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This study examines the determinants of private car ownership in China. The target cities are 32 provincial capital cities and the target period is from 2001 to 2011. In order to capture the individual effects (heterogeneity), the fixed and random effect models are adopted and compared, in which 8 explanatory variables are selected to include economic characteristics, urban characteristics, and transportation characteristics. Moreover, double natural logarithm model is employed to measure the elastic relationship between the private car ownership and regressors. The estimated results show that the fixed effect model performs better than pooled regression model and the random effect model. In addition, there are variations of private car ownership among cities and regions. Finally, the influence of factors responsible for these variations is also presented and discussed in this paper. 相似文献
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激光焊接钢质夹层结构在国外已用于实船,其连接形式是亟待解决的关键问题之一。基于有限元分析软件ANSYS,研究了面内载荷作用下,I型金属夹层结构外接平板型连接构件的失效模式和极限承载能力,以及5种典型初始缺陷的尺寸和连接构件的设计参数对极限载荷的影响规律。结果显示,连接构件较短时,结构失效的主导因素是焊接接头形成了塑性铰;连接构件较长时,主导因素是连接构件失稳。对于各种类型的初始缺陷,随初始缺陷尺寸的增大,极限载荷均降低;连接构件、以及靠近连接构件的夹层面板和夹层腹板的初始缺陷对极限载荷的影响较大。在控制重量的条件下,欲增大极限承载能力,最有效的途径是增大连接构件厚度,并选取合适的连接构件长度。 相似文献
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This paper investigates the modal shift patterns of e-bike users in the Dutch context. We focus on the change in e-bikers’ travel behavior to assess whether this change benefits sustainability. Our study provides direct ecologically valid evidence on modal shift by using a longitudinal dataset from the Netherlands Mobility Panel survey. We examine e-bikers’ modal shift patterns before and after acquiring an e-bike. The findings indicate that after e-bike adoptions, conventional bike use reduces significantly, while car use reduces less strongly. Nonetheless, the share of car kilometers is much larger than that of conventional bikes at the baseline. Besides, the emission rate per passenger kilometer of an e-bike is several times lower than that of a car. These imply a net environmental gain after e-bike adoptions. The present study also sheds light on modal shifts at a disaggregated level by investigating those e-bikers who are more likely to drive less after e-bike adoption. The findings suggest that e-bikers younger than 50 and those around retirement age (60–69) seem more likely to step out of their cars. Additionally, people living in rural areas tend to be more likely to reduce their car use than their counterparts in highly urbanized areas. Based on our findings, we present policy recommendations for achieving a greener shift in mobility systems. 相似文献
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Chandra R. Bhat Raghuprasad Sidharthan 《Transportation Research Part B: Methodological》2011,45(7):940-953
This paper evaluates the ability of the maximum approximate composite marginal likelihood (MACML) estimation approach to recover parameters from finite samples in mixed cross-sectional and panel multinomial probit models. Comparisons with the maximum simulated likelihood (MSL) estimation approach are also undertaken. The results indicate that the MACML approach recovers parameters much more accurately than the MSL approach in all model structures and covariance specifications. The MACML inference approach also estimates the parameters efficiently, with the asymptotic standard errors being, in general, only a small proportion of the true values. As importantly, the MACML inference approach takes only a very small fraction of the time needed for MSL estimation. In particular, the results suggest that, for the case of five random coefficients, the MACML approach is about 50 times faster than the MSL for the cross-sectional random coefficients case, about 15 times faster than the MSL for the panel inter-individual random coefficients case, and about 350 times or more faster than the MSL for the panel intra- and inter-individual random coefficients case. As the number of alternatives in the unordered-response model increases, one can expect even higher computational efficiency factors for the MACML over the MSL approach. Further, as should be evident in the panel intra- and inter-individual random coefficients case, the MSL is all but practically infeasible when the mixing structure leads to an explosion in the dimensionality of integration in the likelihood function, but these situations are handled with ease in the MACML approach. It is hoped that the MACML procedure will spawn empirical research into rich model specifications within the context of unordered multinomial choice modeling, including autoregressive random coefficients, dynamics in coefficients, space-time effects, and spatial/social interactions. 相似文献
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介绍了一种新型的基于可变信息标志(VMS)的网络级城市快速路交通诱导系统的设计方法。该系统是一个由“重要决策点图形式VMS”、“次要节点图文混合式VMS”、以及“地面一般道路VMS”三类VMS组成的VMS系统。文章在归纳VMS系统设计流程基础上,重点介绍了VMS的路网布局和功能设计、显示格式和显示技术的确定、VMS设立位置(前置距离)的确定、图形式VMS的面板设计和交通信息发布策略等关键技术,最后给出系统的应用实例,说明该新型交通诱导系统的应用效果。可供交通管理部门规划、设计城市快速路网交通诱导系统参考。 相似文献
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通过对以尼龙块为导向的提升架结构计算分析发现,尼龙块和螺栓在受到外力时均产生较大的变形,应力超过其许用值;提出了采用自润滑铜块代替尼龙的方案,同时增大所用螺栓的规格,分析表明自润滑铜块和螺栓的强度及变形均满足要求,现场试验结果与理论分析一致,试验表明自润滑铜块能够确保滑板提升结构使用的可靠性。 相似文献
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基于LabVIEW虚拟仪器软件开发平台,设计了一套汽车空调控制面板按键测试系统。介绍了测试系统的测试原理、硬件组成和软件设计,并针对某型空调面板样件进行了测试试验。结果表明,该测试系统采集的数据完全符合实际运行工况,未出现数据丢失和失真等情况,能够满足汽车空调厂商对汽车空调控制面板按键的测试要求,可为产品抽样检测、优化设计和改进生产过程提供依据。 相似文献
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Most applications of discrete choice models in transportation now utilise a random coefficient specification, such as mixed logit, to represent taste heterogeneity. However, little is known about the ability of these models to capture the heterogeneity in finite samples (as opposed to asymptotically). Also, due to the computational intensity of the standard estimation procedures, several alternative, less demanding methods have been proposed, and yet the relative accuracy of these methods has not been investigated. This is especially true in the context of work looking at joint inter-respondent and intra-respondent variation. This paper presents an overview of the various different estimators, gives insights into some of the theoretical properties, and analyses their performance in a large scale study on simulated data. In particular, we specify 31 different forms of heterogeneity, with multiple versions of each dataset, and with results from over 16,000 mixed logit estimation runs. The findings suggest that variation in tastes over consumers is captured by all the methods, including the simpler versions, at least when sample size is sufficiently large. When tastes vary over choice situations for each consumer, as well as over consumers, the ability of the methods to capture and differentiate the two sources of heterogeneity becomes more tenuous. Only the most computationally intensive approach is able to capture adequately the two sources of variation, but at the cost of very high run times. Our results highlight the difficulty of retrieving taste heterogeneity with only cross-sectional data, providing further evidence of the benefits of repeated choice data. Our findings also suggest that the data requirements of random coefficients models may be more substantial than is commonly assumed, further reinforcing concerns about small sample issues. 相似文献