Ana Rivas

Matrix Tools for General Observability Analysis in Traffic Networks

We deal with the problem of observability of a given subset V1 of flows in terms of another subset V2, no matter which type of flows [link, origin-destination (OD), route, node, plate scanned, etc.] they contain or whether they are mixed types. Two problems are stated: The first consists of determining which subsets of flows in V1 can be calculated in terms of the observed flows V2. The second consists of determining which subset of flows V2 needs to be observed to calculate a given subset V1. A theorem providing necessary and sufficient conditions for observability is provided and used in the proposed methods to solve the two problems. Two theorems, one lemma, and one corollary provide the bases for optimizing the numerical procedures to solve these problems. Some examples of applications are used to illustrate the proposed methods.

Optimal Use of Plate-Scanning Resources for Route Flow Estimation in Traffic Networks

This paper discusses the problem of optimizing the use of scanning resources for route flow estimation in traffic networks. Three problems are considered: (1) Minimize the number of cameras to be used for estimating a given subset of route flows; (2) identify the subsets of links to be scanned for a given number of available cameras, assuming that several runs can be done; and (3) solve the previous problems with consideration of scanning errors and error recovery. In addition to the main objective, which consists of minimizing the number of cameras, minimizing the total number of links to be scanned in all runs and maximizing the number of determined route flows are also considered as secondary and tertiary objectives, respectively. A simple and a medium-size real network are used to illustrate the proposed methods and prove the feasibility of the proposed methodology.

A Markovian-Bayesian Network for Risk Analysis of High Speed and Conventional Railway Lines Integrating Human Errors

The article provides a new Markovian-Bayesian network model to evaluate the probability of accident associated with the circulation of trains along a given high speed or conventional railway line with special consideration to human error. This probability increases as trains pass throughout the different elements encountered along the line. A Bayesian network, made up of a sequence of several connected Bayesian subnetworks, is used. A subnetwork is associated with each element in the line that implies a concentrated risk of accident or produces a change in the drivers attention, such as signals, tunnel, or viaduct entries or exits, etc. Bayesian subnetworks are also used to reproduce segments without signals where some elements add continuous risks, such as rolling stock failures, falling materials, slope slides in cuttings and embankments, etc. All subnetworks are connected with the previous one and some of them are multi-connected because some consequences are dependent on previous errors. Because drivers attention plays a crucial role, its degradation with driving time and the changes due to seeing light signals or receiving acoustic signals is taken into consideration. The model updates the drivers attention level and accumulates the probability of accident associated with the different elements encountered along the line. This permits us to generate a continuously increasing risk graph that includes continuous and sudden changes indicating where the main risks appear and whether or not an action must be taken by the infrastructure manager. Sensitivity analysis allows the relevant and irrelevant parameters to be identified avoiding wastes of time and money by concentrating safety improvement actions only on the relevant ones. Finally, some examples are used to illustrate the model. In particular, the case of the Orense-Santiago de Compostela line, where a terrible accident took place in 2013.

Alta velocidad ferroviaria e integración metropolitana en España: el caso de Ciudad Real y Puertollano

Ciudad Real and Puertollano, two small Spanish cities approximately one hour’s travelling time from Madrid on the Madrid-Sevilla High Speed Train (HST) line, are of particular interest in the study of the impact of HSTs on such centres of population. Both cities had been separated from the main transportation corridor between Madrid and Andalusia since the end of the 18 th Century and, at the end of 1992, the HST line reintegrated them into this corridor. That same year the Autopista de Andalucia (Andalusia Freeway), whose route runs some 50 kilometres to the east of Ciudad Real and Puertollano, entered into service. The current article has three basic objectives. The first one is to determine the most appropriate type of methodology to analyse the effect produced by an HST ten years after its inception. The second is to describe the observed changes in the mobility patterns of the inhabitants of Ciudad Real and Puertollano. The article concentrates on the employment profile and the frequency of use of those who habitually travel on the HST to and from Madrid. Thirdly, the article analyses the role the HST has played firstly in integrating the two cities with each other, and secondly in integrating both with the metropolitan area of Madrid. It then analyses the distinct effects of each of the two transport routes (freeway and HST) on each of the two cities, paying attention to their economic peculiarities (Ciudad Real being a tertiary city and Puertollano being an industrial one).

Deriving the Upper Bound of the Number of Sensors Required to Know All Link Flows in a Traffic Network

It is demonstrated that the minimum number of sensors required to know all link flows in a traffic network can be determined only if path information is available. However, not all paths need to be enumerated but, at most, a small subset defining the rank rw of the link-path incidence matrix W. If this rank for a reduced subset of paths is already m - n, where m and n are the number of links and noncentroid nodes, respectively, we can conclude that m - n sensors are sufficient. It is also shown that the formulas providing the dependent link flows in terms of the independent link flows can be obtained by the node-based or path-based approaches with the same results only when rw = m - n. Finally, an algorithm to obtain the small subsets of linearly independent path vectors is given. The methods are shown by a parallel network example and the Ciudad Real and Cuenca networks, for which the savings in link counts with respect to the m - n bound are larger than 16%. The corresponding savings in path enumeration are larger than 80%.

An Alternate Double–Single Track Proposal for High‐Speed Peripheral Railway Lines

Alternate double-single track (ADST) lines are presented as an alternative to double-track lines in this article. The Palencia–Santander line is used to explain the proposal and some suggestions for using the ADST lines in several countries are presented. A linear programming program is given that is used to decide the optimal sequence of single and double tracks and also to optimize the timetables for the best or other alternative sequence. The idea consists of using single track where the infrastructure is very expensive (tunnels and viaducts) and double track where it is cheaper (smooth orography). This, combined with other small changes in departure times so that trains may cross in the double-track segments will normally result in no travel time reductions. The solution is shown to be very efficient for traffic demands between 30 and 40 trains per day and costs are reduced by about 40%.

Observability of traffic networks. Optimal location of counting and scanning devices

In this paper, we deal with the observability problem in traffic networks and the optimal location of counting and scanning devices. After explaining what we mean by observability, the problems of what to observe, how to observe traffic data and how to incorporate prior or obsolete information together with the cases of genuine and pseudo-samples of flow data are discussed. Plate scanning information is dealt with and the flow amount of information measure of information corresponding to a subset of scanned links is analysed. Some pivoting and matrix techniques are given for solving the most common problems of observability of traffic flows in a network. Finally, the problem of optimal location of counters and plate scanning cameras is analysed and several examples are given.

Vertical Track Stiffness as a New Parameter Involved in Designing High-Speed Railway Infrastructure

The criteria currently employed for the design of railway infrastructure on ballasted track are based on the elements of the superstructure, traffic, and bearing capacity of the subgrade. In high-speed railway, the elements of the superstructure are relatively well defined because they are based on existing experience. The category of traffic is a variable that has an influence from the point of view of the number of axles, weight per axle, and speed; i.e., it is determined a priori, depending on the operating characteristics of the line in question. The third and last point refers to the quality of the subgrade that is based on the values of the California bearing ratio test. The quality of the subgrade has a considerable influence on the behavior of the track that manifests itself in the value the deformation and settlement takes, which is caused to the rail on the passage of traffic. This is attributable to the relationship between the vertical track stiffness and the quality of the subgrade. In turn, ...

A percentile system optimization approach with and without path enumeration

In this paper we deal with the travel time reliability PUE (probabilistic user equilibrium) problem studied by Lo et al. (2006) 12] and Nie (2011) 15] and we propose an alternative model that assumes a location-scale family for the path travel times, whose means and variances are evaluated in terms of link travel times. This avoids the use of the central limit theorem and convolutions providing a flexible and simple alternative. Contrary to the most existing models that require path enumeration or an iterative method to add paths sequentially, we present a percentile system optimization in its two versions: with and without path enumeration. Two examples of applications, one of them real, are used to illustrate the power of the proposed method. The cpu times required to solve the problem seem reasonable. In addition, we answer an open question raised by Nie (2011) 15] about the permutability of percentiles and partial derivatives of route travel times with respect to route flows. A family of counterexamples is given to demonstrate that the two operations: (a) obtain percentiles and (b) partial derivation of route travel times do not commute. Finally, to reproduce the trial-and-error sequence followed by users when selecting paths, we also present an algorithm that simulates this iterative process and shows that the final long-term user behavior coincides with PUE (probabilistic user equilibrium) problem resulting from some existing models.

Improving Civil Engineering Education: Transportation Geotechnics Taught through Project-Based Learning Methodologies

Previous studies have found that nontechnical skills, like, for example, communication, team work, and solving open-ended problems, are abilities that civil engineers must possess to perform their professional duties. However, the traditional teacher-centered methods employed in civil engineering schools do not encourage students to develop these skills. To address this concern, the educational program at the School of Civil Engineering of Ciudad Real in Spain was designed using a project-based learning methodology, which produced satisfactory results. Recently, to meet new requirements coming from the higher education European degrees, this program modified its curriculum. To further improve the program, the Transportation Infrastructure course, which was previously taught using traditional methods, was redesigned within a project-based learning framework and was renamed Transportation Geotechnics and Pavement Engineering. Because the school is still transitioning from the old program to the new program, a survey was conducted to compare and discuss the opinions of two groups of students who completed these subjects during the 2012–2013 academic year. The results of both the survey and the final marks of the respective groups illustrate better performance of project-Based learning methodologies compared with traditional teaching techniques.