SCATS is more than a method of linking traffic signals to provide for coordination. It is a sophisticated traffic engineering tool which gives Traffic Engineers the means to implement complex, objective oriented, traffic management strategies. Depending on how SCATS is implemented it can:
- • Reduce accidents, both vehicular and pedestrian.
- • Reduce fuel consumption.
- • Reduce delay and number of stops.
- • Increase capacity.
- • Improve journey time.
- • Reduce pollution and noise associated with vehicles having to stop and start unnecessarily.
If programmed to do so, SCATS can also:
- • Reinforce the desired road hierarchy.
- • Implement capacity restraint measures.
- • Protect environmentally sensitive areas by improving the arterial road network or by limiting access and egress to protected areas. This can be used to encourage vehicles to use the arterial roads rather than residential streets.
- • Provide bus and tram priority measures.
- • Give priority to emergency vehicles; eg. exiting ambulance or fire stations
Unfortunately, many of the above aims are conflicting, and the traffic engineer must determine the objectives and rationalise the various trade-offs in achieving those objectives. SCATS allows this to be achieved by the power of its hardware and software which maintains maximum flexibility for the traffic engineer. SCATS hardware, with its hierarchical structure of mini and microcomputers and the communications system, allows four major elements of SCATS to be introduced, namely:
- • Traffic monitoring - on street measurement of demand and capacity.
- • Fault reporting - automatic equipment fault detection and reporting.
- • Traffic control - the traffic adaptive control algorithms are capable of full dynamic signal operation.
- • A fully coordinated fallback mode of operation.
In terms of traffic control, the major contribution of SCATS is of considering all aspects of controlling the street network when establishing its times. Here in response to demands on the network, SCATS:
- • Determines stage splits at intersections.
- • Alters cycle time of systems.
- • Calculates time relationships between intersections.
- • Constructs coordination routes through the network.
- • Introduces cycle or plan dependent options.
It does this by using data input from vehicle detectors and from information supplied by the traffic engineer. Under various conditions, it implements maximum throughput, minimum stops and minimum delay strategies, under conditions defined by the operator. All this adds up to a very advanced coordinated signal system, but the major benefits to be achieved by SCATS will only be obtained if the data inserted by the operator is accurate and conforms to the principles and methods detailed in this manual. Lack of adherence to these principles or errors in data will cause SCAT system malfunctions.
SCATS provides the operator with a range of manual functions to override the normal automatic operation. These functions allow manual control of signal lamps to "on", "flash" or "off"; manual selection of link mode to Masterlink, Flexilink or Isolated mode; manual selection or alteration of split, cycle time or offset either for an individual intersection or for a whole sub-system; a dwell facility which allows any signal to be held on a nominated green phase for as long as required.
SCATS also allows for system operation to be varied by a timetable. Almost any function which can be executed manually can also be set up to occur at specified times on specified days. For example, in the Sydney central area, pedestrian walks are automatically introduced between 0800 and 1800 Monday - Friday, and on Thursday evenings and Saturday mornings when pedestrian activity is high.
A range of special routines is also available in SCATS which allows the user to define special operations to occur under specified conditions. These routines are used to achieve special requirements not covered by the general operation of SCATS. It is features of this type which enable every detail of signal operation to be tailored to meet the operational needs of each individual intersection. SCATS is the only system to offer such a feature.