Exploring ride-hailing fares: an empirical analysis of the case of Madrid

Transportation - Ride-hailing is an emerging service that is transforming door to door mobility in urban areas. Users can easily request a ride through a smartphone app that informs them of the...     

The influence of variable message signs on en-route diversion between a toll highway and a free competing alternative

Transportation - In the field of road transport, Advanced Traveller Information Systems represent a relevant tool to manage road traffic, improve drivers’ utility and make a more efficient...     

Bayesian kriging regression for the accuracy improvement of beam modeled T-junctions of buses and coaches structures with a methodology based on FEM behavioral analysis

This paper has been developed in the framework of the alternative beam T-junction solution previously propoused by the authors (Alcalá et al., 2013), with the scope of optimizing the behavior of buses and coaches upper structures modeled with beam type elements. The alternative beam T-junction model proposed by the authors, had a total of six elastic elements at the junction level allowing to modify the localized rigidity of any modeled T-junctions, therefore improving their behavior and avoiding the well known rigidity issue these elements have. A fundamental aspect behind the use of these alternative beam models is related to the necessity of correctly estimating the rigidity values of the elastic elements for each modeled T-junction. In this context, we propose applying a surrogate model for the reference calculations which is based on statistical Bayesian kriging predictors. Statistical predictions have the added value, with respect to deterministic solutions, of providing a quantification of uncertainty. The development of the kriging predictors has required the application of a statistical methodology including computer experiment design, computation of moments of inertia, graphical and ANOVA type sensitivity analysis and Monte Carlo computation of Bayesian inference. The results of the application have been a very satisfactory trade-off between accuracy of approximation (prediction) and computational cost. The surrogate kriging models also provide an useful tool for a better understanding of the input-output relationships involved in the reference computations.     

Late Holocene history of the rainfall in the NW Iberian peninsula—Evidence from a marine record

This study reconstructs climatic variability over the last 4700 yr in the NW Iberian Peninsula on the basis of lithological, sedimentological, biogeochemical, micropaleontological (diatoms and biosiliceous compounds) and AMS ¹⁴C analyses conducted in a gravity core retrieved from the Galician continental shelf. The core was recovered at the Galicia Mud Patch, a muddy sedimentary body highly influenced by the terrestrial supply of the Miño and Douro rivers, and thus controlled by the rainfall variations over the catchment area. River plume transports the lithogenic and continental-derived compounds to the shelf area allowing us to recognize several periods of terrestrial/marine influence. These periods are well correlated with the lithological units identified. Coarser sediments, high values of Ca/Al, low values of Fe, Al and lithogenic Si (LSi) are representative of the marine-influenced periods. These stages are related to dry conditions and winds coming from the NE under a NAO positive-like phase.Terrestrial-influenced stages are characterized by muddy sediments, with high content of Fe, Al and LSi, freshwater and benthic diatoms, continental-derived organisms (crysophycean cysts and phytoliths) and high amount of land-derived organic matter as reported by the C/N ratios. The influence of NAO positive- and NAO negative-like periods and solar activity are the two mechanisms quoted to explain the climatic variability during the last 4700 years.Proxies for the lithogenic input and terrigenous content (non-organic material) show an increase at around 2000–1800 cal. yr BP, linked to the warmer conditions and high precipitation patterns during the Roman Warm Period, and soil erosion due to forest degradation and other anthropic activities. A strong river flow event is recorded in shelf sediments during 800–500 cal. yr BP. A pervasive NAO negative-like period, and the high irradiance registered during the Grand Solar Maximum (GSM) controlled the precipitation and induced a high run-off and riverine influx during this event.     

Inferring origin–destination trip matrices from aggregate volumes on groups of links: a case study using volumes inferred from mobile phone data

The origin–destination matrix is an important source of information describing transport demand in a region. Most commonly used methods for matrix estimation use link volumes collected on a subset of links in order to update an existing matrix. Traditional volume data collection methods have significant shortcomings because of the high costs involved and the fact that detectors only provide status information at specified locations in the network. Better matrix estimates can be obtained when information is available about the overall distribution of traffic through time and space. Other existing technologies are not used in matrix estimation methods because they collect volume data aggregated on groups of links, rather than on single links. That is the case of mobile systems. Mobile phones sometimes cannot provide location accuracy for estimating flows on single links but do so on groups of links; in contrast, data can be acquired over a wider coverage without additional costs. This paper presents a methodology adapted to the concept of volume aggregated on groups of links in order to use any available volume data source in traditional matrix estimation methodologies. To calculate volume data, we have used a model that has had promising results in transforming phone call data into traffic movement data. The proposed methodology using vehicle volumes obtained by such a model is applied over a large real network as a case study. The experimental results reveal the efficiency and consistency of the solution proposed, making the alternative attractive for practical applications. Copyright © 2011 John Wiley & Sons, Ltd.     

A simulation tool for bicycle sharing systems in multimodal networks

This paper presents a methodology for modelling an urban transport system, integrating public bicycles in a multi-modal network. A bike cost function that reproduces the effect of slopes on cycling speeds is proposed. Also, the effect of traffic levels on the attractiveness of cycling routes is taken into account. The model applies the modal split and network assignment phases in a multimodal network with different classes of users. It has been verified over a test network and then validated by applying it to a real case in the city of Santander in Spain. The results obtained make this model a useful decision-making tool to encourage the use of the public bicycle from a sustainable development point of view.     

Research on the Brayton cycle design conditions for reliquefaction cooling of LNG boil off

This paper analyses the Brayton cooling cycle for the reliquefaction of the boil off on liquefied natural gas (LNG) vessels. By performing a thermodynamic study, we analysed and evaluated the conditions, parameters and energy consumption required in the process, including the influence of the choice and variation of diverse factors on the operating conditions and power.     

Estimating traffic volumes on intercity road locations using roadway attributes,socioeconomic features and other work-related activity characteristics

Traffic volume data are key inputs to many applications in highway design and planning. But these data are collected in only a limited number of road locations due to the cost involved. This paper presents an approach for estimating daily and hourly traffic volumes on intercity road locations combining clustering and regression modelling techniques. With the aim of applying the procedure to any road location, it proposes the use of roadway attributes and socioeconomic characteristics of nearby cities as explanatory variables, together with a set of previously discovered patterns with the hourly traffic percent distribution. Test results show that the proposed approach significantly produces accurate estimates of daily volumes for most locations. The accuracy at hourly level is a bit more reduced but, for periods when traffic is significant, more than half of the estimates are within 20% of absolute percentage error. Moreover, the main peak period is approximately identified for most cases. These findings together with its great applicability make this approach attractive for planners when no traffic data are available and an estimate is helpful.     

Seasonal productivity dynamics in the pelagic central Benguela System inferred from the flux of carbonate and silicate organisms

Flux of bulk components, carbonate- and silicate-bearing skeleton organisms, and the δ¹⁵N-isotopic signal were investigated on a 1-year time-series sediment trap deployed at the pelagic NU mooring site (Namibia Upwelling, ca. 29°S, 13°E) in the central Benguela System. The flux of bulk components mostly shows bimodal seasonality with major peaks in austral summer and winter, and moderate to low export in austral fall and spring. The calcium carbonate fraction dominates the export of particulates throughout the year, followed by lithogenic and biogenic opal. Planktonic foraminifera and coccolithophorids are major components of the carbonate fraction, while diatoms clearly dominate the biogenic opal fraction. Bulk δ¹⁵N isotopic composition of particulate matter is positively correlated with the total mass flux during summer and fall, while negatively correlated during winter and spring. Seasonal changes in the intensity of the main oceanographic processes affecting the NU site are inferred from variations in bulk component flux, and in the flux and diversity patterns of individual species or group of species. Influence from the Namaqua (Hondeklip) upwelling cell through offshore migration of chlorophyll filaments is stronger in summer, while the winter flux maximum seems to reflect mainly in situ production, with less influence from the coastal and shelf upwelling areas. On a yearly basis, dominant microorganisms correspond well with the flora and fauna of tropical/subtropical waters, with minor contribution of near-shore organisms. The simultaneous occurrence of species with different ecological affinities mirrors the fact that the mooring site was located in a transitional region with large hydrographic variability over short-time intervals.     

Assessment of the influence of different cooling system configurations on engine warm-up, emissions and fuel consumption

One of the major goals of engine designers is the reduction of fuel consumption and pollutant emissions while keeping or even improving engine performance. In recent years, different technical issues have been investigated and incorporated into internal combustion engines in order to fulfill these requirements. Most are related to the combustion process since it is responsible for both fuel consumption and pollutant emissions. Additionally, the most critical operating points for an engine are both the starting and the warming up periods (the time the engine takes to reach its nominal temperature, generally between 80°C and 90°C), since at these points fuel consumption and pollutant emissions are larger than at any other points. Thus, reducing the warm-up period can be crucial to fulfill new demands and regulations. This period depends strongly on the engine cooling system and the different strategies used to control and regulate coolant flow and temperature. In the present work, the influences of different engine cooling system configurations on the warm-up period of a Diesel engine are studied. The first part of the work focuses on the modeling of a baseline engine cooling system and the tests performed to adjust and validate the model. Once the model was validated, different modifications of the engine coolant system were simulated. From the modelled results, the most favourable condition was selected in order to check on the test bench the reduction achieved in engine warm-up time and to quantify the benefits obtained in terms of engine fuel consumption and pollutant emissions under the New European Driving Cycle (NEDC). The results show that one of the selected configurations reduced the warm-up period by approximately 159 s when compared with the baseline configuration. As a consequence, important reductions in fuel consumption and pollutant emissions (HC and CO) were obtained. On doctoral leave from Universidad Technológica de Pereira (Colombia)