experiences. Focus groups and focused interviews are conducted to identify those perspectives the survey does not capture, enhancing the quantitative results with firsthand accounts from contractors. This research reveals that many barriers prevent underrepresented businesses from competing effectively and having a more efficient bonding structure. The main obstacles include lack of funds, redundancies in the system such as the retention requirement, insufficient availability of necessary resources, the presence of unconscious bias, problems encountered in guaranteeing faster payments by having a payment clause that works very similarly to the federal system, and relatively high percentages required for bonding and lack of statewide consistency of funding assistance in the bonding process. These businesses exhibit a lack of information and trust regarding the efficacy and accessibility of these programs. The findings indicate the need for legislative changes that prioritize increasing these contractors' access to resources, transparency, prompt automatic payment, and mentee-mentor support. The study also recommends reorganizing the current support systems, such as by implementing an online forum to assist underrepresented contractors, enabling them to compete and cooperate more effectively and contribute to a more equitable and sustainable zero-emission transportation sector in California.]]></description>
      <pubDate>Tue, 12 Nov 2024 09:14:03 GMT</pubDate>
      <guid>https://trid.trb.org/View/2445215</guid>
    </item>
    <item>
      <title>Fatigue Behavior in the Carbon-Fiber-Reinforced Polymer-to-Concrete Bond by Cyclic Pull-Out Test: Experimental and Analytical Study</title>
      <link>https://trid.trb.org/View/2174440</link>
      <description><![CDATA[Today’s construction industry has been more inclined to apply innovative rehabilitation techniques, including externally bonded (EB) fiber-reinforced polymer (FRP) composites on existing RC structures, rather than traditional strengthening methods. Indeed, the higher fatigue resistance of carbon FRPs (CFRPs) has made them superior strengthening tools for structures subjected to fatigue loading, such as RC bridge girders against daily traffic loads. However, the performance of RC structures retrofitted with EB–CFRP composites can be highly influenced by the bonding mechanism at the CFRP-to-concrete interface. The occurrence of debonding failure at the CFRP-to-concrete interface can result in premature failure of the EB–CFRP retrofitting system, thereby leading to rupture of the deficient structure. Therefore, an in-depth understanding of the bond behavior, especially under fatigue loading, would contribute to improving the efficiency of EB–CFRP strengthening techniques. To this end, in this work, the authors investigated the bond fatigue behavior through an experimental study. The parameters of CFRP composite type (laminate vs. fabric sheet), bond length, and CFRP-to-concrete width ratio were considered herein in order to examine their effectiveness on fatigue bond performance at the CFRP-to-concrete interface. The research results revealed that the CFRP composite system composed of the fabric sheet CFRP and the corresponding epoxy adhesive performed better than the CFRP-bonded joint with laminate CFRP in terms of fatigue life and residual load-carrying capacity. Furthermore, a modified bond fatigue-life model (S–N model), validated with existing research data, was proposed that successfully takes into consideration the effects of fatigue loading, concrete compressive strength, and CFRP-to-concrete width ratio.]]></description>
      <pubDate>Wed, 28 Jun 2023 16:29:13 GMT</pubDate>
      <guid>https://trid.trb.org/View/2174440</guid>
    </item>
    <item>
      <title>Interfacial bond in concrete-to-concrete composites: A review</title>
      <link>https://trid.trb.org/View/2060111</link>
      <description><![CDATA[Concrete-to-concrete composites have been widely used in a broad range of applications such as buildings, bridges, pavements, dams and tunnels. Numerous studies have been carried out to characterize the structural performance of these composites. This paper presents a state-of-the-art review and key information on the performance of concrete-to-concrete composites. Specifically, design and environmental factors (interface condition, bonding agents, concrete properties, mismatch in overlay and substrate, fibers and admixtures, temperature, humidity) are reviewed and discussed. The test methods developed to determine bond strength under various load combinations are also described. The findings show that a proper selection of overlay and bonding agent composition, interface condition, casting and curing conditions as well as assessment techniques not only result in greater structural performance and durability but also in an optimized material usage and casting cost, leading to a more sustainable approach. Considering the growing application of layered concretes in the recent decade, this review aims at clarifying the parameters that maximize the performance of these composites and at supporting engineers and practitioners in optimizing their composites.]]></description>
      <pubDate>Fri, 30 Dec 2022 09:17:44 GMT</pubDate>
      <guid>https://trid.trb.org/View/2060111</guid>
    </item>
    <item>
      <title>Fundamental Development of Monitoring for Signal Bonds</title>
      <link>https://trid.trb.org/View/2047363</link>
      <description><![CDATA[When the signal bond for a track circuit falls off, the train operation will be suspended. East Japan Railway Company regularly conducts visual inspection and checks the state of signal bonds many times. However, that takes much labor and is very difficult. The authors thus studied abnormality detection for signal bonds by image recognition in order to reduce the number of periodic inspections.]]></description>
      <pubDate>Fri, 23 Dec 2022 14:07:04 GMT</pubDate>
      <guid>https://trid.trb.org/View/2047363</guid>
    </item>
    <item>
      <title>Bonding vs. Pay-as-You-Go</title>
      <link>https://trid.trb.org/View/2087690</link>
      <description><![CDATA[The objective of this study is to determine the value of financing infrastructure improvements through bonding versus a program of pay-go improvements.]]></description>
      <pubDate>Mon, 31 Jul 2023 08:21:16 GMT</pubDate>
      <guid>https://trid.trb.org/View/2087690</guid>
    </item>
    <item>
      <title>TCRP Research Report 222: Green Bonds and the Transit Industry</title>
      <link>https://trid.trb.org/View/1926610</link>
      <description><![CDATA[Transit Cooperative Research Program (TCRP) Research Report 222: Analysis of Green Bond Financing in the Public Transportation Industry provides transit agencies and other stakeholders with more detailed information about green bonds and resources to develop green bond programs. The report covers key concepts, such as the main components of green bonds, elements that differentiate green bonds from traditional bonds, and costs and benefits of issuing green bonds instead of traditional bonds. This article includes an overview of green bond funding, types of investors attracted to green bonds, advantages and disadvantages of green bonds, and practical tips for the use of green bonds in transit.]]></description>
      <pubDate>Wed, 16 Mar 2022 10:19:37 GMT</pubDate>
      <guid>https://trid.trb.org/View/1926610</guid>
    </item>
    <item>
      <title>Effects of the COVID-19 crisis on airport investment grades and implications for debt financing</title>
      <link>https://trid.trb.org/View/1764317</link>
      <description><![CDATA[While a rich body of literature on airport performance has been established during the last three decades, significantly less attention has been given to related financing aspects — although these are directly influencing the cost structure of an airport, thus affecting financial performance. This paper discusses bond financing as one of the funding options of an airport company and how it is impacted on by the COVID-19 pandemic. According to the law of risk and return, the price (interest) which the issuer needs to pay to raise money in the capital markets correlates to its risk profile as reflected by an investment grade. Such bond ratings are opinions assigned by credit rating agencies of the creditworthiness of the issuer’s debt. Globally reputable examples are Fitch Ratings, Moody’s Investor Service and Standard & Poor’s. The black swan COVID-19 brought air transportation to a standstill and keeps eroding credit metrics of airlines and airports. This study is compares the credit ratings of 113 airports per year end 2019 vs investment grades assigned during the first semester 2020 (1H20). Comparable to the global financial crisis 2008/09, the number of downgrades has been limited, with most actions resulting in a one notch decrease. Privately owned airport operators have been concerned higher-than-average. The negative outlook, however, almost affected the entire sector. Investment grades appear to be more stable than share prices, which seem to be more volatile and to trigger rating actions. Nevertheless, the cost of capital for the bond financed share of debt tends to go up according to the risk and return trade-off.]]></description>
      <pubDate>Tue, 25 May 2021 16:20:03 GMT</pubDate>
      <guid>https://trid.trb.org/View/1764317</guid>
    </item>
    <item>
      <title>Analysis of Green Bond Financing in the Public Transportation Industry</title>
      <link>https://trid.trb.org/View/1766770</link>
      <description><![CDATA[This report provides public transit agencies with an introduction to green bonds and how they can be used to advance the sustainability goals of those agencies. The report uses case studies to provide public transit agencies with the context and knowledge needed to understand the complexity of green bond issuance. The target audiences are public transit systems of all sizes and their stakeholders, including policymakers, transit board members, elected officials, and public transit agency managers and financial officers who are seeking new opportunities to finance public transportation. The report will also be useful to financial and legal advisors, as well as individual investors. The report is organized into eight chapters; the initial chapters introduce green bonds and provide an overview of the green bond market and transit green bonds. Subsequent chapters explain the costs and risks of green bonds versus traditional bond financing, the benefits of green bonds, how green bonds advance sustainability goals of public transit agencies, and alternatives to green bonds. Chapters 6 and 7 provide agencies interested in issuing green bonds with practical steps to follow, and they highlight case studies and lessons learned. The appendix at the end of this report provides several valuable resources that public transit agencies can utilize to expand their understanding of sustainable finance and make informed decisions on how best to incorporate the available resources into their strategies going forward.]]></description>
      <pubDate>Tue, 16 Feb 2021 15:58:36 GMT</pubDate>
      <guid>https://trid.trb.org/View/1766770</guid>
    </item>
    <item>
      <title>Whatever floats your vote: understanding voter support for public port infrastructure investments</title>
      <link>https://trid.trb.org/View/1754690</link>
      <description><![CDATA[Ports are a cornerstone of the local, state, and national economy, especially for coastal cities. However, ports face growing economic challenges that require infrastructure financing, and a relevant avenue of securing funds is through government assistance via bond issues. We examine voter support for the public financing of port infrastructure investments using a 2016 referendum in Rhode Island. Through our multiple regression voting model, we find strong evidence that public spending on ports in Rhode Island was more of a bipartisan issue compared to other public financing efforts on the ballot. Additionally, neighborhoods with a larger minority presence and those with higher median per capita income were more likely to support port development. In contrast, areas with a higher homeowner population and those communities farther from ports were less likely to support port spending. As a key novelty to our paper, we use our voting model results to forecast how a hypothetical port infrastructure bond might fare in other states, and find that regardless of socioeconomic and political differences, all coastal states in the US would be expected to pass a port referendum.]]></description>
      <pubDate>Mon, 21 Dec 2020 10:02:00 GMT</pubDate>
      <guid>https://trid.trb.org/View/1754690</guid>
    </item>
    <item>
      <title>Persistent, Historic Factors Correlated with Airport Bond Returns</title>
      <link>https://trid.trb.org/View/1756001</link>
      <description><![CDATA[The factors that are associated with returns on airport bonds are explored, using a proxy for an airport bond portfolio with the S&P Municipal Bond Airport Index. Six spread-based factors representing the tax status, term length, credit quality, bond type, infrastructure, and insurance status of airport bonds provide the independent variables. Five models are developed to test for bonds’ risk exposure to these characteristics and to analyze how these exposures for airport bonds differ from those of general transportation bonds or municipal bonds. Over 90% of the variation in returns on the airport index is explained by these factors. When determining risk premiums on airport bonds relative to other transportation bonds, investors appear to consider the bond type and infrastructure factors as being most relevant. However, when transportation bonds are compared with other municipal bonds, all factors except the insurance factor act as risk premiums. The component of airport bond returns not associated with these factors is partially explained by monthly changes in jet fuel prices and enplanements across all U.S. airports. These results can help airport bond issuers to evaluate the relative costs of raising funds through debt issues, and understand the trends in the bond market that are more strongly associated with prices and expected returns in the airport bond sector. Hedges against fuel price, enplanement changes, or both, may also be actions that airport bond issuers could consider outside of traditional financial planning practices to manage trends in the bond markets.]]></description>
      <pubDate>Mon, 07 Dec 2020 11:58:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/1756001</guid>
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