Papers by rodrigo garrido
Transport, 2018
The port choice problem consists in predicting the selection of a port, made by an agent who has ... more The port choice problem consists in predicting the selection of a port, made by an agent who has alternatives to choose from. Most of the literature has tackled this problem assuming a discrete choice model dependent on the ports’ characteristics and agents’ attributes. However, in practice the port choice decision depends also on the choices made by other agents as well as decisions made by these agents in the past. There are only a few examples that incorporate the complexity generated by spatio-temporal interactions between agents. However, those modelling structures are rather cumbersome, precluding their use in practical cases. This article presents a new modelling framework to predict port choice decisions, based on the theory of Cellular Automaton (CA), which is simple in structure and can be quickly calibrated and applied. This framework is a probabilistic CA intended to imitate the decision processes made from multiple shippers that interact with each other. These shippers ...
Transportation Research Part A: Policy and Practice, 2017
Transport Survey Quality and Innovation, 2003
A standard assumption in stated preferences modelling is the independence between repeated respon... more A standard assumption in stated preferences modelling is the independence between repeated responses from an interviewee. The rationale for this strong assumption is that the mathematical treatment of the choices becomes rather cumbersome when dependency is incorporated in the analysis. Assuming dependence between the various responses given by one individual is known as the repeated observations problem and its mathematical formulation is similar to that of the autocorrelation in panel data surveys. These type of problems can only be studied with the aid of flexible models such as the multinomial probit (MNP) or mixed logit (MXL). However, these models need the computation of a multidimensional integral to obtain values for the choice probabilities. The integration process is usually complex. Therefore, approximation methods must be applied-typically simulation, to evaluate the choice probabilities. The standard simulation approach relies on the Monte Carlo (MC) method, which basically replaces a continuous average (the integral) by a discrete average over a set of points randomly distributed within the region of integration. The numerical analysis literature shows various procedures to choose smart points from a deterministic series instead of random realizations. This type of points are known as low discrepancy sequences (LDS). However, the use of these techniques in econometrics is rather limited and recent, and consequently there are several open questions to be answered before the use of LDS becomes a standard. The evidence found in the fields of mathematics and physics indicates that a LDS called the Sobol sequence, would be a superior alternative to the more known Halton sequences, especially for large dimensions. Nevertheless, the Sobol sequences (to the knowledge of the authors) have not been tested yet in transportation. This paper compares the MC simulation method in three versions: traditional, Halton based, and Sobol based for the estimation of the MXL.
Xataka Android Mexico, 2013
International Series in Operations Research & Management Science, 2013
Most logistics systems are designed to operate under standard conditions, i.e., when the transpor... more Most logistics systems are designed to operate under standard conditions, i.e., when the transportation and communication networks are fully operative, the suppliers are able to deliver what they are asked for and the demand patterns fluctuate within (somewhat) known boundaries, as well as availability of human resources and vehicles to distribute products and services from production sites to consumption points.
Security and Environmental Sustainability of Multimodal Transport, 2010
Malicious entities may use hazardous materials as a weapon by hijacking a vehicle and transportin... more Malicious entities may use hazardous materials as a weapon by hijacking a vehicle and transporting it to a desired target. This work presents a methodology to identify possible hijacked vehicles’ routes to vulnerable targets, assuming that probabilities of interception by law enforcement agents depend on the investment in defense resources. The methodology to identify hijacked vehicles’ routes incorporates the dual
Transportation Research Part A: Policy and Practice, 2000
This paper presents an analysis of the spatial and temporal interactions between truck¯ows across... more This paper presents an analysis of the spatial and temporal interactions between truck¯ows across the Texas±Mexico border. The system of¯ows is modeled as a multivariate stochastic process with interactions both in time and space dimensions. A novel modeling approach, the space time autoregressive moving average (STARMA) model, is applied to capture the autocorrelations between the¯ows. These autocorrelations are the base to compute direct and crossed demand elasticities between the¯ows. The demand elasticities are used to estimate the degree of dependence between the truck¯ows both southbound and northbound, revealing that uneven adjustments take place in the truck¯ows pattern for southbound and northbound trac. In fact, the southbound¯ows are more sensitive to changes in their own demand over time than the corresponding spatial changes. On the other hand, the northbound¯ows are more sensitive to changes in the demand for the main¯ow (Laredo's bridge) rather than their own variations in previous periods.
Transportation, 1994
Stated preference (SP) rating experiments are easy to design and conduct. Furthermore, they const... more Stated preference (SP) rating experiments are easy to design and conduct. Furthermore, they constitute a generalisation of SP choice experiments in terms of the information about preferences that can be achieved. However, its results are sensitive to the numerical values assigned by the analyst to the semantic scale used by individuals to express their preferences. We consider this problem in depth using a variety of statistical techniques, including ordinaI probit and a novel optimal scale linear regression approach.
Transportation, 1994
... A practical assessment of stated preferences methods JUAN DE DIOS ORTI~IZAR & ... Onl... more ... A practical assessment of stated preferences methods JUAN DE DIOS ORTI~IZAR & ... Only in two cases (ie members of staff in the ratings and ranking games) we found a slight indication of systematic errors (ie R 2 greater than 0.1) as shown in Table 4. Page 10. 298 ...
Transportation Research Record: Journal of the Transportation Research Board, 1998
A framework for analyzing, describing, and forecasting freight flows for operational and tactical... more A framework for analyzing, describing, and forecasting freight flows for operational and tactical purposes is presented. A dynamic econometric model is proposed. This model incorporates the spatial and temporal characteristics of freight demand within a stochastic framework. The model was applied in an actual context and its performance was compared with standard time series models (benchmark) for forecasting ability. The proposed model outperformed the benchmark from the econometric viewpoint. Extensive diagnostic checking and sensitivity analysis confirmed the robustness of the modeling methodology for short-term forecasting applications.
Transportation Research Part E: Logistics and Transportation Review, 2001
The derivation of a subjective value of time (SVT) requires ®nding the marginal rate of substitut... more The derivation of a subjective value of time (SVT) requires ®nding the marginal rate of substitution between travel time and cost in a travel choice model. In the typical case of models with linear-inparameters utility functions, the SVT is equal to the ratio between the parameters of travel time and cost. However, since model estimation yields an estimator of the true values of their parameters (with a certain probability distribution), the computed SVT is also an estimator with another probability distribution; then, it is important to devise a method to incorporate the randomness of the estimated SVT in project evaluation. In this paper, we consider this problem rigorously and propose methods to replace the typical SVT point estimates by the construction of con®dence intervals for a certain probability level. This allows, in addition, to estimate the SVT limits (lower and upper) which may be used in sensitivity analyses of the calculation of project revenues in transport infrastructure investment. The paper proposes two forms for building these intervals: the t-test and the LR-test, and discusses the construction of intervals for Multinomial Logit (MNL), Hierarchical Logit (HL) and Box±Cox Logit (BCL) models. We use two samples where the values of the level-of-service attributes have been measured with an unusually high degree of precision. Other methods proposed in the literature are also studied (simulation of multivariate normal variates (MVNS), SVT normal approximation (NA), and re-sampling techniques) using the above data, and their advantages and disadvantages are analysed. In addition, the eects of dierent modelling elements on the size and quality of the constructed intervals are scrutinised, such as model speci®cation, sample size and individual income. Finally, the proposed methods are compared and recommendations about the use of each one in practice are indicated.
Uploads
Papers by rodrigo garrido