Document Library

Traditional crash-based intersection monitoring fails to capture the critical near-miss events that precede collisions involving vulnerable roadway users (VRUs). To provide a proactive alternative, this report investigates how emerging roadside LiDAR and AI/ML technologies can enhance intersection safety observability through three interconnected research thrusts. First, an infrastructure-based sensing survey identifies LiDAR as a premier primary modality due to its high geometric precision and robustness under varying lighting conditions. Second, a systematic study simulating vertical beam loss across six 3D detection architectures establishes a critical 20% beam-loss maintenance threshold. Beyond this point, VRU detection deteriorates rapidly, with concentrated, contiguous beam loss from sensor occlusion proving far more detrimental than dispersed loss.

Building upon these foundational insights, the third thrust introduces a real-world application via an end-to-end, auditable safety-analysis framework deployed at a signalized intersection in New York City. Utilizing a newly established, manually annotated 8,000-frame roadside dataset, the framework integrates 3D detection, tracking, stabilization, and structured human-in-the-loop quality assurance to convert raw sensor data into defensible near-miss evidence. A heavy vehicle-bicycle interaction case study demonstrates that contrasting direction-agnostic and longitudinal time-to-collision (TTC) metrics can successfully isolate lateral-intrusion conflict mechanisms that single-metric approaches miss. Together, these efforts validate roadside LiDAR as a scalable, interpretable, and highly defensible tool for proactive traffic safety management.

This publication is an official federal Traffic Safety Facts Research Note issued in May 2026 by the National Highway Traffic Safety Administration’s (NHTSA) National Center for Statistics and Analysis. The document details the methodology and structural framework of the National Occupant Protection Use Survey (NOPUS), which is the only annual, probability-based observational study in the United States designed to monitor daylight restraint usage. Rather than relying on self-reported driver surveys or post-crash police reports, the study's design utilizes trained field observers who physically stand at randomly selected roadside locations or ride along expressways to record actual seat belt behavior in real-time without stopping vehicles or interviewing motorists. The survey employs a complex, multistage probability sampling protocol—executed in partnership with Westat, Inc.—that annually catalogs observations of over 140,000 front-seat occupants across varying vehicle types, roadway classes, environmental settings, traffic densities, and regional jurisdictions. Ultimately, this publication acts as a highly standardized, objective statistical instrument used by safety planners to evaluate the long-term effectiveness of state legislative policies (such as primary versus secondary enforcement laws) and national occupant protection campaigns.

In recent years, the public transit industry has seen a significant trend toward establishing formal Customer Experience (CX) programs, with over 60 U.S. transit agencies creating programs to better understand rider needs, instill a customer-first approach to their services, and build ridership and community support. However, the rapid adoption of these programs has occurred without industry-wide standards, leading to a wide variety of organizational models and approaches.

TCRP Synthesis 187: Transit Agency Customer Experience Programs, produced by TRB’s Transit Cooperative Research Program, identifies emerging practices within transit agency CX programs across key themes, including program design, organizational structure, and performance measurement. In addition to results from an industry scan and survey, the report includes five case examples and highlights how CX programs are evolving within the transit industry, becoming a distinct professional specialization that increasingly relies on integrated data, performance measurement, and multidisciplinary collaboration. The report addresses the importance of strategic planning, investment, and the use of an “Influence Model” to guide CX initiatives. It also finds that CX programs are delivering measurable improvements for riders, and it identifies gaps and opportunities for future research to strengthen program effectiveness and advance the field.

Transportation construction activities involving in-stream work can mobilize sediment and elevate turbidity, which can affect sensitive aquatic species such as freshwater mussels. Although cofferdams are used to isolate construction areas and limit sediment mobilization, their installation and removal create some degree of sediment release as a result of unavoidable streambed disruptions. To support more informed impact assessments and survey requirements for aquatic species protection, this study determined the transport distances of sediment associated with the installation and removal of cofferdams. Related objectives were to compare the effect of cofferdam-related construction events on sediment loads and to document the factors that affect recovery times and sediment loads.

Streams associated with two bridge replacement projects in Virginia involving different but commonly used cofferdam types (sheet pile and sandbag or Jersey barrier) were instrumented with 19 turbidity sensors positioned upstream and up to 2,600 feet downstream of construction. In addition to continuous turbidity monitoring, data collection included water sampling and field measurements used to determine suspended sediment concentration and site-specific rating curve development. Suspended sediment loads were calculated using stream discharge, suspended sediment concentration, and duration of cofferdam-related construction events.

Across both sites, peak turbidity increases occurred immediately downstream of the cofferdam, with values as high as 238 Formazin Nephelometric Units at Site 1 and 3,324 Formazin Nephelometric Units at Site 2, which returned to background levels within 50 to 100 feet downstream. Sediment loads attributable to construction ranged from 3 to 636 pounds, and for most cofferdam-related construction events, more than 75% of the sediment load occurred in the first 50 feet downstream. The use of sandbag or Jersey barrier cofferdams generated higher turbidity and sediment loads than sheet piles, largely because installation and removal required more streambed disturbance. For all cofferdam-related construction events, turbidity levels returned to background levels between 5 and 90 minutes. Sediment load calculations from evaluated precipitation events were one to three orders of magnitude higher than loads from cofferdam-related construction events.

The findings can help inform assessments of potential mussel impacts from in-stream projects involving cofferdams conducted under comparable conditions. It is recommended that the Virginia Department of Transportation’s Environmental Division share this report with the Virginia Field Office of the U.S. Fish and Wildlife Service and aquatic program staff of the Virginia Department of Wildlife Resources to support agency evaluation of area-of-impact determinations and associated survey requirements for projects comparable with those this study examines.

NCHRP Research Report 1183: Determining Fleet Mix and Vehicle Size in the Rural Transit Setting, produced by TRB’s National Cooperative Highway Research Program, addresses the complex decisions that rural and tribal transit agencies and state DOTs face when determining the appropriate mix and size of vehicles to serve their communities effectively. The report is designed to help these agencies make informed, data-driven decisions about vehicle type, size, and fleet composition. Through detailed analysis, the research captures the full range of factors that influence fleet planning and vehicle selection in rural transit systems.

NCHRP Research Report 1184: Post-Implementation Evaluation of Transportation Projects: A Guide, produced by TRB’s National Cooperative Highway Research Program, is intended to demystify, promote, and support the adoption of PIE by providing an eight step implementation framework. The framework encompasses both technical and organizational strategies to support enterprise-wide adoption. The guide and its accompanying spreadsheet-based tool are designed to help practitioners institutionalize PIE throughout the project development process, regardless of their organization's level of readiness or data maturity.

State and local transportation agencies increasingly rely on proactive safety analysis to inform roadway design and improvement decisions before crashes occur. However, uncertainty regarding the potential use of proactive safety methodologies, manuals, and guidance in tort litigation has raised concerns about increased exposure to liability.

NCHRP Legal Research Digest 95: Addressing Liability Issues of Proactive Safety Improvements, produced by TRB’s National Cooperative Highway Research Program, examines the legal considerations facing transportation agencies that adopt proactive, data-driven approaches to roadway safety. The digest reviews relevant statutes, case law, and agency practices; identifies litigation in which proactive safety concepts have been raised; evaluates defenses and outcomes; and documents strategies used by transportation agencies to mitigate liability concerns. Based on this analysis, the research explores potential legal, administrative, and policy approaches that may support the use of proactive safety methods while preserving established processes for prioritizing and funding roadway improvements.

This research describes a new method for work zone monitoring that allows for more continuous, accurate intelligence. The project focused on the design, deployment, and validation of a statewide, real-time work zone monitoring and traffic performance intelligence platform for Iowa known as ReactorIQ. Unlike traditional systems that depend on fixed roadside sensors, manual contractor logs, or delayed 511 updates, ReactorIQ is built around high-resolution connected vehicle (CV) telemetry as its primary data source. The platform continuously transforms naturalistic vehicle movement into detailed measures of mobility, safety, and operational performance across Iowa’s uninterrupted flow network, demonstrating that CV telemetry data can support a complete work zone intelligence workflow.

The TRC 2303 report presents a comprehensive analysis of the impacts of bridge closures across the Mississippi River in Arkansas, focusing on four key crossings: I-40, I-55, HWY 49, and HWY 82. Prompted by the emergency closure of the I-40 Hernando de Soto Bridge in 2021, the study evaluates both full and partial closures to quantify economic, safety, and mobility consequences. Using ARDOT’s Road User Cost (RUC) framework and the Arkansas Statewide Travel Demand Model (ARSTDM), the report estimates daily costs and system-level changes in Vehicle Hours Traveled (VHT) for autos, single-unit trucks (SUT), and tractor-trailer trucks (TTT). Partial closures of high-volume bridges like I40 and I-55 result in substantial daily costs, e.g., up to $2.4 million for I-40 along with widespread VHT increases. This is especially so for TTT, for which 6,902 miles of roadway exhibited more than a 4% increase in VHT under the I-40 closure scenario. In contrast, HWY 49 and HWY 82 closures had more localized effects, with HWY 82 showing the highest auto and SUT impacts but minimal freight disruption. Waterway disruption costs, derived from Automatic Identification System (AIS) data, also rose sharply between 2021 and 2024, with HWY 49 carrying the highest vessel volumes and HWY 82 showing the fastest growth. To support planning, the study delivered a web-based Bridge Closure Impact Analysis Tool that automates cost calculations and visualizes impacts. Mitigation strategies include operational measures, maintenance practices, and planning-based approaches, with partial closures recommended where feasible. Overall, the report equips ARDOT with data-driven tools to prioritize investments, manage emergencies, and maintain transportation resilience across river crossings.

Artificial Intelligence (AI) has the potential to be used in many applications across rural and Tribal transit agencies, including operations, safety, human resources, and other areas. As with any technology, there are benefits and challenges. This technical brief describes the range of uses of AI for transit agencies, as well as issues including AI regulation and funding. Case studies share real-world applications of this technology by rural transit agencies.

This annual report provides a snapshot of state-by-state investment in public transportation from federal, state, and local funding sources. With detailed tables and charts, the report explains how different funding and tax mechanisms are used to support transit operations and capital projects; compares differences across modes and the latest ridership trends; and features a selection of innovative state funding initiatives and case studies that highlight the efforts by states to apply state funding to support transit programs beyond federal funding levels. All funding and ridership data has been updated to reflect FY 2024 survey results.

This year’s report includes new information on commuter rail, new assessments of ridership trends by transit modes, and information on the continuing impact of the COVID-19 pandemic on state transit programs.