The Sydney Coordinated Adaptive Traffic System, abbreviated SCATS, is an traffic light control system and intelligent transportation system platform for monitoring, controlling, and optimising the movement of people and goods in cities through the operation of traffic signals.
SCATS manages the dynamic (on-line, real-time) timing of signal phases at traffic signals, meaning that it tries to find the most efficient 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 typically uses detectors at each traffic signal to detect vehicle presence in each lane and push-buttons for pedestrians waiting to cross. The vehicle detectors are generally inductive loops installed within the road pavement, but microwave (radar) detectors can be used as a temporary measure when loop detectors fail. Similar loop detectors can detect metal bicycles or metal parts on bicycles. Push button detectors are usually provided for pedestrians. 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 more than 63,000 intersections in over 216 cities in 33 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, the state capital of which is Sydney. Transport for NSW (TfNSW) is the transport and road agency in New South Wales. In December 2019, TfNSW began to look into commercialising the SCATS system, however these plans were abandoned in 2021.
The Transport for NSW Transport Future Sustainability program forecasts SCATS to triple its revenue in 2025-2026.
Overview Along with Sydney, SCATS is also used in New Zealand, Hong Kong, Shanghai, Guangzhou, Amman, Tehran, Dublin, Rzeszów, Gdynia, Central New Jersey, in part of Metro Atlanta, and Cebu City, among several other places. In Hong Kong, SCATS is currently adopted in the area traffic control systems at Hong Kong Island, Kowloon, Tsuen Wan and Shatin.
The system may be referred to by an alternative name in a specific installation. However, since deployment outside Australia, New Zealand and Singapore, localised names do not appear to be commonly used. The following are some local alternative names that have been or are in use:
Canberra "CATSS" (Canberra Automated Traffic Signal System) Melbourne "SCRAM" (Signal Co-ordination for Regional Areas of Melbourne) Adelaide "ACTS" (Adelaide Co-ordinated Traffic Signals) Perth "PCATS" (Pedestrian Countdown at Traffic Signals) Singapore "GLIDE" (Green Link Determining System) Northern Territory "DARTS" (Dynamic Arterial Responsive Traffic System)
Features Default operation The architecture of SCATS is at two basic levels, Tactical control (local) and Strategic control (regional, known as MASTER). The on-site local controller (cabinet at the roadside) processes of traffic information deduced from the vehicle detectors and allocates green time, extending, terminating early, or skipping demand-dependent phases.
Strategic control (regional) is a regional computer which target cycle length, splits, and offsets for subsystems based on detector data. It 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.
Typical operating modes for SCATS intersections include SCATS Isolated, Flexilink, Masterlink and Non-SCATS sites.
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 previously operated this way.
SCATS increases cycle times to accommodate as much vehicle traffic as possible. The relationship between the Degree of Saturation and Cycle Time is based on two cycle time calibration factors provided by operators.
Public vehicle priority 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.
Roads & Maritime Services commissioned Prioritize to develop the SCATS Priority Engine.
PTIPS began as collaboration between the University of Technology and the Roads and Traffic Authority. The basis was developed by Ghassan Jarjees in his doctoral thesis. It was productionised from 2005.
Pedestrian and bicycle priority
Pedestrian priority can be achieved by using lower cycle times, double cycling, 'Walk for Green', automatic introduction of pedestrian phases, countdown timers, and 'delinking' or 'divorcing'. Lower cycle times reduce the wait time and delay for pedestrians. Other factors impacting pedestrian access include the number of opportunities in the cycle when pedestrian can cross (often one), and pedestrian demands not being recorded in time for action by the signal controller.
SCATS records the first button press for each movement. Later button presses normally add no count. While SCATS records pedestrian demands (which can be accessed from event logs in SCATS History) it does not evaluate pedestrian delay. Setting MSS flags or XSF flags by variation routines can be used to show pedestrian delays.
The SIDRA User Guide states when pedestrians have to wait 20 or 30 seconds (average delay per pedestrian) the delay is noticeable. When the delay is 30-40 seconds there is an increased likelihood of risk taking as the delay is irritating. Risk taking behaviour is likely with a delay of 40-50 seconds and above 60 seconds there is a high likelihood of risk taking as the delay exceeds tolerance level.
Cycle times
In SCATS the nominal cycle length (nCL) is a reference in used to set initial splits and coordination. The running cycle length (rCL) varies from cycle to cycle because phase times vary with demand. SCATS can change nCL dynamically. Actual (rCL) cycle times can exceed nominal (nCL) cycle times: an example diagram of nCL vs rCL, including skipped phases, shows actual cycle times (rCL) of between 108 s to 176 s for an intersection with nominal cycle time (nCL) of 140 s.
A graphical program called SCATS History Viewer has export functionality for actual phase and cycle statistics. The program facilitates the extraction of this data into commonly used formats that can be easily consumed by other systems....History Viewer - Summarises general historical traffic signal operation. This information is presented through various tabular and graphical displays which could be used for traffic modelling or diagnostic purposes. It also facilitates the extraction of this data into commonly used formats that can be easily consumed by other systems...
Longer or more frequent green signals for pedestrians can reduce unsafe crossing by 34%.
Instant fault detection and quick repair 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.
Traffic Adaptive Operation 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.
Simulation
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.
Aimsun has a comprehensive SCATS interface which can be retrieve historical signal data. Aimsun is a simulation program rather than an optimisation program. In 2018, a newly-built interface between Aimsun and SIDRA 8 was published.
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.
The Sydney Strategic Travel Model was designed by Hague Consulting Group in 1997.
Products
Current SCATS-developed products include SCATS Roadside, SCATS Console and SCATS Data Insights.
In 2026, Control Centre and Data Insights are planned to support Data insights APIs to support external access to road network metrics.
SCATS Ramp Metering System The SCATS Ramp Metering System (SRMS) is a SCATS subsystem and controls traffic signals at the entries of motorways and integrates with SCATS intersection control for promoting integrated real-time management of the traffic corridor as a whole. The objective of SRMS, based on current traffic conditions, is to efficiently determine: When ramp metering signals start and end ramp metering operation The metering flow rates of the operating ramp metering signals Which actions shall be taken to signalised intersections of the corridor to promote network-wide benefits. SRMS achieves these objectives by implementing a collection of pre-configured adaptive intelligent strategies either automatically or manually. In manual mode, the SRMS operator can create new or manipulate existing rules in order to adjust the ramp metering system for effective operation during any planned or unplanned events (e.g. incidents). SRMS is a distributed control system that operates on a central control server and road-side traffic controllers. The central control server is a component of SCATS and inherently provide integrated motorway and arterial real-time management. The road-side controllers are installed on motorway on-ramps and are used to: Set the traffic signal times Set the state of on-ramp changeable signs Manage the sequences start and end ramp metering operation; and Measure traffic states using vehicle detectors. Metering rates are determined by the local traffic signal controller or by the central control server. Metering rates can be determined in two ways: adaptive operation, or time-of-day-based operation typically when a communications failure or critical vehicle detector failures take place