Determination both of the plaza size and of the proper gate type sequence, i.e. toll station layout, in the actual planning process is quite important for an optimal design of the toll station, moreover, it is essential to its future operational efficiency. The planning process is basically a two-stage process: initial planning and then fine-tuning, usually with a microscopic simulation model that can simulate the random nature of vehicle arrivals and the stochastic service performance of the different types of gate. The whole process should generally include the field data collection and analysis, finally resulting in three steps: 1) data collection and analysis; 2) preliminary planning; 3) fine-tuning and adjustments. The way to proceed can be implemented by a unified step that assigns a prefixed number and type of gates (i.e., according to operating policy) in view of a design criterion, i.e. circulation safety. Trajectories of higher speed vehicles directed to automatic vehicle identification (AVI) gates need to be managed in respect to lower speeds of vehicles approaching any other type of stop gate, i.e. manual gate. In order to cope with such a problem, the knowledge of the relationships between traffic flow, driver's habits, number and type of open toll gates and vehicle arrival and departure patterns is essential from any network-wide design point of view. This paper presents our research progress in developing a toll station layout optimisation methodology based on toll plaza circulation safety analysis. The decision variables are mainly related to the assignment of a gate type - manual gate with operator, AVI gate, semiautomatic or short stop gate - to each gate position in the station. Although from a theoretical perspective, the problems of this kind are in general difficult, it was possible to obtain optimal solutions for medium sized toll stations (note that 15 gates is generally considered an actual upper bound) in a few minutes on a personal computer. The first group of computational experiments performed tend to support the evidence that gates associated to higher risk traffic flows, e.g. traffic directed to AVI gates which approaches the toll station at speeds significantly above the average, should be located in a central position with respect to other gate types. These first conclusions are quite supported by results of a second group of computational experiments performed on a set of observed data which were gathered by camera films in some toll-plazas of Italian motorway network. For the covering abstract see ITRD E126595.
Abstract