Sydney Coordinated Adaptive Traffic System

Default operation

The architecture of SCATS is at two basic levels, Tactical control (local) and Strategic control (regional, known as MASTER^{[citation needed]}).^[9]: 182 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.^[9]: 182

Strategic control (regional) is a regional computer which target cycle length, splits, and offsets for subsystems based on detector data.^[9]: 181 It provides area based traffic control, i.e. area traffic control (ATC) or urban traffic control (UTC).^{[citation needed]} 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.^[9]: 182

SCATS is able to operate over PAPL, ADSL, PSTN and 3G IP network connections to each intersection.^{[10][11][12][13][circular reference]} 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.^[11][12]

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.

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'.^[14] Lower cycle times reduce the wait time and delay for pedestrians.^[14]: 10 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.^[15]: 8 SCATS records pedestrian demands and this can be accessed from event logs in SCATS History.^[16][17]

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.^{[18][15]: 8}

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.^[9]: 183 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.^[9]: 183

A graphical program called SCATS History Viewer has export functionality for actual phase and cycle statistics.^[9]: 185 The program facilitates the extraction of this data into commonly used formats that can be easily consumed by other systems.^[19]

Longer or more frequent green signals for pedestrians can reduce unsafe crossing by 34%.^[20][6]

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.

In New South Wales, Australia

Transport for NSW (TfNSW) is responsible for controlling signals in New South Wales, the same agency which develops the SCATS software. As of November 2025, there were 4860 traffic signals across NSW.^[31]

In January 2018, Transport for NSW reduced the cycle time for a subset of the Sydney CBD from 110^[32] to 90 seconds.^[33][34] The Lord Mayor of the City of Sydney council wrote to the Roads Minister to request a broader rollout of 90 second cycle times on the 8th of November 2018.^[33][34] The Roads Minister declined to comment on the request.^[34]

In Western Australia, Australia

Main Roads Western Australia previously published a real-time websocket feed of signal timing.^[35] As of 2025 WA Main Roads publishes historical SCATS traffic signal phase data under an open source Creative Commons CC BY 4.0 license.^[36] Data is published in monthly machine-readable Parquet files.^[37] Data includes times for each phase and measured volume.^[38]

On the TrafficMap website WA Main Roads openly publish Detector Volume Data,^[39] Pavement and Signage Drawings,^[40] Traffic Signal Arrangement Drawing,^[41] Signal Data (including Phase Times, Pedestrian Phase Times, Special Times, Link and Offset Plans, and SCATS Phase History tables)^[42] and Phase Sequence Charts^[43] for every signal in the state.^[44]

In Victoria, Australia

The Department of Transport and Planning are responsible for the safety and efficiency of traffic signals throughout Victoria.^[45] SCATS was trialled in Melbourne in 1978 and adopted for use throughout Victoria in 1980. In 2018, SCATS controlled more than 4,000 sets of traffic signals across Melbourne and other Victorian rural cities such as Ballarat, Bendigo, Traralgon, Geelong and Mildura.^[46]

DataVic publish Traffic Signal Volume Data sourced from the detector loops and the SCATS system under an open-source Creative Commons CC BY 4.0 license.^[47] Historical data is published back to 2014.^[48] Historical Annual Average Daily Traffic Volume data is published from 2001 to 2019 in the GeoJSON format under CC BY 4.0.^[49]

DataVic also publishes Traffic Signal Configuration Data Sheets, also known as 'operation sheets' or 'op-sheets'.^[50] These operation sheets detail signal group and detector functions at each intersection along with the phasing of the site. They include detailed notes outlining the specific operation of signal groups, phases, detectors and general site operation, the traffic signal sequences (phases), and the phase and pedestrian time settings which govern how the site operates.^[51]

In South Australia, Australia

The City of Adelaide typically has green walk signals in the range of 5-8 seconds.^[15]: 11

Auto pedestrian demand was implemented in the City of Adelaide before 2015. As of March 2025 it was is enabled at 49 locations between 7am and 7pm. Some sites, including North Terrace at the Railway Station, and the intersection of King William Street and Rundle Mall and Hindley Street, are enabled 24/7.^[15]: 7

A March 2025 review of signal timing along O’Connell Street in North Adelaide in found that reducing the cycle length could reduce the average pedestrian delay by 14 seconds and allow between 6-21 extra opportunities for people walking to cross during midday peak hour. Reducing signal cycle times was also found to reduce queue lengths and reduce average delays for vehicles by 38-46% in the PM and 50-54% in the midday peak.^[15]: 19

In Queensland, Australia

In March 2019, the Minister for Transport and Main Roads announced a $3 million investment for smart technology at up to 300 key pedestrian crossings. The minister stated one-third of all pedestrian fatalities and hospitalisations occurred at intersections.^[52] The Brisbane Times described a benefit of the technology as "motorists will no longer be stuck waiting when jaywalkers have crossed early".^[53] The Queensland Transport and Roads Investment Program had a $4.5 million line item for "Smart Crossings project, statewide".^[54]

By September 2025 the Queensland Government Smart Crossings (SX) Project had installed 112 Smart Crossings at 70 intersections.^[55] When radar footpath detectors are used, demand indicators lights (on pedestrian buttons) must be present or installed.^[56]

For smart crossings, the flashing red (don't walk) time is calculated using 1.0 m/s where slow walking is not expected to be encountered, or otherwise 0.8 m/s.^[56]

In Singapore

In 1988, SCATS was adopted in Singapore and named GLIDE, replacing a fixed time system.^[57]

Singapore has a system called Green Man+ which allows a longer green time for elderly pedestrians (over 60 years old) or people with a disability. Green duration is extended by 3 to 13 seconds depending on the crossing width. Identification cards are required to be tapped onto a reader mounted above signal push buttons. Green light duration is otherwise fixed and pre-determined.^[58]

Green Man+ has been installed at over 1,000 crossings and installation of 1500 more is planned by the end of 2027,^[58][59] covering half of pedestrian crossings in all residential estates.^[59]