Aruna Sivakumar

Comprehensive Econometric Microsimulator for Daily Activity-Travel Patterns

The Comprehensive Econometric Microsimulator for Daily Activity-Travel Patterns (CEMDAP) is a microsimulation implementation of an activity-travel modeling system. Given as input various land use, sociodemographic, activity system, and transportation level-of-service attributes, the system provides as output the complete daily activity-travel patterns for each individual in each household of a population. The underlying econometric modeling framework and the software development experience associated with CEMDAP are described. The steps involved in applying CEMDAP to predict activity-travel patterns and to perform policy analysis are also presented. Empirical results obtained from applying the software to the Dallas-Fort Worth area demonstrate that CEMDAP provides a means of analyzing policy impacts in ways that are generally infeasible with the conventional four-stage approach.

An Analysis of the Impact of Information and Communication Technologies on Non- Maintenance Shopping Activities

This paper examines the use and travel impacts of two forms of information and communication technologies (ICTs): mobile telephones and computers. The travel impacts are examined in the context of participation in out-of-home non-maintenance shopping activities over a multiweek period through the modeling of the duration between successive shopping activity participations. The empirical analysis uses a continuous six-week travel survey collected in the cities of Halle and Karlsruhe in Germany in the Fall of 1999. The results indicate that the effects of ICTs on activity-travel patterns are mediated by individual sociodemographic and locational factors, as well as by unobserved individual characteristics. The results also show that the substitution between mobile phone use and shopping travel is grossly underestimated if the effects of common unobserved factors affecting mobile phone use and shopping travel are not considered. In addition, there is quite substantial intra-individual variation in intershopping duration.

Fractional Split-Distribution Model for Statewide Commodity-Flow Analysis

A relatively simple, but comprehensive, approach to modeling interregional commodity-flow volumes is proposed and applied. The approach estimates the fraction of commodity consumed at each destination zone that originates from alternate production zones. The resulting fractional split model for commodity-flow distribution is more general in structure than the typical gravity model used today for statewide freight planning. The empirical analysis applies the fractional split model to analyze interregional commodity flows in Texas.

Comprehensive, Unified Framework for Analyzing Spatial Location Choice

This paper develops a conceptual and econometric framework of non-work activity location choice that is comprehensive in its incorporation of spatial cognition, heterogeneity in preference behavior, and spatial interaction. The proposed framework subsumes a variety of restricted models, including the multinomial logit, first-order state-dependence logit, spatially correlated logit, and mixed spatially correlated logit models. The applicability of the framework is demonstrated through an empirical analysis with German Mobidrive data.

Simulation Estimation of Mixed Discrete Choice Models with the Use of Randomized Quasi-Monte Carlo Sequences: A Comparative Study

The overall performance of the quasi-Monte Carlo (QMC) sequences proposed by Halton and Faure, as well as their scrambled versions, are numerically compared against each other and against the Latin hypercube sampling sequence in the context of the simulated likelihood estimation of a mixed multinomial logit model of choice. In addition, the efficiency of the QMC sequences generated with and without scrambling is compared across observations, and the performance of the Box-Muller and inverse normal transform procedures is tested. Numerical experiments were performed in five dimensions with 25, 125, and 625 draws and in 10 dimensions with 100 draws. Results indicate that the Faure sequence consistently outperforms the Halton sequence and that the scrambled versions of the Faure sequence perform best overall.

Emerging Simulation-Based Methods

The incorporation of behavioral realism in econometric models helps establish the credibility of the models outside the modeling community, and can also lead to superior predictive and policy analysis capabilities. Behavioral realism is incorporated in econometric models of choice through the relaxation of restrictions that impose restrictive behavioral assumptions regarding the underlying choice process. For example, the extensively used multinomial logit (MNL) model has a simple form that is achieved by the imposition of the restrictive assumption of independent and identically distributed error structures (IID). But this assumption also leads to the not-so-intuitive property of independence from irrelevant alternatives (IIA).