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This paper presents the formulation of a new optimization problem designated as the express minibus problem, which intends to form small groups of clients with compatible boarding/exiting points in time and space for a new type of urban mobility service. This new transport option, as a competitive alternative to the private car, aims to provide almost direct services between dispersed demand poles in places where high-capacity and efficient public transport options are scarce, thus combining the major strengths of both public transport and private vehicles. Conventional public transport systems can present efficient space and energy consumption, whereas private vehicles have high levels of flexibility, are fast, and are always available. The proposed algorithm aims at assessing the potential demand of this new service by developing a clustering algorithm in which the groups of clients formed for each minibus route should present the following characteristics: there is a small number of boarding and exiting points, where in each point there is only boarding or alighting; boarding points should be close to each other, as well as the exiting points; there must be a reasonable distance between the last boarding point and the first exiting point; the average load factor must be high; and for all clients the overall detour time relative to the direct service should be small. This paper presents the rationale and structure of the clustering algorithm, followed by an application for the Lisbon metropolitan area during the morning peak, which could be adapted to the afternoon peak with some slight modifications.

The viability of implementing a new alternative intermediate transport mode in the Lisbon, Portugal, metropolitan area was examined. The intention of this new system was to combine the major strengths of both public transport and private vehicles to provide a competitive transport alternative for commuters from low and intermediate density areas, who do not create enough demand to sustain a high-quality public transport service. Conventional public transport systems can provide efficient space and energy consumption, whereas private vehicles have high levels of flexibility and are fast and always available. A comprehensive methodology is presented to encompass the generation of input data of the model on the basis of transport demand data involving spatial-temporal constraints, the possible location of the service stops, and the detailed characterization of the service operation. The global objective of the model is to design a self-sustainable system that would maximize the operator's profit, not one that would satisfy all potential demand. The developed model uses supply parameters obtained through current bus operators in the region. However, the estimated values should be refined before service deployment. This assessment was performed, as an initial test bed for Lisbon and will be expanded to the whole metropolitan area. Results suggest that this service might be significantly profitable to the operator and a good alternative for single private car drivers. Implementation of this system may relieve some congestion during peak periods.

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