轨枕间距对钢轨波磨的影响

主要研究轨枕间距对钢轨波磨发展的影响。研究小半径曲线内轨的小矢跨比波磨。这些出现问题的曲线段属于西班牙毕尔巴鄂区域的地铁轨道,铺设着混凝土道床和两层STEDEF型支承垫层。当初始轨枕间距为1000mm时,仅有92万组轮对通过后所测得的波磨深度峰-峰值已经达到0.42mm。随后更换产生波磨的钢轨,比较列车通过时轨枕上方和轨间中部的内轨垂向、横向加速度。当轨枕间距为1000mm时,轨间中部出现频率为204和244Hz的强烈响应,在轨枕上方却未出现。在相邻轨枕中间铺设一个轨枕,使轨枕间距变为500mm,钢轨波磨停止发展。该结论是根据2年的观测结果得到的。     

Effects of bulbous bow on cross-flow vortex structures around a streamlined submersible body at intermediate pitch maneuver: A numerical investigation

A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found.     

Transit service quality analysis using cluster analysis and decision trees: a step forward to personalized marketing in public transportation

A transit service quality study based on cluster analysis was performed to extract detailed customer profiles sharing similar appraisals concerning the service. This approach made it possible to detect specific requirements and needs regarding the quality of service and to personalize the marketing strategy. Data from various customer satisfaction surveys conducted by the Transport Consortium of Granada (Spain) were analyzed to distinguish these groups; a decision tree methodology was used to identify the most important service quality attributes influencing passengers’ overall evaluations. Cluster analysis identified four groups of passengers. Comparisons using decision trees among the overall sample of all users and the different groups of passengers identified by cluster analysis led to the discovery of differences in the key attributes encompassed by perceived quality.     

The Increasing Role of Latent Variables in Modelling Bicycle Mode Choice

The growing interest in promoting non-motorised active transport has led to an increase in the number of studies to identify the key variables associated with bicycle use, and especially those related to the bicycle mode choice problem. This paper presents a comprehensive survey of the modelling literature on the choice of the bicycle for utilitarian purposes, and summarises and assesses the evolution of the explanatory variables and methodologies used. We review both the evolution of the incorporation of latent variables in bicycle mode choice models and the critical role they play. The chronological evolution of the studies is divided into three stages —initial, intermediate and late — according to the different ways of introducing attitudinal or perceptual indicators and latent variables into the models. Our review shows that the incorporation of latent variables in bicycle choice models has increased in the last decade, with a progressive use of more sophisticated methodologies until the arrival of complex models that explicitly and properly deal with psychological latent variables. In fact, with the use of hybrid choice models, latent variables have nowadays become the core of bicycle mode choice models. Based on our review, a set of questions is proposed as a uniform measurement scale to identify attitudes towards bicycling. Recommendations for future research are also presented.     

Modelling bicycle use intention: the role of perceptions

Users’ perceptions are identified as key elements to understand bicycle use, whose election cannot be explained with usual mobility variables and socio-economic characteristics. A hybrid model is proposed to model the intention of bicycle use; it combines a structural equations model that captures intentions and a choice model. The framework is applied to a case of a university campus in Madrid that is studying a new internal bike system. Results show that four latent variables (convenience, pro-bike, physical determinants and external restrictions) help explaining intention to use bike, representing a number of factors that are linked to individual perceptions.     

Forecasting vs. observed outturn: Studying choice in faster inter-island connections

Passenger demand and, in particular, mode choice between the islands of Gran Canaria and Tenerife has experienced important changes in the last decade. In 2005 the jetfoil, which had been the dominant mode for many years, was replaced by a slower but cheaper fast ferry service. This induced important changes in the market shares of all competing modes (airplane, slow ferry and another fast ferry with a shorter in-sea time, but needing a bus connection in land). We estimated several discrete choice models, with data collected two years before, with the aim to test their forecasting performance in relation with observed behaviour. Interestingly, we found that an easy to interpret multinomial logit model allowing for systematic taste variations performed best in forecasting. We also discuss some model assumptions related to forecasting that allow replicating the effects of introducing a new mode more accurately. We finally show how the model can be used to examine the social benefits of a related infrastructure improvement project in the island of Gran Canaria.     

A joint time-assignment and expenditure-allocation model: value of leisure and value of time assigned to travel for specific population segments

Transportation - Based on a time-use model with a sound theoretical basis and carefully collected data for Austria, the value of leisure (VoL) for different population segments has been estimated....     

Using best–worst scaling to identify barriers to walkability: a study of Porto Alegre,Brazil

This paper pursues three goals: (1) determining the relative importance of built environment barriers limiting walkability, (2) analyzing the existence of an asymmetry in the way people evaluate positive and negative built environment characteristics, and (3) identifying solutions to tackle the main barriers and quantify their impact in walkability. A best–worst scaling survey was developed to compare the importance of eight different attributes of the built environment regarding walkability. Model results show an asymmetry negative–positive in the judgment and choice of built environment characteristics that promote and impede walkability. The most important barriers, obtained from worst responses, are connectivity, topography, sidewalk surface and absence of policemen. Walkability scores were computed for different neighbourhoods and different policy scenarios were forecasted. Simulation results from the worst responses indicate that improvements in sidewalk quality, along with an increase in the number of police officers, lead to an 85% increase in the walkability score for the lower income neighbourhoods.

     

Traffic congestion and economic context: changes of spatiotemporal patterns of traffic travel times during crisis and post-crisis periods

Transportation - This paper aims to evaluate the impacts of the economic context on traffic congestion and its consequential effects on private vehicle accessibility. We conduct a long-term...     

Port competition in Latin America and the Caribbean: the role of concessions and competition policy

Appropriate port regulation and competitive forces tend to be related to higher levels of operational and economic performance of ports. From a policy-making perspective, pursuing efficiency and securing competition in ports to reach a level playing field is a two-step process requiring (1) ex-ante regulations to set the rules that maximize the competition for the market, especially when the policy objective is to attract private operations to ports on competitive concession processes and (2) ex-post competition policy to monitor and preserve competition in the market. This paper studies port regulation in Latin America and the Caribbean (LAC) from a competition perspective, analyzing both ex-ante and ex-post policies implemented in the region. The analysis reveals that the competitive environment in LAC is low, giving room for possible anticompetitive practices in the LAC port sector. Since the end of the 1990s, approximately 80% of container terminals in the region were granted to only five companies. Chile and Mexico have been found to be the best practices in the region, with better conditions assuring robust competition in the market. The main policy implication from this analysis is the need for a stronger involvement of antitrust agencies throughout the port concession processes.