Friday, August 30, 2024

Friction Enhancements to Asphalt Pavement Surfaces

Maintaining the appropriate amount of pavement friction is critical for safe driving. Missouri Department of Transportation (MoDOT) has used high friction surface treatment (HFST) since 2013 to restore pavement surface friction where traffic has worn down pavement surface aggregates and to improve wet crash locations. Conventional HFST application consists of a polymer resin layer, which is used to bond the pavement with high abrasion, high angularity and texture, and polish resistant aggregates (e.g., Calcined Bauxite (CB) / (chat, slag)). Construction routines and pre-existing pavement conditions affect the performance of HFST made with polymer resin. Highway agencies examine existing pavement surface conditions before determining whether HFST can be used, as it is not intended as a repair for surface distress conditions, such as rutting. The relatively high cost of constructing, and removing, HFST with polymer resins along with the durability concerns due to existing pavement conditions, has led state agencies to consider high friction surface treatment with asphalt-based binders as an alternative. This research evaluates alternative asphalt binders for use in surface friction treatments. The research program evaluated the friction performance of HFST applications made with asphalt-based binders including newly developed modified asphalt binders. An updated Life-Cycle-Cost (LCC) EXCEL program was developed to conduct cost analysis based on the performance of the tested binder-aggregate combinations. The study showed acceptable asphalt-based binders for HFST applications and recommended continuing the development of asphalt-based binders to enhance the performance of HFST applications.


Report number: cmr 24-015
Published: August 2024
Project number: TR202206
Authors: Alireza Roshan and Magdy Abdelrahman
Performing organization: Missouri University of Science & Technology

Monday, August 26, 2024

Analysis of Asphalt Mixtures Using Alternative Aggregate in SMA and Superpave

To identify locally available, cost-effective, and durable crushed coarse aggregates for Stone Matrix Asphalt (SMA) and high-level Hot Mix Asphalt (HMA) mixes, multiple well-distributed aggregates have been evaluated in this study as candidate aggregates, including traprock (control), chat, gravels, steel slag, limestone, and dolomite. Aggregate screening and durability evaluations were conducted to eliminate unqualified candidates. Subsequently, SMA and HMA mixtures were designed with qualified candidate aggregates following AASHTO R 46 and R 35, respectively. Performance verification included Hamburg Wheel Tracker rutting test (HWTT) and IDEAL-CT cracking test to finalize the mix designs, and balanced mix design methods (BMD) were used to complete the designs if the volumetric optimum designs failed to meet the performance requirements. The testing results showed that while the SMA and HMA mixes with traprock and gravel could satisfy both volumetric and performance thresholds. SMA and HMA mixes with blended aggregates (i.e., limestone and chat, and dolomite and chat) passed volumetric limits as well. For SMA and HMA mixtures with steel slag, the binder contents from the volumetric designs had to be increased to meet the cracking resistance requirements. Additional performance tests including fatigue and rutting on the Asphalt Mixture Performance Tester (AMPT), low-temperature Indirect Tensile (IDT) tests, and the Accelerated Friction Tests (AFT) were conducted to fully evaluate the mixtures’ performance and durability. Analyses on both the material and pavement structural levels were performed, and cost-effective analysis for projects with mixtures using different aggregates were also used in this study. The results indicated that mixes with alternative aggregates performed comparably to those with control aggregates.


Report number: cmr 24-014
Published: August 2024
Project number: TR202205
Authors: Jenny Liu, Emad Kassem, Yizhuang David Wang, Bo Lin
Performing organization: Missouri University of Science & Technology

Monday, August 19, 2024

iTrain – Immersive Training of Department of Transportation Work Zone Inspectors using Virtual Reality

This report presents the development, implementation, and evaluation of Virtual Reality (VR) training modules designed to enhance work zone safety training for the Missouri Department of Transportation (MoDOT) staff. The project aimed to provide immersive, realistic, and interactive training environments that improve knowledge retention, engagement, and practical skills application. The developed VR training modules were integrated into MoDOT’s Advanced Work Zone Training and Flagger Training courses. For Advanced Work Zone Training, the modules focused on understanding typical applications and identifying deficiencies within work zones. For Flagger Training, the module emphasized hands-on practice of the 3-2-1 Cone Procedures. Both training programs incorporated measures of participants’ actions and post-training surveys. Feedback from the surveys indicated high levels of training effectiveness and participant satisfaction of the realistic work zone representations and ease of VR use. Behavioral performance measures, not feasible with traditional training methods, showed that participants effectively performed flagger operations and identified work zone deficiencies. Outreach efforts and hands-on demonstrations in other states further validated the positive reception of the VR training modules, highlighting their potential for broader adoption across other DOTs and agencies. The feedback collected was used to further refine the VR training program. In summary, the VR training modules enhance work zone safety training, offering a more immersive, interactive, and effective learning experience to supplement existing training.


Report number: cmr 24-013
Published: August 2024
Project number: TR202118
Authors: Praveen Edara, Zhu Qing, Carlos Sun, Henry Brown, and Bimal Balakrishnan
Performing organization: University of Missouri-Columbia

Thursday, August 15, 2024

Mitigating and Preventing MoDOT Safety-Related Incidents through Root-Cause Elimination and Utilization of Leading Safety Indicators

This report thoroughly investigates and analyzes the diverse factors influencing incident occurrence in work zone environments, aiming to identify areas where proactive planning can enhance incident mitigation. Drawing from an extensive review of existing literature on work zone safety, 37 factors affecting both public and occupational safety were identified. Two surveys were then conducted among MoDOT employees and contractors to assess the relative criticality of these factors on worker safety within work zones. Survey results highlight driver-related factors, such as the driver's level of attention and unsafe driving, as the most critical to worker safety in work zones. Additionally, MoDOT employees and contractors evaluated MoDOT’s performance on the studied factors. While MoDOT's performance received substantial ratings overall, contractors consistently rated it lower than MoDOT employees, indicating a divergence in perspectives between stakeholder groups. Notably, both groups identified the presence of law enforcement as a critical area requiring further improvement in Missouri work zones. Furthermore, MoDOT employees rated field compliance with safety policies and the overall safety culture in their workplaces. Variations in policy compliance were observed, with certain policies, such as those related to backing movements, requiring attention to improve adherence—a crucial aspect for occupational safety in work zone environments. Additionally, while MoDOT employees demonstrated strong knowledge of policies and safety procedures provided by MoDOT, they expressed lower satisfaction with the timely investigation of safety incidents and the effectiveness of subsequent improvements. This comprehensive analysis provides a benchmark for MoDOT and other stakeholders to address identified deficiencies and enhance work zone safety practices effectively.


Report number: cmr 24-012
Published: August 2024
Project number: TR202212
Authors: Bahaa Chammout and Islam El-adaway
Performing organization: Missouri Center for Transportation Innovation

Tuesday, August 13, 2024

Safety Evaluation of J-turn Intersections in Missouri

The design of J-turn intersections has gained its prevalence in Missouri due to their demonstrated safety benefits. However, with the growing number of J-turns and the availability of more crash data, there is a renewed need to deepen the understanding of the safety performance of J-turns. This study presents a comprehensive safety evaluation of J-turn intersections, analyzing their effectiveness in reducing total and fatal & injury crashes using crash data from 47 J-turn intersections between 2005 and 2021. Employing a robust methodology including both comparison group and empirical Bayes analyses, this study assesses the impact of J-turns on crash reductions compared to traditional two-way stop-controlled intersections. Two methods were used because they had different tradeoffs such as data requirements, simplicity of implementation, and regression to the mean. The comparison group analysis revealed reductions of 46.6% in fatal and injury crashes and 44.4% in total crashes. Similarly, the empirical Bayes analysis supported these safety improvements, showing reductions of 51.4% in fatal and injury crashes and 40.3% in total crashes. Furthermore, crash frequency models developed for Missouri’s J-turn sites indicate that site characteristics such as loons, deceleration/acceleration lanes, and islands contribute to reduction in crashes. The study also includes detailed collision diagrams that outline crash locations and types at J-turn sites. The study findings provide insights and tools for MoDOT engineers as they consider J-turn design as a safety countermeasure at two-way stop-controlled intersections on rural highways.


Report number: cmr 24-011
Published: August 2024
Project number: TR202320
Authors: Praveen Edara, Zhu Qing, Henry Brown, Carlos Sun, and Ho Jun Baek
Performing organization: University of Missouri-Columbia

Tuesday, August 6, 2024

Implementing the LWD for MoDOT Construction Acceptance of Unbound Material Layers: Phase II

This Phase II project aimed to accumulate more field test data to improve the standards for the implementation of the Zorn lightweight deflectometer (LWD) for the acceptance of unbound materials layers. Five more different soils, including New Florence CL, Holts Summit GM, Sikeston SM, Rolla CL, and Rolla GM, were collected from different project sites in Missouri for this project, and a series of laboratory and field tests were conducted. In addition, a disturbance isolation unit was devised for accurate field moisture measurement, ensuring reliable data collection. Field LWD tests were conducted across four project sites, evaluating moisture content and modulus ratios against specified criteria for compaction acceptance. Results indicated varying degrees of compliance across soil types and testing points. Comparisons of test results obtained from different LWD devices and with traditional density-based methods revealed LWD's effectiveness for fine-grained soils but limitations for coarse-grained soils. Consistency between LWD devices was generally good, though discrepancies were noted at certain sites. Overall, the project advances LWD implementation for unbound materials acceptance, offering insights into soil behavior under different conditions and refining testing methodologies for improved accuracy and efficiency.


Report number: cmr 24-010
Published: August 2024
Project number: TR202323
Authors: Xiong Zhang, Jenny Liu, and Chuanjun Liu
Performing organization: Missouri University of Science & Technology