The estimation of urban traffic condition using an Automatic Vehicle Location System

In the transportation field the problem of the optimal resources management has led to the spreading in the last years of the so-called of TDM (Travel Demand Management) policies. On the other hand the technological progress has contributed to the development of the Intelligent Transportation Systems (ITS). For real-time travel time studies probe vehicles are an important source for measuring congestion, delays and incident detections. Some experiments made in America and in Europe (i.e., Socrates, Advance, Euroscout, Verdi) have shown the positive features and useful expedients in order to implement traffic monitoring system with probe vehicles. The statistical problem of significance of the data surveyed by a limited number of probe vehicles constitutes a non-undervaluable obstacle. Moreover, the cost of collecting travel time data depends on the number of probe vehicles required. The improvement of the road network performances does not justify the costs of acquisition and management of a probe vehicle fleet. Since both the buses and cars often operate on the same roadway and under the same traffic conditions, there should be some correlations between these two modes. Consequently, this work proposes the use of buses, equipped with a system of Automatic Vehicle Location (AVL), as probe in the traffic in order to estimate the real-time traffic flow conditions. The aim of this paper is the implementation of a method to estimate road network performances through a function that joins bus travel time and car travel time. The results demonstrate the robustness of the model in describing the status of the road transportation system. Research perspectives can be addressed to the definition of network control strategies and to the emergency management using the proposed methodology.