Hybrid Fixed and Flexible Transportation Service

Most transportation systems fall into two broad categories:fixed route systems that are cost efficient but lack of flexibilityand demand responsive transit (DRT) systems which are flexible butcostly. The Mobility Allowance Shuttle Transit (MAST) service is anew concept in transportation merging the flexibility of DRTsystems with the low cost operability of fixed route systems.Vehicles follow a base fixed route composed by a few mandatorycheckpoints conveniently located at major connection points; givenan appropriate slack time, vehicles may deviate from the fixed pathwithin a proper service area to serve passengers at their desiredlocations. We look at the system from a design, optimization andoperational points of view. We first develop relationships betweenthe longitudinal velocity of the vehicles and the demand by usingcontinuous approximations to aid in the design of the service.Then, we provide its MIP formulation and we develop a set of validinequalities to strengthen it. Finally, we develop a customizedinsertion scheduling algorithm, whose control parameters prevent a`wild` consumption of the slack time and significantly improve theoperational performance.