The Sydney coordinated adaptive traffic system

Abstract

The Department of Main Roads, New South Wales is currently installing a utc system of 1,000 sets of traffic signals in the Sydney metropolitan area of 1500 km2. The system comprises 11 regional minicomputers which are supervised by one centrally located minicomputer. All of the local controllers are microcomputers. The system architecture is one of distributed intelligence with a comprehensive and flexible communication system. An important feature is its integral cableless link mode of operation as a fall back option. The plans and schedules for this operation are stored in the microcomputers from the regional computer and the local clocks are regularly checked. The normal mode of coordination is the dynamic method first developed for the Sydney CBD system of 150 sets of signals. The method dynamically adjusts cycle, split and offsets in response to variations in traffic demand and capacity. Sufficient evidence exists to show that the method can produce significant improvements in delay reduction when compared to the optimised fixed time methods preferred by most other authorities. The system design incorporates facilities for centralised volume counting, control of reversible lanes and variable message signs (a).