Approximations to the magic formula

Pacejka’s tire model is widely used and well-known by the automotive engineering community. The magic formula describes the brake force, side force and self-aligning torque in terms of the longitudinal slip and slip angle, plus several corrections. This paper uses approximation theory to obtain different types of approximations to the magic formula: rational functions (RA) resulting from the Remez algorithm, expansions in a series of Chebyshev polynomials (ACh), a series of Chebyshev rational polynomials (ARChPs), a series of rational orthogonal functions (ORF) and a series of ARChPs that result from grade-1 ORFs. The last expansion shows the fastest convergence and most effective computation. Jacobi rational polynomials can also be obtained to complement this expansion and facilitate fine-tuning in specific areas of the error curve. This work is complemented by obtaining the original rational approximations to the inverse tangent function, which take advantage of the curve symmetry to reduce the computation load and provide models that include the influence of the vertical load. The convergence properties of the development in series and the error values resulting from numeric examples for the three types of stress are shown. The proposed final ARChP expressions show very low error (1%) compared to the original magic formula. They can be computed 20 times faster; they can be evaluated, derived and integrated analytically easily; and their coefficients can be obtained from tests using common least-squares algorithms.     

Robust lane markings detection and road geometry computation

Detection of lane markings based on a camera sensor can be a low-cost solution to lane departure and curve-over-speed warnings. A number of methods and implementations have been reported in the literature. However, reliable detection is still an issue because of cast shadows, worn and occluded markings, variable ambient lighting conditions, for example. We focus on increasing detection reliability in two ways. First, we employed an image feature other than the commonly used edges: ridges, which we claim addresses this problem better. Second, we adapted RANSAC, a generic robust estimation method, to fit a parametric model of a pair of lane lines to the image features, based on both ridgeness and ridge orientation. In addition, the model was fitted for the left and right lane lines simultaneously to enforce a consistent result. Four measures of interest for driver assistance applications were directly computed from the fitted parametric model at each frame: lane width, lane curvature, and vehicle yaw angle and lateral offset with regard the lane medial axis. We qualitatively assessed our method in video sequences captured on several road types and under very different lighting conditions. We also quantitatively assessed it on synthetic but realistic video sequences for which road geometry and vehicle trajectory ground truth are known.     

A multi-criteria decision method for the analysis of the Motorways of the Sea: the application to the case of France and Spain on the Atlantic Coast

Despite European Union (EU) political support to identify the most feasible Motorways of the Sea, the final decision can only be made by Private Shipping Companies, which are operators of a unique stretch of the intermodal chain. This paper provides a multi-criteria decision method to identify the most suitable Motorways of the Sea taking into account the competitiveness of whole intermodal routes versus the alternative of road transport from the loader’s perspective. The analysis is carried out assuming a ‘many-to-many’ transport model. Firstly indexes of time and cost were defined and evaluated for every available route in the model in accordance with a multi-criteria decision matrix. Secondly, through a Monte Carlo simulation a sensitivity analysis was carried out in order to evaluate the influence on the results of the forecast assumed to construct the matrix. The results obtained are not only quantitative, but also qualitative. The development of intermodal routes via Motorways of the Sea is especially relevant for the peripheral EU countries. Due to the relevance of the freight flow between France and Spain and the congestion of their connections through the Pyrenees, the method proposed was applied to the analysis of this particular case     

Incentives in Bus Concession Contracts: A Review of Several Experiences in Latin America

Abstract

This paper reviews the incentive structure of concession contracts in several Latin American transit reforms. It also presents a conceptual analysis of the optimal design of concession contracts. The conceptual discussion and case studies reviewed indicate that payment to operators should be linked to operational variables and that some demand risk should optimally be transferred to operators. Performance standards linked to fines and penalties are not sufficient to guarantee good quality of service, particularly in citywide reforms and where institutional capacity ― in terms of size, experience and expertise of staff ― is lacking and regulatory processes are slow, bureaucratic and cumbersome. This review may be useful for policy-makers designing transit reforms in other countries. The policy lessons of the paper are particularly relevant to cities in the developing world but they are also important for reforms in other countries.     

A proposal for cost-related and market-oriented train running charges

This paper examines some key aspects of a charging system for promoting railway transport, including charges reflecting a clear relationship with costs (transparency) and charges reflecting the quality of the infrastructure manager's service. Train running charges recover track-related costs and can help to develop a charging system that meets these requirements. To orient train running charges to the market, a method for processing track maintenance and renewal costs is proposed whereby the quality of the service provided by an infrastructure is measured according to its utility to the railway undertaking. To achieve transparency, a single indicator is used for cost planning and the subsequent levying of costs on railway undertakings. The paper includes an example of how proposed train running charges would be calculated according to data from 14 European countries. The example shows that short-distance trains generate the lowest maintenance and renewal costs, followed by long-distance trains and freight trains.     

Benthic megafauna communities under the influence of the South Atlantic Central Water intrusion onto the Brazilian SE shelf: A comparison between an upwelling and a non-upwelling ecosystem

The structure and dynamics of the benthic invertebrate megafauna of the Southeastern Brazilian shelf were studied over a 2-year period. Two regions presenting different oceanographic conditions, Ubatuba-SP and Cabo Frio-RJ were compared in terms of biomass, density of organisms and species richness. Two to three 30-min tows were undertaken at each of the stations, located at 40 and 100 m isobath, in a normal transect offshore of both regions. Faunal distributional patterns correlated with water mass dynamics, depth and sediment parameters. In the Cabo Frio region, subjected to a Ekman-driven seasonal coastal upwelling, the impact of the South Atlantic Central Water (SACW) on the inner shelf leads to a change in the benthic communities, with a high dominance of top carnivores such as the crab Portunus spinicarpus and the sea-star Astropecten brasiliensis, which accounted for the larger part of the total biomass. Distinct species associations were found in each of the two regions and the total biomass at Cabo Frio inner shelf was almost twice that of Ubatuba during the 2002 summer, when a marked upwelling was verified. The relationship between megabenthic biomass and input of organic matter to the sea floor during upwelling events is discussed.     

Safety Management Evaluation in Bus and Coach Companies

Abstract

In recent years, different initiatives have been carried out to develop Safety Management System guides or standards for coach and bus companies. They all consist of a set of safety and management requirements to be followed by organizations. However, none of them offers a complete set of tools to evaluate the safety level of the company and find the main weak points in order to improve them. The INSIA (Automotive Research Institute of Madrid, Spain) has developed a complete model that includes not only a set of elements that determine the safety level of the company but also a set of indicators and criteria to evaluate these elements by a team of auditors. The model allows companies to measure their safety level, find the weakest points and propose improvement actions.     

A fractional perspective to the modelling of Lisbon’s public transportation network

Transportation - Urban growth originates multiscale spatial patterns, such as those of transportation networks. Here, the public transportation network (PTN) of the city of Lisbon is analysed from...     

A velocity and payload dependent emission model for heavy-duty road freight transportation

The paper develops a forecasting model of emissions from traffic flows embracing the dynamics of driving behavior due to variations in payload. To measure of emissions at the level of individual vehicles under varying payloads a portable emission measurement system is used. This paper reports on a model based on data at the level of individual vehicles for a representative road trajectory. The model aggregates the data to the level of a homogeneous flow dependent of velocity and specific power, which is dependent on payload weight. We find a lean specification for the model that provides emission factors for CO₂, NO_x, HC, CO, and NO₂. The results indicate that, in comparison with earlier models, NO_x emissions in particular tend to be underestimated.     

Assessment of Vulnerability and Integrated Management of Coastal Dunes in Veracruz,Mexico

Dune systems are essential to the ecological balance and sediment inputs of coastal environments and they provide numerous environmental services; however, their existence is threatened by natural and human stressors that contribute to their degradation. Future impacts are expected to be greater because of global climate change in association with further rises in sea level. Beaches and dune systems occupy large areas along the coastline of the state of Veracruz on the Gulf of Mexico. The aim of this study is to establish the intrinsic vulnerability of nine dune fields in Veracruz to current and future impacts and to assess their integrated management status. These dune–beach systems are more vulnerable to the effects of economic activities and land use change than to those induced by natural forces. Results show that six of these dune systems have medium vulnerability and an ecological conservation policy should be adopted; the other three, with high or very high vulnerability, are candidates for a restoration policy.