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    <title>Research in Progress (RIP)</title>
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    <atom:link href="https://rip.trb.org/Record/RSS?s=PHNlYXJjaD48cGFyYW1zPjxwYXJhbSBuYW1lPSJzdWJqZWN0aWQiIHZhbHVlPSIxNzgzIiAvPjxwYXJhbSBuYW1lPSJkYXRlaW4iIHZhbHVlPSI3MzAiIC8+PHBhcmFtIG5hbWU9InN1YmplY3Rsb2dpYyIgdmFsdWU9Im9yIiAvPjxwYXJhbSBuYW1lPSJ0ZXJtc2xvZ2ljIiB2YWx1ZT0ib3IiIC8+PHBhcmFtIG5hbWU9ImxvY2F0aW9uIiB2YWx1ZT0iMTYiIC8+PC9wYXJhbXM+PGZpbHRlcnMgLz48cmFuZ2VzIC8+PHNvcnRzPjxzb3J0IGZpZWxkPSJwdWJsaXNoZWQiIG9yZGVyPSJkZXNjIiAvPjwvc29ydHM+PHBlcnNpc3RzPjxwZXJzaXN0IG5hbWU9InJhbmdldHlwZSIgdmFsdWU9InB1Ymxpc2hlZGRhdGUiIC8+PC9wZXJzaXN0cz48L3NlYXJjaD4=" rel="self" type="application/rss+xml" />
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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>
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      <title>Research in Progress (RIP)</title>
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      <link>https://rip.trb.org/</link>
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    <item>
      <title>Active-Inference Control and Sensor-Fusion Simulation for Bicycle Stabilization in Aging Rider Mobility Systems </title>
      <link>https://rip.trb.org/View/2762039</link>
      <description><![CDATA[Low-speed fall events are the leading cause of cycling injuries among older adults, generating 25,000–40,000 annual emergency-department visits and more than $50B in national medical costs. (CDC, 2022; Weiss & Elixhauser, 2012; NCBI, 2012) These incidents primarily occur during mounting, slow riding, deceleration, and stopping—contexts where traditional steering-based stability controls, passive safety devices, and prior gyroscopic concepts fail to prevent loss of balance. 
StaeblTECH has developed a dual–Control-Moment-Gyroscope (CMG) stabilization prototype designed to proactively prevent these falls. Its success depends on a predictive, adaptive control architecture that can learn individual rider characteristics and manage uncertainty. Active Inference (AIF), a unified probabilistic framework for perception, prediction, and action, offers capabilities not available in conventional PID or Model Predictive Control (MPC) systems. (Bagaev & de Vries, 2023) 
This project develops the simulation-based control and sensor-fusion foundation required to integrate AIF into StaeblTECH’s stabilization platform. Leveraging MnRI’s robotics simulation environment, the research team will: (1) build a high-fidelity digital twin of bicycle, rider, and dual-CMG dynamics; (2) implement and tune AIF controllers using message-passing variational inference; (3) integrate IMU, optical-flow, and load-sensor data to evaluate latency, noise sensitivity, and perceptual accuracy; and (4) benchmark AIF performance against PID and MPC baselines using a 7-degree-of-freedom bicycle model. 
All outputs including AIF controllers, sensor-fusion models, stability metrics, and digital-twin datasets directly support StaeblTECH’s NIH Direct-to-Phase II proposal by providing validated simulation results and de-risking subsequent hardware development. This project strengthens Minnesota’s leadership in artificial intelligence (AI)-assisted mobility, addresses a critical aging-transportation challenge, and positions the UMN–StaeblTECH partnership for future federal funding. ]]></description>
      <pubDate>Wed, 19 Aug 2026 10:45:20 GMT</pubDate>
      <guid>https://rip.trb.org/View/2762039</guid>
    </item>
    <item>
      <title>Extending the Simple for Dead Load and Continuous for Live Load (SDCL) Steel Bridge System to Short Span Box Sections with Shallow Depth and Thin Bottom Flanges for ABC Application</title>
      <link>https://rip.trb.org/View/2745181</link>
      <description><![CDATA[The project develops a new box configuration formed by bending a flat steel plate into a U-shape and welding tension flanges to complete the section. This fabrication approach reduces depth, simplifies detailing, and allows integration with reinforced concrete decks while preserving SDCL behavior. To enhance local buckling resistance of the thin bottom flange near supports, a thin concrete layer will be added externally. Additionally, Ultra-High-Performance Concrete (UHPC) diaphragms will be explored to improve force transfer, simplify connection details, and increase durability in pier regions.
The research includes (1) development of detailed nonlinear finite element models to evaluate structural behavior and conduct parametric studies; (2) laboratory testing of prototype shallow SDCL box sections to validate the analytical findings; (3) development of practical design recommendations, tables, and provisions tailored for spans up to 80 ft; and (4) preparation of sample design plans to facilitate immediate adoption by state DOTs and consulting engineers.]]></description>
      <pubDate>Fri, 07 Aug 2026 08:32:50 GMT</pubDate>
      <guid>https://rip.trb.org/View/2745181</guid>
    </item>
    <item>
      <title>Synthesis and Verification of Link Slab Practices for Jointless Bridge Decks in Accelerated Bridge Construction (ABC)</title>
      <link>https://rip.trb.org/View/2744923</link>
      <description><![CDATA[Bridge deck expansion joints are among the most maintenance-intensive
components of highway bridges, often leading to premature deterioration,
increased repair costs, and reduced service life. Link slabs provide an effective
alternative by enabling jointless deck configurations, improving durability, and
reducing long-term maintenance demands. Despite their proven benefits,
inconsistencies in design methodologies particularly regarding the need for deck
debonding and the use of advanced materials such as Ultra-High-Performance
Concrete (UHPC) have limited their broader adoption in Accelerated Bridge
Construction (ABC) applications. Early studies recommended partial debonding
near girder ends, while more recent large-scale investigations, such as SHRP2
R19A, concluded that debonding may not be required. At the same time, UHPC-based link slabs have demonstrated excellent crack control and durability, yet
remain without standardized design guidance. This project aims to synthesize
existing research, field applications, state DOT practices, and emerging material
innovations to establish practical best practices for link slab design. To this end,
the current study will (1) compile and evaluate past research and
implementations, (2) compare conventional and UHPC-based link slab
approaches, (3) conduct analytical and limited experimental verification to resolve
conflicting recommendations, and (4) develop design provisions and example
details suitable for ABC applications. The proposed work will produce a
comprehensive synthesis report, validated guidance, and actionable
recommendations for DOTs and practitioners. By clarifying design assumptions,
addressing uncertainties in debonding requirements, and evaluating the role of
UHPC, this study will promote the consistent and reliable use of link slabs in
jointless bridge decks.]]></description>
      <pubDate>Fri, 07 Aug 2026 08:21:45 GMT</pubDate>
      <guid>https://rip.trb.org/View/2744923</guid>
    </item>
    <item>
      <title>Enhanced Understanding of Concrete Pavement Performance</title>
      <link>https://rip.trb.org/View/2731921</link>
      <description><![CDATA[Michigan’s wet-freeze climate causes pavement durability issues such as freeze-thaw scaling, while salt exposures
significantly impact the long-term performance of Jointed Plain Concrete Pavements (JPCP). These environmental stressors
initiate joint staining and can progress to joint spalling, eventually lead to structural failures like shear cracking under traffic
loads. Structural inputs like slab thickness and modulus of rupture govern mechanical performance, while durability factors
influence how a JPCP pavement degrades over time. These material properties affect roughness and service life. In addition,
the University of Michigan (UofM) Center can provide specialized technical expertise and examinations related to further development of its pavement
design program, specifically as it relates to Pavement Mechanistic-Empirical Design (PMED).]]></description>
      <pubDate>Fri, 17 Jul 2026 13:20:05 GMT</pubDate>
      <guid>https://rip.trb.org/View/2731921</guid>
    </item>
    <item>
      <title>Enhanced Understanding of Hot Mix Asphalt (HMA)</title>
      <link>https://rip.trb.org/View/2731920</link>
      <description><![CDATA[Michigan Department of Transportation (MDOT) interest is to have the Michigan State University (MSU) Center provide specialized technical expertise and examinations related to further development of its pavement design program, specifically as it relates to Pavement Mechanistic-Empirical Design (PMED).]]></description>
      <pubDate>Fri, 17 Jul 2026 13:08:30 GMT</pubDate>
      <guid>https://rip.trb.org/View/2731920</guid>
    </item>
    <item>
      <title>Designing and Constructing Permanent Stable Foundation Layers in Areas of Sulfate Rich Soils</title>
      <link>https://rip.trb.org/View/2727387</link>
      <description><![CDATA[The presence of a suitable foundation layer plays a significant role in the constructability and long-term performance of pavements. During construction, these layers must provide sufficient support for placement and compaction of subsequent pavement layers, and during service life, these foundation layers play a critical role in the pavement structure by supporting the upper pavement layers and spreading loads to provide long-term pavement performance. When designed correctly, lime stabilized layers have a long history of providing permanent support in areas of plastic soils. However, lime has been removed from recent projects because of concerns over soluble sulfates. The use of select fill and geogrids has not provided projects with the support needed to successfully complete construction, and in some cases even handle construction traffic. These failures cost millions of dollars to fix and result in significant project delays. Adequate and permanent foundation layers are critical to performance of both flexible and rigid pavement structures. The research team will document the effectiveness of current practices for identifying sulfates on construction projects and determine if new or improved technologies exist to more effectively and reliably detect sulfates. The research team will deploy these tools on actual construction projects and document their effectiveness. Using advanced lab testing, the research team will determine treatment alternatives for soils containing sulfates. Based on the findings, the research team will recommend soil treatment or pavement structural design alternatives to provide permanent and stable foundation layers. The findings from this project shall be used to recommend updates to project selection, treatment guidelines, test procedures, specifications, and the Pavement Manual.]]></description>
      <pubDate>Fri, 10 Jul 2026 16:37:15 GMT</pubDate>
      <guid>https://rip.trb.org/View/2727387</guid>
    </item>
    <item>
      <title>Load Capacity of Temporary Railcar Bridges in Western North Carolina</title>
      <link>https://rip.trb.org/View/2726549</link>
      <description><![CDATA[As a result of Hurricane Helene in late 2024, the spanning members of nearly three dozen temporary bridges in Western North Carolina (WNC) are (or were recently) comprised fully or partially of repurposed flatbed railroad cars.  Many of these bridges will need to stay in operation for long durations before permanent replacements can be completed, necessitating a detailed study of these temporary structures, especially from the perspective of load rating.  The bulk of published literature on railroad flatcar (RRFC) bridges is generally focused on permanent structures with composite concrete decks, which the temporary structures in WNC do not have.  Additionally, prior work on RRFC bridges with non-composite steel or timber decks and/or non-composite asphalt wearing surfaces is generally focused on RRFCs of a different geometry and/or span than the RRFCs currently in use in WNC.  As such, proposed study of the WNC RRFCs is justified by a goal to develop load rating methods and tools for the current temporary applications (or similar applications in the future).  In addition, a secondary goal involves determining the rated load capacities of existing RRFCs in a variety of potential future use scenarios, as the Department plans to store RRFCs for future use once existing temporary structures are removed from service. A chart of load ratings for different types of flatcars in different conditions supported on different spans would be useful for future deployments.

The proposed work will accomplish the goals by first measuring the geometry and documenting the condition of a wide range of existing RRFC bridges in WNC.  An estimated 10-15 bridges will be measured using traditional methods.  These measurements are necessary because railroad flatcar designs are not standardized – many manufacturers have existed over the years that have produced many specific flatcar designs for different railroad specifications.  Thus, while the RRFCs in use in WNC appear to be of one general type (Type FM, F-class, 90’ length), at least two variations are currently in temporary bridge service in the state.

With the likely range of geometry and structural condition of the WNC railcar fleet documented, finite element models will be developed in Abaqus to reflect idealized versions of this geometry for all significant flatcar variants in service.  Rolling loads will be applied numerically to the models, enabling a detailed study of RRFC bridge performance under a variety of conditions. Parameters can then be varied in the models to study the effects of material properties, span lengths, damage levels, adjacent connected flatcars, and other relevant factors.

Critical to developing a finite element model (FEM) will be validating that model with experimental data prior to running the parametric analyses.  Data from limited field testing will be available from recently completed preliminary work, but full-scale experimental tests are proposed as part of this research.  Two full-scale railroad flatcars are proposed to be tested to failure in the structures laboratory at NC State University or at a North Carolina Department of Transportation storage yard.  Data will be collected during each test to include loads, deflections, and strains, enabling validation and benchmarking of the FEM.  Together, the experimental and analytical results will be used to create outputs useful for load rating temporary bridges, including proposed load rating methods and simplified design tools, such as capacity charts, specific to the types of cars in WNC and a variety of possible RRFC bridge configurations. 
]]></description>
      <pubDate>Thu, 09 Jul 2026 08:53:50 GMT</pubDate>
      <guid>https://rip.trb.org/View/2726549</guid>
    </item>
    <item>
      <title>Effectiveness of IDEAL-RT Test in Assessing Rutting Resistance of NC Asphalt Mixtures</title>
      <link>https://rip.trb.org/View/2726545</link>
      <description><![CDATA[To limit rutting in asphalt pavements, North Carolina Department of Transportation (NCDOT) requires that surface asphalt mixtures meet the Asphalt Pavement Analyzer (APA) test criteria. Mixtures with rut depths below the specified threshold under APA loading are accepted. However, the APA test has several limitations: (1) it requires six hours of temperature conditioning and over two hours of testing, making its long turnaround time suitable only for mix design and acceptance; (2) the device is expensive, heavy, and requires significant laboratory space, limiting accessibility for contractors; and (3) state highway agencies (SHAs) have reported high variability in test results and insufficient correlation with field performance. To ensure pavement performance while reducing testing costs, it is imperative to identify a practical alternative method for evaluating the rutting resistance of asphalt mixtures in North Carolina.

The IDEAL-RT test has recently gained prominence due to its simplicity, rapid execution, and strong predictive capability. Multiple SHAs have adopted it for mix design, acceptance, and quality assurance. As a promising alternative to the APA, it is essential to evaluate the effectiveness of the IDEAL-RT test for North Carolina mixtures.

Correspondingly, the objectives of the proposed research project are to: (1) evaluate the effectiveness of the IDEAL-RT test using NC mixtures, (2) determine the optimum testing condition of the IDEAL-RT test, (3) determine preliminary performance criteria for NC mixtures, and (4) draft testing specifications for its implementation in NC. These objectives will be accomplished by executing the following six tasks: (1) Literature Review: Conduct a comprehensive review to collect information on procedures, testing conditions, acceptance limits, and validation methods for rutting performance tests used by other SHAs. Identify NC mixtures with documented rutting performance. (2) Material Acquisition and Testing: Acquire twelve NC surface mixtures and perform APA, IDEAL-RT, and Stress Sweep Rutting (SSR) tests. (3) Evaluation of IDEAL-RT Effectiveness: Compare IDEAL-RT results with APA rut depths and RSI indices from the SSR test at the material level. At the structural level, compare rankings of mixtures from the IDEAL-RT with both field performance and predicted performance from FlexPAVE (using SSR results as inputs). (4)  Testing Conditions and Thresholds: Recommend the appropriate air void level for IDEAL-RT samples and establish preliminary threshold limits based on findings from Task 3.
(5) Specification Development: Develop a draft testing specification for IDEAL-RT within the framework of NCDOT standards. The specification will consider applications in both mix design and quality assurance (QA). (6) Final Report: Prepare a comprehensive final report summarizing all tasks, findings, and recommendations.

The research will produce an improved testing specification to ensure asphalt mixture quality and performance in both mix design and QA. Implementation of the specification will also reduce the cost and turnaround time of rutting susceptibility testing for asphalt mixtures in North Carolina.

]]></description>
      <pubDate>Thu, 09 Jul 2026 08:35:20 GMT</pubDate>
      <guid>https://rip.trb.org/View/2726545</guid>
    </item>
    <item>
      <title>IMG2Speed: Generative AI and Multimodal Machine Learning for Predicting Operating Speed Distributions from Roadway Design and Context</title>
      <link>https://rip.trb.org/View/2725360</link>
      <description><![CDATA[Designers set target speeds to achieve safe operations, yet observed operating speeds often diverge because the influence of geometric and contextual elements (e.g., lane width, medians, trees, curb extensions, etc.) is not quantified in a way that is practical for design. A modern data-driven machine learning approach can be a potential solution to learn the quantitative mapping from observable design elements to operating speed distributions. This project proposes to (i) automate data curation from spot-speed reports using Generative Artificial Intelligence (AI) like Large/Vision Language Models (LLMs/VLMs); (ii) fuse the curated evidence base with street-view imagery and Geographic Information System (GIS)/context layers to extract geometric and streetscape attributes; and (iii) develop a machine learning (ML) model that estimate the percentiles of operating speeds used in practice (e.g, median, 85th) from cross-section and visual/context features.]]></description>
      <pubDate>Wed, 08 Jul 2026 16:24:39 GMT</pubDate>
      <guid>https://rip.trb.org/View/2725360</guid>
    </item>
    <item>
      <title>Developing Guidance on the Safety Performance of Edge Line Pavement Markers and Guardrail Delineations on Rural Oregon Roads</title>
      <link>https://rip.trb.org/View/2724855</link>
      <description><![CDATA[Despite Oregon's efforts to reduce fatalities and serious injuries, crashes along curves (statewide) continue to be high-risk locations, particularly those involving roadway departures.  Contributing factors such as speed, visibility, pavement quality, limited delineation, and adverse weather conditions exacerbate these risks.  While Oregon incorporates edge line pavement markers and guardrail delineations, there is limited research on their safety performance on Oregon specific rural roads. It will also investigate whether combining edge line pavement markers with guardrail and barrier delineations as part of a systemic safety countermeasure strategy provides greater safety benefits than applying treatments individually.

This research will produce a guidance document outlining recommendations for the use of edge line pavement markers and guardrail delineations on rural curves.  The document will provide: (1) criteria for identifying high-risk curves where these treatments will be most effective, considering factors such as crash history, speed, curve geometry, and environmental conditions; (2) guidance on combining edge line pavement markers with guardrail and barrier delineations as a systemic safety countermeasure strategy to achieve greater safety benefits; (3) scalable solutions tailored to rural curves that address Oregon’s unique roadway environments and crash patterns; and (4) performance evaluation framework for ongoing assessment and monitoring of these countermeasures.]]></description>
      <pubDate>Wed, 08 Jul 2026 15:06:03 GMT</pubDate>
      <guid>https://rip.trb.org/View/2724855</guid>
    </item>
    <item>
      <title>Design Guidelines for Bridge Pile Foundations Subjected to Combined Inertial and Liquefaction-Induced Lateral Spreading Loads</title>
      <link>https://rip.trb.org/View/2724825</link>
      <description><![CDATA[Earthquake induced soil liquefaction can result in significant displacements in sloping ground. This type of displacement is referred to as lateral spreading and is considered a substantial hazard to Oregon bridges. One current challenge facing bridge foundation design is the knowledge gap regarding appropriate selection of load factors for combining lateral spreading loads (kinematic) and superstructure inertial loads (inertia). Unfortunately, there is no consensus in design codes for how to combine inertial and kinematic loads. Failure to address this knowledge gap presents challenges for Oregon Department of Transportation (ODOT) engineers and designers. If lateral spreading and superstructure inertial loads interact during an earthquake, neglecting their combined effects could lead to inadequate and unsafe designs. Conversely, overconservatively combining these loads may result in costly, non-constructible foundations, particularly for piles passing through stiff, non-liquefiable crusts overlying deep liquefiable soils on sloped grounds. 

The primary objective of this research is to solidify ODOT’s design guidelines for combining superstructure inertial and lateral spreading loads in a pseudo-static analysis. The inertial and kinematic load interaction factors will be characterized by accounting for differences in seismicity in Eastern and Western Oregon, foundation types, and the complexity levels of design methods utilized in various ODOT projects. The proposed methodology for combining superstructure inertial and lateral spreading loads in a pseudo-static analysis will be detailed in a practice-ready recommended amendment to the ODOT Geotechnical Design Manual (GDM) and ODOT Bridge Design Manual (BDM).]]></description>
      <pubDate>Wed, 08 Jul 2026 14:50:18 GMT</pubDate>
      <guid>https://rip.trb.org/View/2724825</guid>
    </item>
    <item>
      <title>Efficacy, Advancement, and Monitoring of Carbon Fiber Composite Cable (CFCC)</title>
      <link>https://rip.trb.org/View/2724770</link>
      <description><![CDATA[Carbon Fiber Composite Cable (CFCC), and the Carbon Fiber Reinforced Polymer (CFRP) materials are being used for prestressing
applications in Michigan bridge rehabilitation and replacement projects with the most recent generation of CFCC is a 0.7-inch strand
configuration. The quantity of stands is similar to conventional strands, and concomitant updated design criteria. Determining the
efficacy of the new 0.7-inch CFCC strand long-term behavior is essential for future design and construction considerations.
Monitoring the CFCC elements in newly constructed bridges (with 0.7-inch strands) and some prior construction (from OR14-039)
will provide an understanding of the long-term behavior and realizations of recommendations on future designs, and continued
considerations of field deployment.]]></description>
      <pubDate>Tue, 07 Jul 2026 10:05:57 GMT</pubDate>
      <guid>https://rip.trb.org/View/2724770</guid>
    </item>
    <item>
      <title>Evaluating Cross-Slope Safety Impacts on Freeways in Georgia</title>
      <link>https://rip.trb.org/View/2717526</link>
      <description><![CDATA[The main objective of this proposed project is to quantify the relationship between freeway cross-slopes and grades and crashes during wet-weather conditions. Given the study’s focus on evaluating the safety impacts of cross-slopes, the analysis will concentrate on tangent freeway segments, as these are more representative of basic freeway sections and are subject to consistent cross-slope design guidance. 
]]></description>
      <pubDate>Wed, 24 Jun 2026 13:02:14 GMT</pubDate>
      <guid>https://rip.trb.org/View/2717526</guid>
    </item>
    <item>
      <title>Development of an IDEAL-Low Temperature (IDEAL-LT) Test for Balanced Mix Design and Acceptance in Cold Regions</title>
      <link>https://rip.trb.org/View/2717330</link>
      <description><![CDATA[State departments of transportation (DOTs) in cold regions are increasingly encountering premature pavement failures, including low-temperature transverse and block cracking, despite adherence to existing design standards, construction methods, and material specifications. These cracks form when thermal stress exceeds the asphalt mixture’s strength during severe temperature drops. Thermal stress accumulation is driven by thermally induced strain, which depends on the mixture’s coefficient of thermal contraction (CTC) and relaxation modulus. However, current mix design practices primarily rely on asphalt binder properties such as stiffness and m-value (a parameter indicating the rate at which asphalt binder stiffness changes over time under stress) from the Bending Beam Rheometer while neglecting CTC and mixture strength at low temperatures. This limits the reliability of evaluation of a mixture’s resistance to thermal cracking and its integration into the Balanced Mix Design (BMD) for cold regions. If this failure mechanism is not properly addressed in BMD, premature thermally induced surface cracking can occur even when the mixtures comply with existing standards. Although the Thermal Stress Restrained Specimen Test (TSRST) and the Disk-Shaped Compact Tension [DC(T)] Test could account for mixture resistance to thermal cracking, they involve complex procedures and labor-intensive sample preparation, discouraging their routine use. 

For NCHRP 20-30/IDEA 266, the research team will develop a simple, reliable alternative, the IDEAL-LT test, for evaluating asphalt mixture resistance to thermal cracking that could then be integrated into a comprehensive BMD framework for cold regions. The test will streamline testing by eliminating the need for specimen cutting, coring, notching, and gluing while enabling simultaneous testing of three replicates and improving correlation with field ranking and with established thermal cracking tests, such as the TSRST and ABCD tests. 

The research will involve building and refining a system unit, validating its field performance, and comparing the results with traditional low-temperature cracking tests. The test frame will be modified to test three replicates simultaneously, improving efficiency and reducing variability. The procedure will be standardized for integration into the BMD. Validation will involve selecting relevant field sections in cold regions with varying levels of thermally induced surface distresses and correlating IDEAL-LT test results with observed field performance. Additionally, the IDEA-LT results will be compared with TSRST/DC(T) and binder ABCD test results to confirm its reliability. Minnesota and Ohio DOTs will collaborate in field evaluations.]]></description>
      <pubDate>Tue, 23 Jun 2026 13:33:42 GMT</pubDate>
      <guid>https://rip.trb.org/View/2717330</guid>
    </item>
    <item>
      <title>A Novel Method to Optimize N-design for Balanced Performance and Compactability</title>
      <link>https://rip.trb.org/View/2717326</link>
      <description><![CDATA[The Superpave gyratory compaction number, N-design, represents the number of gyrations a hot mix asphalt is subjected to in a gyratory compactor to simulate field compaction and achieve desired volumetric properties. However, currently specified gyration levels have recently come into question as being rather excessive. High N-design values can reduce voids in mineral aggregates, lower the design asphalt binder content, and ultimately compromise the compactibility and durability of the asphalt mixture. Quite a few state departments of transportation (DOTs) have resorted to modifying their design specifications to lower N-design values, but these adjustments mostly rely on a trial-and-error approach and lack a strong correlation with field compaction behavior and long-term performance. A method with scientific basis would be more appropriate for optimizing N-design, particularly in alignment with the Balanced Mixed Design concept to ensure an optimal trade-off between rutting resistance and cracking performance. 

For NCHRP 20-30/IDEA 267, the research team will conduct research based on the theory that particle rotation under compacting effort serves as a fundamental parameter linking laboratory and field compaction. The method employs the rotation parameter and wireless sensors along with artificial intelligence to bridge the gap between laboratory and field compaction and establishes a scientifically sound approach to determine N-design criterion for balanced performance and improved field compactibility. It also enables laboratory compaction to serve as an effective tool for mix design optimization, specimen preparation for field performance evaluation, and field compaction guidance. 

With a focus on optimizing N-design criteria and evaluating performance, Superpave gyratory compaction tests with wireless sensors will be conducted along with performance tests for rutting and cracking. Laboratory and field compactibility will be evaluated along with volumetric properties and performance. Using the obtained results, N-design for balanced performance and compactibility will be optimized. Next, the optimized N-design and compaction will be validated. Designed mixtures with reduced N-design numbers will be verified and their field compactibility analyzed. Field pavement performance will be monitored, and the reasonableness of the reduced N-design numbers will be confirmed. To facilitate transfer to practice, an implementation plan will be developed, including an Excel-based tool and a training module with a video.]]></description>
      <pubDate>Tue, 23 Jun 2026 13:22:57 GMT</pubDate>
      <guid>https://rip.trb.org/View/2717326</guid>
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