bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptation of Logit Kernel to Route Choice Situation
Authors: Bekhor Shlomo , Ben-Akiva Moshe E. , Ramming M. Scott
Published: April 2007

An adaptation of the general logit kernel (LK) model to the route choice context is presented. Recent intelligent transportation systems applications have highlighted the need for better models of the behavioral processes involved in route choice. Several route choice models have been developed recently. However, few studies concentrated on the model estimation and applications for large urban networks. How LK can be adapted to route choice situations by suitably defining the elements of the model is described. The model is estimated using a sample formed from a route choice survey combined with network variables. Preliminary estimation results are presented and discussed.
Mixed Logit (or Logit Kernel) Model: Dispelling Misconceptions of Identification
Authors: Walker Joan
Published: April 2007

Mixed logit is a discrete choice model that has both probit-like disturbances and an additive independent and identically distributed extreme value (or Gumbel) disturbance à la multinomial logit. The result is an intuitive, practical, and powerful model that combines the flexibility of probit (and more) with the tractability of logit. For that reason mixed logit has been deemed the “model of the future” and is becoming extremely popular in the literature. It has been experimented with in almost all stages of transportation modeling and has been included in widely used statistical software packages as well as a recent edition of a popular econometrics textbook. Although the basic structure of mixed logit models is well understood, there are important identification issues that are often overlooked. Misunderstanding these issues can lead to biased estimates as well as a significant loss of fit. Some misconceptions concerning identification of mixed logit models that have led to misspecified models in the literature are highlighted. The purpose is simply to whet the appetite for the identification issue. The important idea presented here is that seemingly obvious specifications and estimation practices (starting with a multinomial logit specification and adding random parameters) can have unintended consequences. Technical details are not provided; rather the emphasis is on highlighting some of the interesting identification issues and providing empirical and conceptual supporting arguments. Readers interested in rigorous arguments behind these results are encouraged to read the parallel papers, which are referenced throughout.
Design of an Integrated Land Use and Activity-Based Travel Model System for the Puget Sound Region
Authors: Waddell Paul , Outwater Maren , Bhat Chandra , Blain Larry
Published: April 2007

Results of a design process for new integrated land use and transportation models recently completed for the Puget Sound Regional Council (PSRC) are presented. The design process, which began with an analysis of policy requirements and assessment of the current models in use at PSRC and nationally, employed an iterative and participatory approach to ensure that model requirements were clearly identified and that the proposed model design would address those requirements. Development of the model requirements drew on a broad survey of the literature and of operational models; the proposed model design offers a unique approach to the development of a new land use and travel model system that corresponds to a behavioral integration of the choice processes across relevant time frames.
Transportation Investments and Urban Form
Authors: Forkenbrock David J.
Published: April 2007

A practical framework is offered for predicting the effects of transportation investments on urban land use patterns. The framework is based on the premise that a key determinant of the value of a parcel of land is its accessibility. Relatively valuable parcels tend to be developed more intensively. Because transportation investments influence the spatial nature of accessibility provided to different land parcels, such investments can substantially influence the evolving pattern of urban land uses. Following a discussion of the conceptual underpinnings of the economic linkages between transportation, accessibility, and land use, two stereotypical types of urban form are explored—polycentric and corridor—and the sorts of transportation investments that would facilitate their development are considered. These illustrative examples are intended to highlight the power of transportation investments as formative mechanisms to produce the sort of spatial structure a community’s residents desire.
Analytically Based Approach to Rutting Prediction
Authors: Deacon John A. , Harvey John T. , Guada Irwin , Popescu Lorina , Monismith Carl L.
Published: April 2007

An analytically based (mechanistic-empirical) procedure was conducted to estimate the development of rutting in asphalt pavements as a function of both traffic loading and environment as defined by pavement temperatures. The procedure uses permanent strain determined for a representative asphalt concrete mix as a function of load repetitions, shear stress, and elastic shear strain. It combines multilayer elastic analysis for determining key shear stresses and strains in the asphalt concrete resulting from traffic loading to be used in the permanent strain expression with a time-hardening procedure for the accumulation of permanent strain as a function of both traffic loading and environment. The WesTrack test sections were used to calibrate the methodology, with results of rutting predictions evaluated for four different test sections from that experiment. Based on the results of the regression analyses, an expression can be used to determine coefficients for use in the permanent strain expression that reflect the permanent deformation characteristics of a specific mix as measured in repeated simple shear test at constant height. In addition to the WesTrack examples, results illustrated the use of the approach to predict rutting development in a controlled loading condition at 50°C (122°F) using the heavy vehicle simulator.
Effective Tool for Enhancing Elastostatic Pavement Diagnosis
Authors: Guzina Bojan B. , Osburn Robert H.
Published: April 2007

The falling weight deflectometer (FWD) test is one of the most commonly used tools for nondestructive evaluation of flexible pavements. Although the test is intrinsically dynamic, the state-of-practice back-calculation techniques used to interpret the FWD records are primarily elastostatic based, partly because of the high computational cost of dynamic multilayered solutions. It has long been known that the foregoing discrepancy may lead to systematic errors in the estimation of pavement moduli in situations of pronounced inertial and resonance phenomena due to the presence of bedrock or seasonal stiff layer. In this investigation, a simple, yet effective algorithm is proposed that allows the static backcalculation analyses to perform well even when dynamic effects are significant. The technique is based on the use of the discrete Fourier transform as a preprocessing tool to filter the dynamic effects and extract the static pavement response from transient FWD records. With the filtered (i.e., zero-frequency) force and deflection values in lieu of their peak counterparts, the static backcalculation can be further performed in a conventional manner, but free of inconsistencies associated with the neglect of dynamic effects. Results based on synthetic deflection records demonstrate a marked improvement in the elastostatic prediction of pavement moduli when the proposed modification is used. The filtering algorithm can be implemented on a personal computer as a preprocessor for the conventional FWD data interpretation, requiring only a minimal increase in the computational effort to backcalculate the pavement moduli.
Approach to Determining In Situ Dielectric Constant of Pavements: Development and Implementation at Interstate 81 in Virginia
Authors: Lahouar Samer , Al-Qadi Imad L. , Loulizi Amara , Clark Trenton M. , Lee David T.
Published: April 2007

A major problem in using ground penetrating radar (GPR) for estimating pavement layer thickness is assuming the dielectric properties of that layer. Pavement dielectric properties may vary significantly due to aggregate type, moisture presence, and other conditions. Therefore, uncertainties in the dielectric constant, which may vary from 3 to 15, will result in misleading thickness determination. Obtaining cores for calibration may reduce the error, but the variation in the dielectric constant along the roadway often leads to errors in the thickness determination. A method was developed to determine the dielectric constant, and therefore the thickness, of the hot-mix asphalt (HMA) layer of a pavement using GPR. Because of the different compositions and ages of the layers forming HMA in older pavements, dielectric constant estimation based on the surface reflection may not be accurate and may lead to wrong thickness estimations. The developed method uses a modified common midpoint technique (usually used in seismic testing) to estimate the dielectric constant, based on the reflections from a common point at the bottom of the layer. Data were collected from a 27-km portion of Interstate 81 and processed with this technique. Comparison between the thickness estimated by this method and that measured on cores extracted from the highway revealed a mean error of 6.8%.
Thirty-Three-Year Performance of Jointed Concrete Test Sections in North Carolina
Authors: Corley-Lay Judith , Morrison Clark S.
Published: April 2007

Eight test sections of jointed portland cement concrete (PCC) pavement were constructed in 1967 on I-95 in North Carolina. The test sections were rediscovered this year when six of the eight fell within the project limits of an interstate rehabilitation project. Outlined are the performance of those six sections, the control section using data collected in 2001, and the historical data found in an old research file. Performance was measured and ranked based on distress surveys, roughness reported as the international roughness index, and joint faulting. All six sections were 9 in. thick with flexible paved shoulders and 30-ft joint spacing. The test section with the best overall performance consisted of undoweled PCC placed on a bituminous base course. This section remains in fair to good condition after 33 years, resulting in the most favorable annual cost. Where direct comparison sections were available, dowels reduced faulting by 1 to 1.5 mm over the 33-year period. Longitudinal, transverse, and multiple-break cracking were common in the sections having cement-treated base or subbase, reducing their service lives and increasing their annual costs.
Data Analysis of Real-Time System for Automated Distress Survey
Authors: Wang Kelvin C.P. , Gong Weiguo , Li Xuyang , Elliott Robert P. , Daleiden Jerry
Published: April 2007

Accurate data collection and interpretation of pavement data are critical for the decision-making process in pavement management. This study focused on the data analysis portion of a new automated system capable of collecting and analyzing pavement surface distress, mainly cracks, in real time through the use of a high-resolution digital camera; efficient image processing algorithms; and multicomputer, multi-CPU-based parallel computing. Features and performance of the automated system for distress survey were surveyed. Three protocols of producing distress indices incorporated into the automated system were examined: the AASHTO interim distress protocol, the World Bank’s Universal Cracking Indicator, and the Texas Department of Transportation’s method. It was found that distress results from the automated system were consistent for multiple passes of the same pavement sections.
Geometric Descriptors of Road Surface Texture in Relation to Tire-Road Noise
Authors: Anfosso-Lédée Fabienne , Do Minh-Tan
Published: April 2007

The paper deals with the determination of geometric parameters for studying the relationship between tire-road noise and texture of road surfaces. The approach was found to be an alternative to classical spectral analyses and numerical simulations of the tire-road contact. Texture parameters were derived from previous works at the Laboratoire Central des Fonts et Chaussées related to the influence of the microtexture of road surfaces on skid resistance. Use of these parameters was justified by consideration of generation mechanisms of rolling noise. Texture, rolling noise, and absorption measurements were performed on 12 road surfaces. The measuring devices and the test methods produced texture profile analyses, including the spectral and geometric approaches. Geometric parameters were defined. Correlation between the noise and texture spectra showed results similar to those published in previous works. Fair tendencies were found between the global noise level at 90 km/h and the geometric parameters. Unexpected results obtained on the porous asphalt surfaces were partially explained by the attenuation effect, which was quantified by means of existing models. Results from the correlation between the third-octave-band noise levels and the geometric parameters corroborated those of the spectral analyses.
Utility-Maximizing Model of Household Time Use for Independent, Shared, and Allocated Activities Incorporating Group Decision Mechanisms
Authors: Zhang Junyi , Timmermans Harry , Borgers Aloys
Published: April 2007

Existing activity-based models of transport demand typically assume an individual decision-making process. The focus on theories of individual decision making may be partially due to the lack of behaviorally oriented modeling methodologies for group decision making. Therefore, an attempt has been made to develop a new model (called the g-Logit household time-use model) for time-use analysis that incorporates group decision-making mechanisms. To do that, it is proposed that household utility function be defined in the form of multilinear utility function, which can represent interactions among household members and interactions among their activities (four types of activity: in-home, out-of-home independent, allocated, and shared). By introducing this household utility function into the time allocation approach, each member’s time-use functions for different types of activities are obtained. The function for independent activities has a structure similar to the one for allocated activities, except the weight parameters are different. In contrast, the time-use function for shared activities has a completely different structure, which results from the complicated processes and strategies for household decision making. The effectiveness of the proposed model is confirmed with activity-travel diary data.
Stationary and Time-Varying Patterns in Activity Diary Panel Data: Explorative Analysis with Association Rules
Authors: Keuleers Bertold , Wets Geert , Timmermans Harry , Arentze Theo , Vanhoof Koen
Published: April 2007

The question of identifying temporal patterns in activity diary data has received only scant attention in the transportation literature, but interest is rapidly increasing. Most of the existing research uses well-known econometric methods to quantify change. Use of association rules to explore activity diary panel data, involving two waves, for possible stationary and time-varying patterns in activity-travel patterns is reported. The data for this analysis stem from the municipality of Voorhout in the Netherlands. Data were collected in 1997 and 1998 before and after opening of a new railway station. Results of the analysis indicate that specific household and individual attributes have a larger effect on daily activity patterns than others and that the effect of these attributes has significantly changed. Because changes in other sociodemographic attributes are almost nonexistent and activity patterns for communities are known to be stable, this study claims that the observed shifts in dependencies come from this new station.
Comparison of Morning and Evening Commutes in the Vickrey Bottleneck Model
Authors: de Palma André , Lindsey Robin
Published: April 2007

Dynamic user equilibrium has received considerable theoretical attention for morning peak-period travel but very little for the evening peak. In an attempt to redress this imbalance, morning and evening travel are characterized and compared by using Vickrey’s bottleneck model. To focus ideas, it is assumed that morning and evening travel differ in just one respect: scheduling preferences for the morning are defined in terms of arrival time at work, whereas preferences for the evening are defined in terms of departure time from work. Sufficient conditions are identified for the existence and uniqueness of a deterministic dynamic user equilibrium in terms of departure times for the morning and evening peaks. These conditions, which go well beyond previous work, involve relatively general assumptions about the schedule delay cost functions for morning and evening and essentially no restrictions on the degree of heterogeneity in trip-timing preferences of travelers. Plausibility of the conditions is examined in light of the limited empirical evidence. A numerical example is developed at length to illustrate the importance of traveler heterogeneity and the extent of differences between morning and evening in the time pattern of departures and aggregate travel costs.
Investigating Travel and User Characteristics of Toll Roads: Travel Survey of the Central Florida Expressway System
Authors: Abdelwahab Hassan T. , Abdel-Aty Mohamed A.
Published: April 2007

The differences between E-Pass (an electronic toll collection device) users and non-E-Pass users are examined based on an extensive travel survey of users of central Florida’s expressway system. The survey was designed to capture travel patterns of expressway users. A statistical comparison was conducted between the E-Pass and non-E-Pass users by age, occupation, household income, vehicle occupancy, trip distance, trip purpose, and trip time. Results of the comparison indicated significant differences between the two groups. A log-linear model was developed to understand the effect of trip-maker characteristics on E-Pass use. Results indicated that the odds of using E-Pass are small for young users (16 to 25 years old). The odds of choosing the E-Pass system increase with income; professionals have higher odds of being E-Pass users. Also, a bivariate probit model was developed to understand the interdependence between the use of E-Pass and vehicle occupancy. Results indicated that time of day, day of week, E-Pass use, trip purpose, and trip distance affect vehicle occupancy.
Incorporating Variety Seeking and Seasonality in Stated Preference Modeling of Leisure Trip Destination Choice: Test of External Validity
Authors: Kemperman Astrid , Borgers Aloys , Timmermans Harry
Published: April 2007

The results of a test to assess the external validity of a stated preference model of destination choice in the context of leisure trips are reported. This model differs from conventional stated preference models in transportation in that it incorporates variety seeking and seasonality in specification of the choice model. The results indicate that the model performed reasonably well; seasonality is predicted quite well, but in some specific situations the model overpredicts observed variety-seeking choices.
Nested Logit Models and Artificial Neural Networks for Predicting Household Automobile Choices: Comparison of Performance
Authors: Mohammadian Abolfazl , Miller Eric J.
Published: April 2007

Over the past few years, machine-learning techniques have expanded enormously. These approaches are increasingly being applied to traffic and transportation problems formerly reserved for formal statistical approaches such as discrete choice models. Part of the reason for this has to do with research trends, but there are some potential advantages associated with such techniques, including the ability to model nonlinear systems; the ease with which symbolic, nominal, or categorical variables can be included; and the ability of these methods to deal with noisy data. The use of two modeling techniques, the nested logit model and the multilayer perceptron artificial neural network, was investigated in terms of their applicability to the household vehicle choice problem. Both methods generated strong results, although the multilayer perceptron artificial neural network yielded better predictive potential.
Untangling Factors Behind Temporal Evolution of Mobility: Case of São Paulo, Brazil
Authors: Strambi Orlando , van de Bilt Karin-Anne
Published: April 2007

Mobility in the metropolitan region of São Paulo has declined in recent decades in spite of a general growth in motorization and living standards. Some important factors have been overlooked in the analysis of mobility. These relate to the evolution of sociodemographic attributes and to temporal changes in behavior: ( a) changes in the population structure, primarily concerning the characteristics and social roles of women; ( b) changing behavior concerning car ownership, a key factor behind mobility; and ( c) temporal changes in the travel behavior of homogeneous groups of the population. Three results stand out from a cross-section analysis: the main factors behind mobility concern attributes that are changing in the population; these factors affect men and women differently; and significant differences in the travel behavior of men and women are related to the sociodemographic and economic categories that are changing faster in the population. Also, a longitudinal analysis, comparing data from 1987 and 1977, indicates that the mobilities of men and women have followed different paths. The results raise some methodologic challenges: population forecasting at a very disaggregate level and predicting temporal changes in travel behavior.
Application of Stochastic Learning Automata for Modeling Departure Time and Route Choice Behavior
Authors: Ozbay Kaan , Datta Aleek , Kachroo Pushkin
Published: April 2007

Stochastic learning automata (SLA) theory is used to model the learning behavior of commuters within the context of the combined departure time route choice (CDTRC) problem. The SLA model uses a reinforcement scheme to model the learning behavior of drivers. A multiaction linear reward-ϵ-penalty reinforcement scheme was introduced to model the learning behavior of travelers based on past departure time choice and route choice. A traffic simulation was developed to test the model. The results of the simulation are intended to show that drivers learn the best CDTRC option, and the network achieves user equilibrium in the long run. Results indicate that the developed SLA model accurately portrays the learning behavior of drivers, while the network satisfies user equilibrium conditions.
Mobility Styles and Travel Behavior: Application of a Lifestyle Approach to Leisure Travel
Authors: Lanzendorf Martin
Published: April 2007

Recently, several efforts have been made to include individuals’ attitudes, values, and orientations within travel behavior research. The restrictions of the traditional modeling variables become obvious when one is trying to explain changes in travel patterns related to changes in Western societies. Traditional modeling efforts also neglect the intrinsic dimensions of traveling and of nonwork travel. A lifestyle approach has been used to construct mobility styles by applying factor and cluster analysis to leisure and mobility orientations. A data set was collected in four neighborhoods of Cologne (Germany). The analysis focuses on leisure travel on weekends, because it is assumed that mobility styles are more important for leisure than for work-related traveling. The key question is whether the utility of mobility styles as a tool for the analysis of travel behavior can be demonstrated. The results indicate, first, that there is a correlation of mobility styles with several other factors, such as personal and household characteristics, availability of transport modes, and urban form elements (e.g., residential neighborhood, garden ownership, and dwelling type). Furthermore, a correlation is observed between mobility styles and participation, frequency, and car use for leisure travel. Finally, multivariate analysis indicates that the mobility styles largely explain the participation in traveling for different leisure purposes and the distances traveled by car. For the mode choice, other factors such as availability of transport modes and workday use of a transport mode appear to be more important than the mobility style.
State-of-Practice Review of Deep Soil Mixing Techniques in China
Authors: Han Jie , Zhou Hong-Tao , Ye Fen
Published: April 2007

Deep soil mixing techniques have been widely adopted in China since the late 1970s and mainly used for ground improvement for structural support and earth-retaining structures for excavations. A comprehensive state-of-practice review on development, applications, soil-cement properties, mechanistic studies, design methods, and quality control of deep soil mixing techniques in China is presented. These research results will serve as a reference for advancing deep soil mixing techniques in the United States and other countries.
Road Stabilization, Reconstruction, and Maintenance with a Combined Mechanically Stabilized Earth and Secant Pile Wall: Zion National Park, Utah
Authors: Anderson Scott A. , Williams Jennifer L.
Published: April 2007

A 1995 landslide diverted the North Fork of the Virgin River in Zion National Park, Utah, causing complete erosion of 180 m (590 ft) of the Valley Floor Highway, the park’s main access road. Buried utilities were damaged and 450 people were left stranded. Road reconstruction and maintenance have been ongoing in many phases since 1995 and have proved to be difficult because of environmental and physical constraints imposed by the river and by steep slopes of recent and historic landslide debris on both sides of the valley. In an effort to limit disturbance to the landslide slope while maintaining a two-lane access road adjacent to the river, a compound retaining wall was designed and constructed through the narrow reach of the valley. The lower part of the wall consists of cantilevered secant piles, providing 3.6 m (12 ft) of scour protection, and the upper part of the wall is a mechanically stabilized earth wall. Intermittently spaced foundation piles reduce the lateral loads on the secant piles, making cantilever support practical.
Laboratory Simulation of Field Compaction Characteristics on Sandy Soils
Authors: Virgil Ping W. , Yang Zenghai , Leonard Michael , Putcha Sastry
Published: April 2007

As a result of the development of much heavier earth-moving and vibratory roller compaction equipment, soil compaction densities in the field are reaching levels that are not attainable in the laboratory. Higher compaction efforts, routinely seen in the field, not only result in higher unit weights but also lower optimum moisture contents than those found by the modified Proctor test. An experimental study was undertaken to evaluate field and laboratory compaction characteristics and to study laboratory compaction techniques further, such as gyratory compaction, in addition to impact and vibratory compaction, for the laboratory simulation of field compaction of A-3 sandy soils. Field test sections were constructed using typical field compaction techniques of today. Earth pressure cells were installed at the base of each lift to monitor total vertical stresses. A series of laboratory gyratory compaction tests for A-3 soils were conducted. Factors including vertical pressure, gyration angle, and gyration numbers were evaluated for the effects on the dry unit weight. The gyratory compaction curves using 200-kPa (29 psi) vertical pressure, a 1.25-degree gyration angle, and 90 gyrations were close to the field compaction curves.
Calibration of Load and Resistance Factor Design: Resistance Factors for Drilled Shaft Design
Authors: Kuo Ching L. , McVay Michael C. , Birgisson Bjorn
Published: April 2007

The AASHTO load and resistance factor design specification was approved for use in 1994 with phi factors determined from fitting allowable stress design (ASD). Unfortunately, the latter did not provide resistance factors for shafts founded in sand, gravel, and rock or identify the influence of construction (dry, wet, and cased). Using a database of 273 shafts, of which 185 failed (settlement equal to 5% of the diameter) and have sufficient soil information, the resistance factors were determined for a number of different AASHTO design methods based on probability of failure. Effects of skin friction, combined skin and end bearing, and method of construction were investigated for different soils/rock. It was found that all the methods had resistance factors between 0.3 and 0.6, which correspond to a factor of safety of 2.5 to 4.5 in ASD. Current FHWA design methods gave the highest resistance factors in soils with the cased method of construction. In the case of rock, the dry hole method of construction and the intermediate geomaterials design method gave the highest resistance factors.
Mitigating Highway Runoff Constituents via a Wetland
Authors: Mitchell Gayle F. , Hunt Christopher L. , Su Yuming
Published: April 2007

During rainfall/snowfall runoff events, constituents are conveyed from highway surfaces, which may degrade receiving water quality. Utilization of a natural wetland to mitigate storm water constituents from a portion of a 30,000-average-daily-traffic highway was studied. The runoff area consisted of two innermost lanes of a four-lane highway draining to a median drain via a vegetated median; a conduit conveyed this runoff into the wetland. Distributed runoff from the outermost lane along the wetland flowed across a vegetated highway embankment into the length of the wetland. During 57 rainfall-runoff events, in situ data collection included rainfall volume and frequency, conduit flow rate, and temperature, conductivity, pH, and dissolved oxygen. During each event, sequential samples were obtained and analyzed for metals, total suspended solids, and chemical oxygen demand from the wetland inlet and outlet. Flow-proportioned composite samples of sheetflow from the highway pavement edge were analyzed along with rainfall samples. Sediment samples were analyzed for metal constituents and organic material. Heavy metal concentrations in the storm water runoff consisted primarily of iron, zinc, lead, nickel, and copper. Concentration of metals was reduced via flow through the grassy median and then the wetland system. Over a 1-year study, average removals of heavy metals were 45% to 67%. First-order reaction rate constants were estimated to be 2.8,3.7, and 6 per day for iron, nickel, and zinc, respectively. Metals in bed sediments were representative of the hierarchy of concentrations analyzed in the runoff, and concentrations trended to increase with sediment organic fraction.
Accelerated Testing Procedures for Evaluating Separation Layer Performance in Open-Graded Base Courses
Authors: Signore J. M. , Dempsey B. J.
Published: April 2007

An accelerated testing procedure was developed to evaluate pumping and deformation performance of separation layers used between open-graded bases and lime-treated and untreated subgrade soils. A pneumatically driven, electronically controlled repeated loading laboratory apparatus was developed. A low plasticity clay and a silty clay till soil were tested. A nonwoven geotextile and a dense-graded base aggregate were evaluated as separation layers. Tests were conducted at various loading levels and durations to develop the testing procedure. Comparisons of specimen pumping and deflection performance for stabilized, separated specimens were made relative to nonseparated and nonstabilized control specimens. Ultimately, loading at levels upwards of five times that expected in the field, for short durations (20,000 cycles or less), was performed to evaluate separation layer performance. Separation layer performance under accelerated loading correlated well to long-term field loading level performance. The testing method was sensitive to the use of geotextiles for separation between soils and open-graded aggregates, though some pumping of fines still occurred. The dense-graded separation level showed a marked drop-off in performance as moisture contents increased above optimum. A distinct breakpoint in subgrade soil performance occurred at a cone index of 200 (California bearing ratio 4). Soils with strengths less than cone index of 200 performed poorly, whereas soils above that strength pumped and deformed minimally regardless of separation layer type. Based upon performance comparisons with nonseparated test cases, the use of a separation layer between lime-stabilized subgrades and open-graded aggregate bases is recommended.
Geotechnical Issues with Large Design-Build Highway Projects
Authors: Higbee James B.
Published: April 2007

Design–build is gaining popularity as an attractive alternative to the conventional design-bid-build approach, particularly for larger highway projects. Among the several aspects of design–build projects, geotechnical issues play an important role. On the Legacy Parkway project, a new four-lane, 14-mi-long highway located north of the Salt Lake metropolitan area, these issues offer unique challenges as a result of the deep soft-soil profiles and high seismic potential of the area. Approaches, examples, and incidents on the project are given that demonstrate both the pluses and the deficiencies in how geotechnically related concerns on the project were addressed, and suggestions are made for improvements in the design–build process.
Implementation of Cone Penetration Test Technology in Design and Analysis of Driven Piles
Authors: Titi Hani H. , Abu-Farsakh Murad Y. , Morvant Mark J.
Published: April 2007

The design and analysis of pile foundations in Louisiana are based on traditional subsurface exploration methods. This procedure is expensive and time consuming, and it often results in a pile design that is too conservative. The Louisiana Department of Transportation and Development (LA DOTD) has recently adopted the cone penetration test (CPT) technology to design and analyze driven piles. A research effort was undertaken at the Louisiana Transportation Research Center to identify the most appropriate CPT methods for predicting the ultimate axial load carrying capacity of piles driven into Louisiana soils. An evaluation was conducted to rank the CPT methods based on their capability to predict the measured pile load carrying capacity. The top three performance methods were programmed into software, called Louisiana Pile Design by CPT, to facilitate their use in the design and analysis of driven piles by LA DOTD engineers. The current LA DOTD implementation plan is to use the CPT technology to supplement conventional subsurface exploration techniques and to reduce the number of soil borings and pile load tests. A plan for eliminating conventional subsurface exploration completely and replacing it with CPT is still under investigation. The best performing CPT methods were implemented in the design of driven piles on several highway bridges. In these projects, the CPT was capable of identifying the soil stratification at the pile bent location and predicting the pile load carrying capacity. The benefit of implementing the CPT technology in the design and analysis of driven piles over the conventional subsurface exploration methods was also demonstrated.
Thermal Gradients in Concrete Pavements in Tropical Environment: Experimental Appraisal
Authors: Balbo José T. , Severi Andréa A.
Published: April 2007

Fifteen concrete slabs were instrumented with thermal resistors, allowing the monitoring of temperatures in concrete pavements slabs in São Paulo, Brazil, where a typical tropical hot and wet environment prevails. Over the course of 1 year, this research sought the influence of climatic conditions such as temperature and moisture on the daily and seasonal variations of temperature differentials through the slab depths. Daytime temperature differentials of more than 15°C were observed during typical summer days (e.g., high air temperature of 32°C and 7.6 h of solar radiation) and of about 10°C during typical winter days (e.g., low air temperature of 11°C and 3 h of solar radiation). The absolute values of nighttime temperature differentials are not as extreme as the daytime differentials and are significant mostly during spring and summer (from September to March). Nonlinear quadratic temperature distributions through the slab thickness were evident in most cases; nevertheless, distributions that are almost linear may be present at some times during the day and even at night. Positive temperature differentials were recorded even at night, and discussions of those particularities are addressed. The effects of tropical rains on temperature differentials are presented, and empirical models for the prediction of temperature differentials in slabs are suggested.
Closed-Form and Graphical Solutions for Three-Layered Concrete Pavements
Authors: Sanjeevirao Krishnakumar , Ioannides Anastasios M.
Published: April 2007

Analysis and design of three-layered portland cement concrete pavement systems incorporating a base layer have long been hampered by the scarcity of theoretically sound closed-form approaches. This study is focused on verifying and extending the method of transformed sections (MTS), a closed-form approach derived in 1992 on the basis of dimensional analysis and engineering mechanics. The applicability of the MTS to dense liquid and elastic solid foundations is studied in detail using a wide range of numerical test data for all three fundamental loading conditions (interior, edge, and corner). Both unbonded and bonded interface conditions between the two man-made layers are considered. To make the analysis easier, the MTS is incorporated into computer program WESTERX, a compendium of closed-form solutions for two- and three-layered concrete pavements. Maximum responses (bending stresses, deflections, and subgrade stresses) predicted by plate theory MTS are compared with those obtained from the finite-element computer program ILSL2X. Formulas developed to apply a compressibility correction to these responses are verified using results obtained from layer-elastic analysis (computer program DIPLOMAT). Critical responses from plate theory MTS are presented in the form of dimensionless charts, which can be used as an alternative to the closed-form approach with either of the two subgrade idealizations for all three fundamental loading positions. Graphical solutions are also developed for maximum responses that account for the compressibility of the two man-made layers under interior loading conditions for both foundation types.
Validating Top-Down Premature Transverse Slab Cracking in Jointed Plain Concrete Pavement
Authors: Hansen Will , Smiley David L. , Peng Yanfei , Jensen Elin A.
Published: April 2007

Built-in negative temperature gradients from hot weather construction have the effect of shifting the entire temperature gradient distribution such that the slab is predominantly upward curled. This condition in turn greatly increases loss of slab support, which was the major factor promoting premature top-down midslab transverse cracking for a jointed plain concrete pavement (JPCP) Interstate project in southeastern Michigan. Finite element analysis predicts that loss of slab support, maximum at the joints, shifts the maximum stress during truck loading at the joints toward midslab in JPCP, coinciding with maximum curling stresses. A built-in upward-curled slab condition was quantified from joint corner deflections and slab temperature measurements. Slab surface elevation profiling using the dipstick device verifies that these slabs are permanently upward curled and that loss of joint support is a function of daily changes in slab surface temperature. Detailed falling-weight deflectometer slab deflection profiles show that loss of slab support along the outer edge for this project exceeds 800 microns at the joint during morning temperature conditions typical for summer and fall in Michigan, corresponding to a nearly fivefold increase in outer edge joint deflection as measured during the afternoon, during which time the slab is in full contact with the base. The loss of slab support extends inward toward the slab middle, creating a “rocking chair” condition typical for short slab behavior, which allows the slab to rock if loaded only at one joint. This condition is underscored by field observations. During morning and evening testing, when the pavement surface was cooler, there was a noticeable rocking sensation at the joints when loaded trucks passed in the adjacent lane. Later in the afternoon, after the pavement temperature rose, the movement stopped.
Factors Affecting Rapid Roughness Progression on Portland Cement Concrete Pavements in Kansas
Authors: Akhter Mahmuda , Hossain Mustaque , Boyer John , Parcells William J.
Published: April 2007

Portland cement concrete pavement (PCCP) with favorable as-constructed smoothness and lower rates of roughness progression is expected to have a longer service life. This study was done to quantify the effect of as-constructed smoothness and other design, construction, traffic, and climatic variables on the rate of roughness progression on concrete pavements in Kansas. Selected inventory, construction, climatic, and annual roughness data were obtained for 21 PCCP projects constructed after 1992. From the annual roughness data in terms of international roughness index (IRI), collected by the South Dakota—type profilome-ters, the rate of roughness progression was obtained through regression analysis. Multiple linear regression analysis was then done to find the functional relationships between the rate of roughness progression and the independent variables selected. The results show that the concrete modulus of rupture, subgrade material, number of wet days, and initial IRI roughness (roughness measured during the first-year network-level survey after construction) significantly affect the rate of roughness progression. Higher flexural strength tends to help retain as-constructed smoothness longer on some projects. Some pavements with high initial IRI roughness tend to become smoother as traffic passes over them, presumably because of smoothening of minor surface irregularities and stabilization of subgrade soil moisture during early years of pavement life. Finally, a trend analysis of annual IRI roughness data showed that the as-constructed smoothness tends to wear out in about 3 to 5 years and thus does not influence future roughness development.
Methodology to Assess Impacts of Alternative Truck Configurations on Flexible Highway Pavement Systems
Authors: Suleiman Nabil , Varma Amiy
Published: April 2007

Assessing the appropriateness of truck axle weight limits and truck configurations from the standpoint of the impact on infrastructure is a critical issue in the determination of North American truck size and weight harmonization. A methodology is discussed for determination of pavement response, estimation of load equivalencies, and development of performance curves for different cases of flexible highway pavement and heavy-vehicle interactions for normal environmental and thaw conditions. The pavement response model uses the MSC Software Corporation’s general-purpose finite element program, MSC.MARC. Seven different truck configurations, using North American axle weight limits, are used to illustrate the impacts of alternative truck configurations on flexible highway pavement systems. Three progressive schemes are employed for impact assessment: the truck-factor scheme, the repetitions-to-failure scheme, and the tonnage-over-life scheme.
Laboratory Study of Resistance of Bituminous Overlays to Reflective Cracking
Authors: Gibney Amanda , Lohan Gearóid , Moore Vivian
Published: April 2007

Recent increases in traffic volumes in Ireland have led to severe loadings on pavements, which are showing some signs of distress, primarily in the form of rutting and reflective cracking of overlays. The particularly short life of bituminous overlays on concrete pavements has prompted an examination of both the materials currently in use and possible alternative materials. The research program undertaken at University College Dublin to assess the resistance to reflective cracking of a variety of bituminous mixtures currently in use in Ireland is described. Laboratory-prepared slabs were provided with variable support conditions and subjected to loading through a reciprocating wheel. This setup allowed a variety of mixtures and binders, including polymer-modified binders, to be compared under accelerated test conditions that simulated long-term field performance. The setups used to examine the resistance to reflective cracking are detailed, and the results obtained ranking both mixture and binder performance are summarized. In addition, standard wheel-tracking tests were carried out on the mixtures used to determine their resistance to permanent deformation.
Performance, Analysis, and Repair of Ultrathin and Thin Whitetopping at Minnesota Road Research Facility
Authors: Vandenbossche Julie M. , Fagerness Aaron J.
Published: April 2007

Thin and ultrathin whitetopping overlays are becoming a more common method of pavement rehabilitation. It is important to gain information on the types of distresses that occur in the overlays and effective repair techniques. In 1997 the Minnesota Department of Transportation constructed several thin and ultrathin whitetopping test cells at the Minnesota Road Research (Mn/ROAD) facility. Typical distresses included corner breaks, transverse cracks, and reflective cracks. The finite element program ISLAB2000 was used to investigate stress patterns and their relation to the distresses. Different techniques for repairing ultrathin whitetopping were investigated. Various techniques were also used to deter reflective cracking, including various bond-breaking materials and full-depth sawing at strategic locations along the longitudinal joint to prevent cracks from propagating into adjacent panels at misaligned transverse joints. Four of the six sections had present serviceability indexes (PSIs) greater than 3.5 before the repairs, showing that a good level of performance has been maintained after 4.7 million equivalent single-axle loads. The two sections that exhibited the largest drop in PSI were the overlays with 1.2- × 1.2-m (4- × 4-ft) panels. The repairs made in sections containing these panels have brought the PSI back up to an acceptable level (PSI > 3). The thin and ultrathin whitetopping test sections at Mn/ROAD have shown that whitetopping is a viable rehabilitation alternative for asphalt pavements. The importance of choosing an optimum panel size was exhibited. It has also been shown that when necessary, it is easy to repair ultrathin whitetopping sections. Various techniques for repairing each type of distress have been summarized.