1. Presented by: Betsy Williams TransCore
The Technology Side of the Sydney Coordinated Adaptive Traffic System (SCATS)
I’m Betsy Williams, TransCore’s area manager in the Atlanta office.
SCATS has been around long enough that I expect most of you have at least heard of it. I was asked to talk to you today about the technology side of SCATS, since we’re an ITS organization, not a planning crowd.
I will give you a little bit of background on the system,
Briefly describe the benefits
Tell you about the objectives of the system
Then get into the technology requirements of detections, controllers, server hardware, and communications.
Presented by:
Betsy Williams
TransCore

2. SCATS Background
The Roads and Traffic Authority of New South Wales (RTA)
Developer and primary user of SCATS
Continued innovation through user group involvement
Extensive user base
Effective, mature, practical system
Worldwide - over 21,000 intersections under SCATS control in 71 installations
SCATS was originally developed by the RTA for use in Sydney, thus the name Sydney Coordinated Adaptive Traffic System. RTA continues to be the primary developer for the software, continually making improvements and innovations based on input from users in over 71 installations worldwide.
Since SCATS initial deployment in the 1980s, it has grown to over 21,000 intersections in 71 installations worldwide.

3. SCATS Worldwide System Installations
Dublin
Waterford
Gresham
Park City
Menlo Park
Sunnyvale
Rzeszow
Detroit
Shenyang
Delaware
Durham
Tehran
Mashhad
Cobb Co
Shijuazhuang
Chula Vista
Israel
Yanbu
Yichang
Tianjin
Shanghai, Ningbo
Suzhou Hangzhou
Pasco Co.
Doha
Guangzhou
Mexico City
Toluca
Hong Kong
Dacca Hanoi
Pattaya Vietianne
Manila
Cebu
Kuala Lumpur
Seremban
Singapore
Brunei
Sandakan
Jakarta
Bandung
The majority of SCATS installations are in Australia, southeast Asia, and China. The number of US installations continues to grow.
Suva Fiji
Darwin
Perth Adelaide Sydney
Melbourne
& many other cities
Pietermaritzburg
Concepcion
Auckland Wellington Christchurch + 11 cities

4. SCATS US Installations
The Road Commission of Oakland County Michigan was an early user, even when they had to use imported Australian controllers and install them upside down (just kidding). Now they use 170s at over 600 intersections.
Cobb County’s SCATS installation in the Cumberland/Galleria area is now the 2nd largest in the US, with 74 intersections online.

5. Benefits of SCATS Reduces need/effort for updating signal timing
Accommodates traffic fluctuations
Allow special functions to be installed for event centers
Assist maintenance of signals via monitoring features
Collect volume counts for planning purposes
As expected, SCATS keeps up with changes in volume, whether it’s a temporary change or the result of growth or development, so the need for retiming is reduced.
SCATS also accommodates unexpected traffic changes, such as early peaks, accidents, or special events. Special functions can also be programmed to handle traffic at event centers.
A less well-known benefit is the robust monitoring capabilities of the system, especially for detectors. SCATS sends up a flag if a detector doesn’t place a call for a certain length of time, so the system thinks there’s an open circuit.

6. Typical Adaptive vs. TOD Graph
So… what does SCATS adaptive timing look like compared to a good time of day plan?
This graph shows the cycle lengths of a time of day plan (the red line) compared to SCATS adaptive cycle lengths.
You can see that the TOD plan went to a morning peak cycle length before it was really necessary, it wasn’t long enough for a few times, and it dropped back to a shorter cycle length too soon at the end of the day.
The dark blue space between the necessary cycle length and the TOD cycle length can translate into delay for somebody at the intersection.

7. SCATS Objectives Select cycle length, splits and offsets to achieve
Minimum stops with light demand
Minimum delay with normal demand
Maximum throughput with heavy demand
SCATS uses real-time data from detectors to optimize three parameters (cycle length, splits, and offsets) for the entire system.
With light demand, SCATS minimizes stops.
With normal demand, SCATS minimizes delay.
With heavy demand, SCATS maximizes throughput.

8. SCATS Detection
Now… we’re to the technology part.

9. SCATS Detection Requirements
YES
Stop bar NO
Advanced
Upstream
Downstream
Mid-block
I think the most common misconception about SCATS is that it’s very detection intensive. In reality, the system requires only stop bar detection, not advanced detection, upstream detection, downstream detection, mid-block detection, retina scans, or anything else.

10. SCATS Detector Requirements
Presence detection
Optimal strategic SCATS detectors are 6 ft x 15 ft located at the stop line for all lanes
Detectors can be longer or shorter if needed, however shorter is better than longer
Local actuation detectors may be used at minor intersections and can be varying in size
The detector technology can be loop detection, as is used in Oakland County, or it can be video detection, like Cobb County is using. The system simply needs presence detection.
Optimally, detectors should be 6x15 and located 3 feet behind the stop bar, one detector per lane.
If a detector is longer or shorter, the system can handle it, but shorter is better than longer. As I’ll explain in a minute, SCATS looks at the space between vehicles, so a long detector is less likely to calculate that space accurately.

11. Typical Detector Layout
This illustrates the typical detector layout: one detector per lane, right behind the stop bar.

12. SCATS Detectors SCATS operates by looking at “space” between vehicles
Eliminates vehicle length from equation
Graph is linear with no double curves
Here’s a very simplistic description of the “space time” factor SCATS uses to determine traffic density.
SCATS looks at how much time the detection zone is unoccupied. When there is a lot of “space time” traffic density is low, but when there isn’t much “space time” traffic density is high.
Compare that to an algorithm that uses traffic volumes to determine density. Low volume could mean that there isn’t much traffic on the street, or it could mean that there’s so much traffic that nobody can move and the cars aren’t passing through the detection zone very often.
Loop
Space Time (secs)

13. SCATS Equipment
On to the other hardware and communications

14. SCATS Controllers SCATS uses 2070 controllers Eagle M-50 series
2070 Lite – no VME backplane
Eagle and Econolite 2070s
2070N – reuse of existing cabinets
Eagle M-50 series
170 E controllers
SafeTran or McCain controllers
I’d guess that the second most common misconception is that SCATS still requires Australian controllers. NOT SO!
TransCore invested a lot in getting the SCATS controller software ported to the 170 controller, and now the system will run on both 170s and 2070s.
I have to admit that I’m not very knowledgeable about controllers, but these are all controller models that SCATS is currently running on in various locations around the US.

15. Hardware Requirements
Server Requirements
Minimum 400 MHz Intel processor – 128M RAM
Windows NT or 2000
Laptop and Workstation Requirements
Minimum 400 MHz Intel processor – 128M RAM
Windows NT, XP or 2000
Dial-in access
56K modem
VPN access
As far as the system server in the control center, it doesn’t take much horsepower to run SCATS. The centralized system constantly takes in data from each intersection and optimizes the cycle length, splits, and offsets, and send the operating instructions back to the controller.
The server needs to use Windows NT or 2000, have a minimum 400 MHz Intel processor, and 128meg of RAM.
The workstation, which can be a laptop, has the same requirements except it can also run Windows XP.
Dial-in access only requires a 56K modem, or you can connect remotely by VPN access.

16. Communications
Leased line, twisted pair copper, fiber optic, spread spectrum radio
300 bps per controller
Point-to-point communication
Point-to-multipoint communication
Ethernet/IP communications
If you’re used to high bandwidth ITS devices such as CCTV cameras, SCATS requires next to nothing. The thousands of intersections in Sydney use twisted pair copper communications for years.
Each controller only requires 300 baud comm, so the comm can be leased line, twisted pair, spread spectrum radio, or fiber optics. Cobb County’s system is using county-owned fiber optic cable.
We can use point to point communication, point to multipoint, or IP addressable ethernet comms.

17. SCATS Operation
I really hoped we’d be able to dial in to Cobb County’s system and show you some real-time operation…

18. SCATS Modes Adaptive Mode Time-of-Day Mode Free Mode Master Free Mode
Traffic adaptive coordination mode
Time-of-Day Mode
Fixed-time coordination fallback mode
Free Mode
Vehicle actuated operation
Master Free Mode
Vehicle actuated with SCATS calculated splits
Flash
So I’ll just have to describe some of this to you.
In addition to operating in adaptive mode, SCATS can also run time of day plans. This is how the intersections will run if they lose communications with the central server.
Free mode in SCATS is just like free with other systems: vehicle actuation drives all of the signal operations. This is how most intersections around here run in the middle of the night, unless detectors are malfunctioning, then… well, you know what happens. It stays red for you for a long time until you get so frustrated you run the light.
Master free mode
SCATS intersections go into flash just like other systems, if the conflict monitor is tripped or the controller dies or by manual operation.

19. SCATS GUI Familiar Windows interface Real-time information
Pull down menus
Real-time information
I have a few slides of the SCATS graphic user interface. It’s a windows-based interface with pull down menus and real-time updates on the signal operation.
We can see a lot about the system or an individual intersection at a glance.

20. Active Time-Space Monitor
One display that we use a lot is the active time-space monitor.
You can set up corridors and watch the activity at every intersection along the corridor.
The time-space monitor is pretty similar to most time space diagrams that traffic engineers are used to seeing, except that you don’t see the entire green band progressing down the road.

21. Reports
SCATS has some nice reporting tools. This particular report shows the operation of a single intersection for a 24 hour period. You can see the amount of time each phase got throughout the day.

22. These two graphs are a great illustration of the power of SCATS to adapt to unusual conditions.
The graph on the bottom is typical operation at a signal near the mall on Sunday. The peak comes in around 10:00 a.m. and is steady, with a couple of blips between noon and 3:00.
The graph on top is the previous weekend: Mother’s Day. Traffic picked up several hours earlier and had an unusual peak at about 8:00 when all those nice kids took their mothers to breakfast, and another big spike between 11 and 12 when the rest went out to lunch. The spike at 5:00 must be when the mothers went back to the mall to buy their own present.

23. For additional information contact: Betsy Williams TransCore (770) or Travis White TransCore (801)

25. Proven Performance Chula Vista, CA Menlo Park, CA
Travel Time Reduced By Up To 15%
Travel Speed Increased By Up To 18%
Delay Reduced By Up To 43%
Menlo Park, CA
Stops Reduced By Up To 24%
Travel Time Reduced By Up To 28%
Delay Reduced By Up To 44%

26. Proven Performance Road Commission For Oakland County, Michigan
Corridor Travel-Time Reduction Range 6.56% To 31.8%
Average Travel-Time Improvement 7.8% For Peak Traffic During Peak Periods
Broward County, Florida
Stops Reduced By Up To 28%
Travel Time Reduced By Up To 20%
Delay Reduced By Up To 42%

27. SCATS Functions - CYCLE LENGTH
Automatically calculated to try to maintain Degree of Saturation between 80% and 90% on the lane with the highest DS
Lower and upper limits are user definable (20 secs to 190 secs)
Can vary by up to 21 seconds per cycle – usually only 2 to 5 seconds

28. SCATS Functions - SPLITS
Varied automatically by up to 4% each cycle.
Tries to maintain equal Degree of Saturation on competing approaches.
Minimums are user definable.
Maximums are limited by cycle length and minimum requirements of other phases.

29. SCATS Functions - Linking
Intersections can "marry" or "divorce " with each other
Married intersections operate on a common cycle length (and offset plan)
Intersections marry:
when their CL's are within 10 sec or
when one-way volume exceeds a configured threshold or
when a “forced” / continuous “marriage” is required
SS 1
SS 2
SS 3
SYSTEM

30. SCATS Functions – OFFSETS
The best offsets are selected for the high flow movements.
Preset offset plans automatically vary to compensate for varying cycle lengths.
Directional bias based on measured flows.

31. Intersection Display Currently activated detectors shown blue.
Shown red if faulty

32. Alarm Display
All operator actions and alarms can be sorted, filtered and printed