Frank S. Koppelman

The generalized nested logit model

The generalized nested logit (GNL) model is a new member of the generalized extreme value family of models. The GNL provides a higher degree of flexibility in the estimation of substitution or cross-elasticity between pairs of alternatives than previously developed generalized extreme value (GEV) models. The GNL model includes the paired combinatorial logit (PCL) and cross-nested logit (CNL) models as special cases. It also includes the product differentiation (PD) model, which represents the elasticity structure associated with multi-dimensional choices, and the ordered generalized extreme value model, which represents the elasticity structure associated with ordered alternatives, as special cases. The GNL model includes the two-level nested logit (NL) model as a special case and can approximate closely multi-level nested logit models. It accommodates differential cross-elasticity among pairs of alternatives through the fractional allocation of each alternative to a set of nests, each of which has a distinct logsum or dissimilarity parameter. An empirical example of intercity mode choice confirms the statistical superiority of the GNL model to the paired combinatorial logit, cross-nested logit and nested logit models and indicates important differences in cross-elasticity relationships across pairs of alternatives.

THE PAIRED COMBINATORIAL LOGIT MODEL: PROPERTIES, ESTIMATION AND APPLICATION

The Independence of Irrelevant Alternatives (IIA) property of the multinomial logit (MNL) model imposes the restriction of zero covariance between the utilities of pairs of alternatives. This restriction is inappropriate for many choice situations; those in which some pairs or sets of alternatives share the same unobserved attributes. The nested logit (NL) model relaxes the zero covariance restriction of the MNL model but imposes the restriction of equal covariance among all alternatives in a common nest and zero covariance otherwise. The paired combinatorial logit (PCL) model relaxes these restrictions further by allowing different covariances for each pair of alternatives. This relaxation enables the estimation of differential competitive relationships between each pair of alternatives. The closed form of the PCL model retains the computational advantages of other logit models while the more flexible error correlation structure, compared to the MNL model and NL models, enables better representation of many choice situations. This paper describes the derivation, structure, properties and estimation of the PCL model. The empirical results demonstrate that the PCL model is statistically superior to the MNL and NL models and may lead to importantly different travel forecasts and policy decisions.

A MODEL OF JOINT ACTIVITY PARTICIPATION BETWEEN HOUSEHOLD MEMBERS

A proportional shares model of daily time allocation is developed and applied to the analysis of joint activity participation between adult household members. The model is unique in its simultaneous representation of each decision makers decisions concerning independent activity participation, allocation of time to joint activities, and the interplay between individual and joint activities. Further, the model structure ensures that predicted shares of joint activity outcomes be the same for both decision makers, an improvement over models that do not make interpersonal linkages explicit. The empirical analysis of travel diary data shows that employment commitments and childcare responsibilities have significant effects on tradeoffs between joint and independent activities. In addition, evidence is presented for the continued relevance of gender-based role differences in caring for children and employment participation.

The choice of air carrier, flight, and fare class

This paper reports the development and interpretation of air traveler choice models to gain insights into the tradeoffs air travelers make when they choose among different carriers, flights, and fare classes. Such insights can be used to support carrier decisions on flight scheduling, pricing, seat allocation, and ticket restrictions. This paper develops a conceptual framework and applies it to the choice of carrier, flight, and fare class as a basis for analyzing air travel demand in a competitive market. Model estimation results are used to quantify the importance of carrier preferences, market presence, quality of service, frequent flyer program membership, schedule convenience, and fares on carrier travel demand. The empirical results provide measures of the premium that business and leisure travelers are willing to pay to avoid schedule delays, to choose a carrier in which frequent-flyer program they participate, and to obtain the amenities and freedom from travel restrictions associated with higher fare classes.

Representing the differences between female and male commute behavior in residential location choice models

This research develops multinomial logit models (MNL) of residential location choice for two-worker households in the San Francisco Bay Metropolitan Area to identify household characteristics that account for the relative differences in household sensitivity to female and male commutes when making residential choices. The results reveal that presence of children, occupation of the male worker, and the relative order of the last residential change and the last change in the female workers workplace are important determinants of female and male commuting time parameters in household residential location utility functions.

Activity-Based Modeling of Travel Demand

Since the beginning of civilization, the viability and economic success of communities have been, to a major extent, determined by the efficiency of the transportation infrastructure. To make informed transportation infrastructure planning decisions, planners and engineers have to be able to forecast the response of transportation demand to changes in the attributes of the transportation system and changes in the attributes of the people using the transportation system. Travel demand models are used for this purpose; specifically, travel demand models are used to predict travel characteristics and usage of transport services under alternative socio-economic scenarios, and for alternative transport service and land-use configurations.

Alternative nested logit models: structure, properties and estimation

Two distinctly different nested logit models have been widely used in both research and applications. The differences, not widely recognized, between these models will substantially influence estimation results, behavioral interpretation and policy analysis. The McFadden nested logit model is derived from random utility theory; the Daly or non-normalized nested logit model is based on probability relationships and is not consistent with utility maximization. This paper describes and compares the model structure and properties of these different nested logit models identifying important differences between the different model structures. An empirical application demonstrates that the different nested logit models produce dramatically different results with respect to nesting structure and the relative importance of utility components. Thus, the selection of one or another of the nested logit models has important consequences for model interpretation and prediction with consequent impacts on policy analysis. The authors prefer the McFadden model because of its basis in utility theory, intuitively reasonable elasticity relationships and a clear interpretation of utility function parameters across alternatives.

A conceptual and methdological framework for the generation of activity-travel patterns

This paper develops a conceptual framework for the generation of activity and travel patterns in the context of more general structures and presents an integrated model system as a step toward development of an improved travel demand forecasting model system. We propose a two-stage structure to model activity and travel behavior. The first stage, the stop generation and stop/auto allocation models, consists of the choices for the number of household maintenance stops and the allocation of stops and autos to household members. The second stage, the tour formation model, includes the choices for the number of tours and the assignment of stops to tours for each individual, conditional on the choices in the first stage. Empirical results demonstrate that individual and household socio-demographics are important factors affecting the first stage choices, the generation of maintenance stops and the allocation of stops and autos among household members, and the second stage choices, the number of tours and the assignment of stops to tours.

A CONCEPTUAL FRAMEWORK OF INDIVIDUAL ACTIVITY PROGRAM GENERATION

The research in this paper attempts to better understand the process by which activities are generated at an individual level. Activity-based travel analyses have gained popularity in recent years because they recognize the complexity of activity behavior and view travel as a derivative of this behavior. Most activity-based studies have focused on the spatial and temporal linkage of trips; that is, the scheduling of activities. They consider the agenda of activities for participation, and associated attributes of the activity participation (such as mode to activity and location of activity performance), as predetermined. This paper develops a comprehensive conceptual framework of the relatively unexplored area of activity agenda generation. Such a framework will be valuable in empirical modeling of activity generation behavior. A subsequent paper focuses on translating a part of this conceptual framework into an empirical model.

Behavioral issues in the design and evaluation of advanced traveler information systems

Decisions about implementing Advanced Traveler Information Systems (ATIS) should be based on the individual and social benefits expected from such technologies, which will be strongly dependent on the ways travelers respond to these new information sources. This paper explores the behavioral issues important to understanding traveler reactions to ATIS; it discusses evaluation strategies, including stated preference methods and observation of revealed behavior in laboratory simulations and field tests with various degrees of control and complexity. Advantages and disadvantages of different approaches are reviewed, and the experimental design challenges of site selection, recruitment of test subjects, and measurement of behavior are explored.