Search

This paper presents the results of a laboratory investigation on the performances and mixture combination parameters of railway asphalt concrete (RAC) for supporting high-speed railway slab track. To apply the RAC effectively to high-speed railway infrastructures, modified highway asphalt pavement material tests are conducted to verify mixture parameters. A suitable gradation is recommended based on the test results. The air voids of the material RAC-25 used for railway infrastructure should be controlled from 1 to 3%. The results presented in the paper demonstrate that asphalt content can be determined based on modified mixture parameters. To verify the performance and analyze the mechanistic response of RAC infrastructure, full-scale laboratory dynamic models are established under different environmental temperatures and loading levels. Based on model testing, the reinforced RAC foundation with a 12 cm deep graded gravel layer replaced by RAC-25 shows much better performance compared with the traditional design. [ABSTRACT FROM AUTHOR]

Optimization of wagon flow organization in heavy-haul loading areas is meaningful to develop a heavy-haul railway network and to improve transportation capacity. This paper proposes a multiobjective optimization of the wagon flow organization for heavy-haul railway (MWFHR) to improve the transportation efficiency and the economic performance of a railway network. A bi-level algorithm is constructed to solve this model, where the lower level of the algorithm collects wagon flows for organization through the ant colony optimization algorithm, and the upper level screens for the best solution set that can minimize total cost under various constraints using the traversal search algorithm. The model is numerically examined in a real case study. Comprehensive practical testing results show that the newly proposed multiobjective optimization approach is promising in establishing an efficient railway network. [ABSTRACT FROM AUTHOR]

North American heavy haul railroads are experiencing growth in traffic demand and increases in capacity constraints. An appropriate service-design process is thus crucial to allow for more effective network capacity planning and efficient rail operations. Existing approaches to freight train routing usually ignore the congestion-induced delay and fail to consider the dynamics in link and node delay in response to traffic volume. Furthermore, different train types can have substantially different operating characteristics, including maximum speed, power-to-ton ratio, and dispatching priority. This heterogeneity causes conflicts between trains that can increase delays and reduce capacity. Therefore, traffic volume and heterogeneity should both be incorporated into the decision process for service design. In this research, the authors proposed to add an additional traffic routing process in service design and developed a novel optimization framework to route trains by considering link and node delay, directional traffic, heterogeneity, and various delay costs according to train types. To improve the solution efficiency, a solution algorithm using Lagrangian relaxation (LR) techniques is also presented. Numerical results show that the optimal strategy has the potential to substantially reduce operational costs. Using this tool can help design better traffic routing, more efficient capacity utilization, and reliable services. [ABSTRACT FROM AUTHOR]

Broken rails are the most frequent cause of freight-train derailments in the United States. Consequently, reducing their occurrence is a high priority for the rail industry and the U.S. Federal Railroad Administration. Current practice is to periodically inspect rails to detect defects using nondestructive technology such as ultrasonic inspection. Determining the optimal rail inspection frequency is critical to efficient use of infrastructure management resources and maximizing the beneficial impact on safety. Minimization of derailment risk, costs of inspection vehicle operation, rail defect repair, and corresponding train delay are all affected by rail inspection frequency. However, no prior research has incorporated all of these factors into a single integrated framework. The objective of this paper is to develop an analytical model to address the trade-offs among various factors related to rail defect inspection frequency, so as to maximize railroad safety and efficiency. The analysis shows that the optimal inspection frequency will vary with traffic density, rail age, inspection technology reliability, and other factors. The optimization model provides a tool that can be used to aid development of better-informed, more effective infrastructure management and accident prevention policies and practices. [ABSTRACT FROM AUTHOR]

This paper considers the problem of modeling railway track substructure. The most commonly used methodology for designing the railway substructure cross section does not considerably differ from that proposed in the 1980s. For the bearing capacity of the subgrade, the currently used design methodology implicitly meets one objective: the stresses transmitted to the subgrade must be compatible with its bearing capacity. The bearing capacity depends on the qualities and thicknesses of the soils that compose the subgrade, from the formation layer to the lower layers. In addition, railway administrations have included additional recommendations based on their experience. During the last decade, finite-element models (FEM) have been shown to be a very useful tool for designing cross sections. These models are often very complex and require a very high computational time to be solved. To reduce this complexity and computational time while remaining faithful to the reality to be modeled, this paper proposes some recommendations to develop a parameterized numerical model in three dimensions within the elastic nonlinear range under the static load of a given railway section. To adequately reproduce the real behavior of materials (elastoplastic) and the contact surfaces between very different materials adequately, artifices to use the model in the elastic range are propsed. In addition, the goodness of this design is analyzed using multilayer numerical models. This model may be a very useful tool for analyzing the behavior of different types of railway cross sections. [ABSTRACT FROM AUTHOR]

Railways around the world are experiencing growth in traffic demand and the need to expand their network and line capacity. To accommodate the substantial demand, the conventional railway operator in Taiwan, the Taiwan Railways Administration (TRA), is interested in understanding the potential benefit of adopting various advanced signaling systems, such as hybrid or moving-block systems. In this study, the authors developed a set of analytical capacity models for conventional rail operations with advanced signaling systems, which were implemented in the busiest corridor in the TRA system. The empirical results show that advanced signaling systems generally have positive capacity effects. However, the benefit may not be substantial due to constraints from the station track layouts. Therefore, possible capacity improvement alternatives, such as improving track layouts and upgrading signaling systems, should be considered together to determine the optimal capacity improvement plan. The use of these proposed capacity models can help railway agencies with similar operational environments in their capacity management and resource planning projects. [ABSTRACT FROM AUTHOR]

A realistic assessment of the whole life cost of rail track foundations requires analysis of the effects of the repeated loadings applied by trains. This paper reports the effects of principal stress rotation (PSR) during cyclic loading on the permanent deformations measured in a series of hollow cylinder tests. The tests were carried out on a number of reconstituted soils selected in order to simulate foundation materials on an existing heavy haul railway line. Typical loadings and track geometry together with dynamic finite-element analyses were used to define representative stress changes to be applied to these soils, which were then tested with and without principal stress rotation during loading. It is shown that principal stress rotation has a significant and deleterious impact on permanent deformation of some materials. Therefore, it is concluded that cyclic triaxial testing, which cannot impose principal stress rotation, will not necessarily give good estimates of the long-term performance of rail track foundations. As PSR cannot be ignored when evaluating permanent displacements of rail track foundations, the use of more appropriate (realistic) testing methods such as the cyclic hollow cylinder or the cyclic simple shear apparatus is required. [ABSTRACT FROM AUTHOR]

The need to improve urban transportation systems in order to decrease travel time and increase their reliability while keeping the costs at an affordable level has led governments to develop public-private partnership (PPP) arrangements in urban light rail systems. Many cities around the world have used the PPP model for the construction of urban light rail systems, particularly light rail, since it provides a quicker and easier answer to financing these large investments. However, different models have been adopted. In most cases a typical design-build-operate-transfer model, with long duration (e.g., 30 years), is used, but other innovative models have also been adopted (e.g., a hybrid model with different contracts for infrastructure construction and maintenance-a 20-year contract-and another for the systems operation-a 5-year contract). This paper addresses the advantages and disadvantages of these models, using one case study for each model. The conclusions show that the hybrid model has the potential to decrease the operation costs, but at the same time to mitigate the interface risk (operation <-> infrastructure). [ABSTRACT FROM AUTHOR]