PUBLIC TRANSPORTATION ASSIGNMENT WITH PASSENGER STRATEGIES FOR OVERLAPPING ROUTE CHOICE

This paper presents a new and efficient approach to solve the demand assignment problem on transit, while considering the issue of overlapping bus routes and their influence on passenger flows. This paper is part of a comprehensive transit assignment model which considers most of the realistic situations. One of the most crucial characteristics of a transit network is the existence of overlapping routes that share the same bus stops while running on common segments. Emanating from this is the fact that more than one bus route can serve the demand between a certain origin-destination pair. The problem focuses on the decision-making process of the individual passenger who has to select the most efficient route serving the stop. This process, according to most of the researchers, is the main obstacle in developing efficient models and algorithms of passenger assignment on transit networks. They note the difficulties of encountering the problem of passenger behaviour at a bus stop served by competitive routes. The decision problem of a passenger at such a stop is whether to board an arrived bus or to wait for a faster bus that will have a shorter in-vehicle time. This issue reflects real choice situations in which the passenger can distinguish between two categories of overlapping routes : slow and fast. The objective is to minimize the total travel time (waiting time and in-vehicle time) which yields an optimal strategy in the choice process. This action depends on parameters of path's time between each origin and destination, bus regularity, distribution of passengers' arrival at the stop, and the structure of possible paths compounding the network. This research provides a new and efficient approach to overcome the failures mentioned. It considers passenger behaviour while using waiting strategies at a bus stop served by overlapping routes in order to minimize the total travel time. A mathematical formulation and interpretation of the problem are developed in a probabilistic fashion. Overlapping routes are categorized into slow and fast routes, and the results concerning the route-choice strategies are detailed. In such an instance, the passenger should actually wait for a fast bus, while disregarding subsequent slow buses arriving in the meantime. From the analysis, the proportion of passengers for each category is derived. This depends on a probabilistic function evaluated which considers the bus frequency share, the in-vehicle time difference, and the bus headway distribution. It shows that the intuitive rule by which passengers boarding the buses due to the frequency share is not a good assumption in all cases. This principle can be revised according to the presented analysis, and the circumstances when to implement the simple intuitive rule are given. The suggested approach contributes to understand the exact structure of the entire network (direct and transfer paths and their times) in transit assignment procedure, enabling the determination of the effective frequencies between each origin-destination pair which are not necessarily the frequencies of the routes connected directly to the bus stop. The approach helps to encounter large networks, since it treats each origin-destination pair separately. Subsequently, the entire network can be considered simultaneously, and solved via an iterative process to overcome the circular problem of the mutual dependence of the unknown frequencies and demand flows.