42 research outputs found
A general approach for the location of transfer points on a network with a trip covering criterion and mixed distances
In this paper we consider a trip covering location model in a mixed planar-network space. An embed- ded network in the plane represents an alternative transportation system in which traveling is fasterthan traveling within the plane. We assume that the demand to be covered is given by a set of origin- destination pairs in the plane, with some traffic between them. An origin-destination pair is covered bytwo facility points on the network (or transfer points), if the travel time from the origin to destinationby using the network through such points is not higher than a given acceptance level related to the traveltime without using the network. The facility location problems studied in this work consist of locatingone or two transfer points on the network such that, under several objective functions, the traffic throughthe network is maximized. Due to the continuous nature of these problems, a general approach is pro- posed for discretizing them. Since the non-convexity of the distance function on cyclic networks alsoimplies the absence of convexity of the mixed distance function, such an approach is based on a decom- position process which leads to a collection of subproblems whose solution set can be found by adaptingthe general strategy to each problem considered.Ministerio de Econom铆a y Competitividad MTM2012-37048Ministerio de Econom铆a y Competitividad MTM2015-67706-PJunta de Andaluc铆a P10-FQM-584
Locating Two Transfer Points on a Network with a Trip Covering Criterion and Mixed Distances
In this paper we consider a set of origin-destination pairs in a mixed model in which a
network embedded in the plane represents an alternative high-speed transportation system,
and study a trip covering problem which consists on locating two points in the network
which maximize the number of covered pairs, that is, the number of pairs which use the
network by acceding and exiting through such points. To deal with the absence of convexity
of this mixed distance function we propose a decomposition method based on formulating
a collection of subproblems and solving each of them via discretization of the solution set.Ministerio de Educaci贸n, Ciencia e Innovaci贸n MTM2009-14243Ministerio de Econom铆a y Competitividad MTM2012-37048Junta de Andaluc铆a P09-TEP-5022Junta de Andaluc铆a P10-FQM-584
Improved results for the k-centrum straight-line location problem
The k-Centrum problem consists in finding a point that minimises the sum of the distances to the k farthest points out of a set of given points. It encloses as particular cases to two of the most known problems in Location Analysis:
the center, also named as the minimum enclosing circle, and the median. In this paper the k-Centrum criteria is applied to obtaining a straight line-shaped facility. A reduced finite dominant set is determined and an algorithm
with lower complexity than the previous one obtained.Ministerio de Ciencia y Tecnolog铆
Optimal Alignments for Designing Urban Transport Systems: Application to Seville
The achievement of some of the Sustainable Development Goals (SDGs) from the recent
2030 Agenda for Sustainable Development has drawn the attention of many countries towards
urban transport networks. Mathematical modeling constitutes an analytical tool for the formal
description of a transportation system whereby it facilitates the introduction of variables and the
definition of objectives to be optimized. One of the stages of the methodology followed in the
design of urban transit systems starts with the determination of corridors to optimize the population
covered by the system whilst taking into account the mobility patterns of potential users and the
time saved when the public network is used instead of private means of transport. Since the capture
of users occurs at stations, it seems reasonable to consider an extensive and homogeneous set of
candidate sites evaluated according to the parameters considered (such as pedestrian population
captured and destination preferences) and to select subsets of stations so that alignments can take
place. The application of optimization procedures that decide the sequence of nodes composing the
alignment can produce zigzagging corridors, which are less appropriate for the design of a single line.
The main aim of this work is to include a new criterion to avoid the zigzag effect when the alignment
is about to be determined. For this purpose, a curvature concept for polygonal lines is introduced,
and its performance is analyzed when criteria of maximizing coverage and minimizing curvature are
combined in the same design algorithm. The results show the application of the mathematical model
presented for a real case in the city of Seville in Spain.Ministerio de Econom铆a y Competitividad MTM2015-67706-
Designing robust rapid transit networks with alternative routes
The aim of this paper is to propose a model for the design of a robust rapid transit network. In this paper, a
network is said to be robust when the effect of disruption on total trip coverage is minimized. The proposed
model is constrained by three different kinds of flow conditions. These constraints will yield a network that
provides several alternative routes for given origin鈥揹estination pairs, therefore increasing robustness. The
paper includes computational experiments which show how the introduction of robustness influences
network design.Uni贸n Europea FP6-021235-2Ministerio de Fomento PT2007-003-08CCPPMinisterio de Educaci贸n y Ciencia TRA2005-09068-C03-01 MTM2006-15054Ministerio de Ciencia e Innovaci贸n TRA2008-06782-C02-01Natural Sciences and Engineering Research Council of Canada 39682-0
The variance location problem on a network with continuously distributed demand
Most location problems on networks consider discrete nodal demand. However, for many problems, demands are better represented by continuous functions along the edges, in addition to nodal demands. Several papers consider the optimal location problem of one or more facilities when demands are continuously distributed along the network, and the objective function dealt with is the median one. Nevertheless, in location of public services it is desirable to use an equity criterion.
One of the latter is variance of distance distribution which has been studied only for discrete nodal demands. In this paper the variance problem has been generalized to the case where one allows the demand to arise discretely on the nodes as well as continuously along the edges. Properties and behaviour of the objective function are studied. Likewise we present an exact algorithm for solving this problem in a network, which reduces the complexity of the exhaustive procedure.Spanish Research Council (DGICYT
Railway traffic disturbance management by means of control strategies applied to operations in the transit system
Railway systems in metropolitan areas support a high density of daily traffic that is exposed to different types of disturbances in the service. An interesting topic in the literature is to obtain action protocols in the presence of contingencies which can affect the system operation, avoiding the propagation of perturbation and minimizing its negative consequences.
Assume that, with a small margin of time (e.g. one day), the decision-maker of the transportation network is knowing that a part of the train fleet will become inoperative temporarily along a specific transit line and none additional vehicle will be able to restore the affected services. The decision to be taken in consequence will require to reschedule the existing services by possibly reducing the number of expeditions (line runs). This will affect travellers who regularly use the transit system to get around. Consider that the decision-maker aims to lose the least number of passengers as a consequence of
having introduced changes into the transit line. A strategy that could be applied in this context is to remove those line runs which are historically less used by travellers without affecting the remaining services. Another alternative strategy might be to reschedule the timetables of the available units, taking into account the pattern of arrivals of users to the boarding stations and the user behavior during waiting times (announced in situ).
The aim of this work consists of assessing the strategy of train rescheduling along the current transportation line when the supply must be reduced in order to reinforce the service of another line, exploited by the same public operator, which has suffered an incidence or emergency.Ministerio de Econom铆a y CompetitividadFondo Europeo de Desarrollo Regiona
A generalized model of equality measures in network location problems
In this paper, the concept of the ordered weighted averaging operator is applied to define a model which unifies and generalizes several inequality measures. For a location x, the value of the new objective function is the ordered weighted average of the absolute deviations from the average distance from the facilities to the location x. Several kinds of networks are studied: cyclic, tree and path networks and, for each of them, the properties of the objective function are analyzed in order to identify a finite dominating set for optimal locations. Polynomial-time algorithms are proposed for these problems, and the corresponding complexity is discussed.Future and Emerging Technologies Unit (European Commission)Ministerio de Educaci贸n y Cienci
Center location problems on tree graphs with subtree-shaped customers
We consider the p-center problem on tree graphs where the customers are modeled as continua subtrees. We address unweighted and weighted models as well as distances with and without addends. We prove that a relatively simple modification of Handler鈥檚 classical linear time algorithms for unweighted 1- and 2-center problems with respect to point customers, linearly solves the unweighted 1- and 2-center problems with addends of the above subtree customer model. We also develop polynomial time algorithms for the p-center problems based on solving covering problems and searching over special domains