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  • Mobility and traffic research  (7)
  • 1
    Online Resource
    Online Resource
    Convenient Method for On-Site Check of Single Steel I-Girder Stability during Erection
    SAGE Publications ; 2010
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2172, No. 1 ( 2010-01), p. 59-65
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2172, No. 1 ( 2010-01), p. 59-65
    Abstract: The behavior of a single steel I-girder during erection is quite different from that of a girder under service: the girder during erection usually has limited or no lateral bracing along the span. Elastic lateral torsional buckling of the steel girder may occur if the girder span becomes too large. Rules of thumb have been used to check girder stability during erection by using the ratio of unbraced length L to compression flange width b; this is based on experience. For any longitudinally unstiffened girder section, formulas were developed on the basis of the current AASHTO load and resistance factor design code for the unique maximum L/b ratio. Parametric studies were then conducted to calculate L max and the (L/b) max ratio for a variety of girder sections that cover the range of practical design in order to identify dominant section parameters on the (L/b) max ratio as well as girder stability during erection and to develop simplified formulas for the upper and lower bounds of the (L/b) max ratio for all girder sections within the range of practical design. On the basis of the simplified formulas, an on-site check of single steel I-girder stability during erection could be conducted by checking the girder L/b ratio against the (L/b) max ratio for that given section or, even more easily, by checking the girder L/b ratio against the upper and lower bounds of the (L/b) max ratios for all girder sections.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2172-07
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2010
    detail.hit.zdb_id: 2403378-9
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  • 2
    Online Resource
    Online Resource
    Anisotropic Resilient Modulus Model of Granular Materials Based on Particle Characteristics
    SAGE Publications ; 2021
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2675, No. 11 ( 2021-11), p. 970-984
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2675, No. 11 ( 2021-11), p. 970-984
    Abstract: Granular materials are widely used for bases or subbases in pavement structures. They typically exhibit strong anisotropic properties which relate to stress states and particle characteristics. The conventional design procedure for flexible pavements underestimates the anisotropy of resilient moduli. This study established an anisotropic resilient modulus model for granular materials that considered gradation and particle shape characteristics. Vertical and horizontal resilient moduli of certain granular materials were measured in self-developed triaxial tests to obtain corresponding model parameters and anisotropic coefficients. Gradation and particle shape models were established to quantify the granular material characteristics, and the parameters were regressed. Particle shapes were obtained via image processing, and the ratio ( η) of particle sphericity to roundness was chosen as a shape parameter. Results show that η increases with the decrease in particle size, and the average values of η for graded gravel and natural laterite are 0.54 and 0.63, respectively. The η distribution curves indicate that the proportion of relatively anisotropic particles, rather than extremely anisotropic particles, results in the differences in particle shape characteristics. The regression relationship between the anisotropic calculation parameters and the model parameters of vertical resilient modulus, gradation, and particle shape was established. Thus, the horizontal resilient modulus and the anisotropic coefficient can be predicted via conventional resilient modulus tests and gradation, and particle shape analysis. This study shows that the anisotropy of granular materials decreases with the increase in coarse particles and the uniformization of the particle size distribution, and it increases with the increase in anisotropic particles and the polarization of the η distribution.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/03611981211023770
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2021
    detail.hit.zdb_id: 2403378-9
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  • 3
    Online Resource
    Online Resource
    Capacity Modeling of Weaving Areas on Urban Expressways with Exclusive Bus Lanes Based on Gap Acceptance Theory
    SAGE Publications ; 2019
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2673, No. 8 ( 2019-08), p. 365-376
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2673, No. 8 ( 2019-08), p. 365-376
    Abstract: Intense lane-changing maneuvers at weaving sections often cause traffic turbulence on expressways, especially in the presence of a concurrent medium exclusive bus lane (XBL) and general purpose lanes. Such intense lane-changing activity usually affects the operation and reduces the capacity of weaving sections in relation to their equivalent basic expressway segments. In this context, a study on the capacity model of weaving areas on an expressway with a median XBL is conducted based on the analysis of lane-change behaviors using gap acceptance theory. Two weaving sections on expressways with median XBL are selected as case studies to obtain the estimated capacity as well as the maximum traffic throughput under a certain bus saturation on the XBL. The results show that estimated capacity is larger than maximum traffic throughput because of low utilization rate of buses on the XBL, and capacity is significantly affected by weaving demand. Error measures based on the estimated and observed maximum traffic throughput are analyzed to verify the validity of the proposed model. A sensitivity analysis shows that, compared with the increase of on-ramp bus flow ratio, the increase of off-ramp bus flow ratio results in a more obvious trend of the reduction of capacity and maximum traffic throughput.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/0361198119843235
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2019
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  • 4
    Online Resource
    Online Resource
    Evaluation of Effectiveness of Coordinated Signal Control in Reducing Vehicle Emissions during Peak Hours versus Nonpeak Hours
    SAGE Publications ; 2011
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2233, No. 1 ( 2011-01), p. 45-52
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2233, No. 1 ( 2011-01), p. 45-52
    Abstract: Traffic signal coordination is not only an effective traffic flow operational strategy to smooth the traffic in urban areas but is also considered a potentially effective means to reduce vehicle emissions. Nevertheless, when traffic flow speed decreases, the effectiveness of using traffic signal coordination to reduce emissions may be substantially weakened. This paper evaluates the effectiveness of signal coordination in reducing vehicle emissions during peak versus nonpeak hours, two speed scenarios. The operating mode binning approach is used as a statistical technique to calculate emission rates, and the difference in emissions is adopted as the measure of effectiveness in the study. Data used in the study include Global Positioning System data and emission data collected from real-world tests. It was found from the study that coordinated signal control could reduce vehicle emissions in the following order (most to least reduction): oxides of nitrogen, carbon dioxide, hydrocarbons, and carbon monoxide. However, its effectiveness would be impaired during peak hours when the speed was decreased. Meanwhile, the test shows that the effectiveness will be affected by driver behavior. Either low average speed or intentionally slow driving will weaken the effectiveness of coordinated control in reducing vehicle emissions. The research in this paper is a pilot study and the same methodology will be used to conduct a more thorough study.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2233-06
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2011
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  • 5
    Online Resource
    Online Resource
    Factors Associated With the Severity of Motor Vehicle Crashes Involving Electric Motorcycles and Electric Bicycles: A Random Parameters Logit Approach With Heterogeneity in Means
    SAGE Publications ; 2023
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2677, No. 8 ( 2023-08), p. 691-704
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2677, No. 8 ( 2023-08), p. 691-704
    Abstract: Exploring the heterogeneity of factors influencing the severity of electric bicycle crashes and electric motorcycle crashes can help target accident prevention policies to improve traffic safety. Therefore, this paper establishes a mean heterogeneity random parameter logit model using crash data from 2016 to 2020 in Guangxi to explore the different factors influencing the severity of crashes involving electric motorcycles and electric bicycles. The results show that the key influences on crash severity differ in electric motorcycle crashes and electric bicycle crashes. At the same time, some common factors affect the two types of crashes to different degrees. In addition, the complex interaction effects of unobserved heterogeneity were considered to explore the random parameters of the two types of crashes. The effect of unobserved heterogeneity on the distribution characteristics of the random parameters was then determined. For example, in electric motorcycle crashes, street lighting at night has a random parameter characteristic. The likelihood of serious crashes decreased when both street lighting at night and vehicle left turn were involved, and decreased when both street lighting at night and no signal control were involved. In electric bicycle crashes, large trucks have a random parameter characteristic. The likelihood of serious crashes increased when both large trucks and motor vehicle lights not turned on were involved, and increased when both large trucks and visibility less than or equal to 200 meters were involved. The results provide a basis for improving the road safety of electric motorcycles and electric bicycles.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.1177/03611981231157716
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2023
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  • 6
    Online Resource
    Online Resource
    High-Speed Rail and Urban Decentralization in China
    SAGE Publications ; 2015
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2475, No. 1 ( 2015-01), p. 16-26
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2475, No. 1 ( 2015-01), p. 16-26
    Abstract: The construction of a large-scale high-speed rail (HSR) network in China is altering the time–space relationships between cities. As a result, HSR is changing the traditional hierarchical urban system in China, and regions with large-scale networks of cities are forming. At the city level, the construction of HSR new towns could contribute to urban decentralization. The focus in this study is on the impact of HSR at the city level and how HSR is transforming cities in China through urban spatial restructuring. Case studies on two cities located on the Beijing–Shanghai HSR corridor were conducted, and the impact of the planned HSR new towns on the decentralization patterns of these two cities as well as the potential effects on their economic development are discussed. For large cities, the decentralization is actively driven by HSR because these cities are able to carefully choose the locations of their HSR stations. An HSR new town (i.e., a new district built around an HSR station) serves as an opportunity for well-planned spatial restructuring and as a catalyst for sustainable economic growth. For medium-sized to small cities, decentralization is often passively driven by HSR because the site selections of HSR stations are beyond the cities' control. The long distance between the HSR new town and the urban center weakens the economic strength of the existing urban core. The HSR new town presumably functions as a distraction rather than an attraction to the economic growth of the city as a whole. The leapfrog type of development also induces a wasteful use of land and other resources and further increases the living costs of the city's people and the operation costs of its firms.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2475-03
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2015
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  • 7
    Online Resource
    Online Resource
    Thermally Induced Water Flux in Soils
    SAGE Publications ; 2013
    In:  Transportation Research Record: Journal of the Transportation Research Board Vol. 2349, No. 1 ( 2013-01), p. 63-71
    Details
    In: Transportation Research Record: Journal of the Transportation Research Board, SAGE Publications, Vol. 2349, No. 1 ( 2013-01), p. 63-71
    Abstract: A comprehensive study is presented for the formulation of thermally induced water flux. For conditions without ice lenses, either frozen or unfrozen conditions, a theory is proposed to address the underestimation of water flux by the model of Philip and de Vries. In addition, experiments with a modified capillary rise method are proposed to calculate a gain factor that accounts for this underestimation. For thermally induced flux in frozen soils with ice lenses, a theoretical formulation is derived for the segregation potential, which is the key parameter in the model of Konrad and Morgenstern. This theoretical formulation, which is lacking in previous research, is expressed in a simple mathematical form and can be conveniently used for accurate prediction of segregation potential. The validity of the theory is proved with reported data, and more auxiliary relationships are provided for accurately predicting the segregation potential with the proposed formulation.
    Type of Medium: Online Resource
    ISSN: 0361-1981 , 2169-4052
    URL: Article
    DOI: 10.3141/2349-08
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2013
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