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Time allowances and recovery margins in rail scheduling are incorporated into travel time estimation and minimum headways to prevent delays from affecting subsequent trains. These margins act as a buffer against service irregularities, such as variations in station dwell times and train performance, and they are a key factor in rail capacity calculations. Most contemporary tools used to analyze or construct timetables calculate running times specific to each train. However, the factors influencing running times are inherently uncertain, including human behavior, weather conditions, train composition, ongoing infrastructure projects, rolling stock, and route conditions. To accommodate these uncertainties, transit planners and agencies incorporate time allowances into running time estimation, while applying operating or recovery margins to minimum headways to limit delay propagation.

TCRP Research Results Digest 122: Operating Margin and Recovery Factor Practices for Travel Time Estimation and Rail Scheduling, produced by TRB’s Transit Cooperative Research Program, explores the methodologies used by transit agencies to estimate more robust runtimes. These methodologies, among other elements, help establish operating margins and recovery factors in rail scheduling. This research informed updates to Chapter 8 of the TCQSM 4th edition. The digest describes one of 12 small research tasks conducted to support the development of new content for the 4th edition.

The article describes the Washington State Department of Transportation’s (WSDOT) efforts to implement wildlife crossing structures, which aim to improve habitat connectivity and reduce wildlife-vehicle collisions. It highlights the state’s data-driven prioritization framework, established under the Washington Habitat Connectivity Action Plan, to identify and target high-risk highway segments. Additionally, the text underscores the importance of long-term monitoring, often done in partnership with universities, to document the ecological and safety successes of these structures.

Adverse weather conditions such as rain, snow, fog, and high winds pose significant challenges to roadway safety and mobility. These conditions not only increase the risk of crashes but also contribute to travel delays, congestion, and unpredictable driving behavior. To mitigate these risks, transportation agencies are increasingly deploying variable speed limit (VSL) and real-time warning (RTW) systems, which use real-time data to dynamically adjust speed limits and provide timely hazard alerts.

NCHRP Research Report 1176: Real-Time Warnings and Variable Speed Limits— Safety and Travel Reliability During Weather Events, produced by TRB’s National Cooperative Highway Research Program, is a guide designed to support transportation professionals in understanding, evaluating, and implementing these systems in response to adverse weather conditions. The strategies and case studies included in this guide are intended to help transportation agencies enhance roadway safety, improve traffic flow, and ensure drivers receive accurate, timely information to navigate hazardous conditions effectively.

The same project that produced NCHRP Research Report 1176 also documented its methodology and findings in NCHRP Web-Only Document 447: Evaluating the Impacts of Real-Time Warnings and Variable Speed Limits on Safety and Travel Reliability During Weather Events.

This publication is an official Crash-Stats Brief Statistical Summary issued in July 2026 by the National Highway Traffic Safety Administration's (NHTSA) National Center for Statistics and Analysis. The report's primary purpose is to provide early, near-real-time statistical projections of national, regional, and state-level motor vehicle traffic fatalities and fatality rates per 100 million vehicle miles traveled (VMT) for the first quarter of the year. To generate these early projections before final census data is completed, NHTSA employs a time series cross-section regression methodology that models the relationship between monthly data from the Fatality Analysis Reporting System (FARS), NHTSA’s non-public Early Notification (EN) program, and Monthly Fatality Counts (MFC). These traffic safety estimates are further calculated using VMT projections provided by the Federal Highway Administration (FHWA). Overall, this document serves as a preliminary forecasting instrument designed to rapidly catalog and share safety trends with the broader highway safety community, with the understanding that these early estimates will undergo minor statistical revisions over the next two years as final FARS files are processed.

The Montana Department of Transportation installed nearly 600 miles of sinusoidal centerline rumble strips (SCLRS) in 2021. These were mostly installed on high-speed, two-lane rural highways, in the Kalispell Division and Missoula area. The sinusoidal pattern produces lower exterior noise levels than conventional centerline rumble strips, but the safety effects of the pattern have not been quantified. This study performed an observational before-after analysis of the SCLRS installation on two-lane rural highways using the Empirical Bayes (EB) methodology. Crash modification factors (CMFs) for a variety of crash types were less than 1.0, indicating that SCLRS were associated with a reduction in crash frequency. The CMF associated with total target crashes—defined as opposite direction collisions—was 0.711 while the CMF associated with fatal plus injury target crashes was 0.624. The only CMF that exceeded 1.0 was for the single-vehicle run-off-the-road crash type; however, this result was not statistically significant. This study also compared the safety performance of the SCLRS to that of conventional centerline rumble strips in Montana. Because the installation dates of the conventional pattern were unknown, a causal inference framework was used for evaluation. The results indicate that the CMFs for the conventional and sinusoidal patterns have confidence intervals that overlap, suggesting similar safety performance associated with the two patterns. An economic evaluation found that both centerline rumble strips patterns have a benefit-cost ratio exceeding 1.0.

The objective of this research project was to identify the obstacles or impediments to successfully and reliably using HESC for structural bridge deck overlays on Oregon bridges and to develop the standards, specifications, processes, and practices necessary to using them on ODOT bridges. Rapid strength gain is a desired property for fast and efficient bridge deck overlay reconstruction. Three calcium sulfoaluminate (CSA) cement systems, an ASTM C 150 Type III ordinary portland cement (OPC), and a CSA-OPC blended system were evaluated in this research project for potential use as high early strength structural overlay materials for Oregon Department of Transportation (ODOT) concrete bridge decks. A high-performance concrete (HPC) mixture that is representative of ODOT bridge deck mixture designs from the early 2000s to present was also analyzed in this project. CSA cement systems performed satisfactorily when subjected to compressive strength tests, workability tests, curing tests, bond strength tests, early age cracking tests, freeze-thaw cracking tests, and thermal expansion tests when compared with HPC. Resistivity and formation factors of CSA concretes were measured and compared poorly to HPC resistivity and formation factors. While these values would normally suggest rapid rates of corrosion, the collected data is insufficient to conclusively indicate high corrosion rates since these tests were developed for OPC systems and may not be applicable to CSA systems. Additional work to elucidate the role of curing and conditioning of CSA systems is merited before definitive conclusions can be drawn regarding chloride-based corrosion in these systems.

In 2023, fatalities that involved workers on foot being struck by a vehicle accounted for 60% of all fatal highway worker injuries (National Work Zone Safety Information Clearinghouse, n.d.). Increasing the visibility of road workers to oncoming drivers may help reduce this crash risk. Wearable lighted apparel has the potential to increase the visibility of road workers, but its impact on visibility and any potential drawbacks are not well understood. Additionally, regulations and codes governing safety apparel and the use of lights within work zones do not specifically address personal lighted apparel, so it is unclear how it fits within current standards. This study sought to fill these gaps in knowledge. First, a market review was conducted to determine the range of lighted apparel options currently available. Second, a review of legal and regulatory barriers was conducted to determine what types of lighted apparel may be allowed under current standards. Third, a closed-course human factors study was conducted to gather both objective and subjective measures of worker visibility using a variety of lighted apparel options. Fourth, a field study was conducted to gather user feedback from road workers who used various lighted apparel devices.Fourteen different lighted apparel ensembles (including one no-lighting baseline ensemble) were selected for inclusion in the closed-course testing. The ensembles utilized three distinct lighted apparel devices (a lighted vest, a helmet light, and a shoulder-mounted light) in various configurations so that the impact of various aspects of lighted apparel could be tested. These included the lighting design (where the light was located on the worker), the light color (amber, green, red, or white), the flash pattern (flashing or steady-on), and intensity (high or low). Closed-course testing was conducted on the Virginia Smart Roads Highway test track. Three simulated work zones of varying complexity were set up. Within each work zone, an experimenter acting as a worker wore one of the selected ensembles. Participants drove an experimental vehicle along the test track and verbally indicated when they could first detect a worker in a work zone. The detection distance was measured using the differential GPS coordinates of the vehicle at the time of detection. Participants drove 15 laps to ensure that they saw each ensemble within each work zone. Results indicated that a combination of lights on the torso and lights on the head significantly improved detection distance in medium- and high-complexity work zones when compared to the standard retroreflective safety apparel. Green lights significantly improved detection distance across all conditions. Steady-on lights performed significantly better than flashing lights in the high-complexity work zone, but no difference was found in low- and medium-complexity work zones. No consistent effect of intensity was found. The field study equipped Virginia Department of Transportation and contractor personnel with a subset of five ensembles for use in their daily activities. Feedback was gathered through surveys and a focus group discussion. Users agreed that green was the most effective color. Users also tended to prefer the helmet-mounted lights over torso or shoulder-mounted lights. Users indicated a desire for more flashing options. Based on the results of this study, the research team recommends using a green, steady-on, helmet-mounted light to increase the visibility of road workers.

Low slump overlays are an important method to extend the life of bridge decks. The concrete mixture for low slump overlays has not changed in the last 30 years and these overlays show extensive cracking within a few years of placement. The objective of this research project is to minimize the cracking in low slump concrete overlays for mixtures placed with a volumetric mixer. These mixtures need to obtain a low permeability in the NT Build 492 and achieve a 28-day compressive strength of 4000 psi. The objectives of the research include:
i. Examining the most promising mixtures and documenting their performance
ii. Determining the impact of glass fibers to reduce cracking but still provide constructible concrete
iii. Implementing a mixture with and without fibers on separate field projects and documenting the construction and performance of low slump overlays
This work has already been implemented on six field projects, and based on talks with MnDOT engineers, these projects have been deemed a success for having a low amount of cracking while meeting specifications. Also, the contractors who have used these mixtures have requested to use them on other projects. This shows the success of the work.

This article examines how transportation agencies are adopting the Safe System Approach (SSA) to reduce road fatalities. Rather than attempting to eliminate all crashes, the SSA accepts that human error is inevitable and focuses on designing infrastructure, managing speeds, and building system redundancy so that accidents do not result in death or severe injury. Highlighting proven international successes alongside recent U.S. initiatives—such as roundabouts in Minnesota, road diets in Kansas City, and safer speed guidelines in Colorado—the authors show how prioritizing safety over driving speed and implementing practical, multi-layered design changes can transform road safety across communities.

State departments of transportation (DOTs) face a critical and growing gap in their bridge inspection workforce. Traditional on-the-job (OTJ) and instructor-led training models, while essential, are becoming increasingly difficult to scale because the experts who deliver them are leaving the workforce. In addition, classroom training alone cannot capture the tacit, context-dependent judgment that experienced inspectors rely on every day.

TRB’s NCHRP IDEA Final Report for Project 260, Bridges to the Future: Training Inspectors with Simulation-Based Interactive Storytelling, describes a simulation-based training platform that uses interactive storytelling to accelerate the development of entry-level bridge construction inspectors by immersing them in realistic, branching scenarios built from the tacit knowledge of senior inspectors. The platform addresses reinforcing steel placement, bearing pile driving, and post-construction inspection.

The platform supports dual-platform deployment, delivering training as both a desktop video game for standard PCs and an augmented reality experience using the Microsoft HoloLens 2 head-mounted display. It also includes a replicable methodology and open-source toolkit, including the interview protocol, narrative construction template, assessment instruments, and complete Unity codebase, that state DOTs can use to develop their own training scenarios tailored to their inspection priorities, enabling them to reuse and expand the platform without rebuilding it from scratch.

The U.S. transit bus market is heavily strained by extensive vehicle customization, where individual transit agencies frequently order small, highly bespoke batches of buses to fit local climates or legacy fleet inventories. While locally logical, this fragmentation destroys economies of scale in an already small market (fewer than 5,000 heavy-duty buses sold annually), resulting in inflated prices—such as a $995,000 median cost for battery-electric buses—and prolonged delivery times that far exceed more standardized, lower-cost international peers like Europe and India. To stabilize this fragile industry as vehicles grow more technologically complex, the report outlines six coordinated recommendations for Congress, the Federal Transit Administration (FTA), and transit agencies. These strategies aim to build procurement capacity, increase price transparency, require agencies to formally justify non-standard designs, and introduce federal financial incentives to reward standardized purchasing without forcing a rigid, one-size-fits-all manufacturing mandate.