All characterization of asphalt mixtures must begin with the properties of the mixture in an undamaged state. Subsequent tests of the mixture in different stress or strain states at a level to cause damage can be referred to this undamaged state to assess the degree to which the mixture has been changed. All forms of such change from an original state by such damaging processes as fatigue, plasticity, healing, moisture damage, and aging can only be properly assessed by comparison with an accurately measured undamaged state. This is particularly the case with the use of pseudostrain dissipated energy to characterize the departure of a material from an original linear viscoelastic state. This paper presents a new test and data analysis protocol based on linear viscoelasticity theory to characterize the master curves of the viscoelastic properties of an asphalt mixture. Instead of running a relaxation modulus test in which controlling the test apparatus is a serious challenge, the proposed test protocol applied a uniaxial monotonically increasing tensile stress to the test specimen. The axial and radial deformations of the specimen were recorded and used to calculate the axial and radial strains. The uniaxial tensile loading rate and time were carefully controlled to assure that the strain of the specimen was limited to the small-strain condition $\left(<100\mu \epsilon \right)$ under which the specimen was assumed not to be damaged during the test. The applied stress and measured strain were fitted with functions of time. Applying the Laplace transform to the stress and strain functions, the relaxation modulus as a function of time was determined using the Boltzmann superposition principle and the convolution theorem. The relation between the relaxation modulus and the complex modulus was used to determine the complex modulus as a complex function of frequency. Then the magnitude and phase angle of the complex modulus were obtained from the real part and imaginary part of the complex modulus. The proposed test and data analysis protocol were performed on the same specimen at three temperatures, 10, 20, and $30°\text{C}$ , so master curves of the magnitude and phase angle of the complex modulus were constructed using the time-temperature superposition principle. The master curves of the magnitude and phase angle of the complex modulus were fitted with mathematical functions that were reported in the literature and were modified to be more comprehensive. The parameters in the mathematical functions were searched simultaneously using the Solver Function built into the Microsoft Excel. Compared to the traditional relaxation modulus and the dynamic modulus test protocols, the newly developed test protocol was more efficient to characterize the viscoelastic properties of asphalt mixtures. The newly developed test method did not introduce any damage to the specimen so the same specimen may be retested for its fatigue, healing, and other properties.

This paper summarizes the literature review as well as the documented use and performance of airfield pavements that used reclaimed asphalt pavement (RAP) in hot-mix asphalt (HMA). A review of in-service airfield pavements with RAP-containing HMA mixes was conducted as part of this study. Two civilian airports and one military airport were identified as currently using RAP in the HMA surface course. The three airports are Logan International Airport (BOS), Griffin-Spalding County Airport (6A2), and Oceana Naval Air Station (NTU). Furthermore, the impact of RAP on the performance life of HMA airfield pavements on a large hub, small hub, and general aviation was evaluated using actual airport traffic mixes. The performance life analysis used the characteristics and mechanical properties of HMA mixes in the linear elastic airfield pavement design software (LEDFAA1.3) to compare the estimated performance life of HMA pavements with and without RAP materials. The documented research effort has recently been conducted as part of the Airfield Asphalt Pavement Technology Program, Project 05-06.

This paper presents a finite-element model of a jointed concrete pavement with aggregate interlocking load transfer system. Interlocking mechanism has been modeled by a set of discrete springs. A new parameter “modulus of interlocking joint $\left(K_j\right)$ ” has been introduced to represent the load transfer characteristics of the interlocked joint. Guidelines have been proposed for the selection of the modulus of interlocking joint as a function of aggregate size and joint opening. Stiffness values for the linear springs can be selected using the modulus value $K_j$ . The numerical model, with the joint spring stiffness values selected from the present guidelines, has been validated with experimental results available in literature.

The falling weight deflectometer (FWD) test is the most widely accepted and used technique for nondestructive evaluation of pavements. In this test, the pavement response to the impulse load of a falling weight is analyzed or back-calculated to evaluate the in situ pavement layer moduli. FWD back-calculation is mathematically an inverse problem that can be approached deterministically or probabilistically. In this paper, the probabilistic approach to FWD back-calculation is used as a tool to investigate the reliability of different dynamic and static back-calculation procedures. The probabilistic approach to FWD back-calculation, a relatively new approach, is initially introduced and a brief overview of its numerical implementation is presented. The approach is then applied to back-calculate moduli from a set of synthetic FWD data using different back-calculation procedures, such as static and dynamic deflection bowl or dynamic time history procedures. Based on the probabilistic solution for back-calculated moduli from each procedure, the reliability of each procedure is then compared to the others. It is shown that, although widely used, the static FWD back-calculation procedures fail to capture the essential dynamic nature of the test and consequently cannot be relied upon to correctly back-calculate the layer moduli. It is also demonstrated that there is little redundancy in the dynamic deflection bowl back-calculation procedures, potentially producing relatively large uncertainties in the obtained back-calculation results. Finally, it is shown that the dynamic deflection time history back-calculation is the most reliable approach for FWD back-calculation. Using the back-calculated moduli from different procedures, effect of different back-calculation approaches on the pavement life is illustrated.

Deterioration modeling is a key component in a transportation infrastructure management system. It serves to capture and predict the performance of a facility. A sound deterioration model should incorporate: (1) relevant variables that affect deterioration process; (2) physical principle that reflects deterioration mechanism; and (3) rigorous statistical approach to estimating the model. This paper addresses these critical aspects with particular focus on highway pavements. Data collected from in-service pavement sections as part of the Minnesota Road Test project are used to capture the real-world pavement deterioration process. A number of variables involved in the system are thoroughly investigated, which include pavement design, materials, traffic, environment, and maintenance factors. Performance uncertainty due to unobserved heterogeneity is incorporated in the proposed model. The unobserved heterogeneity stems primarily from variability in the materials and the construction process. The model is estimated through maximum simulated likelihood estimation. It is demonstrated that the results are consistent with observations and engineering judgment in the context of pavement design and performance. In addition to population-level parameters representing the general deterioration mechanism, section-specific or individual-level parameters are obtained through Bayesian approach. The two levels of parameters can be used to accommodate network- and project-level analysis in pavement management.

To facilitate the use of recycled materials in pavement construction, a mechanistic-based approach is required to better characterize pavement base materials. This paper demonstrates the application of the shakedown theory to characterize the behavior of traditional and recycled base materials based on laboratory repeated load triaxial (RLT) tests and full-scaled accelerated loading tests. A new approach that is based on dissipated energy is proposed to explain different shakedown responses of tested materials under repeated loading. The dissipated energy approach illustrated that there are two responses during RLT tests, namely, stable and unstable responses, which are dependent on the loading levels and type of tested material. It was also observed that the transition from the stable to unstable response represents gradual microstructural adjustments of tested materials to accommodate the applied loading. This gradual transition explains the difficulties in identifying some material responses within the shakedown theory based only on the permanent strain rate criteria. Based on the results of this study, a mechanistic-based design procedure to incorporate various recycled materials into pavement bases is recommended.

Geometric data in transportation, such as roadway geometry, are important for asset management and for safety analysis. Traditional roadway geometric data are measured in the field, which is time consuming, costly, and dangerous. This paper proposes an algorithm to compute roadway geometric data, including roadway length, lane width, line width, and pavement marking size, from images. This paper makes two major contributions. First, the paper proposes a generalized roadway geometry computation algorithm using emerging vision technology based on two-dimensional (2D)/three-dimensional (3D) image reconstruction. The proposed algorithm consists of four steps, which are camera calibration from vanishing points, roadway vanishing line computation, homography computation and 2D/3D reconstruction, and, finally, roadway geometry computation. Second, the paper develops an error model, called roadway geometry error model (RGEM), to spatially quantify and visualize computation errors so that decision makers can choose measurement locations with an acceptable error. The geometric interpretation to RGEM is also presented in terms of roadway vanishing line. The proposed algorithm has been tested using two sets of images that were collected from the Georgia Tech campus and from actual video log images provided by the Georgia Department of Transportation. The roadway geometry was computed and the computation errors were analyzed. The test results show that the computation errors increase when the computation locations approach the roadway vanishing line. For the computation location with a distance of 190 pixels to the roadway vanishing line, the pavement lane width computation error is less than 3 cm. The experimental results also demonstrate that the proposed error model, RGEM, is able to reliably evaluate the roadway geometry computation errors. Applications of the proposed algorithm for modern and intelligent transportation system are also discussed.

In this paper, we develop a model of bidirectional pedestrian streams with an oblique intersecting angle that represents the crossing interaction of pedestrians moving in different directions on a walking facility. We formulate the model based on Drake’s model in the traffic flow literature, and calibrate it using results from a set of controlled experiments in which two groups of pedestrians were asked to walk in different directions and cross on designated walkways with different levels of pedestrian flow and different intersecting angles. Their movements were video recorded, and macroscopic quantities such as speed, density, and flow were extracted to calibrate the model of bidirectional pedestrian streams. All of the parameters of the calibrated model are statistically significant at the 0.1% level.

The rapidly growing number of work zones on national highways is having significant operational impacts due to the temporary loss of capacity. Work zone impact on safety and mobility creates a strong need to alleviate work zone congestion and protect road users and workers, which requires a sufficient understanding of work zone impact on traffic flow. Previous studies and field observations demonstrated the importance of considering diversion phenomena when performing work zone impact analysis. To overcome the limitations of deterministic queuing approaches applied in most work zone impact analysis tools, an interactive process combining microsimulation and logistic regression was developed to imitate diversion behavior dynamically in the upstream of work zones with a number of entrance and exit ramps. Specifically, the logistic regression model based on the field observations was incorporated into a well-calibrated VISSIM model to simulate traffic flow in work zones with diversion behavior. The integration of the two models was achieved via the development of diversion calculation module using a COM interface provided by VISSIM. The comparison between simulated results and field observations suggested that the diversion calculation module using logistic regression can simulate the queue propagation process due to lane closure in an efficient and effective manner. It was demonstrated that the interactive process can improve work zone impact analysis by using real-time traffic feedback information to emulate the diversion phenomenon upstream of work zones.

Activity-based travel demand forecasting consists of modeling activity type, location, and duration with a view to improving transportation planning and creating effective traffic management systems. Research to date has focused primarily on weekday activity patterns, but given its steady increase, weekend activities and related travel demand also deserve attention. Limited research studied weekend activities, and none of them was found to provide detailed specifications with respect to best-fit hazard functions and lifetime regression models. This study, which took place in Calgary, Alberta (a Canadian city of $1,000,000+$ ), is meant to address that gap. Ten activity patterns of eight demographic groups were assessed and nearly 13,000 observations analyzed. Results affirm that most weekend activities are neither work nor school related and tend to begin mid-day or later; analysis of activity participation by demographic group shows that adults (19–64 years old) are the most active components of our society. Likelihood ratio tests confirm that a two-level modeling exercise is required to handle the heterogeneity within the data: first, analysis by activity type and second, analysis by demographic group. Eleven candidate hazard functions were examined for 10 weekend activities such as shopping or entertainment, then best-fit hazard functions and lifetime regression models were determined. The results show a high degree of fit. It was found that the best-fit parametric models for demographic subgroups are generally consistent with those based on activity type at the aggregate level, a discovery that should simplify future applications. Lifetime regression models show that the starting time of a given activity and personal mobility are the most significant factors influencing activity duration. The applicability of fully parametric, nonparametric, and semiparametric model is discussed and addressed at various points within the paper. The rounding problem of reported durations is also noticed and discussed during the process of identifying best-fit hazard functions and lifetime regression models.

The Manual on Uniform Traffic Control Devices has grown much more complex since 1961, the year that a section on signs for freeways and expressways was added to the manual. Yet that growth has been reflected primarily in the addition of more regulatory signs and a great deal of qualifying language. The standards for sign legibility and layout have changed little; however, the complexity of the roadway environments and the demand placed on the system has changed substantially. This paper builds upon previous work by the writers, which proposed similar formatting for conventional road guide signing. The intent of the system proposed in this new work is to improve the consistency and uniform readability of freeway and expressway guide signs based on defined proportions for key dimensions including: border, figure and field relationship, and line space. This design scheme rests on a foundation of proportional relationships made uniform for all common applications based on the common dimension (“ $X$ ”) of the height of the primary legend’s lead capital letter.