Sydney Coordinated Adaptive Traffic System

The Sydney Coordinated Adaptive Traffic System, abbreviated SCATS, is an intelligent transportation system that manages the dynamic (on line, real time) timing of signal phases at traffic signals, meaning that it tries to find the best phasing (i. e. cycle times, phase splits and offsets) for a traffic situation (for individual intersections as well as for the whole network). SCATS is based on the automatic plan selection from a library in response to the data derived from loop detectors or other road traffic sensors. SCATS uses sensors at each traffic signal to detect vehicle presence in each lane and pedestrians waiting to cross at the local site. The vehicle sensors are generally inductive loops installed within the road pavement. These are unable to detect bicycles. The pedestrian sensors are usually push buttons. Various other types of sensors can be used for vehicle presence detection, provided that a similar and consistent output is achieved. Information collected from the vehicle sensors allows SCATS to calculate and adapt the timing of traffic signals in the network. SCATS is installed at about 55,000 intersections in over 180 cities in 28 countries. In Australia, where the system was first developed, the majority of signalised intersections are SCATS operated (around 11,000). The SCATS system is owned by the Australian state of New South Wales, whose state capital is Sydney. In December 2019, Transport for NSW, the transport and road agency in New South Wales, began to look into commercialising the SCATS system.

The architecture of SCATS is at two basic levels, LOCAL and MASTER. The LOCAL is the control cabinet at the roadside, which provides the normal signal control as well as processing of traffic information deduced from the vehicle detectors. The MASTER is a remote computer which provides area based traffic control, i. e. area traffic control (ATC) or urban traffic control (UTC). Detailed traffic signal and hardware diagnostics are passed from the LOCAL to the MASTER, with the ability to notify staff when a traffic signal has a fault. SCATS is able to operate over PAPL, ADSL, PSTN and 3G IP network connections to each intersection. SCATS can also operate on a network of private cables not requiring third party telecommunications support and large parts of inner Sydney have always operated this way.

Public vehicle priority in SCATS (using data provided from PTIPS) caters for both buses and trams. SCATS has a facility to provide three levels of priority:

High – In the high priority mode the "hurry call" facility is used. (i. e. the phase needed by a bus, tram or emergency vehicle is called immediately, skipping other phases if necessary)
Medium (Flexible window) – Phases can be shortened to allow the bus/tram phase to be brought in early. The bus/tram phase can occur at more than one place in the cycle. Low – takes its turn. Trams would normally be given high priority, the aim of which is to get the tram through without it stopping. Buses would normally expect to receive a medium level of priority.

The ATC system is equipped with the function of fault detection and logging the fault detected in order to facilitate repair and maintenance. Should there be a telecommunication breakdown, the ATC junction controller concerned will switch to standalone mode and continue to function.

ATC systems provide advanced method of traffic signal control called Traffic Adaptive Control where the operational timing plans including cycle length, splits and offsets are continuously reviewed and modified in small increment, almost on a cycle by cycle basis, to match with the prevailing demand measured by the detectors connected to the on street traffic controllers.

SCATS can be simulated in the loop (SCATSIM) using third party traffic simulation tools. SCATSIM offers an interface supported by Aimsun, PTV VISSIM, Quadstone Paramics and Commuter. SCATSIM offers kerb side hardware and firmware emulation that interfaces seamless to the SCATS Region and Central Manager offering the same control strategies used in field deployments for both intersections and ramp metering (SRMS). The configuration files prepared by authorities for the Central Manager, Region, SRMS and kerb side controllers can be re used without modification by SCATSIM. When Commuter software was acquired by Autodesk, Azalient Ltd support for the Commuter interface was deprecated. Azalient Ltd also developed a plugin that enabled the Quadstone Paramics interface to SCATSIM. This plugin is also deprecated.