bluuebunny/crossref_metadata_2025 huggingface dataset:
Accelerated Loading Testing of Stainless Steel Hollow Tube Dowels
Authors: Khazanovich Lev , Yut Iliya , Tompkins Derek , Schultz Arturo
Published: May 2018

The use of dowels in rigid pavements to provide adequate load transfer is a common practice in current pavement design. Since the use of deicing salts in cold climates results in significant deterioration of dowels, the need to optimize performance and reduce pavement life-cycle cost prompts the need for alternatives to common round steel dowel bars. These alternative dowels must be able to withstand corrosion while providing adequate long-term load transfer performance across jointed slabs. Results are presented of the accelerated loading of two jointed test pavement specimens that incorporate one of two types of dowels: a stainless steel hollow tube dowel or an epoxy-coated solid steel dowel. The accelerated loading of these test specimens was accomplished courtesy of the second generation of the Minnesota Accelerated Loading Facility (MinneALF-2), a 10-year-old joint project between the Minnesota Department of Transportation and the University of Minnesota that allows for the realistic simulation of repeated truck loading of concrete pavement joints. For this study, each specimen was subjected to 10 million 9-kip loading cycles. Deflections between jointed slabs were measured with linear variable differential transformers, and the load transfer efficiency (LTE) for each case was calculated from these measurements. Although the LTE for the stainless steel hollow tube dowels was lower than that for the epoxy-coated dowels, the results suggest that the stainless steel tubes are capable of providing a sufficiently high long-term LTE for concrete pavement joints. At the same time, the stainless steel hollow tube dowels considerably reduce the risk of joint deterioration due to dowel corrosion.
Concrete Pavement Performance in Midwestern Argentina Compared with Long-Term Pavement Performance Data
Authors: Bustos Marcelo G. , Marcet Juan E. , Cordo Oscar V. , Mancini Pablo Girardi , Pereyra Miguel O. , Altamira Aníbal L.
Published: May 2018

Portland cement concrete pavements have been constructed in many areas in Argentina that feature heavy traffic and freeways and highways in freezing areas. To predict their performance, computational programs such as the World Bank's HDM-4 may be used. This particular software includes distress models that need to be adjusted to local conditions in order to optimize the evaluation of maintenance strategies and resource allocation. The main objective of this study is to evaluate the performance of concrete pavements in the midwestern region of Argentina by using the HDM-4 software to obtain calibration coefficients for each distress model. A specific methodology for model calibration was applied to concrete pavements of the national road network located in the provinces of San Juan, Mendoza, and Córdoba. Such roads include jointed plain and jointed reinforced concrete pavement (JPCP and JRCP), with an ample range of traffic levels and climate conditions. Calibration coefficients were determined individually for each road and for road groups with similar characteristics; the results were subsequently compared with data calibration results from the Long-Term Pavement Performance database obtained from previous studies. Many similarities were found in the ability of the models to predict distress levels. Some models show an irregular pattern in predicting distress without calibration, but other models show better results, such as those to predict joint faulting and international roughness index.
Pilot Study in Sampling-Based Sensitivity Analysis of NCHRP Design Guide for Flexible Pavements
Authors: Graves R. Clark , Mahboub Kamyar C.
Published: May 2018

The mechanistic–empirical pavement design guide (MEPDG), developed under the recently completed NCHRP Project 1–37A, is a complex tool. Sensitivity analyses typically vary a single input parameter while holding other parameters constant. A pilot project is outlined to identify the feasibility of a global sensitivity analysis of the design process by using random sampling techniques over the entire input parameter space. This study sampled the following flexible pavement input variables: hot-mix asphalt (HMA) base nominal aggregate size, climate location, HMA thickness, annual average daily truck traffic (AADTT), subgrade strength, truck traffic category, construction season, and binder grade “bump.” A total of 100 design sections were randomly sampled from these input parameters. The resulting predicted performance of longitudinal and alligator cracking, HMA and total rutting, and international roughness index were analyzed by using the Pearson's and Spearman's correlation coefficients. These coefficients indicate that AADTT, HMA thickness, and subgrade strength have a significant impact on performance, whereas the remaining parameters have lesser impacts. The performance predicted with trial designs with default values of the least significant variables was compared with the original performance predictions using the original input factors. This comparison indicated that the default parameters produced similar performance to designs using all the input parameters. These results demonstrated that this type of sensitivity analysis may be used to identify important input parameters across the entire parameter space. The utilization of a “bumped” binder grade did not appear to have a significant influence on the performance predicted by the MEPDG models. These results indicate that further research to refine the MEPDG performance models may be necessary.
Evaluation of Subgrade Resilient Modulus Predictive Model for Use in Mechanistic–Empirical Pavement Design Guide
Authors: Khazanovich Lev , Celauro Clara , Chadbourn Bruce , Zollars John , Dai Shongtao
Published: May 2018

The characterization of unbound materials in the mechanistic–empirical pavement design guide (MEPDG), also known as the 2002 design guide, is reviewed, and this characterization is applied to Minnesota subgrades. The main emphasis is on the collection of k1-, k2-, and k3-parameters for Minnesota fine-grained soils and the procedure for the interpretation of the resilient modulus test to provide an input to the multilayer elastic theory (MLET) analysis (Level 2 input). This is an important aspect of adaptation of the MEPDG, because the guide recommends measurement of resilient moduli from laboratory testing, but the procedure does not specify how to interpret the test data to obtain an input for an MLET analysis. The resilient modulus test results from 23 samples collected from several Minnesota locations were used to provide information for the nonlinear finite element program and multilayer elastic theory program. The obtained elastic moduli were compared with the MEPDG recommended ranges for subgrade modulus of elasticity based on the soil classification (Level 3 inputs). The MEPDG Level 3 ranges were found to be reasonable.
Comparisons of Flexible Pavement Designs
Authors: Carvalho Regis L. , Schwartz Charles W.
Published: May 2018

Flexible pavement designs and performance predictions derived from the empirical 1993 AASHTO pavement design methodology and the mechanistic–empirical NCHRP Project 1–37A approach are compared for a range of locations within the United States, each with its own climate, subgrade, and other material properties and local design preferences. Particular emphasis is devoted to the influence of traffic and reliability levels. The results suggest that relative to the NCHRP Project 1–37A predicted performance, the 1993 AASHTO guide overestimates performance (i.e., underestimates distress) for pavements in warm locations and at high traffic levels. Trends of pavement performance with reliability level were similar for both methodologies. The results suggest that the default design criteria incorporated in the NCHRP Project 1–37A software are broadly consistent with what would be observed historically from pavements designed with the 1993 AASHTO guide.
Model to Evaluate Roadway Concessions in Brazil
Authors: Cybis Helena Beatriz Bettella , Guzen Érico Reis , Lindau Luis Antonio , Ribeiro José Luis Duarte , Michel Fernando Dutra
Published: May 2018

This paper describes the construction and application of a model to evaluate roadway concessions. The model is based on the perception of users and experts about physical aspects of roads and services provided by Brazilian concessionaires. Information was gathered from previous studies, interviews with road users, and focus groups with experts. The paper describes the conceptual stages of the model, presents a field application, and discusses the results generated for one case study. The model allows a dynamic monitoring program of the conditions of roads, road segments, and entire concessions, considering the individual or joint perception of users and experts. The model is transferable to other scenarios where it is important to have a tool to help the negotiation process between public and private sectors concerning new roadway investments by the concessionaires.
Understanding Statistics in Maintenance Quality Assurance Programs
Authors: Schmitt Robert L. , Owusu-Ababio Sam , Weed Richard M. , Nordheim Erik V.
Published: May 2018

From the 1990s to now, transportation maintenance quality assurance (MQA) programs have been developed to ensure that maintenance quality is being achieved. MQA programs must be capable of detecting insufficient maintenance efforts, poor material performance, and incorrect procedures when evaluating end-product performance. At the Maintenance Quality Assurance Peer Exchange held at Madison, Wisconsin, in October 2004, participants expressed interest in exploring how statistical tools might be more effectively applied in MQA programs. The purpose of this paper is to provide maintenance practitioners with knowledge of how to understand and use statistics in MQA programs. Literature pertaining to recent efforts in this area was reviewed and synthesized. In addition, hazardous debris data from Wisconsin and level of service data from North Carolina were analyzed to demonstrate how an agency could apply traditional statistical methods such as analysis of variance, confidence limits, means comparison, data stratification, and sample size determination to an MQA program.
Improving Compliance with Work Zone Speed Limits
Authors: Brewer Marcus A. , Pesti Geza , Schneider William
Published: May 2018

Thousands of crashes occurring in work zones each year lead to numerous fatalities and injuries. The sizeable portion of these crashes attributed to excessive speed emphasizes the need to motivate drivers to comply with speed limits in work zones. A recent research project was conducted to determine effective measures to motivate and encourage drivers to observe posted speed limits in work zones. Three devices were tested in that project: a speed display trailer, changeable message sign with radar, and orange-border speed limit sign. Results from field testing indicate that devices with the ability to display drivers’ speeds have considerable potential for reducing speeds and improving compliance. Orange borders greatly improve the visibility and conspicuity of speed limit signs, but they do not have a consistent measurable effect on compliance. In the absence of active enforcement, data from this project indicate that drivers are likely to drive as fast as they feel comfortable, regardless of the posted speed limit.
Dynamic Late Merge Control at Highway Work Zones
Authors: Kang Kyeong-Pyo , Chang Gang-Len , Paracha Jawad
Published: May 2018

The purpose of this study is to present the evaluation result of a dynamic late merge (DLM) system for highway work zone operations, experimented by the Maryland State Highway Administration and International Road Dynamics Inc. The evaluation focuses mainly on the operational efficiency such as the input–output analysis, work zone throughput, volume distribution, and resulting queue length. Evaluation results reveal that a properly deployed DLM system can indeed outperform the conventional merge control with respect to the total work zone throughputs. Such a system, however, may result in excessive traffic conflicts if not properly integrated with existing static warning signs for work zone operations. Some suggestions and guidelines developed from field observations and analysis results for potential improvement of the DLM performance are also presented in this paper.
Effectiveness of Alternative Chemicals for Snow Removal on Highways
Authors: Fu Liping , Sooklall Rudolph , Perchanok Max S.
Published: May 2018

This paper describes an empirical study aimed at quantifying and comparing the effectiveness of several alternative chemicals for snow and ice control under specific weather, site, and traffic conditions. Data collected from a large scale field test are used in this analysis, involving measurements on snow cover, weather and pavement conditions, and treatment operations at 10-min intervals over 16 snowstorms. The paper details a case-by-case comparison of several alternative chemical treatments including dry salt and salt prewetted with different agents. Statistical models are developed and used to explain the effects on snow melting trend of various weather and treatment factors.
Collaborative Adaptive Sensing of the Atmosphere
Authors: Brotzge Jerald A. , Droegemeier Kelvin , McLaughlin David J.
Published: May 2018

An Engineering Research Center for the Collaborative Adaptive Sensing of the Atmosphere (CASA) was formed in the fall of 2003 by the National Science Foundation to develop a dense network of small, low-cost, low-power radars that could collaboratively and adaptively sense the lower atmosphere (0 to 3 km above ground level). Such a network is expected to improve sensing near the ground dramatically through a process called distributive collaborative adaptive sensing. The CASA network is a dynamic, data-driven application system, whereby strategy for scanning is an optimized network solution among competing end-user needs and weather constraints. Decision making is made in real time, with end users providing automated or manual input, or both, to the system. Furthermore, each radar will have dual-polarization capability and signal processing designed to minimize ground clutter contamination. Data collected from the CASA network will be assimilated in real time for use in detection algorithms, numerical weather prediction and transportation models, and output disseminated to a wide array of end users. Because of distinct advantages of such a radar network, significant improvements are expected from the system, in analysis and prediction of surface weather conditions.
Effects of the Provision of Wide-Area Snowstorm Information on Winter Driving
Authors: Matsuzawa Masaru , Kajiya Yasuhiko , Yamagiwa Yuji
Published: May 2018

In Hokkaido, Japan, a system that provides road weather information to drivers is in operation and under further development. With regard to visibility in snowstorms, observation data collected at ground-level observation stations have been available, but not wide-area information on the distribution of visibilities. A method was developed to estimate visibility from the weather conditions, and it was applied to estimation of visibilities in a wide area. Such wide-area visibility information, together with snowfall information, was provided to road users on an experimental basis. Sixty percent of drivers who received this information changed their transportation behavior at some point, and more than 90% viewed the information as effective in increasing their sense of security. This finding confirmed that visibility information is valuable winter road information for drivers and that the visibility estimation method will be useful in providing wide-area visibility information.
Development of Roadway Weather Severity Index
Authors: Strong Christopher , Shvetsov Yurii
Published: May 2018

Winter weather conditions play a significant role in the operation of the surface transportation system, including heightening safety risks for motorists. Previous research has sought to correlate winter weather severity with maintenance costs through the use of indices, although few have been developed to relate winter weather parameters to safety. This paper summarizes a research project using data from California, Montana, and Oregon to quantify relationships between winter weather and safety. Many model forms were reviewed, and then linear models were developed to predict the cubic root of the crash rate as a function of weather parameters. Models were developed for different topographic zones and on a statewide level, with correlations ranging from 0.12 to 0.67. These models were used to develop indices that may be used for traveler information purposes. The indices show promise for application in traveler information and winter maintenance; therefore, recommendations for research are included.
In-Place Determination of Stiffness of Subsurface Reclaimed Layers in Thin Surface Hot-Mix Asphalt Pavements
Authors: Mallick Rajib B. , Bradley Julie E. , Nazarian Soheil
Published: May 2018

Seismic testing and analysis using a nondestructive method was developed to determine the moduli of reclaimed layers in thin surface hot-mix asphalt pavements. This method is particularly useful when accurate backcalculation of moduli is difficult because of the existence of unknown layers and when the extraction of intact cores for laboratory testing is impossible. Sixteen Maine Department of Transportation projects with foamed asphalt and plant-mixed recycled asphalt pavement reclaimed layers were tested according to this method using a portable seismic property analyzer. Layer thickness uniformity was checked with a ground-penetrating radar, and falling weight deflectometer was used at multiple load levels to acquire deflection data. Seismic test data were analyzed to estimate layer moduli. The collected data were found to have very low variability. The deflections calculated with the predicted moduli and actual deflections were found to compare well, and the use of predicted moduli as seed moduli resulted in backcalculations with relatively low root-mean-square errors. The moduli were corrected for temperature, and design moduli were recommended. This newly developed method can be used effectively to determine the moduli of subsurface layers, and its use is important for collecting a large amount of data, specifically because of the highly variable nature of the reclaimed layers. A logical next step will be to develop artificial neural networks to automate the process of data reduction from seismic testing. This would allow departments of transportation and industry to fully use the benefits of this fast, nondestructive testing method.
Detection of Stripping in Hot-Mix Asphalt
Authors: Hammons Michael I. , Von Quintus Harold , Geary Georgene M. , Wu Peter Y. , Jared David M.
Published: May 2018

Damage mechanisms that lead to stripping significantly affect the dynamic modulus and tensile strength of hot-mix asphalt (HMA). When stripped HMA is unexpectedly encountered below the planned milling depth during routine mill and overlay rehabilitation projects, it must be removed and replaced; this causes significant cost overruns and delays. A procedure was developed to identify the extent and depth of stripping in in-place HMA pavement sections. Several nondestructive survey methods were analyzed to determine their capability to locate areas of stripping, either by themselves or in various combinations. Cores were extracted and used to calibrate the methods. Visual inspections of the cores and laboratory tests on selected cores were used to validate the results. The procedure involved observation of surface distresses, complete ground penetrating radar survey, seismic testing of selected areas, limited coring, and laboratory testing of selected cores. With these procedures, areas with stripping can be distinguished so that effective rehabilitation strategies can be developed.
Finite Element Method Modeling of Reflective Cracking Initiation and Propagation
Authors: Baek Jongeun , Al-Qadi Imad L.
Published: May 2018

In overlaid pavements, working cracks in existing pavement systems propagate upward to the new pavement surface and cause reflective cracking, one of the most serious causes of deterioration in overlay systems. Several techniques to reduce reflective cracking have been introduced. However, the reflective cracking mechanism is not yet well understood. Fracture mechanics have been applied in pavement analysis to investigate crack development. A single-edge notched beam test was simulated with the finite element method with the cohesive zone model, which has been widely used to simulate a cohesive crack. The effects of steel reinforcement, interface, and hot-mix asphalt (HMA) properties on crack initiation time and crack propagation rate were investigated. A damage value, an indication of the degradation of the initial stiffness of the material in cohesive elements, was used to define the degree of softening and to trace crack formation. On the basis of elastic analysis, the crack initiation time for the reinforced beam was five times greater than that of the unreinforced beam, and crack propagation rate was reduced by two and one half to six times at –10°C. Conversely, when viscoelastic analysis, which is a more realistic simulation of HMA behavior, is used, the improvement in controlling reflective cracking is approximately half the improvement for the same loading and temperature conditions. This improvement depends on shear stiffness at the interface, crack length, and HMA temperature. In general, steel reinforcement, when installed properly, enhanced the resistance to reflective cracking.
Cold In-Place Recycling and Full-Depth Reclamation Projects by Nevada Department of Transportation
Authors: Bemanian Sohila , Polish Patty , Maurer Gayle
Published: May 2018

One of the biggest challenges that public agencies face is how to optimize available funding. With the price of bituminous materials 70% higher than 2 years ago and increased demand for capacity improvement projects, it is more important than ever to use in-place materials when rehabilitating pavement structural sections. Cold in-place recycling (CIR) and full-depth reclamation (FDR) are two pavement rehabilitation strategies that the Nevada Department of Transportation (NDOT) has used for more than 20 years. These strategies have allowed NDOT to save more than $600M over the past 20 years compared with complete reconstruction costs. In addition, traffic interruptions are minimized during construction, and natural resources are preserved. According to the Highway Performance Monitoring System data, NDOT has the highest percentage of its combined National Highway System Interstate and other roadways rated in the “good” category. The reason for this achievement is that NDOT uses a proactive Pavement Management System (PMS) to prioritize its pavement preservation projects. A considerable amount of CIR and FDR rehabilitation work is performed in conjunction with the proactive PMS. Because these strategies are more cost-effective than overlay, mill and overlay, or reconstruction, NDOT can rehabilitate more roads with less money. This report will describe how to select, design, and construct successful CIR and FDR projects. The performances of the strategies are evaluated, and life-cycle cost analysis is developed to demonstrate the cost–benefit of CIR and FDR versus conventional rehabilitation strategies.
Evaluation of Backcalculation Methods for Nondestructive Determination of Concrete Pavement Properties
Authors: Fwa T. F. , Setiadji B. H.
Published: May 2018

Different backcalculation algorithms often give different answers in backcalculated pavement properties. This is because of the differences in the type of pavement models, solution search procedure, and deflection matching criteria used in the backcalculation analysis. Regardless of the theory applied and the backcalculation algorithm adopted, a logical basis of selection of the backcalculation procedure for practical applications would be to assess whether the backcalculated pavement properties could provide good estimates of the actual pavement properties. Today, the ease and the convenience of access to the Long-Term Pavement Performance (LTPP) database of actual measured data enable a highway agency to adopt this approach to select a backcalculation algorithm that meets its needs. With the LTPP-measured data, this approach was applied to evaluate the relative merits of four backcalculation algorithms (two versions of ILLIBACK, NUSBACK, and LTPP best-fit method) by a comparison of the computed elastic modulus of concrete pavement slab and the modulus of subgrade reaction of concrete pavements against the LTPP measured values. The performance of the four algorithms was greatly affected by the constraints imposed by the deflection theory adopted and was significantly dependent on their respective criteria used to match the computed and measured deflections. The number of sensors used in the backcalculation, as well as the choice of sensor configuration, can significantly affect the performance of the backcalculation algorithms.
Analysis of Effectiveness of Longitudinal Grooving against Hydroplaning
Authors: Ong G. P. , Fwa T. F.
Published: May 2018

Longitudinal pavement grooving has been applied in highways to reduce the occurrence of hydroplaning at accident-prone locations. However, to date there has not been a systematic study of its effectiveness against hydroplaning. This lack can be attributed to the difficulty in conducting such experiments and the extreme complexity of the theoretical analysis involved. A numerical model was developed to simulate the hydroplaning phenomenon. Then a systematic study was conducted on the effectiveness of various designs of longitudinal grooving against hydroplaning. The analysis covers groove widths of 2 to 10 mm, groove depths of 1 to 10 mm, and groove center-to-center spacing of 5 to 25 mm. Groove dimensions were found to have significant effects on the effectiveness of a grooving design against hydroplaning. The results show quantitatively how the use of larger groove width and depth and smaller groove spacing reduces hydroplaning risk, by computation of the changes in the expected hydroplaning speed. For the range of groove dimensions studied, the expected hydroplaning speed for a typical passenger car increased by approximately 2.8 km/h for every mm increase of groove depth, by approximately 3.5 km/h for every mm increase of groove width, and by approximately 1.0 km/h for every mm decrease of groove spacing. The model also was applied to evaluate the hydroplaning potential of different grooving designs used in practice and past studies and to explain the conflicting findings of past studies on whether longitudinal pavement grooving does improve traction and reduce hydroplaning risk.
Precision of Smooth and Ribbed Tire Locked Wheel Testers for Measurement of Roadway Surface Friction Characteristics
Authors: Choubane Bouzid , Holzschuher Charles R. , Gokhale Salil , Fletcher Jim
Published: May 2018

The present state-of-the-art locked wheel testers for roadway surface friction evaluation are fully automated. As with any testing using subject-driven instrumented devices, the major concerns of the end usefulness of the resulting data are accuracy and precision. Although a level of uncertainty is always inherent in any measurement process, it also must be appropriately quantified or assessed. Therefore, the Florida Department of Transportation (FDOT) initiated a field study to assess the level of precision of its own locked wheel testers for field measurements. Friction measurements were acquired with four friction locked wheel testers concurrently on a number of asphalt section sites. These test sections were randomly selected to include both open and dense-graded surface mixtures. The collected friction data were first analyzed to determine the friction characteristics at each test location in terms of a friction number at 40 mph with a standard ribbed (FN40R) and smooth tire (FN40S). The results were then used as the basis for an evaluation of the repeatability (within-unit precision) and reproducibility (between-unit precision) of the friction units.
Mechanistic Comparison of Wide-Base Single versus Standard Dual Tire Configurations
Authors: Priest Angela L. , Timm David H.
Published: May 2018

Wide-base tires are gaining renewed interest in the U.S. trucking industry as tire and rim technology and design continue to improve. First introduced in the early 1980s and termed “super-singles,” new generation, wide-base tires have been developed to allow for lower inflation pressures and larger contact areas than their predecessors. Single tires are of interest to freight haulers because with fewer tires and lighter rims, cargo capacity can increase. Early theoretical and physical modeling studies of super-singles largely found them to be more damaging to highway pavement structures than standard dual tire configurations. However, in light of new tire advancements, the impact on pavement response and performance of the wide-base configuration should be reevaluated. In addition, the accuracy of theoretical models in predicting pavement response under the new wide-base tires should be evaluated because models are often used by agencies to determine single-tire weight limits and permitting. A conventional dual tire assembly (275/80R22.5) was evaluated versus a newly developed single wide-base tire (445/50R22.5) at the National Center for Asphalt Technology Test Track. Embedded asphalt strain gauges and earth pressure cells allowed for direct pavement response measurements and comparisons between the two configurations. In addition, theoretical modeling using layered elastic theory was used to evaluate both configurations. The pavement response measurements indicated no statistical difference between the two configurations. The theoretical model tended to overpredict the response under the wide-base configuration. Future studies should attempt to model the tire-pavement contact area precisely to improve accuracy under the wide-base tire.
Preliminary Estimation of Asphalt Pavement Frictional Properties from Superpave Gyratory Specimens and Mix Parameters
Authors: Goodman Stephen N. , Hassan Yasser , Abd El Halim A. O.
Published: May 2018

Changes in pavement texture because of temperature, moisture, and polishing reduce the available friction for vehicles to perform routine maneuvers under normal operating conditions and thereby increase the potential for skid-related accidents. Optimization of texture and frictional properties at the mix design stage requires that specimens prepared in the laboratory accurately represent the pavement surface in the field. Initial findings from an investigation of the texture and frictional properties of specimens prepared in the Superpave® gyratory compactor compared with field measurements are presented. In addition, the mix design properties that may be altered for increased friction are presented. The surfaces of the field specimens were different from their respective gyratory surfaces but were well correlated in the case of macrotexture measurements from the sand patch test. High correlation also was observed between field macrotexture and select mix properties, including the fineness modulus, voids in the mineral aggregate, percentage passing the 4.75-mm sieve, and bulk relative density. Poor correlation was observed between the British pendulum numbers recorded on unpolished field specimens and gyratory specimens, although the bottom gyratory surfaces best matched with field values. Preliminary results suggest the gyratory compactor orients the aggregate particles in a different manner from field compaction equipment. Further, the aggregate breakdown imposed by the gyratory compactor results in additional microtexture exposure not observed on newly compacted pavements in the field until trafficking removes the upper layer of asphalt cement from the coarse aggregate particles.
Use of Propensity Score Matching Method and Hybrid Bayesian Method to Estimate Crash Modification Factors of Signal Installation
Authors: Aul Nathan , Davis Gary
Published: May 2018

In recent years increased attention has been given to predicting the effects of roadway improvements on traffic safety. Tools have been developed in cooperation with FHWA and TRB that attempt to predict crash experience, and they require estimates of crash modification factors (CMFs) to produce predicted reduction benefits. The tools make use of empirical Bayes statistics, which currently require that crash data be overdispersed. The main purpose of this paper is to illustrate two alternative methods of estimating CMFs that can be applied whether or not the crash data are overdispersed. The first combines the hierarchical Bayes model with a model that allows for temporal changes in the covariates. The second uses an estimated propensity score to match a group of locations that had a countermeasure installed with a comparison group that was not treated. Both methods were used to compute estimates for the CMFs associated with signalizing a set of nonrural intersections. Neither method found evidence of an overall reduction or an increase in crashes following signalization. However, use of the first method indicated that right-angle crashes decreased while rear-ending crashes increased, as has been observed in other studies.
Bayesian Multivariate Poisson Regression for Models of Injury Count, by Severity
Authors: Ma Jianming , Kockelman Kara M.
Published: May 2018

In practice, crash and injury counts are modeled by using a single equation or a series of independently specified equations, which may neglect shared information in unobserved error terms, reduce efficiency in parameter estimates, and lead to biases in sample databases. This paper offers a multivariate Poisson specification that simultaneously models injuries by severity. Parameter estimation is performed within the Bayesian paradigm with a Gibbs sampler for crashes on Washington State highways. Parameter estimates and goodness-of-fit measures are compared with a series of independent Poisson equations, and a cost–benefit analysis of a 10-mph speed limit change is provided as an example application.
Refinement of Accident Prediction Models for Spanish National Network
Authors: Mayora José M. Pardillo , Manzo Rafael Bojórquez , Orive Alberto Camarero
Published: May 2018

This paper describes a research project conducted at Madrid Polytechnic University with the objective of refining the negative binomial accident prediction models that had been developed previously for two-lane rural roads in Spain. Cumulative scaled residuals plots were used to identify the value ranges of annual average daily traffic (AADT) where the model over- or underestimated accident frequencies. They were also used to determine whether the calibration sample contained redundant information for some values of the explanatory variables that was detrimental to the model-fitting process. On the basis of the results of these analyses, two approaches were explored to refine the models. First, a random reduction of the sample size was tried to mitigate the effect of redundancies in the statistical information. Second, the sample was stratified, and independent models were fitted for the regions of AADT values where the cumulative residuals plot showed moderate fluctuations. These processes reduced considerably the amount of over- and underestimation of the models, which indicates that in some cases they may be a valid tool to refine accident prediction models and to overcome the lack of flexibility in the functional forms commonly used in multivariate regression modeling.
Calibration of Safety Prediction Models for Planning Transportation Networks
Authors: Tarko Andrew P.
Published: May 2018

The current planning practice addresses safety implicitly as a by-product of adding capacity and operational efficiency to the transportation system. Safety-conscious planning is a new proactive approach to the prevention of crashes based on establishing inherently safe transportation networks through integrating consideration of safety into the transportation planning process. One of the major concerns in predicting crashes in transportation networks is the applicability and accuracy of crash prediction models. The paper presents two alternative formulations of the calibration problem consistent with the maximum likelihood approach. The proposed formulations can be viewed as a generalized version of the existing calibration procedure proposed in the past for individual crash prediction models. The formulations are useful for road networks and for any transportation mode, provided that the needed prediction models are available. The proposed calibration applied to individual elements of the test network yielded crash estimates that exhibited a considerable bias accumulation at the system level. The calibration task was redefined to focus on the prediction of the cumulative number of crashes in the user-defined subnetworks. The second method gave more acceptable results. The paper demonstrates the feasibility of the proposed approach, which may be helpful in developing a new class of tools for safety-conscious planning.
Development of an Airport Choice Model for General Aviation Operations
Authors: Baik Hojong , Ashiabor Senanu , Trani Antonio
Published: May 2018

The general aviation airport choice model is used to estimate general aviation (GA) person trips and number of aircraft operations through a set of airports given initial trip demand (GA person trips) from a set of counties. A pseudogravity model embedded in the model is used to distribute the intercounty person trips to the set of airports. The interairport person trips are then split into person trips by aircraft type (single, multiple, or jet engine). To split the trips, an attractiveness factor is developed on the basis of average occupancy, level of use, a distance distribution factor, and number of operations of each aircraft type. The person trips by aircraft type are then converted to aircraft operations with the use of occupancy factors for each aircraft type. The final model output is the number of aircraft operations by each aircraft type, in the form of three interairport trip tables. The estimated GA operations provide a means of assessing the impact of GA activities on the National Airspace System. The model output may also be used to assess the viability of GA aircraft as a competitive mode of transportation for intercity travel.
Emergence of a Market for Southwest Airlines Frequent Flyer Awards
Authors: Ng Chen Feng
Published: May 2018

The Internet has facilitated the emergence of a secondary market for Southwest Airlines flight tickets awarded by its frequent flyer program. Possible reasons for the existence of this market are explored, because Southwest bans the sale of these travel vouchers. With data from eBay auctions, hedonic regression results show that a later expiration date, no blackout dates, and the inclusion of drink coupons have positive effects on the prices of these vouchers. Additional security fees and whether a voucher is in paper or electronic form do not appear to affect the price. It is calculated that by selling the voucher, the seller receives, on average, a $34 rebate on each round-trip flight traveled on Southwest.
Aviation Infrastructure Taxes and Fees in the United States and the European Union
Authors: Yamanaka Shiro , Karlsson Joakim , Odoni Amedeo
Published: May 2018

The impact of infrastructure-related add-on taxes and fees on the cost of domestic U.S. air travel and of domestic and intraregional EU air travel is estimated. For the United States, an analysis of the Origin and Destination Data Bank 1A Ticket Dollar Value database shows that the average effective tax rate increased from 10.9% in 1993 to 16.1% in 2004. A large portion of the increase is due to a striking 25% decline in the real average base fare. The relative impact of taxes and fees is greatest on the least expensive tickets. The effective tax rate for low-cost carriers is moderately greater than for legacy carriers. For the European Union, a sample of about 335,000 tickets from January 13 and 14, 2004, was used, with the effective tax rate estimated at 12.5%. However, EU taxes and fees do not cover the cost of air navigation services, and thus the 12.5% effective tax rate should not be compared with the 16.1% U.S. rate. A preliminary correction for this difference suggests that the true effective tax rate is higher in the European Union than in the United States. The intra-European Union average of 12.5% also masks large differences among countries (which range from 6.6% for Luxembourg to 24.4% for the United Kingdom). The relative impact of taxes and fees on the least expensive tickets is even greater than in the United States.
Predictive Reliability of Airport Ground Access Mode Choice Models
Authors: Gosling Geoffrey D.
Published: May 2018

Airport ground access mode choice models provide an essential analytical capability to support airport ground transportation planning studies as well as studies addressing the allocation of air travel demand among multiple airports in a region. A growing number of such models have been described in the literature: the models vary widely in functional form, explanatory variables, and estimated parameter values. However, almost no attention has been given to how reliably these models predict air passenger mode choice for time periods different from those for which they have been estimated or when available ground access services change. Both considerations are critical to the application of such models for forecasting. In attempting to rectify this situation, the predictive reliability of typical airport ground access models is addressed from two perspectives: ( a) the variability of airport ground access mode use over time and implications of this variation for the application of ground access mode choice models and ( b) how well models estimated on data collected at one time predict air traveler ground access mode use at other times or in different situations. The requirements for an empirical analysis that would apply an existing model to predict mode use in a later year or for a different airport are discussed, and the predicted mode use is compared with the actual mode use observed in air passenger surveys to assess the predictive reliability of the model.
Developing Safety Indicators for New Zealand Airspace
Authors: Majumdar Arnab , Dupuy Marie-Dominique , Ochieng Washington Yotto , Nalder Peter
Published: May 2018

The New Zealand (NZ) government actively sets safety targets for its airspace, and the level of safety traditionally has been measured by accident rates. However, numerous problems have arisen from the use of this indicator. With the Heinrich pyramid of common causation of accidents and incidents, focus has turned to the use of incident data–-particularly loss-of-separation (LoS) incidents between aircraft in airspace–-for safety indicators. This paper uses LoS data from New Zealand, Australia, and the United Kingdom to develop safety indicators specific to a particular airspace. A survey of previous research on factors affecting LoS incidents led to the selection of seven variables: airspace environment, altitude, traffic profile of the pair of aircraft in conflict, presence of one aircraft in altitude transition, geometrical configuration, causal agent (i.e., last human instigator of the incident), and degree of severity or risk of collision (i.e., level of risk reached during the LoS incident). A high-level data analysis is followed by log-linear categorical analysis to determine significant interactions between variables, and, on the basis of these interactions, specific safety indicators are obtained for NZ airspace. Significant interactions include type of airspace and aircraft in altitude transition, type of airspace and conflict geometry, aircraft in altitude transition and conflict geometry, and causal agent and severity. The results can be used to develop refined country-specific safety indicators and allow for targeted methods of improving safety.
Does Periodic Maintenance Cause Unscheduled Outages?
Authors: Berkeley Emily , Rakas Jasenka , Handal Jady
Published: May 2018

It has been suspected for some time that unscheduled outages of National Airspace System equipment increase during core working hours; to date, however, no research has been done to determine their cause. First, aggregate trends in scheduled periodic maintenance (PM) activities and unscheduled outages are examined for calendar years 2000 through 2004. The reported increase in unscheduled outages is postulated to be due to increased levels of maintenance activities that may occur during this period. A detailed analysis is presented, and the individual pieces of equipment that suffer unscheduled outages after receiving PM are examined. If PM activities have an effect on unscheduled outages, then higher levels of unscheduled outages would be expected to occur in the first hours after the completion of a PM task. Further data analysis shows evidence for this hypothesis.
Aggregate Morphology Affecting Resilient Behavior of Unbound Granular Materials
Authors: Pan Tongyan , Tutumluer Erol , Anochie-Boateng Joseph
Published: May 2018

The resilient modulus (MR) defines the nonlinear elastic response of pavement geomaterials, such as the unbound aggregate base–subbase materials, under repeated traffic loading. The resilient behavior of unbound aggregate layers is affected by the stress states experienced because of wheel loading and physical properties of aggregate materials. Among the physical properties, the influence of aggregate morphology on the resilient behavior of base–subbase materials is not yet well understood because of a lack of quantitative measurements of shape, angularity, and surface texture characteristics of aggregate particles. This paper focuses on investigating the influence of aggregate angularity and surface texture properties on the resilient behavior of unbound granular materials expressed by a nonlinear, stress-dependent resilient response model. With an image analysis approach, two important aggregate morphological indices [the angularity index (AI) and the surface texture index (ST)] were defined to quantify accurately the angularity and surface texture properties of six types of commonly used aggregate materials with varying surface irregularities. Twenty-one unbound specimens were prepared with the blending of six aggregate materials and tested for resilient moduli in a laboratory triaxial setup as per the AASHTO T 307-99 protocol. Both AI and ST were found to be closely linked to MR values of the aggregate specimens blended in different percentages. As the aggregate angularity and surface roughness increased, the resilient moduli were considerably improved, which was primarily because of the increased shear strength with better aggregate interlock and frictional properties and the increased confinement levels expressed by higher bulk stresses.