998 resultados para Railroad transportation


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Mode of access: Internet.

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This paper describes the formalization and application of a methodology to evaluate the safety benefit of countermeasures in the face of uncertainty. To illustrate the methodology, 18 countermeasures for improving safety of at grade railroad crossings (AGRXs) in the Republic of Korea are considered. Akin to “stated preference” methods in travel survey research, the methodology applies random selection and laws of large numbers to derive accident modification factor (AMF) densities from expert opinions. In a full Bayesian analysis framework, the collective opinions in the form of AMF densities (data likelihood) are combined with prior knowledge (AMF density priors) for the 18 countermeasures to obtain ‘best’ estimates of AMFs (AMF posterior credible intervals). The countermeasures are then compared and recommended based on the largest safety returns with minimum risk (uncertainty). To the author's knowledge the complete methodology is new and has not previously been applied or reported in the literature. The results demonstrate that the methodology is able to discern anticipated safety benefit differences across candidate countermeasures. For the 18 at grade railroad crossings considered in this analysis, it was found that the top three performing countermeasures for reducing crashes are in-vehicle warning systems, obstacle detection systems, and constant warning time systems.

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New knowledge has raised a concern about the cost-ineffective design methods and the true performance of railroad prestressed concrete ties. Because of previous knowledge deficiencies, railway civil and track engineers have been aware of the conservative design methods for structural components in any railway track that rely on allowable stresses and material strength reductions. In particular, railway sleeper (or railroad tie) is an important component of railway tracks and is commonly made of prestressed concrete. The existing code for designing such components makes use of the permissible stress design concept, whereas the fiber stresses over cross sections at initial and final stages are limited by some empirical values. It is believed that the concrete ties complying with the permissible stress concept possess unduly untapped fracture toughness, based on a number of proven experiments and field data. Collaborative research run by the Australian Cooperative Research Centre for Railway Engineering and Technologies (Rail CRC) was initiated to ascertain the reserved capacity of Australian railway prestressed concrete ties that were designed using the existing design code. The findings have led to the development of a new limit-states design concept. This paper highlights the conventional and the new limit-states design philosophies and their implication to both the railway community and the public. © 2011 American Society of Civil Engineers.

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Railroad corridors contain large number of Insulated Rail Joints (IRJs) that act as safety critical elements in the circuitries of the signaling and broken rail identification systems. IRJs are regarded as sources of excitation for the passage of loaded wheels leading to high impact forces; these forces in turn cause dips, cross levels and twists to the railroad geometry in close proximity to the sections containing the IRJs in addition to the local damages to the railhead of the IRJs. Therefore, a systematic monitoring of the IRJs in railroad is prudent to mitigate potential risk of their sudden failure (e.g., broken tie plates) under the traffic. This paper presents a simple method of periodic recording of images using time-lapse photography and total station surveying measurements to understand the ongoing deterioration of the IRJs and their surroundings. Over a 500 day period, data were collected to examine the trends in narrowing of the joint gap due to plastic deformation the railhead edges and the dips, cross levels and twists caused to the railroad geometry due to the settlement of ties (sleepers) around the IRJs. The results reflect that the average progressive settlement beneath the IRJs is larger than that under the continuously welded rail, which leads to excessive deviation of railroad profile, cross levels and twists.

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The chemical industry has to face safety problems linked to the hazards of chemicals and the risks posed by the plants where they are handled. However, their transport may cause significant risk values too: it’s not totally possible to avoid the occurrence of accidents. This work is focused on the emergency response to railway accidents involving hazardous materials, that is what has to be done once they happen to limit their consequences. A first effort has been devoted to understand the role given to this theme within legislations: it has been found out that often it’s not even taken into account. Exceptionally a few countries adopt guidelines suggesting how to plan the response, who is appointed to intervene and which actions should be taken first. An investigation has been made to define the tools available for the responders, with attention on the availability of chemical-specific safety distances. It has emerged that the ERG book adopted by some American countries has suggestions and the Belgian legislation too establishes criteria to evaluate these distances. An analysis has been conducted then on the most recent accidents occurred worldwide, to understand how the response was performed and which safety distances were adopted. These values were compared with the numbers reported by the ERG book and the results of two devoted software tools for consequence analysis of accidental spills scenarios. This comparison has shown that there are differences between them and that a more standardized approach is necessary. This is why further developments of the topic should focus on promoting uniform procedures for emergency response planning and on a worldwide adoption of a guidebook with suggestions about actions to reduce consequences and about safety distances, determined following finer researches. For this aim, the development of a detailed database of hazardous materials transportation accidents could be useful.