since november 1967 the transport and road research laboratory has been carrying out a series of full-scale experiments in glasgow to assess the benefits of various systems of co-ordinating traffic signals. these experiments, which until now have all taken place during normal working days, have established that substantial savings in journey times can be achieved by co-ordinating the signals in a network on a fixed-time basis; no further advantage has been found with the vehicle-responsive systems tried. this report describes two further tests which were carried out in glasgow in the evening and early morning. in the evening the flow in glasgow was approximately half the day-time value; in the early morning the flow was very light indeed, with only about 70 vehicles on the network on average. the schemes tested were the vehicle-actuated flexible progressive system, which was implemented in the evening, and completely isolated vehicle actuation in the early morning. in each case the performance was compared with that of an optimised fixed-time plan. during the evening journey times were 13% longer with the vehicle-responsive system than with the basic fixed-time linking. early morning journey times were the same with the optimised fixed-time system as with isolated vehicle-actuated signals. a trial carried out in west london by the traffic control development division of doe shows that a slightly different version of the vehicle-actuated flexible progressive system also gave no measurable improvements in journey time over the basic fixed-time linking during the evening. a speed/ flow relationship for the glasgow network when controlled by transyt has been obtained. it is linear over the whole range of flows observed in glasgow. (a)

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