Feeder-trunk and direct-link schemes for public transit: a model to evaluate the produced accessibility

In a public transport network, a more intense integration between lines generally involves, on one hand, the reduction in the number of direct links, which forces users to perform more transfers, and on the other hand, the possibility of achieving a greater number of rides with the same whole mileage. Thus, the move towards feeder-trunk schemes produces both negative and positive effects on accessibility and on the quality of service perceived by users. That implies the need to evaluate accessibility realized on a territory by transit service patterns characterized by different levels of line integration. This research was focused on the development of an accessibility model able to estimate an equivalent travel time and to consider the discomfort resulting from possible transfers between vehicles and the benefits arising from available transit rides. As reported in this paper, the proposed model, that measures accessibility through an equivalent travel time, determines the latter as a function, in addition to the time spent inside the vehicle, also of the time and discomfort consequent to the transfers as well as of the number of supplied rides. With reference to the regional public transport, the values obtained by the calibration of the constants show how the waiting time has a weight for the user twice as much compared to the time spent on the vehicle, whilst the time required for the transfer has about a one and a half weight. Finally, the discomfort caused by each transfer is evaluated by the user as an increase to the overall travel time of about 3 and a half minutes. The calibrated model has been applied to a real case, in order to validate it and highlight benefits and limitations resulting from feeder-trunk supply patterns. The developed tool is useful in the design of a public transport service, especially in areas with weak demand, allowing to compare, in terms of produced accessibility, supply schemes with different levels of line integration, variable from direct-link type (also called point to point) to that feeder-trunk.