This paper critically reviews models to predict the performance of flexibly routed transfortation services such as taxi and dial-a-ride. Models of these services have been developed to assist in system design, in evaluation of alternatives, and in regulation. The approaches to modelling such services have been simulation, empirical, deterministic queuing and stochastic processes. Application of several models is illustrated by forecasting the level-of-service on six existing systems. While a good deal of effort has gone into model development and while some of the models appear to be quite accurate, an open question remains as to the acceptance and use of these models by planning and operating agencies.

Performance models of flexibly routed transportation services

A model system for forecasting patronage on demand responsive transportation systems

Analytical models for comparison of alternative service options for the transportation handicapped

The demand and capacity of a van dial-a-ride service for elderly and disabled passengers are analyzed together. The service demand is based on a survey of an advanced public transit system for an elderly and disabled persons van service. Demand is estimated by the Poisson regression on individual demand and by aggregating over individuals in the market. Service supply is modeled in two ways—a deterministic queuing model and a regression model—and is estimated by using drivers' manifest data. Market demand is compared with market supply derived from each method to identify the equilibrium level of ridership and travel time, which are used to measure the service quality. The model is used to predict a trade-off between ridership and travel time and to present this trade-off conveniently on a simple tabulation form. The service provider can use this form to determine combinations that maximize the management objective without engaging in simulation or estimation for all possible choices.

Equilibrium model based on a microfoundation for forecasting dial-a-ride ridership

Explicit performance models of a transit system are often very useful for system design, optimization, alternative comparison, and gaining insights into relevant system relations. In this paper, a performance metamodel has been developed for many-to-many dial-a-ride service, in which flexible routes and schedules are provided and service quality is guaranteed by time constraints. The model predicts minimum vehicle fleet size requirements. A simulation-based response surface methodology is used to model the functional relation between performance and contributing factors through experiments and statistical analysis. A detailed vehicle routing and scheduling algorithm and passenger time constraints, which are oversimplified or omitted in most other analytical approaches, are incorporated in the simulation experiments from whose results our model is statistically estimated. A face-centered central composite design is used to determine the experiment design points. The metamodel is validated using an additional set of randomly generated data. The resulting model is relatively simple in structure, inexpensive to use and fairly robust.

Fleet Size Metamodel for Dial-a-Ride Services with Time Constraints

This study has developed a method for estimating patronage of demand responsive transportation (DRT) systems. This procedure requires as inputs a description of the intended service area, current work trip patterns, characteristics of the served population, and the major design choices, such as the vehicle fleet size, changes in fleet size over the day, types of vehicles being used (buses or taxis), and the fare level. Using these data, the model predicts patronage and service levels for each user-specified interval during the day. The modern system has been developed as a software package which includes a set of disaggregate demand models, a set of analytic supply models, and an equilibration procedure. In addition, a simple sketch planning procedure has been developed which can be used for quick, preliminary analysis of DRT sites. /GMRL/

R. E. Nestle

Papers

Method for Estimating Patronage of Demand Responsive Transportation Systems