this paper describes an experiment, which was carried out co-operatively by the seccion de circulacion y transportes of the ayuntamiento de madrid, gec elliott traffic automation ltd., and the transport and road research laboratory in autumn 1970, to compare two methods of co-ordinating traffic signals in an area. the signals in madrid are controlled according to a dynamic signal plan generation system which was the first of its type in the world. the dynamic signal plan generation system uses information for detectors to calculate on line the cycle time, splits and offsets to be used at each signal. this was compared with a system similar to the most successful fixed-time scheme that had been tried in glasgow. it was found that the dynamic system as tested in madrid in autumn 1970 gave longer journey times by about 9 per cent during the working day; the differences were statistically significant at the 5 per cent level. no observations were made at weekends or during the night when the dynamic system might be expected to have an advantage over a fixed-time one. a number of improvements have since been made to the dynamic system in use in madrid. further research is being carried out by the ayuntamiento de madrid and also by gec elliott traffic automation ltd., in association with the laboratory on various aspects of systems for dynamic signal plan generation. (a)

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