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  • Mobility and traffic research  (13)
  • 1
    Online Resource
    Online Resource
    Application of Artificial Neural Networks to Predict Speeds on Two-Lane Rural Highways
    SAGE Publications ; 2001
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 1751, No. 1 ( 2001-01), p. 9-17
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 1751, No. 1 ( 2001-01), p. 9-17
    Abstract: The ability to predict accurately vehicular operating speeds is useful for evaluating the planning, design, traffic operations, and safety of roadways. Operating speed profile (OSP) models are used in the geometric design of highways to evaluate design consistency. Design consistency refers to the condition where the geometric alignment does not violate driver expectations. Existing OSP models have been developed using ordinary linear regression methods. However, the assumptions and limitations inherent to linear regression may at the very least complicate model formulation. If not acknowledged and corrected for, deviations from these assumptions can also adversely affect the efficacies of such models. Artificial neural networks (ANNs) are modeling tools that do not impose the stringent assumptions and limitations imposed by regression. It is therefore of interest to know whether ANNs are viable alter natives to linear regression for OSP modeling. Two backpropagation ANNs for operating speed predictions for passenger cars on two-lane rural highways are evaluated, and their performances with regression-based models are compared. The results of these comparisons indicate that the explanatory powers of the ANN models are comparable with those developed by regression. The predictive powers of the two types of models were observed to be comparable, and ANNs were not limited by distributional or other constraints inherent to regression. Therefore, ANNs were determined to be a viable alternative to regression for OSP model construction.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/1751-02
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2001
    detail.hit.zdb_id: 2403378-9
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  • 2
    Online Resource
    Online Resource
    Field Test of Energy Information Feedback : Driver Responses and Behavioral Theory
    SAGE Publications ; 2011
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2252, No. 1 ( 2011-01), p. 7-15
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2252, No. 1 ( 2011-01), p. 7-15
    Abstract: The Energy Information Administration estimates that, in 2007, U.S. domestic passenger vehicles burned 113 billion gallons of fuel and thus generated more than 16% of U.S. greenhouse gas emissions. Past field experiments and simulations suggest that energy information feedback to drivers could have spared 10% to 25% of those gallons. However, the theoretical underpinnings of past experiments have primarily been ad hoc, with application of their results limited to specific conditions of the experiment and feedback design. More rigorous behavioral theory would allow researchers to account for more variation in driver response to feedback, create testable hypotheses about the effectiveness of current systems, and provide a basis for designing more-effective systems. This paper presents drivers’ responses to energy feedback in a field test involving 98 participants from 43 households in California and compares the results with the concepts that underlie the theory of planned behavior and the extended model of goal-directed behavior. About 40% of participants reported more economical driving behaviors after viewing the feedback; estimation of actual changes in fuel use is left for future research. After viewing real-time energy information, numerous drivers reported setting goals, having emotional reactions, and creating new driving behaviors. Distraction from the primary driving task was a persistent problem for some drivers. Web-accessible information was not as motivating to participants. Finally, the study finds evidence of correspondence between theoretical behavioral factors and drivers’ responses.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2252-02
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2011
    detail.hit.zdb_id: 2403378-9
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  • 3
    Online Resource
    Online Resource
    Unbound Aggregate Rutting Models for Stress Rotations and Effects of Moving Wheel Loads
    SAGE Publications ; 2005
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 1913, No. 1 ( 2005-01), p. 41-49
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 1913, No. 1 ( 2005-01), p. 41-49
    Abstract: The latest research findings on stress rotations caused by moving wheel loads and their effects on permanent deformation or rut accumulation in pavement granular layers are presented. Realistic pavement stresses induced by moving wheel loads were examined in the unbound aggregate base and subbase layers, and the significant effects of rotation of principal stress axes were indicated for a proper characterization of the permanent deformation behavior. To account for the rutting performances of especially thick granular layers, a comprehensive set of repeated load triaxial tests was conducted in the laboratory. Triaxial test data were obtained and analyzed from testing aggregates under various realistic in situ stress paths caused by moving wheel loading. Permanent deformation characterization models were then developed on the basis of the experimental test data to include the static and dynamic stress states and the slope of stress path loading. The models that also considered the stress path slope variations predicted the stress path dependency of permanent deformation accumulation best. In addition, multiple stress path tests conducted to simulate the extension–compression–extension type of rotating stress states under a wheel pass gave much higher permanent strains than those of the compression-only single path tests. The findings indicated actual traffic loading simulated by the multiple path tests could cause greater permanent deformations or rutting damage, especially in the loose base or subbase, when compared with deformations measured from a dynamic plate loading or a constant confining pressure type laboratory test.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/0361198105191300105
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2005
    detail.hit.zdb_id: 2403378-9
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  • 4
    Online Resource
    Online Resource
    Variation of Resilient Modulus with Soil Suction for Compacted Subgrade Soils
    SAGE Publications ; 2005
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 1913, No. 1 ( 2005-01), p. 99-106
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 1913, No. 1 ( 2005-01), p. 99-106
    Abstract: The variations of resilient modulus with the postconstruction moisture content and soil suction for cohesive subgrade soils were evaluated. In particular, the effects of relative compaction of the subgrade on the suction and resilient modulus were investigated. To simulate subgrade soils at in-service conditions, soil specimens were compacted at various relative compactions and optimum moisture content and then saturated to equilibrium moisture content to test for resilient modulus and soil suction. The filter paper method was used to measure the total and matric suctions of two cohesive soils. Test findings demonstrated that resilient modulus correlated better with the matric suction than with total suction. Matric suction was found to be a key parameter for predicting the resilient modulus of cohesive subgrade soils. A prediction model incorporating deviator stress and matric suction for subgrade soil resilient modulus was established.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/0361198105191300110
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2005
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  • 5
    Online Resource
    Online Resource
    Exploring Vehicle–Pedestrian Crash Severity Factors on the Basis of In-Car Black Box Recording Data
    SAGE Publications ; 2017
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2659, No. 1 ( 2017-01), p. 148-154
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2659, No. 1 ( 2017-01), p. 148-154
    Abstract: This study investigated the main factors affecting the severity of injury to pedestrians in taxi–pedestrian crashes on urban arterial roads. Video data recorded by an in-car black box were used. Because the video data provided direct crash observation, they were more reliable than the crash data, and video images and speed profiles retrieved from the black box were advantageous for safety studies. For analysis of the black box data, this study defined new explanatory variables that affected injury severity; these variables could not have been identified by the conventional method, which was based on crash reports. A multiple-indicator and multiple-cause model was used to investigate the relationship between the explanatory variables and injury severity. A total of 484 taxi–pedestrian crash scenes over 2 years was used for the multivariate analysis in the city of Incheon, South Korea. The crash characteristics most strongly associated with increased crash severity were failure by the pedestrian to watch for approaching vehicles, jaywalking by the pedestrian, the pedestrian being elderly, excessive vehicle speed, failure by the driver to immediately stop, limited driver vision, and nighttime. This study emphasized the potential of individualized black box video recording data for crash severity analysis and investigation of the causal factors of crashes.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2659-16
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2017
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  • 6
    Online Resource
    Online Resource
    Dynamic Viscoelastic Response of Asphalt Pavement With Random Transversely Isotropic Base Courses
    SAGE Publications ; 2023
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2677, No. 8 ( 2023-08), p. 37-53
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2677, No. 8 ( 2023-08), p. 37-53
    Abstract: Diagnosis of the dynamic response of an asphalt pavement structure coupled with involving inherent anisotropic properties of pavement materials serves as a vital tool for pavement analysis and design platforms. The mechanical response of asphalt pavement is strongly influenced by the random anisotropic properties (simplified as transversely isotropic properties in this study) because of the shape, distribution, orientation, degree of compaction, void structure, and so forth, of the granular materials in asphalt pavements. This study aims to introduce a computational framework by generating a three-dimensional finite element-based program to analyze the influence of thermo-viscoelasticity of the asphalt layer and transverse isotropy of the base courses and its randomness on asphalt pavements under the effect of moving vehicle loading. The accuracy and efficiency of the developed numerical program were verified by comparing our results with previous studies. Concurrently, the influences of random field conditions, transversely isotropic properties, and the temperature field were involved in assessing their action on the fatigue life prediction of pavement. It was concluded that the fatigue life of the asphalt pavement model, considering the transverse isotropy of the material, random field, and temperature field, was reduced by 48.1%, which would mislead the state assessment of asphalt pavements. Therefore, during asphalt pavement design and its viscoelastic response analysis, it is recommended to consider the influence of the random modulus, temperature fields, and transversely isotropic properties on the structural assessments.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/03611981231155417
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2023
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  • 7
    Online Resource
    Online Resource
    Quantification of Coarse Aggregate Angularity Based on Image Analysis
    SAGE Publications ; 2002
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 1787, No. 1 ( 2002-01), p. 117-124
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 1787, No. 1 ( 2002-01), p. 117-124
    Abstract: Aggregate angularity affects the shear strength properties of asphalt concrete and granular base layers in pavements. It also improves aggregate interlock and load transfer properties of jointed concrete pavements. The development of a quantifiable index based on image analysis to characterize the angularity of coarse aggregate used in pavement layers is described. The new angularity index (AI) was developed as part of the University of Illinois Aggregate Image Analyzer, and the procedure was calibrated for two aggregate samples, rounded gravel and crushed stone, which possess the two extremes of particle angularity. A statistical study demonstrated that the AI computation technique is not only able to distinguish crushed stone from gravel but also is robust enough to give similar AI values regardless of the particle size and orientation. Furthermore, the crushed stone and gravel samples together with a 50–50 blend of the two samples by weight were tested for shear strength under triaxial loading conditions. The AI value computed for these samples could be correlated to the angle of internal friction and thus the shear strength properties of the samples. The AI distributions of representative aggregate samples from Illinois, crushed gravel, limestone, and dolomite, were also computed. The newly developed index has also demonstrated the capability to distinguish between crushed stone and crushed gravel samples. With this AI value as a measure of aggregate angularity, pavement engineers can objectively quantify the influence of aggregate angularity on asphalt concrete, portland cement concrete, and granular mix performance and thereby establish meaningful criteria relating aggregate properties to performance indicators.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/1787-13
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2002
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  • 8
    Online Resource
    Online Resource
    Modulus Anisotropy and Shear Stability of Geofiber-Stabilized Sands
    SAGE Publications ; 2004
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 1874, No. 1 ( 2004-01), p. 125-135
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 1874, No. 1 ( 2004-01), p. 125-135
    Abstract: A systematic laboratory approach is established to evaluate shear stability or bearing capacity improvement of sand-geofiber stabilization for rapid road and airfield construction. The approach deals with the investigation of directional dependency, anisotropy, and modulus properties and links stability to shear stress levels typically applied on specimens during testing in relation to their strength. An advanced triaxial testing machine referred to as the University of Illinois FastCell is used together with direct shear tests for determining the anisotropic resilient moduli and the strength properties of two geofiber-reinforced sands (poorly and uniformly graded sands) prepared with three 51-mm geofibers: fibrillated, monofilament, and tape. The use of different geofiber types and the various amounts of clay and silt fines present in the sand mixtures significantly affected the recorded horizontal and vertical moduli and the shear stresses at applied stress states. Monofilament-type geofiber stabilization was found to be the most effective, with the recorded highest vertical moduli and the highest shear strength and stability improvement indicated by the lowest shear stress ratios, especially when mixed with 10% to 20% clay. The tape-type geofiber reinforcement generally was not very effective. For the geofiber stabilization of sands to be a viable construction alternative, the sand-geofiber mixtures should contain an optimal amount of fines needed for geofibers to mobilize the shear strength of the mix effectively and thereby improve the shear stability and resistance to permanent deformation.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/1874-14
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2004
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  • 9
    Online Resource
    Online Resource
    Homogenization Model Examining the Effect of Nanosilica on Concrete Strength and Stiffness
    SAGE Publications ; 2010
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2141, No. 1 ( 2010-01), p. 28-35
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2141, No. 1 ( 2010-01), p. 28-35
    Abstract: Composite homogenization is a numerical simulation method that allows determination of the effect of microstructure constituents on the mechanical properties of composite materials. This homogenization technique allows cement paste to be modeled as a composite material in which microparticles are randomly dispersed in the cement paste matrix. By using microstructural homogenization, a representative volume element (RVE) can be developed and used to simulate the constitutive model of the composite cement paste by considering its constituent phases. A four-phase cement paste model is considered to describe cement paste incorporating nanosilica. Cement paste microstructures are divided into Phase I, hydrated cement paste; Phase II, unhydrated cement paste; Phase III, nonreacted nanosilica; and Phase IV, capillary porosity. Cement hydration models are used to predict the volume fraction of the four phases on the basis of the mixture proportion of the cement paste mix. Constitutive models for Phases I, III, and IV are assumed on the basis the literature. A constitutive model for Phase II is identified with the RVE model by matching the stress–strain curves of the cement paste extracted from nanoindentation experiments. The validated RVE model is then used to examine the effect of changing the nanosilica content in the cement paste on the stress–strain curve of the composite cement paste. It is evident computationally that increasing the nanosilica content will increase the strength and stiffness of the cement paste and therefore will increase the ability of the cement paste to absorb energy represented by the area under the stress–strain curve.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2141-06
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2010
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  • 10
    Online Resource
    Online Resource
    Field Validation of Airport Pavement Granular Layer Rutting Predictions
    SAGE Publications ; 2006
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 1952, No. 1 ( 2006-01), p. 48-57
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 1952, No. 1 ( 2006-01), p. 48-57
    Abstract: This paper presents research findings on the prediction performances and field validations of the recently developed granular base–subbase layer permanent deformation models using the full-scale pavement test section data from the FAA's National Airport Pavement Test Facility (NAPTF). The FAA-designated P209/P154 aggregate materials were used in the construction and testing of the NAPTF flexible pavement test sections with variable-thickness base and subbase courses. To account for the rutting performances of these substantially thick granular layers, a comprehensive set of repeated load triaxial tests, considering both constant and variable confining pressure (CCP and VCP) conditions, were conducted on the P209 base and P154 subbase granular materials. On the basis of the laboratory test results, both CCP- and VCP-type permanent deformation models were developed to predict maximum ruts that occurred at the NAPTF under both six-wheel and four-wheel gear loadings applied following a wander pattern. The developed rutting models were first calibrated for the field conditions and then evaluated for predicting the field accumulation of permanent deformations by properly taking into account the NAPTF trafficking data, effects of stress rotation due to moving wheel loads, and loading stress history effects. A comparison of the measured and predicted permanent deformations indicated that a good match for the measured rut magnitudes and the accumulation rates could be achieved only when the magnitudes and variations of stress states in the granular layers, number of load applications, gear load wander patterns, previous loading stress history effects, trafficking speed or loading rate effects, and finally, principal stress rotation effects due to moving wheel loads were properly accounted for in the laboratory testing and permanent deformation model development.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/0361198106195200106
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2006
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