TRB Publications Index

Classifying the Autonomous Future: Latent Profile Analysis of Public Attitudes Toward Automated-Vehicle Adoption

Sat, 12 Sep 2026 14:46:58 GMT

The integration of automated vehicles (AVs) in urban transportation systems continues to generate public interest, particularly concerning safety, accessibility, and societal readiness. While technical progress in AV systems has been rapid, public support remains a central factor influencing their deployment. In this study, latent profile analysis is applied to a nationally representative survey to identify distinct public support profiles for AV use cases, including taxis, 18-wheelers, buses, and delivery vehicles. Three primary subgroups emerge: enthusiasts, pragmatists, and skeptics, each exhibiting unique attitudes and demographic patterns. Enthusiasts show consistent support across all vehicle types, pragmatists favor limited AV applications, and skeptics demonstrate general opposition, especially toward AV freight. For comparison, k-means clustering is used; findings are consistent with the latent profiles, confirming the robustness of classification. Support is highest for AV taxis and delivery vehicles, while 18-wheelers receive the least support, highlighting significant variation across use cases. Demographic analysis reveals age, education, income, gender, and political ideology as significant predictors of support profiles. Notably, older adults and conservative individuals are more likely to be skeptics, while younger, more educated, and liberal respondents tend to be enthusiasts. These findings highlight the complexity and diversity of public opinion on AVs and suggest that broad-based deployment strategies might be ineffective. Instead, tailored communication and policy approaches are needed to address specific concerns and expectations of different population groups. The study provides a data-driven understanding of how different population segments perceive AV technologies, informing equity-focused planning and tailored policy approaches in urban transportation.

Motion Cues and Field of View in Virtual Truck-Driver-Training Under Crosswinds: Effects on Driving Control, Simulator Sickness, and User Experience

Sat, 12 Sep 2026 14:46:58 GMT

Virtual reality (VR)-based training provides a safe and cost-effective solution for truck-driver-training tasks. However, the effectiveness of VR training in replicating real-world driving conditions remains underexplored. This study examines how vestibular motion cues and field of view (FOV) affect driving control, VR sickness, and user experience in truck-driving simulations under crosswind disturbances. Fifty-four participants (35 undergraduates and 19 truck drivers) performed simulated highway driving tasks under Motion (vestibular feedback) and No Motion conditions, using either a head-mounted display (HMD) with a larger vertical FOV or a three-screen setup. Steering control was assessed via wind-steering correlation (the alignment between steering adjustments and wind disturbances), entropy, and reversal rate (corrective steering adjustments), while VR sickness and user experience were evaluated using standardized questionnaires. The absence of vestibular motion cues in the HMD condition led to poorer steering control, reflected in lower wind-steering correlation, higher entropy, and increased corrective adjustments. It also received the lowest ratings for perspicuity and efficiency, particularly among experienced drivers. Simulator sickness symptoms (nausea, oculomotor strain, disorientation) increased in the absence of motion cues in the HMD condition. Overall, motion conditions improved steering performance and were rated higher in efficiency, perspicuity, and novelty. These findings underscore the importance of integrating vestibular motion cues and realistic disturbances in VR truck training to support skill transferability. Optimizing FOV and motion feedback can enhance training fidelity, reduce simulator sickness, and improve driver adaptation. This research informs VR simulator design, improving safety, efficiency, and cost-effectiveness in driver education programs.

Framework and Development of Structural Layer Coefficient for Engineered Emulsion–Stabilized Cold Recycled Materials

Sat, 12 Sep 2026 14:46:58 GMT

This study presents a performance-based analytical framework for the calibration of structural layer coefficients for engineered emulsion (EE) stabilized cold recycled pavement materials for use within the AASHTO 1993 empirical design guide. A comprehensive database which includes 16 engineered emulsion–stabilized cold recycled (cold in-place recycled [CIR-EE] and full depth reclaimed [FDR-EE]) field pavement sections, seasonal falling weight deflectometer back-calculated pavement layer stiffness data, regional climate and soil characteristics, International Roughness Index (IRI) metrics, and traffic loading information derived from a rutting-based allowable load repetition mechanistic analysis was established to aid the calibration efforts. Results and recommendations from the calibration process, incorporating seasonal variability and statistical-based analysis, yielded layer coefficient values of 0.31 and 0.27 for CIR-EE and FDR-EE, respectively. The overall analytical framework provides a rational and performance-aligned basis for incorporating cold recycled materials into empirical pavement design procedures, advancing the sustainable design and structural reliability of cold recycled rehabilitated pavement systems.

In Situ Testing Informed Sublayering Approach for Mechanistic Analysis and Design of Geogrid-Stabilized Pavement Foundations

Sat, 12 Sep 2026 14:46:58 GMT

This study introduces a sublayer-based modeling approach to characterize the stress-dependent modulus behavior of pavement unbound aggregate layers stabilized using geogrids. Current modeling and design approaches either apply a higher uniform layer modulus or disregard geogrid stabilization benefits. A uniform increase in modulus in the depth profile, however, does not capture the localized stiffening caused by an installed geogrid, also referred to as the mechanically stabilized layer (MSL). Using instrumentation and testing during an actual highway reconstruction project in Indiana, the MSL concept was modeled by discretizing the aggregate base into sublayers. Automated Plate Load Tests (APLTs) conducted during construction of the aggregate base test sections provided field data to characterize the modulus behavior for each sublayer using a nonlinear stress-dependent resilient modulus model. The calibrated model parameters for each sublayer were then implemented in a finite element solution for the field experiment to predict the APLT-measured deflection basins. Once validated, the sublayer model was used to estimate and report on the subgrade vertical stresses and strains. The results revealed that geogrid-stabilized sections exhibited lower subgrade stresses and strains compared with the no-geogrid control section. Therefore, this study demonstrated the implementation of a new sublayer-based parameterization technique that captures stiffness gradients and geogrid stabilization effects. The methodology provides a mechanistic and field-calibrated pathway for incorporating geogrid stabilization into mechanistic-empirical (ME) pavement design. A broader adoption of testing and field sensor data-informed ME frameworks linked to digital twins will enable accurate and sustainable pavement foundation designs.

Assessing the Effect of Law Enforcement on Traffic Crashes: Segment-Level Spatiotemporal Approach

Sat, 12 Sep 2026 14:46:58 GMT

Law enforcement is commonly acknowledged as effective in enhancing traffic safety by deterring dangerous driving behavior. However, questions remain about how the safety benefits of enforcement unfold over time and whether they vary across different locations. This paper reports an investigation of the dynamic relationship between traffic citations (a proxy for enforcement intensity) and crash occurrences at a fine spatiotemporal scale. We analyze 2 years of daily citation and crash data on a 400-mi interstate corridor (I-15, UT), divided into 10 segments, using vector autoregression (VAR) and structural VAR time-series models. Impulse response functions derived from these models quantify immediate (same-day) and lagged (next-day) associations between citations and crashes on each segment. The results reveal that increased citations are associated with a significant reduction in the incidence of crashes on the same day, and that this effect dissipates by the following day. The magnitude of the immediate crash reduction varies substantially by segment, with urban freeway segments exhibiting much stronger effects than rural segments. To ensure statistical robustness and policy relevance, the segmentation was guided by effective sample size considerations and aligned with administrative boundaries. This approach balances model stability with practical enforcement needs and offers a transferable guideline for future segmentation efforts. These findings suggest that enforcement has a short-lived but noticeable effect on crashes, and that its effectiveness differs by location. Building on these insights, we outline a segment-level spatiotemporal analysis framework for traffic safety and discuss how it can inform more targeted and efficient enforcement strategies.

Comparative Performance Evaluation of Clear and Conventional Asphalt Emulsions for Microsurfacing Applications

Sat, 12 Sep 2026 14:46:58 GMT

This study presents a laboratory evaluation of microsurfacing mixtures incorporating conventional cationic slow-setting polymer-modified emulsions (CSS-1P) and clear asphalt emulsions (CAE) and utilizing three aggregate types: granite, limestone, and mine chat. The mixtures were assessed for mixing time (ISSA TB 113), cohesion (ISSA TB 139), lateral displacement (ISSA TB 147), sand adhesion (ISSA TB 109), and wet track abrasion (ISSA TB 100). Results indicated that all CSS-1P mixtures met the minimum required mixing time of 120 s, whereas granite and limestone mixtures with CAE failed to achieve this, despite adjustments in water and residual emulsion contents. Mine-chat mixtures satisfied the mixing-time requirement with both emulsions, requiring less water and emulsion than other aggregates. Cohesion values for CSS-1P and CAE mixtures showed normal mode of rupture. Effects of water and emulsion content on cohesion were significant and nonlinear. Loaded-wheel-test results revealed that CAE mixtures experienced higher deformation (22%–28% lateral, 31%–40% vertical); granite aggregates exhibited the highest rutting susceptibility, whereas CSS-1P mixtures showed improved stability, with limestone recording the lowest deformation. Sand adhesion results demonstrated that CSS-1P mixtures produced higher adhered sand values because of the formation of thicker asphalt films; CAE mixtures resulted in lower sand adhesion values, desirable for minimizing flushing risk. Wet track abrasion results further emphasized emulsion type effects, with CSS-1P mixtures showing higher abrasion loss than CAE mixtures, particularly for mine chat. Findings indicate that aggregate and emulsion type play a vital role in microsurfacing performance, while aggregate characteristics and water and emulsion content further influence durability and deformation resistance.

Binder Source Matters: A Simplified DSR Approach for Identifying Performance Variability at Intermediate and Low Temperatures

Fri, 11 Sep 2026 08:43:50 GMT

This study validated two rheological parameters, the Glover–Rowe (G–R) parameter at 15°C and 10 rad/s and the phase angle δ at a complex modulus G* of 10 MPa δ10MPa, as tandem indicators of asphalt binder quality with respect to intermediate-temperature cracking susceptibility. Seven binders were evaluated: four good-quality and three poor-quality. A Superpave 12.5 mm dense-graded mixture was prepared with each binder and tested using the Indirect Tensile Asphalt Cracking Test, Texas Overlay, dynamic modulus, and cyclic fatigue tests. Across all tests, G–R and δ10MPa together consistently differentiated good from poor-quality binders, validating their combined use as a reliable cracking resistance indicator. This study also extended a simplified Dynamic Shear Rheometer (DSR) protocol, originally developed for intermediate-temperature grading, to low temperatures as a practical alternative to the Bending Beam Rheometer (BBR). BBR stiffness (S = 300 MPa) and m-value (0.300) thresholds were converted into equivalent DSR values (G* ≈ 111 MPa and δ ≈ 27.0°) in the high-stiffness range most critical to thermal cracking. Using time–temperature superposition, the BBR loading frequency (0.0167 rad/s) was shifted to 10 rad/s in the DSR, corresponding to an 18°C warmer test temperature while maintaining equivalent rheological behavior. For example, a binder tested at –18°C in the BBR (PGXX-28) could be evaluated at 0°C in the DSR. Integrating these tandem parameters with the simplified DSR method into Balanced Mix Design and quality assurance can improve binder selection and reduce cracking, particularly when binder sources or formulations change without altering the performance grade.

Role of Risk Perception in Predicting the Intentions of Wakeful and Drowsy Drivers

Fri, 11 Sep 2026 08:43:50 GMT

Driver intention recognition algorithms play a crucial role in understanding driver–vehicle interactions. In highly automated vehicles, drivers are occasionally instructed to take control. Driver–vehicle interaction is, therefore, an important research topic. This paper uses risk levels and risk dynamics to provide a ground for developing intention recognition algorithms. It also investigates the effect of drowsiness on a driver’s ability to perform defensive actions. As human controllers are primarily event-based, the driver is modeled as an event-based controller that monitors risk-based signals and interacts with the vehicle pedals. A Gaussian support vector machine (SVM) model was used to predict the reaction type. A car-following experiment was conducted, in wakeful and drowsy phases, to assess wakeful driver actions and the ability of drowsy drivers to confine risk-based variables. Twenty-one drivers were tested in a wakeful state. The results achieved maximum and minimum accuracies of 81.9% and 60.8% in predicting the type of driver’s defensive action. The rate of the accelerator pedal release was affected by the risk and its time derivative, while the duration of switching from the accelerator to the brake was only affected by the time derivative of risk. Subsequently, the effects of drowsiness on driver performance were explored. Finally, a long short-term memory (LSTM) model was employed to predict drivers’ actions. The findings suggest that monitoring drivers’ risk estimations and their defensive pedal responses reveal patterns for predicting both the timing and the type of driver reactions.

Experimental Study on a New Connection Joint between Prestressed High-Strength Concrete Piles and Cap

Fri, 11 Sep 2026 08:43:50 GMT

To address issues such as stress concentration, complex construction, and insufficient deformation resistance faced by the connection joints between prestressed high-strength concrete pipe piles and pile caps under seismic action, this study developed a novel direct reinforcement insertion connection system. Based on the Guohe Bridge project along the S209 Highway in Luyi County, Zhoukou City, China, full-scale specimens with two configurations (Z1: conventional welded connection and Z2: proposed insertion connection) were subjected to unidirectional cyclic loading tests and finite element analysis. Results indicate that, compared with the traditional welded connection, the Z2 insertion connection exhibits a 12% increase in critical load capacity. Under 900 kN lateral loading, displacements measured 39.0 mm (pile) and 42.7 mm (cap), with no load-displacement curve separation observed throughout testing. The reinforcement stress gradient rate in Z2 decreased from 2.68 to 0.32 MPa/mm, with peak tensile stress reduced from 385.0 to 192.3 MPa, and no distinct tension-compression transition zones were identified. Both field tests and numerical simulations confirm the reliability of the new connection system, demonstrating enhanced ductility and coordinated deformation capacity in pile-cap joints.

Private Health Sector Investment in NEMT: Volume 2: Developing a Guide

Wed, 09 Sep 2026 08:52:01 GMT

Non-Emergency Medical Transportation (NEMT) can provide reliable transportation to essential healthcare appointments and treatments. NEMT is particularly important for individuals who lack access to personal transportation due to physical or mental disabilities or financial hardships, or who live in areas with limited or no public transportation. Researchers found that improved access to transportation may improve health outcomes, reduce hospital readmissions, and potentially lower overall healthcare costs. NCHRP Web-Only Document 466, Volume 2: Developing a Guide provides a comprehensive summary of the overall project that resulted in the development of NCHRP Web-Only Document 466: Private Health Sector Investment in NEMT, Volume 1: Practitioner’s Guide. The practitioner’s guide is designed to help decision makers considering potential engagement in NEMT. This report provides a complete summary of the overall project. Phase I included a literature review, interviews with entities involved with NEMT, and additional research into the state of the practice. Phase II included an in-depth exploration of key performance indicators (KPIs); benefits, challenges, opportunities, and risks; and additional research into successful collaboration models of NEMT provision and suggestions for incentivizing funding for NEMT services.

Private Health Sector Investment in NEMT: Volume 1: Practitioner's Guide

Wed, 09 Sep 2026 08:52:01 GMT

Non-Emergency Medical Transportation (NEMT) can provide reliable transportation to essential healthcare appointments and treatments. NEMT is particularly important for individuals who lack access to personal transportation due to physical or mental disabilities or financial hardships, or who live in areas with limited or no public transportation. Researchers found that improved access to transportation may improve health outcomes, reduce hospital readmissions, and potentially lower overall healthcare costs. NCHRP Web-Only Document 466: Private Health Sector Investment in NEMT, Volume 1: Practitioner’s Guide is designed to help decision makers considering potential engagement in NEMT. The guide assists with determining community needs, developing action plans to address problems, engaging stakeholders, and conducting continuous evaluation and improvement activities. A conduct of research report for the project that produced NCHRP Web-Only Document 466: Volume 1 was released as NCHRP Web-Only Document 466: Private Health Sector Investment in NEMT, Volume 2: Developing a Guide.

User-Focused Microtransit for Students’ After-School Activities

Wed, 09 Sep 2026 08:49:34 GMT

This study investigates a user-focused microtransit service designed to transport students to after-school activities. The methodology includes generating a synthetic student population and the corresponding trip requests, determining the routes using a metaheuristic approach to solve a Vehicle Routing Problem with Pickup and Delivery and Time Windows (VRPPDTW), and evaluating system performance under a zero-rejection policy. The VRPPDTW includes scheduling drivers with mandatory breaks and maximum shift durations, while minimizing unassigned trips, waiting time, travel time, and route imbalance. The case study focuses on an on-demand transport service for students’ after-school activities in Limassol, Cyprus. Various scenarios are analyzed to assess the effect of fleet size, fare levels, and service parameters on performance. The results show that a fleet of 10 vehicles serving 144 trips for 60 students can reduce the number of cars required by 83%. Larger fleets achieve higher occupancy and better kilometer utilization. Of note, fleets of 20 vehicles or more surpass a system efficiency of one, indicating the distance traveled by the service is lower than individual trips. For service levels, increasing acceptable waiting time by 5 min or travel time by 15 min boosts capacity by 24%. Economically, a zero-rejection policy is sustainable only for large fleets with high fares. However, allowing a small rejection rate of 2% significantly improves viability, enabling the fleet of 10 vehicles to break even with fares 25% lower than local taxi rates.

Shear Wave Reflection Method for Slab-Base Interfaces

Wed, 09 Sep 2026 08:49:34 GMT

The contact between concrete slabs and supporting base layers influences the mechanical and durability performance of pavement systems. This paper presents a new nondestructive evaluation (NDE) methodology for quantifying slab-support contact conditions using shear wave reflections. While current stress-wave NDE methods, such as impact-echo and falling weight deflection, infer the interfacial contact condition given knowledge of layer properties and thickness, the proposed method quantifies the interface contact condition without these initial inputs. The shear wave reflection ratio (SWRz) is defined as the amplitude ratio between successive shear wave echoes reflected from a slab-base interface. To isolate the interface contact from other losses, the signal amplitudes are corrected for geometric spreading and material attenuation. Laboratory experiments were conducted using a phased-array shear wave system on 76-mm-thick plexiglass and 76- and 100-mm-thick mortar slabs, supported by several materials (e.g., air, marbles, sand, and cement) and under multiple vertical pressure levels. The results demonstrated that the SWRZ values showed statistical significance (p < 0.01) between support material type and increasing applied vertical pressure to the slab surface. As expected, the slab-air interface specimens exhibited the highest SWRz of approximately 1.0. Additionally, increasing the vertical pressure at the slab-sand interface reduced the SWRz values, indicating improved slab-base contact. The proposed methodology provides a reliable, NDE tool for detecting changes in slab-base contact conditions (i.e., kissing bond to complete separations or air gaps), which can be effective in evaluating concrete slab-base and concrete overlay contact conditions over time.

The Challenge of Controlling the Queen Elizabeth Way: A Long Heavily Congested Urban Freeway with Dense Consecutive On-Ramp Bottlenecks

Wed, 09 Sep 2026 08:49:34 GMT

Benefits of ramp metering (RM) and variable speed limit (VSL) for a single or a few congested freeway ramp bottlenecks are well established in the literature; however, for a long heavily congested urban freeway with dense consecutive on-ramp bottlenecks, the application of RM and VSL is highly complex. Owing to short distances between consecutive bottlenecks, control actions at some ramps can interfere with other ramps. The main objective of this paper is to analyze and study the effectiveness of RM and VSL application on a full congested urban freeway as opposed to their application on one isolated bottleneck. In this paper, we apply both RM and VSL controllers on single-ramp and multi-ramp networks to compare and analyze the performance and effectiveness of each controller in each setting. We find that in the case of single-ramp bottleneck, both RM and VSL perform well under moderate traffic demand, which is expected and consistent with the literature. However, in heavily congested scenarios, the performance of VSL deteriorates while RM can preserve its performance. On larger multi-ramp networks, applying RM to resolve congestion at upstream bottlenecks causes more congestion at downstream bottlenecks. Further, if only VSL is applied, the lack of adequate distances between the congested bottlenecks and the high unmetered flows merging to the freeways from the on-ramps significantly reduce the efficiency and benefits of applying VSL. We demonstrate and quantify those challenges on a case study of the Queen Elizabeth Way (QEW) freeway in the Greater Toronto Area, Canada.

Where Station-Area Effects Really Peak: Donut Gradients, Temporal Displacement, Spatial Dependence, and Vertical Walkability in Taipei, Seoul, and Tokyo

Wed, 09 Sep 2026 08:49:34 GMT

This conceptual and methodological synthesis examines why the location of the strongest station-area response is not stable across mature metro cities. Instead of estimating a pooled East Asian transit premium, it uses peer-reviewed evidence and official urban and rail indicators for Taipei, Seoul, and Tokyo to clarify how peak location depends on outcome type, project timing, spatial dependence, submarket structure, and station-front pedestrian integration. The Taipei evidence reviewed here is used to examine a temporal-displacement mechanism; the Seoul evidence reviewed here to examine a spatial-confounding mechanism; and the Tokyo evidence reviewed here to examine a core-reintegration mechanism. These are case-dominant mechanisms identified from the reviewed evidence, not exclusive labels for every station in each metropolitan system. The synthesis separates three layers: models estimated in the cited studies, transparent calculations performed in the present manuscript, and modeling templates proposed for future harmonized comparative research. It further specifies how vertical walkability can be measured through multilevel circulation, barrier-free access, entrance permeability, weather-protected continuity, transfer directness, and plaza legibility. The contribution is therefore to develop a comparative framework for identifying edge-centered, donut-shaped, model-sensitive, and re-centered station-area gradients, and for clarifying how different forms of evidence can inform the analysis of peak location across mature metro systems.