conference paper
conference paper
published journal article
working paper
A specification issue which has been handled differently in various empirical applications is whether or not to include alternative specific constants in models of choice behavior. Some applications have excluded constants, others have included a full set of constants, and a third class of examples uses unique constants for some alternatives, but not all. In logit models in which each individual has the same set of alterna tives, the exclusion of constants in the estimation of models when the correct model actually has alternative specific effects leads to inconsistent estimates of the coefficients of the remaining independent variables. However, the inclusion of constants when no such effects exist does not affect the consistency of the estimates of the coefficients. These results are illustrated by simple hypothetical examples and by empirical examples. When nonratio scale variables are used in logit models, the coefficients of the independent variables are not invariant under arbitrary scale shifts when alternative specific constants are excluded. Finally, the use of models to predict the response to new alternatives and the transferability of models which might or might not include alternative specific effects is discussed. The major conclusion is that the inclusion of: a full set of alternative specific constants in logit models estimated with large samples is generally preferred over the exclusion of one or more alternative specific constants.
working paper
The recent fiscal problems of public transit in many large metropolitan areas have stimulated interest in alternative service delivery systems for public transportation. One strategy. that of contracting with private providers for public transportation services. has received particular attention. Private sector contracting is viewed as attractive due to its cost and subsidy savings potential–savings of 25 to 50 percent of public agency transit operator costs have been cited.(1.2.3) The reality. however. is that relatively little transit service contracting currently takes place and that substantial political, organizational, and legal obstacles confront plans to increase the use of this strategy. In addition, little detailed information is available on the extent of service contracting. its economic benefits. and the institutional factors which affect its feasibility. The purpose of this paper is to contribute to remedying this information deficiency by providing a review of selected experiences and issues of transit service contracting. The paper focuses on five major topics. (1) How widespread is transit service contracting. who practices it. and what services are involved? (2) Why do public agencies engage in private sector contracting, and what are typical situations in which they do so? (3) What is the magnitude of the estimated cost and subsidy savings which have been realized from contracting? (4) What are the major obstacles to service contracting and when are they able to be overcome? (5) What issues involving service contracting require additional research?
conference paper
This paper analyzes the impacts of stochastic population changes on the timing of an investment that can reduce congestion in an open, monocentric city with fixed boundaries. Congestion pricing cannot be implemented, but a welfare-maximizing planner can buy land and build transportation infrastructure. Under certainty, the author derives a rule of thumb to evaluate infrastructure investments that corrects a standard benefit-cost analysis. Under uncertainty, the paper shows that relying on a standard benefit-cost ratio could lead to investing in bad projects, or investing prematurely, or ignoring attractive projects because of population barriers and the impacts of the congestion externality on the land market.
conference paper
working paper
Levels of demand over time are analyzed for five modes of passenger transportation. The data are for the modes car driver, car passenger, train, bicycle, and public transit are compiled from week-long travel diaries collected at six-month intervals from a nationwide panel in the Netherlands. Three types of empirical relationships are present in these panel data: (1) autocorrelative relationships, capturing temporal stability in demand for the same mode at different points in time, (2) contemporaneous relationships capturing complementarity and competition among different modes at the same point in time, and (3) cross-lagged effects, potentially capturing systematic shifts in demand. Simultaneous equation systems are used to test the temporal stability of demand for each mode and the stationarity of the contemporaneous relationships among the modes. The dynamic structure of both trip rates and travel times are modeled successfully according to several goodness-of-fit indices. The equation systems capture nonstationarity in the contemporaneous relationships, as well as important cross-lagged effects. These results quantify changes in the structure of demand over time in the Netherlands and are shown to be directly related to the event of a public transit fare increase.
conference paper
MS Thesis
The traditional Four-Step Model is widely used in the Transportation Planning and Forecasting Process. However, the model itself has a structural defect: it is only equilibrium in terms of Trip Assignment. Thus it is often viewed as an inadequate, partial equilibrium model. To achieve an overall equilibrium in the Transportation Planning and Forecasting Process, a feedback process can be introduced into the Four-Step Model. The objective of this research is to incorporate different feedback methods into the traditional Four-Step Modeling process to improve model performance. The specific approach herein is to examine the relative performance of direct and averaging feedback methods, and then to investigate the convergence of this two approaches by replacing User Equilibrium trip assignment with All-or-Nothing trip assignment during each feedback loop, but not in the original four step model application. An evaluation and comparison of these methods is presented. Two measures of effectiveness, the Root-Mean-Square Error (RMSE) and Total Vehicle Hours Traveled (VHT), are employed to test the convergence and evaluate the methods.