Trip Assignment Model for Timed-Transfer Transit Systems

A trip assignment model for timed-transfer transit systems is presented. Previously proposed trip assignment models focused on uncoordinated transit systems only. In timed-transfer transit systems, routes are coordinated and scheduled to arrive at transfer stations within preset time windows. Thus, passengers at coordinated operations terminals may face a choice among simultaneously departing buses serving alternative routes (unlike the case for uncoordinated operations terminals, where passengers generally board the first vehicle to arrive). A general trip assignment model is proposed that applies different assignment rules for three types of transfer terminals: uncoordinated operations terminals, coordinated operations terminals with a common headway for all routes, and coordinated operations terminals with integer-ratio headways for all routes. In addition, the care of missed connections at transfer terminals (due to vehicles arriving behind schedule) is accounted for. The model has been implemented in the LISP computer language, whose “list” data structure is specially suited to handle path search and enumeration. Results from an application to an example network with different combinations of terminal operations and headways indicate the following: (a) demand tends to be assigned to higher-frequency paths in the uncoordinated transit network; (b) demand is more concentrated, and tends to be assigned to paths with higher frequency and lower travel costs in the coordinated transit network; and (c) missed connections have no significant effects on trip assignment.