Leslie Myers McCarthy

Analysis of Sight Distance, Crash Rate, and Operating Speed Relationships for Low-Volume Single-Lane Roundabouts in the United States

AbstractThis paper explores the relationship between sight distance parameters, crash rates, and operating speeds at low-volume single-lane roundabouts in the United States. The understanding of the interaction of design, operations, and crash performance is a step forward in the development and application of performance-based standards for roundabouts. The specific objective of this paper is to quantify the relationship between crash rates, sight distance parameters, and operating speeds to present an approach to establishing performance-based standards that highway practitioners can adopt in roundabout design. Geometric, traffic, and crash data were collected on 72 approaches to 19 low-volume single-lane roundabouts in six states. The data for these sites were broken into two groups based on the posted speed limit (at 40  km/h and greater than 40  km/h). In addition, the associations between different sight distance parameters, crash parameters, and operating speed data were investigated. The research ...

Exploring pay factors based on hot mix asphalt performance using quality-related specification software

A parametric study was conducted that established quality-related specification relationships for hot mix asphalt (HMA) design and construction. Factorial analysis identified the significance of several factors, developed regression models, and explored how variations in specifications led to additional incentive or disincentive pay. The equations may allow contractors and transportation agencies to plan as-built or job mix formula requirements based on incentive/disincentive risk. Approximately 92% of the surface lift rutting and 63% of the binder lift rutting data indicate no difference in pay as a result of discrepancy between predictive model and quality-related specification software-measured pay factors. Observations and recommendations for implementation and further study are presented in this paper.

Comparing Flexible Pavement Performance Using Emerging Analysis Tools

AbstractIn recent years, a variety of tools have been developed to assist in the analysis of flexible pavement service life in the United States. Although the output from many of the approaches is similar, each tool varies in the amount of testing effort, materials, and equipment necessary to arrive at the resulting predictions. Building upon the findings from research conducted in the National Cooperative Highway Research Program (NCHRP) Project 9-22B, this study focused on comparing flexible pavement performance predictions using three emerging analysis tools. One of the pavement analysis software packages, which considered the standard of, predicts performance in terms of incremental distresses and damage accumulation during a pavement’s service life. The other two programs are performance-related specification (PRS) tools that predict pavement performance in terms of service life factors. Three different asphalt mixtures were evaluated including a conventional mixture and two unconventional mixtures m...

Mechanical Responses and Viscoelastic Properties of Asphalt Mixtures Under Heavy Static and Dynamic Aircraft Loads

The introduction of larger aircraft on flexible airfield pavements has led to a need for asphalt mixtures capable of sustaining such heavy loads. This laboratory and analytical study investigated the mechanical responses of a number of modified asphalt mixtures to identify their potential for use in airfield aprons and taxiways that were subjected to heavy, static, or slow-moving aircraft loads. The airfield flexible pavement section constructed at the FAAs National Airport Pavement Test Facility Construction Cycle 1 was modeled by using the three-dimensional finite element analysis software ABAQUS. Laboratory-compacted specimens of each modified asphalt mixture were tested by using AASHTO standards to determine volumetric properties and mechanical responses. The effects of static and dynamic aircraft loading were evaluated in ABAQUS with the material properties of the mixtures determined in the laboratory. On the basis of the findings of this study, it appears that several mixtures more commonly used in highway pavements, including modified mixtures, warm-mix asphalt, and reclaimed asphalt pavement, perform similarly to or even outperformed the FAA standard asphalt mixture. The results of this initial study support the idea that an opportunity exists for airports to implement emerging asphalt paving materials without compromising the pavement design life.

Decision Tree for Postflooding Roadway Operations

When a pavement is flooded, transportation agencies are faced with the decision to leave the road open or close it to traffic. On the one hand, agencies may want to keep the road open and prioritize connectivity if the road serves a critical economic purpose for a region. On the other hand, agencies may choose to close the road to prevent additional structural damage (which may incur significant repair costs) because of high water content in (or even saturation of) the subgrade. Nondestructive testing (NDT) tools such as the falling weight deflectometer (FWD) can be applied to assist decision makers by facilitating a more reliable evaluation of the structural condition of the pavement. Reliable decision making ought to incorporate inherent uncertainties in the process, including the structural state of the pavement after flooding, as well as the reliability of FWD testing and variability in costs. This paper presents a method that uses a Bayesian decision tree approach for highway emergency operations after flooding. Uncertainties in the structural state of the pavement after flooding, NDT, and costs are addressed with Monte Carlo simulations. A case study of a flooded roadway section in North Dakota demonstrated this approach: user delay costs caused by closure of the roadway were explicitly considered. The results of the decision tree analysis provide objective recommendations about opening or closing a road after flooding, as well as whether FWD testing of the flooded road should be conducted once the water recedes.

Quantifying the Performance of Warm-Mix Asphalt and Reclaimed Asphalt Pavement in Flexible Airfield Pavements

Warm-mix asphalt (WMA) is a current paving technology that uses various techniques for producing and constructing asphalt at lower temperatures. The benefits associated with WMA range from reduced carbon dioxide emissions to extended paving seasons. The performance and the environmental benefits of WMA can be enhanced by the addition of reclaimed asphalt pavement (RAP) to the aggregate portion of the mix. This technology has been extensively used in the highway sector, but its use in the airfield sector has not been documented fully. Currently, asphalt mixtures used in the surfaces of airfield pavements are designed in accordance with the FAA P-401 specifications. This study quantified the performance of a WMA-RAP mixture compared with the standard FAA P-401. The asphalt mixture performance tester was used to test the mixtures for flow time and load cycles to failure so as to capture the rutting and fatigue cracking potentials of both mixtures. The laboratory data were used as input to the three-dimensional finite element analysis software ABAQUS, and the mechanical responses were determined within the surface layer of the airfield flexible pavement section modeled to represent the section constructed at the FAA National Airport Pavement Test Facility. The Greenhouse Calculator for State Departments of Transportation, a product of NCHRP Project 25–25, was used to assess the environmental impacts of both mixtures. This studys findings indicate that the laboratory and predicted performance of the WMA-RAP mixture are comparable to the performance of a standard FAA P-401 mixture. The cost and environmental benefits of the WMA-RAP mixture make this type of material a viable alternative to the standard FAA P-401 mixture.

Stochastic Estimation of the In-Place Dynamic Modulus for Asphalt Concrete Pavements

AbstractThe dynamic modulus of asphalt concrete mixtures is a key property in assessing asphalt pavement performance based on its role in the mechanistic-empirical design method. The dynamic modulus is also considered to be used as one of the major characteristics in performance-related specifications for quality assurance. However, no feasible method to estimate the mean and variance of the in-place dynamic modulus for the as-built asphalt pavement has been suggested. This paper presents a methodology of stochastically evaluating the in-place dynamic modulus of the as-built asphalt pavement using a relationship of in-place air voids and a set of single dynamic modulus values measured in the laboratory. The methodology was validated with asphalt mix collected from a construction site. The comparison plot between the estimated in-place dynamic modulus and as-designed asphalt mix demonstrated a simple way to evaluate the as-built mix quality. This methodology provides several practical advantages to determi...

Preliminary Analysis of Quality-Related Specification Approach for Cracking on Low Volume Hot Mix Asphalt Roads

During the last twenty years, efforts have been made to implement performance-related specifications (PRS) for hot mix asphalt (HMA) construction in the United States. The National Cooperative Highway Research Program (NCHRP) Project 9-22: Beta Testing and Validation of Hot Mix Asphalt Performance-Related Specifications created software using models similar to those in the interim American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical Pavement Design Guide (MEPDG). The program predicts an effective dynamic modulus (E*) parameter to determine information pertaining to major distress types. In this study fatigue cracking (bottom-up/alligator cracking) is analyzed. A predicted life difference (PLD) is then calculated between job mix formula (JMF) and as-built conditions, resulting in an assigned pay factor. In this study, a low volume HMA roadway in rural Rhode Island was analyzed using the volumetric-based models. A sensitivity analysis was conducted by varying asphalt contents, in-situ air void targets, and dust-to-asphalt ratios to evaluate their effects on fatigue cracking levels. The aim was to assess the suitability of the software as a tool for pay factor development in Rhode Island. Based on preliminary results, results are significantly sensitive to changes in JMF target in-situ air voids. Future considerations regarding pay factor development for low volume roadway projects include: added costs or savings as a result of implementation, the development of a more simplistic method of computing pay factors, and comparing results with pavement management system (PMS) information on other comparable flexible highway pavements in Rhode Island.

Comparative evaluation of mechanistic–empirical performance models as a tool for establishing pavement performance specifications

In this study, the fatigue performance of 27 mixtures representing various as-built pavement conditions is evaluated using two advanced mechanistic–empirical (M–E) models, layered viscoelastic continuum damage (LVECD) and AASHTOWare Pavement ME Design (Pavement ME)) and one mixture-based index parameter obtained from fatigue testing. The performance trends among the two M–E models are compared by performing simulation on thick and thin pavement sections. Moreover, the performance ranking based on a mixture index parameter is compared to the M–E models. The results from the M–E models clearly show the need for increased compactive effort to achieve the best performance. For the majority of the mixtures, the rankings of the different models are similar. In almost all instances, the rankings based on the M–E models and index parameters were able to distinguish the best and worst performing pavements similarly. This indicates that the approaches can be used interchangeably for differentiating mixture performance between different asphalt and air void levels.

Development of Pavement Preservation Strategies with Pavement ME Design Software for the State of Rhode Island

The objective of this study was to propose an approach to integrate AASHTOWare Pavement ME Design software into pavement preservation strategies of the Rhode Island Department of Transportation. The use of Pavement ME Design software could assist in the prioritization of mitigation alternatives; this procedure would optimize resources in Rhode Island. Four representative pavement sections on state highways in Rhode Island were selected and then analyzed with the Pavement ME Design software. Weigh-in-motion traffic data also were collected from nine stations in Rhode Island to establish representative state traffic patterns. This information was used as input to Pavement ME Design, and the predicted performance measures (i.e., international roughness index, rutting, longitudinal cracking) were then used to determine when the typical Rhode Island pavement mitigation alternatives [e.g., crack seals; level and overlay; mill and overlay with and without friction course; paver placed elastomeric surface treatment; rubberized chip seals; reconstruction and reclamation; and stress-absorbing membrane interlayer (SAMI)] were triggered. In addition, a cost-based approach and an incremental benefit–cost alternative prioritization method were analyzed to determine the most cost-effective alternatives and the most beneficial alternatives, respectively. On the basis of the analysis, the Pavement ME Design software was found to have potential for use in the enhancement of pavement preservation strategies. Crack seals, rubberized chip seals, and SAMI were found to be the most cost-effective and the most beneficial of all alternatives assessed.