Performance Assessment and Comparison between Fixed and Flexible Transit Services for Different Urban Settings and Demand Distributions (SWUTC/08/473700-00090-1)

In the transit business, planners often face a difficult decision when having to choose what type of operating policy to put in place in a given service area. In fact, the decision is not straightforward, mainly because the demand for the service is often unknown beforehand and it will depend on the established system itself. This is especially true for feeder lines, one of the most often used types of flexible transit services connecting a service area to a major transit network through a transfer point. They often switch operations from/to a demand responsive to/from a fixed-route policy. In designing and operating such systems, the identification of the condition justifying the operating switch is often hard to properly evaluate. In this research, we propose an analytical modeling and solution of the problem to assist decision makers and operators in their choice. By employing continuous approximations, we derive handy but powerful closed-form expression to estimate the critical demand densities, representing the switching point between the competing operating policies. Based on the results of one-vehicle and two-vehicle operations for various scenarios and their comparison to simulation generated values, we verify the validity of our analytical modeling approach. Estimated critical demand densities for the one-vehicle case and a service area with L=2 and W=0.5 range from 14 to 30 customers/hr/mile2.