The article describes the ITACA adaptive traffic control system, and its application to traffic control in the Spanish cities of Madrid and Barcelona. ITACA offers realtime response to current and future traffic flow demands, and brings 'intelligence' to fixed-time pattern control approaches. It incorporates: (1) an adaptive system, which is used to evolve the best plan at each junction; and (2) an expert system, which can use all the adaptive system's data and predictions to obtain a global solution for the total traffic plan. This solution is communicated to the adaptive system by a sophisticated use of importance (weight) factors. The adaptive system has cycle, split, and offset optimisers, and uses profiles to update the road network model. The model's components include: (1) queue lengths; (2) congestion indicator; (3) load; and (4) saturation flow modifier. The expert system is an optional part of ITACA, which uses the model's current network data and its rules to adjust the weights of each traffic movement. Its most obvious use is to avoid secondary congestion, the blocking of junction exits by downstream queues. It is expected that congestion strategies will develop differently for each network, and depend strongly on users. Any number of overlapping concurrent strategies can be implemented.
Abstract