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  • Mobility and traffic research  (12)
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  • Mobility and traffic research  (12)
  • 1
    Online Resource
    Online Resource
    Effect of Microbial-Induced Calcite Precipitation on Surface Erosion and Scour of Granular Soils : Proof of Concept
    SAGE Publications ; 2017
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2657, No. 1 ( 2017-01), p. 10-18
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2657, No. 1 ( 2017-01), p. 10-18
    Abstract: Erosion is relevant to a variety of infrastructure problems such as bridge scour, roadway shoulder erosion, coastal erosion, and riverbank and slope stability. This research investigated the feasibility of using microbial-induced calcite precipitation (MICP) as an erosion countermeasure. MICP is a natural phenomenon in which calcite precipitation occurs as a consequence of microbial metabolic activity. The precipitated calcite modifies the soil fabric and provides an additional bonding force between soil particles. In this paper, a preliminary experimental study on the erosional behavior of MICP-treated sand is presented. A standard soil, Ottawa graded sand, was treated with a bacterium (Sporosarcina pasteurii) in a full-contact reactor-one in which the soil in a fabric mold was fully immersed in the bacteria and cementation solution. The morphologies and crystalline structures of the precipitated calcite in porous sediments were characterized using microscopic imaging techniques. The treated soil samples were tested in a flume to investigate the erosional behavior; both surface erosion and bridge scour tests were conducted. Although the untreated soil is highly erodible, the erosion of the treated sand was found to be negligible under the circumstances of the test; however, some concerns were raised regarding practical applications. Efforts will be made in the future to identify alternative treatment procedures that are more applicable to the field.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2657-02
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2017
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  • 2
    Online Resource
    Online Resource
    CFD-DEM Two-Way Coupled Numerical Simulation of Bridge Local Scour Behavior under Clear-Water Conditions
    SAGE Publications ; 2018
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2672, No. 39 ( 2018-12), p. 107-117
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2672, No. 39 ( 2018-12), p. 107-117
    Abstract: Bridge local scour involves extremely complex interactions among the flow, the sediments, and the pier. Our understanding of the underlying mechanism, especially at the microscale, is far from complete. The newly emerged multiphase numerical simulation overcomes the technical limitations imposed on physical experiments. To advance knowledge of the sediment dynamics under turbulent junction flows, this paper employed a CFD-DEM two-way coupled numerical model to simulate the local scour behavior of uniform spherical mass particles around an oblong pier. In this coupled system, the flow phase was described as a continuum by a detached eddy simulation (DES) model, and motion of the discrete particles was governed by Newton’s laws of motion (DEM). The flow–sediment interactions were directly considered through the momentum exchange between the two phases. The two-way coupled model was shown to successfully capture microscopic sediment dynamics similar to those observed in the literature. Sediment grains in the bed-load layer were shown to be eroded in the form of sliding and saltation. The erosional forces acting on two representative target particles, together with their correspondent motions/trajectories, provide valuable insights into the mechanism that dictates the scour initiation.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/0361198118783170
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2018
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  • 3
    Online Resource
    Online Resource
    Understanding the Utilization Characteristics of Bicycle-Sharing Systems in Underdeveloped Cities: A Case Study in Xuchang City, China
    SAGE Publications ; 2017
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2634, No. 1 ( 2017-01), p. 78-85
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2634, No. 1 ( 2017-01), p. 78-85
    Abstract: In recent years, a growing number of cities in China have successively rolled out bicycle-sharing systems to facilitate bicycle use, including not only metropolises but also some underdeveloped cities with populations of less than 1 million. One of those underdeveloped cities, Xuchang, launched its bicycle-sharing system in 2014. This service provides a convenient way for members to cycle for some of their short trips. Interest in the bicycle-sharing systems of metropolises is growing rapidly; however, studies on underdeveloped cities are still limited. This study investigated the factors influencing the adoption of a bicycle-sharing system in Xuchang, by analyzing massive smart card data from July 2014 to mid-April 2015 and 500 intercept survey questionnaires in April 2015. Different questions were ready for members and nonmembers in the questionnaires and the statistical results show the characteristics of users of the Xuchang bicycle-sharing system, including demographic characteristics, travel habits, and degree of satisfaction. Moreover, the space–time distribution characteristics of the Xuchang bicycle-sharing system were analyzed by dividing a massive data set into three groups: weekdays, weekends, and holidays. Results showed that compared with the clearly defined role of “resolve the last-kilometer problem” in a metropolis, bicycle-sharing in underdeveloped cities acts as an alternative way of transportation rather than a transfer traffic mode. Results also showed that bicycle-sharing systems gained more popularity in underdeveloped cities than in metropolises because of the smaller extent of egression, resident travel habits, the traffic environment, and so on.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2634-12
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2017
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  • 4
    Online Resource
    Online Resource
    Surrogate Evaluation Model for Assessing Lane Detection Reliability of Automated Vehicles in Complex Road Environments
    SAGE Publications ; 2023
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2677, No. 7 ( 2023-07), p. 185-195
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2677, No. 7 ( 2023-07), p. 185-195
    Abstract: The reliability of environmental perception is the key to ensuring the stability and safety of autonomous vehicles. Complex road environments pose attentional challenges to automated driving, especially for vehicle perception systems. Therefore, evaluating the performance of autonomous driving algorithms in complex road environments is of great significance. However, as road geometry is complex, with many factors, including curvature, slope, lane marking conditions, and so on, the existing approach in assessing an algorithm through detection tests is of low efficiency. Therefore, this study relies on failure prediction modeled by extreme gradient boosting and recursive feature elimination. An evaluation model that could accomplish a quick set of road evaluations is developed. The proposed model generates recognition reliability merely by such features as road design parameters. In addition, road curvature is the most significant environmental factor affecting the perception of autonomous vehicles. The failure rates of the algorithm in different scenarios demonstrate a negative correlation between the radius of curvature and failure perception. The partial dependence involving the radius of curvature and the perception ability is obtained. Furthermore, other features, such as missing lane lines and illumination conditions, are taken into consideration to explore the potential failure perception mode. The proposed method has a particular significance for finding the failure mode of an autonomous driving perception algorithm.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/03611981231152260
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2023
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  • 5
    Online Resource
    Online Resource
    Integrated Control of Freeway Interchange Model Based on Enhanced Cell Transmission Model
    SAGE Publications ; 2011
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2259, No. 1 ( 2011-01), p. 179-191
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2259, No. 1 ( 2011-01), p. 179-191
    Abstract: Congested freeway interchanges normally suffer from the spillback of off-ramp and on-ramp queues. The traffic signals around a congested interchange can also experience link-blockage and lane-blockage problems. For an overall system performance around an interchange to be improved, both freeway and arterial performance must be considered to optimize signal timings. This study extends the cell transmission concept and proposes a set of new formulations to capture the traffic dynamic with link blockage, lane blockage, and ramp spillback. On the basis of these formulations, an integrated control model for optimizing interchanges and a solution method based on a genetic algorithm are proposed. The model's performance was demonstrated in a case study with different traffic scenarios for the interchange connecting Georgia Avenue (MD-97) and the Capital Beltway (I-495) in Silver Spring, Maryland. The resulting signal timings were compared with those from TRANSYT-7F (Release 10). For fair comparison, this study used CORSIM, a third-party simulation package, as the performance evaluator. Results indicated that the proposed model was promising and could improve freeway and arterial performance.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2259-17
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2011
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  • 6
    Online Resource
    Online Resource
    Streamlining of Bridge Piers as Scour Countermeasures : Effects of Curvature of Vertical Profiles
    SAGE Publications ; 2015
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2521, No. 1 ( 2015-01), p. 172-182
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2521, No. 1 ( 2015-01), p. 172-182
    Abstract: Pier streamlining is proposed as a flow-altering countermeasure to local scour for newly proposed piers. To obtain the optimal geometry, it is necessary to investigate the effect of the horizontal profile and vertical profile on the flow pattern around the piers. In a separate paper, the effect of the cross section was studied, and the optimal cross section was obtained. Continuing the effort, this paper investigates the effect of vertical profile curvatures. To achieve this goal, Bézier curves were used to parameterize the vertical curvatures. Fifty-one three-dimensional computational fluid dynamics models with different curvatures for the pier's vertical profile were constructed by varying the Bézier parameters and computed by COMSOL. All pier models in the flume had the same block ratio to ensure that results from test cases were comparable. Analysis and comparison of the simulation results showed that both a concave (or sloped) nose and a concave sidewall reduced the maximum shear stress around piers and that increasing the concave curvature of the sidewall enhanced the reduction effect. Increasing the concave curvature of the nose, however, tended to diminish the reduction effect. The practical implications from the findings are discussed in this paper.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2521-18
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2015
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  • 7
    Online Resource
    Online Resource
    Heuristics to Improve Efficiency of Solution Algorithm of Path Flow Estimator
    SAGE Publications ; 2015
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2497, No. 1 ( 2015-01), p. 12-22
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2497, No. 1 ( 2015-01), p. 12-22
    Abstract: The path flow estimator (PFE) proposed by Bell and Shield in 1997 is an important demand estimator in ground transportation. The PFE is formulated as a nonlinear optimization model and solved by the iterative balancing solution algorithm given by Bell in 1995. This paper presents several theoretical results about the solution algorithm. In particular, the solution algorithm is shown to maximize the dual problem of the PFE sequentially along the directions defined by unit vectors. A closed-form relationship was identified between the increase in the objective of the dual problem and the optimal step length along each direction. In addition, three heuristics were developed to improve the computational efficiency of the solution algorithm. The first heuristic reduced the computational effects that could not yield significant increases to the objective value of the dual. The second reduced the probability of yielding marginal increases to the objective value of the dual. The third sped up convergence by partially avoiding zigzagging (i.e., approaching the optimal solution in small steps along perpendicular directions). The heuristics could be applied simultaneously with each other or with the methods developed to determine better initial values. The three heuristics were applied to a large-sized network, and the computational results were generally consistent with the theoretical results.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2497-02
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2015
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  • 8
    Online Resource
    Online Resource
    Estimation of Flight Delay Costs for U.S. Domestic Air Passengers
    SAGE Publications ; 2010
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2177, No. 1 ( 2010-01), p. 49-59
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2177, No. 1 ( 2010-01), p. 49-59
    Abstract: Evaluating the economic value of flight delays has always been a keen interest of research groups as well as of federal agencies such as the U.S. Department of Transportation and FAA. However, because of the complexity of the question as well as the incompleteness of available data sets, the estimation of flight delay costs is considered a challenging task in practice. This paper presents a method for estimating domestic air passengers' delay costs incurred by flight delays in U.S. airports. A unique feature of the method is that the costs incurred by flight delays relative to the original flight schedules are imposed at passengers' final destination airports. The underlying assumption of this idea is that the opportunity costs (incurred from compromised business opportunities or personal affairs due to the delayed flights) happen at the destination airports, not at the transfer airports. To reflect the variability of flight delays, both average and 95th percentile flight delays are calculated at each airport and applied to estimate corresponding delay costs. In 2007, total domestic passenger delay cost was estimated at $5.2 billion and $8.7 billion for, respectively, average and 95th percentile gate arrival delays. Assumptions, data sets, and results from this study are summarized and compared with those from previous studies.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2177-07
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2010
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  • 9
    Online Resource
    Online Resource
    New Model for Total Crossing Time of Pedestrian Platoon at a Signalized Crosswalk
    SAGE Publications ; 2015
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2519, No. 1 ( 2015-01), p. 67-74
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2519, No. 1 ( 2015-01), p. 67-74
    Abstract: To calculate a pedestrian platoon's total crossing time accurately, this study considered the condition of bidirectional pedestrian interference and analyzed the following key factors: number of pedestrians, pedestrian directional split ratio, and crosswalk width and length. The study divided the total crossing time into three parts: the discharging time of a pedestrian platoon, the objective pedestrian's basic crossing time, and the frictional delay caused by pedestrians moving in the opposite direction. The latter two factors were called the crossing time. Then a model that reflected bidirectional pedestrian characteristics was established for the pedestrian platoon's total crossing time. In particular, the ratio of the number of objective pedestrians per cycle to the actual crosswalk capacity was analyzed in the model of the frictional delay. Moreover, according to traffic data from three signalized crosswalks in Changchun City, China, the congested lateral distance and comfortable lateral distance were calibrated to 1.03 m and 1.29 m, respectively. Finally, compared with the pedestrians' total crossing time in the Highway Capacity Manual (2000), the results showed that the maximum relative error was 8.33% less than that in the Highway Capacity Manual method. The model can provide a new method and a new way of thinking for traffic researchers, and it can provide a potential reference for design of pedestrian signal timing and crosswalks.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2519-08
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2015
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  • 10
    Online Resource
    Online Resource
    Streamlining of Bridge Piers as Scour Countermeasures : Optimization of Cross Sections
    SAGE Publications ; 2015
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2521, No. 1 ( 2015-01), p. 162-171
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2521, No. 1 ( 2015-01), p. 162-171
    Abstract: Bridge scour is one of the most critical causes of bridge failure. Existing scour countermeasures either passively prevent the development of scour holes by stabilizing the critical shear zone or actively reduce the turbulence intensity in the vicinity of the pier surface. This paper proposes streamlining of the bridge pier as an option to reduce turbulence intensity actively in the local zone and thus decrease overall local scour potential. The effect of the curvature of the pier cross section was evaluated with computational fluid dynamics (CFD) simulations. To reduce computational cost, two-dimensional CFD simulations were conducted to model the flow fields around test cases having different pier cross sections. Simulation results were systematically analyzed and compared to evaluate the effect of streamlining on the flow field. The cross section that resulted in the smallest value of the maximum bed shear stress was selected as the optimal cross section for the subsequent three-dimensional (3-D) study, which investigated the vortex structures around the pier. Results from this 3-D simulation were compared with those from two other test cases, in which piers had cross-section shapes that are commonly seen in practice. The pier model with the optimal cross section was found to significantly reduce the downward velocity in front of the piers, the maximum bed shear stress, and the overall scour potential. These findings are expected to inform the design of optimal streamlined piers for newly proposed bridges, which could diminish the overall scour potential around piers.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2521-17
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2015
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