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This report provides practical guidance for more accurate evaluation of traffic congestion costs and potential congestion reduction strategies. It examines key costing factors including analysis perspective and scope, baseline speeds, congestion exposure (the amount of travel that experiences), travel time valuation, additional impacts (fuel, crash and emission costs, plus pedestrian delays and economic productivity), congestion dynamics, equity analysis and research standards. It discusses principles that should be applied for efficient and equitable congestion analysis, and identifies common biases. It critically evaluates various congestion cost studies, and identifies examples of win-win strategies that reduce congestion and help achieve other goals. It identifies a gap between the performance indicators commonly used in congestion cost studies and what decision-makers need for efficient and equitable planning. This report is more comprehensive and current than most previous studies, and includes novel analysis. It is a companion to Congestion Costing Critique and Smart Congestion Relief.

TCRP Research Results Digest 118: Effects of Strategies to Enforce Bus Lanes, produced by TRB's Transit Cooperative Research Program, describes selected bus lane enforcement strategies currently used by transportation agencies that operate bus lanes and reviews the documented effects of these strategies on bus speeds and reliability. TCRP Research Results Digest 118 summarizes one of 12 small research tasks conducted to support the development of new content for the Transit Capacity and Quality of Service Manual, Fourth Edition.

TCRP Research Results Digest 121: Implementing Microtransit Within Broader Network Design, produced by TRB's Transit Cooperative Research Program, explores the state of the practice for planning, implementing, and operating on-demand microtransit services in the United States. The digest highlights trends and lessons learned from case studies and includes recommendations for incorporating these findings into the Transit Capacity and Quality of Service Manual, Fourth Edition. This digest summarizes one of 12 small research tasks conducted to support the development of new content for the Fourth Edition.

When transportation programs receive federal funding, there are typically domestic preference conditions, or “Buy America” requirements, associated with the use of those funds. The Buy America provision associated with Federal Transit Administration (FTA) grant funds is one of the longest-standing federal transportation Buy America provisions and is probably the subject of more documentation than all the others. The Buy America requirements applicable to FTA-assisted procurements have long provided that all steel, iron, and manufactured products be produced in the United States, except where FTA has issued a waiver of the requirements.

TCRP Legal Research Digest 63: Guide to Buy America Requirements for Transit Agencies—2025 Supplement, produced by TRB’s Transit Cooperative Research Program, provides a comprehensive, updated summary of Buy America requirements applicable to FTA-assisted procurements. It incorporates changes since the publication of TCRP Legal Research Digest 49: Updated Guide to Buy America Requirements—2015 Supplement, including the 2021 Build America, Buy America provision, which expanded Buy America requirements for federally assisted infrastructure projects to include construction materials beyond steel and iron. It also addresses subsequent FTA guidance, decisions and waivers, relevant court cases, and legal disputes identified through outreach to FTA grant recipients.

Drivers leave the roadway for many reasons, including inattention, excessive speed, adverse weather, and medical conditions. Roadside hardware, such as guardrails, guard cable, concrete barriers, impact attenuators, breakaway signposts, and light poles, is designed to reduce crash severity by redirecting vehicles, slowing or stopping them, or absorbing impact. Although roadside hardware consistently saves lives and reduces crash severity, it is frequently the subject of litigation. Transportation agencies are primarily responsible for maintaining these systems but depend on designers, manufacturers, testing facilities, and installation contractors to develop, test, and install them properly. Defendants in personal injury or wrongful death claims may include governmental entities, design consultants, installation contractors, testing facilities, product designers, or manufacturers. These parties may be subject to allegations of negligence, including negligent design, installation, maintenance, or testing. Manufacturers may also face products liability claims.

NCHRP Legal Research Digest 96: Liability for Roadside Safety Hardware Claims, produced by TRB’s National Cooperative Highway Research Program, focuses on the legal theories of negligence, breach of contract, and products liability, which are the primary sources of law in this area. The digest explains the legal theories of negligence, breach of contract, and products liability; summarizes significant case law involving roadside safety hardware; and briefly addresses governmental testing and the evaluation of roadside hardware performance.

Drilled shafts are widely used as deep foundations for transportation infrastructure; however, construction defects such as soil intrusion, concrete segregation, slurry inclusions, necking, and soft-bottom conditions can compromise structural integrity and long-term performance. Conventional crosshole sonic logging (CSL) provides valuable quality-control information but offers limited capability for imaging shaft geometry and defect extent. This study developed, optimized, and field-validated a two-dimensional ultrasonic full waveform Inversion (UFWI) framework for high-resolution drilled shaft imaging using CSL waveform data. The method combines acoustic wavefield modeling, adjoint-state inversion, and regularized model updating to reconstruct cross-sectional P-wave velocity distributions without prior knowledge of shaft boundaries or defect locations. Synthetic studies demonstrated that UFWI can accurately image shaft geometry and detect internal and boundary defects. Parametric analyses further showed that at least five CSL access tubes are required for reliable imaging, while approximately one tube per foot of shaft diameter is recommended for shafts 6 ft in diameter or larger.

Field validation was conducted on a full-scale 6-ft-diameter, 40-ft-long drilled shaft constructed at the Florida Department of Transportation (FDOT) Hawthorne test facility with intentionally embedded defects, including concrete segregation, necking with soil intrusion, slurry inclusions, and a soft-bottom condition. UFWI successfully reconstructed shaft boundaries; identified major defect horizons; and localized anomalies consistent with documented as-built conditions. Compared with conventional CSL, UFWI provided higher spatial resolution and more detailed characterization of defect geometry, demonstrating its potential as a quantitative nondestructive evaluation tool for drilled shaft quality assurance and integrity assessment.

The StreetSavvi project is an effort to bring the power of AI, Digital Twin technology, advanced simulation and visualization to provide stakeholders with a powerful tool for urban development. In an ever-increasing Digital Age, the US DOT has put great effort into developing a large number of databases that encompass infrastructure, travel behavior and safety, and context as a way to answer the formidable challenge of moving people and goods in a safe and efficient way. Interestingly, commercial satellite and street imagery such as those produced by Google and other geospatial data providers emerge as an opportunity for an up-to-date inventory of transportation infrastructure. In addition, the acceleration of Artificial Intelligence through Machine Learning and its inference processes for data processing or the Large Language Models generative processes offer phenomenal opportunities to take a global approach to the field of transportation. In this context, StreetSavvi, an advanced Digital Twin development platform, applies AI computer vision processes to geospatial data, namely satellite imagery, street imagery, and camera data, to develop photorealistic 3D models of neighborhoods and develop a scalable, efficient, and user-centric digital twin platform for urban transportation planning. This project expands on the installation of speed cameras on the Roosevelt Blvd. Simulation and visualization tools allow the research team to partner with local stakeholders to assess the impact of various designs on multiple metrics such as traffic congestion, safety, cost. The StreetSavii framework provides a friendly AI based user interface for ideation to help with street design.

This report evaluates through comprehensive laboratory testing the potential of utilizing quarry by-products (QBs) in Otta seal applications as a sustainable and economical alternative to conventional aggregates. An asphalt surface treatment used on low volume roads, Otta seal consists of a relatively thick application of asphalt binder, covered with a graded aggregate layer that allows the use of locally available and marginal-quality materials. Commonly used chip seal design methods were modified to develop a rational design approach for Otta seal, as the conventional Otta seal design procedure is largely empirical. Material characterization was conducted to determine aggregate gradation, physical properties, and emulsion characteristics required for Otta seal design. A double-layer Otta seal configuration was selected based on laboratory optimization involving testing of various configurations and incorporating QBs. The effect of curing temperature and duration on performance was also investigated through weight-loss monitoring and post-curing sweep testing. The performance of laboratory-optimized, QB-based Otta seals was then evaluated and compared with typical Otta seal aggregate through multiple laboratory tests. Performance assessment included sweep testing to evaluate aggregate retention, a modified Hamburg wheel-tracking (HWT) test to evaluate aggregate retention under simulated braking conditions, and close-range photogrammetry to quantify surface texture. The QBbased Otta seal specimens showed performance trends comparable to those constructed with typical Otta seal aggregate. The best-performing design method was selected, and QB-based specimens were further evaluated for susceptibility to bleeding under repeated wheel passes using modified HWT, friction characteristics using a dynamic friction tester, and changes in composite modulus using a box-test setup with lightweight deflectometer testing. Results indicated that QB-based Otta seal
provides adequate resistance to bleeding and sufficient friction for safe traffic movement, demonstrating strong potential as a sustainable and cost-effective pavement-preservation alternative for low-volume roads.

The Federal Railroad Administration, through a research program to improve transportation safety for tank cars, sponsored the Volpe National Transportation Systems Center to develop and compare techniques to simulate the plastic stress-strain behavior of Association of American Railroads’ TC128, Grade B (TC128) steel [1]. TC128 steel is used in the construction of tank cars designed to carry hazardous materials. This research took place between 2019 and 2025.

This report presents Bridge Data Virtual Validator, which is a prototype web-based tool developed to support automated quality assurance (QA) of INDOT bridge project deliverables. The project focuses on Final Tracings documents, where important bridge data are distributed across bridge plans, cost estimates, and other documents/elements. Two validation components were developed. The first component supports bridge plan format compliance checking by using optical character recognition (OCR), computer vision, and rule-based reasoning to identify missing or inconsistent letting control information such as file numbers, dates, stamps, signatures, and sheet numbers. The second component performs comparative checking of pay items between bridge plans and cost estimates with OCR-based information extraction, rule-based structuring, hybrid matching, and deterministic consistency checking. The comparative-checking algorithms were refined through a data-driven development process and with manually reviewed discrepancy records. Both components preserve source evidence and generate traceable reports so that reviewers can locate, verify, and resolve potential issues. The project demonstrates how existing PDF-based bridge deliverables can be converted into structured validation records without changing current submission formats, providing a practical foundation for future pilot deployment, reviewer feedback integration, and broader bridge data QA automation.

Traffic signals with fixed-time signal timing require retiming often because of traffic volume changes. Traffic signals with a fixed time timings are configured with historical traffic data observations. The traffic signal retiming projects can take several years due to the major undertaking by transportation agencies. This seldom signal retiming can lead to higher vehicle delays. Although vehicle detection is a common technology, many intersections in urban areas are not setup with detection sensors because of their added installation and upkeep costs. In the Las Vegas Valley, there are fixed time and actuated (sensor-activated) traffic signals that we analyze for traffic congestion and to identify suboptimal signals. We built geospatial maps to perform exploratory visual analysis and to generate a list of the most monthly recurrent congested intersections in 2025. We also built an Autoencoder to find anomalous signals that are most likely experiencing congestion and identify important features that influence that congestion. Lastly, we present preliminary results from a traffic signal simulation that reveals that smaller cycle times only worsen average vehicle wait times by a small percentage from the optimal cycle length. The impact of our research has the potential to improve delays for motorist and to aid transportation agencies with signal retiming efforts.