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In many towns, traffic is controlled by signals which are coordinated together on fixed-time plans. The plans are derived to suit the average traffic flows which are expected to occur during a particular time period. since average traffic flows vary with time, it is common practice to derive a number of plans for different times of the day. The report examines what happens during during the changeover from one fixed time plan to another. Five methods of changing plan are described. For each method, the average additional delay experienced by each vehicle in the network is given. The two best methods caused an additional delay of 14 seconds per vehicle in the network. The other methods tested caused an additional delay of at least 36 seconds per vehicle.