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.

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.

State transportation agencies increasingly face major projects whose scale, risk, and financing demands challenge conventional delivery models. Progressive P3 has emerged as an experimental response, combining long-term public–private partnership structures with progressive delivery mechanisms to manage uncertainty prior to final price commitment. This report examines Progressive P3 strategy and how it can be implemented in a manner that protects public value while sustaining private-sector investment.

Based on a review of literature, contractual analysis, and interviews with subject-matter experts, the report focuses on the operational mechanics of Progressive P3 delivery, including bonding, open-book price negotiation, the role of Independent Cost Estimators, risk balancing, and offramp governance. The findings indicate that Progressive P3 is best understood as a contractual tool to mitigate the design and construction risk of complex projects in advance of a concession period, rather than a wholesale redefinition of the P3 model. Progressive mechanisms can improve price realism and delivery stability but can also impose heightened demands on agency capacity and governance. The report concludes that Progressive P3 should be applied selectively, where both P3 financing logic and progressive risk-management benefits are clearly present.

The early 21st century to the present is a pivotal era in the study of travel behavior and time use. This two-decade period has witnessed not only incremental adjustments but also transformative shifts in how individuals allocate their time across various activities and make travel-related decisions within their time and monetary constraints. These shifts are not isolated phenomena; they are deeply intertwined with broader, multidimensional changes driven by factors such as the widespread adoption of Internet and Communication Technologies (leading to innovations in mobility services and online substitutes for many in-person activities) and shifts in demographics and cultural norms. Overall, this period of change holds profound implications for transportation planning and policy development. This multi-stage project aims to navigate this complex terrain to shed light on the trends in time, travel, transit, telework, and treasure (T5) during this period. The project primarily utilizes data from the American Community Survey (ACS), the American Time Use Survey (ATUS), and the Consumer Expenditure Survey (CES), along with insights from field counts and travel estimates, to analyze these trends. Understanding these trends is crucial for effectively addressing current and future challenges and seizing opportunities in transportation management, economic resilience, and societal wellbeing.

This report benchmarks the costs of transitioning to electric bus (e-bus) fleets in Latin America and the Caribbean (LAC), drawing on data from 13 countries and 21 cities covering the period 2021–2025. It examines the full cost structure of e-bus deployment, including vehicle acquisition, charging infrastructure, and operating costs, and explains the substantial variation observed across markets. The findings show that e-bus costs are shaped by vehicle specifications, procurement scale, market maturity, and policy environments, with substantially greater price dispersion than conventional diesel buses. Charging infrastructure costs are highly sensitive to project scale, grid conditions, and depot location, highlighting the need for integrated transport and power sector planning. While e-buses offer clear operational advantages, these benefits depend on sound planning, competitive procurement, and coordinated policies. By improving transparency around key cost drivers, the report aims to support better decision-making and accelerate the sustainable scale-up of e-bus deployment in the region.

This guide provides a structured roadmap for agencies seeking to implement performance-based contracting (PBC) to support proactive road asset management. Drawing on decades of international experience, it outlines how to design, scale, and manage PBC programs—from pilot projects to network-wide applications—across varying levels of agency maturity.

Practitioners will find guidance on using PBC to improve asset condition, enhance safety and resilience outcomes, and shift from reactive maintenance to performance-driven service delivery. The document also includes diagnostic approaches and implementation strategies that help agencies align contracting practices with broader TAM and performance management objectives.