Sydney Coordinated Adaptive Traffic System

The Sydney Coordinated Adaptive Traffic System, abbreviated SCATS, is an intelligent transportation system developed in Sydney, Australia by former constituents of the Roads and Maritime Services in the 1970s, used in Melbourne since 1982,^[1] Adelaide, South Australia since 1982 and Western Australia since 1983.^[2] It is also used in New Zealand, Hong Kong, Shanghai, Guangzhou, Amman, Tehran, Dublin, Rzeszów, Gdynia, Central New Jersey,^[3] and soon in part of Metro Atlanta,^[4] among several other places.

The system may be referred to by an alternative name in a specific installation (except Sydney), although since deployment wider than Australia, New Zealand and Singapore, these 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"
• Adelaide "ACTS" (Adelaide Co-ordinated Traffic Signals)
• Perth "PCATS"
• Singapore "GLIDE"
• Northern Territory "DARTS"

In total, about 42000 intersections in over 154 cities in 25 countries use the system. In Australia, the majority of signalised intersections are SCATS operated (around 11,000).

SCATS primarily 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 the current traffic situation (for individual intersections as well as for the whole network). This is based on the automatic plan selection from a library in response to the data derived from loop detectors or other road traffic sensors.

The system 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. 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.

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 the tram 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 architecture of the system 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.

SCATS is already a recognised worldwide market leader in intelligent transport systems, however the New South Wales Roads and Maritime Services is continuing to develop SCATS to meet emerging technological, user and traffic demands.

Hong Kong
In Hong Kong, SCATS is currently adopted in the area traffic control systems at Hong Kong Island, Kowloon, Tsuen Wan and Shatin.

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.

SCATS Ramp Metering System

The SCATS Ramp Metering System (SRMS)^[5] 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 signalized 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

The adaptive operation optimizes mainline traffic state by using real-time data from vehicle detector stations installed at several mainline locations, ramps and optionally at arterial roads. The adaptive operation determines control actions at 10 seconds intervals and applies some or all of the following strategies simultaneously:

• Coordinated ramp metering
• Ramp queue management
• Automatic begin and end of ramp metering operation
• Variation routines for integration with SCATS intersection control
• Variation routines for automated incident responses and unusual circumstances
• Manual controls for incident responses and unusual circumstances
• Critical lane occupancy calibration
• Fault-tolerant strategies
• Data logging for performance reporting and off-line analysis

SRMS is currently used as the Auckland ramp metering system.

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.

When Commuter software was acquired by Autodesk,^[6] 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.

See also

• PTIPS - works together with SCATS to provide transport vehicles with priority at traffic signals

Other Intelligent Transportation Systems include:

• STREAMS
• BLISS

References

External links

• Roads ACT
• Roads and Maritime Services, NSW
• SCATS - Sydney Coordinated Adaptive Traffic System Website
• SCATS - Main Roads Western Australia
• Traffic Lights in NSW - Roads and Maritime Services Website
• RTA and SCATS at the 17th ITS World Congress in Korea
• Review of Bus Priority at Traffic Signals around the World