Systems engineering documents like concept of operations, system requirements, verification, and validation plans provide a structure for agencies to assess whether adaptive traffic control systems can address their issues. Adaptive systems aim to minimize delays and stops by adjusting cycle lengths, splits, offsets, and other parameters in real-time based on detected traffic. Studies show adaptive systems reduce delays, especially at higher congestion levels, though benefits depend on the location. Common adaptive systems include SCATS, SCOOT, RHODES, and InSync, which vary in their algorithms and architectures. High-resolution performance measures from detectors can evaluate system performance. Agencies should use adaptive selectively where appropriate and evaluate outcomes.

1. Adaptive Traffic Control Systems
and future of Traffic Signal Control
Ali G. Eghtedari, Ph.D.
NW Regional Traffic Operations
Engineer
Martin Dedinsky
NW Region Signal Operations

2. FHWA Systems Engineering Approach
Model Systems Engineering Documents:
• Concept of Operations
• System Requirements
• Verification
• Validation
SE documents provide a structure within which you can examine your current or
near future operation to assess whether or not adaptive control is likely to
address your issues and then decide what type of adaptive control will be right for
you.
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3. Systems Engineering Approach
Model Systems Engineering Documents:
Concept of Operations
• Derive the stakeholder needs that should be accommodated by the proposed system
• Define the environment in which the system will operate
• Provide scenarios that describe how the system is expected to operate in practical
situations
• Provide criteria to be used for validation of the completed system
Define the high-level system concept and justify that it is superior to other
alternatives
System Requirements
• Describes functional requirements of the system, and the conditions it will perform
under
• Defines the necessary requirements to satisfy the operational needs identified in the
Concept of Operations;
• Any other requirements necessary for the system to become fully functional
Does not define how the system is to be built
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4. Systems Engineering Approach
Model Systems Engineering Documents
•Verification Plan - Verifies that every step, if done
correctly, will fulfill the requirements.
• Describes how the system will be tested to ensure that it
meets the requirements
• Details the location of verification testing
FAT > BT > SAT
• Vendor is responsible for developing testing method
• Details actions and time frame the vendor needs to
resolve any non-compliant functions
•Validation Plan- Validates that every step, if done
correctly, will provide a system that meets user needs.
• Describes how the performance of the system will be
measured to determine whether the system requirements
have been met
• Agency is responsible for validation testing and data
collection with vendor assistance
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Con
OPS
Sys.
Req.
Ver.
Val.

5. Traditional Signal Timing Process;
• Traditional signal timing process is time consuming and
expensive
• Requires frequent maintenance and updates – i.e. 2-3 years
• Final Assessment is often based on anecdotal and
observational judgment due to cost.
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6. Adaptive Traffic Control Systems
What is ATCS?
An ATCS usually includes algorithms
that adjusts:
• Cycle Length
• Splits
• Offsets
• Phase Sequence
In order to:
• Minimize Delays,
• Reduce the number of stops,
• Decrease the Travel Time.
Any adaptive traffic control system relies
upon good detection of the current conditions
in real-time in order to allow a quick and
effective response to any changes in the
current traffic situation.
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7. 7
Adaptive Systems Objectives
• Balance phase utilization—fair distribution of green
• Minimize arrivals on red—improve progressed flow
• Minimize queue-time density—serve the most cars waiting the
longest
• Minimize combination of stops and delay—delay-offset optimization
• Pedestrians, Emergency vehicles & RR, Transit vehicles, Light Rail
crossings, Traffic Gating, interface with adjacent systems
operations, and other realities
Operations Options:
• Work within existing coordination parameters
• Override or ignore controller or system coordination
• Provide centralized adaptive operation
• Provide localized adaptive operation
• Optimization suited to grid networks or arterial streets?

8. 8
Architecture Varieties
• Built into central system
• Works in parallel to central system
• Built into local controller
• Separate local-cabinet processor
• Replaces field master
• Built into field master
Infrastructure:
• Separate processor may be required
• Varying interface to controllers/systems
• Varying communications requirements
• Detection
– Existing detection
– Special detection

9. Adaptive Traffic Control Systems
Benefits of ATCS
• Improve performance by adjusting to
real time traffic demand
• Adapt to unexpected traffic changes
• Increases signal timing lifespan
• Captures a rich data set
Where is ATCS Most Effective?
• Where unpredictable traffic changes
results in delays or stops that cannot be
addressed by conventional signal timing.
• Where frequent and unpredictable
changes of demand, events, weather
situations, etc. creates major
unexpected fluctuations in the system.
Adaptive is not solution to all
problems of Traffic Management,
AND it does not necessarily solve
the capacity problem of over
saturated corridors.
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10. 10
Adaptive Benefits & Degree of Saturation
MOE Delay (vehicle-hours)
V/C 0.7 0.8 0.9 1.0 1.1
Intersection
ID#
FT* SC* %
Ben*
FT SC %
Ben
FT SC %
Ben
FT SC %
Ben
FT SC %
Ben
1 32.1 29.0 10% 43.3 36.2 16% 50.0 43.1 14% 68.8 64.5 6% 166.5124.2 25%
2 31.6 29.0 8% 38.4 35.7 7% 47.9 42.5 11% 66.3 67.3 -1% 157.7134.7 15%
3 28.3 25.6 10% 35.4 33.4 6% 44.0 36.6 17% 54.2 54.5 -1% 91.3 116.5-28%
4 29.2 27.9 5% 36.0 33.9 6% 47.3 41.5 12% 59.5 61.2 -3% 102.9144.4-40%
Total 121.2 111.4 153.1139.2 189.2163.7 248.8247.4 518.5519.8
Average
Benefit
8% 9% 13% 1% 0%
Delay Benefits from SCOOT on the Corridor at Different Congestion Levels
*FT = Fixed Time Control, SC = SCOOT Control, % Ben = Percent benefit from SCOOT
University of Utah Study (Jhaveri, Perrin, Martin)

11. 11
Adaptive Benefits & Degree of Saturation
MOE Delay (vehicle-hours)
V/C 0.7 0.8 0.9 1.0 1.1
Intersection
ID#
FT* SC* %
Ben*
FT SC %
Ben
FT SC %
Ben
FT SC %
Ben
FT SC %
Ben
1 32.1 29.0 10% 43.3 36.2 16% 50.0 43.1 14% 68.8 64.5 6% 166.5124.2 25%
2 31.6 29.0 8% 38.4 35.7 7% 47.9 42.5 11% 66.3 67.3 -1% 157.7134.7 15%
3 28.3 25.6 10% 35.4 33.4 6% 44.0 36.6 17% 54.2 54.5 -1% 91.3 116.5-28%
4 29.2 27.9 5% 36.0 33.9 6% 47.3 41.5 12% 59.5 61.2 -3% 102.9144.4-40%
Total 121.2 111.4 153.1139.2 189.2163.7 248.8247.4 518.5519.8
Average
Benefit
8% 9% 13% 1% 0%
Delay Benefits from SCOOT on the Corridor at Different Congestion Levels
*FT = Fixed Time Control, SC = SCOOT Control, % Ben = Percent benefit from SCOOT
University of Utah Study (Jhaveri, Perrin, Martin)

12. 12
Adaptive Products & Differences
• ACS Lite
• BALANCE
• InSync
• LA ATCS
• MOTION
• RHODES
• SCATS
• SCOOT
• Synchro Green
• UTOPIA

13. Adaptive Traffic Control Systems
Implementations:
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International Locations*
Dublin City Council Ireland SCATS
New Zealand
Transport Agency
Auckland, NZ
SCATS
RTA - New South
Wales, Sydney Australia SCATS
UOCT
Concepcion,
Chile SCATS
VicRoads
Victoria,
Australia SCATS
City of Blackpool
Council UK SCOOT
City of Red Deer Canada SCOOT
City of Southampton UK SCOOT
City of Toronto Canada SCOOT
Derby City Council UK SCOOT
Greater Manchester
Urban Traffic Control UK SCOOT
Halifax Regional
Municipality Canada SCOOT
Hampshire County
Council UK SCOOT
I Mo TS Siemans Ltd. Beijing, China SCOOT
*NCHRP Synthesis 403 - 2010
Local Installations* Total ATCS Type
City of Menlo Park CA 32 13 SCATS
City of Sunnyvale CA 128 23 SCATS
City of Gresham OR 130 11 SCATS
City of Longview TX 132 16 ACS LT
City of Ann Arbor MI 150 34 SCOOT
Town of Cary NC 150 16 OPAC
Collier County FL 160 16 SCOOT
Pasco County FL 220 35 SCATS
City of Chula Vista CA 265 11 SCATS
Pinellas County FL 370 33RHODES
City of Tucson AZ 375 15RHODES
Washington State DOT WA 520 10 SCATS
Cobb County GA 526 74 SCATS
Orange County FL 572 70 SCOOT
City of Minneapolis MN 800 56 SCATS
Delaware Department of Transportation DE 850 30 SCATS
Utah Department of Transportation UT 1100 16 SCATS
CALTRANS — District 7 CA 1350 180 LA ATC
Road Commission for Oakland County MI 1500 650 SCATS
City of Toronto Canada 2,100 340 SCOOT
Los Angeles Department of Transportation CA 4,300 3,000 LA ATC

14. 14
SCATS
• Sydney Coordinated Adaptive Traffic System
(SCATS) has the largest number of
worldwide installations – Over 34,000
intersections under SCATS control and
largest number of adaptive signals operated
in the U.S.
• The intersection controller sends the
information collected by detectors to a
central server, which automatically adjusts
the traffic signal green time to match the
traffic flow.
• The central server periodically monitors
network wide traffic flow and adjusts all
traffic signals in the network.

15. SCATS Functions
Major features:
• Stand alone system – Does not require a separate underlying Control
System
• Detectors at each intersection detect vehicles approaching and continuously
analyze traffic flow.
Cycle Length
• C.L. is calculated to try and maintain Degree of Saturation of 80-90% on lane
with highest DS; Lower and upper limits are user defined.
• Algorithm determines critical node in order to calculate the cycle length
Splits
• Varied automatically by up to 4% each cycle
• Tries to maintain equal DS on competing approaches, minimums are user
defined
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16. 16
SCOOT
• SCOOT was originally designed to control dense urban networks,
such as large towns and cities in UK by the Transport For London,
and now is owned by a consortium of TFL, TRL, Siemens and
Imtech (now Dynniq).
• There are over 2000 SCOOT systems worldwide working in large
congested cities, small towns and around freeway interchanges.
There are tens of SCOOT installations in North America, including
Toronto, ON.
• SCOOT continually calculates the required coordination pattern for a
group of signals in real time and immediately implements the
changes.
• Bus priority, traffic gating, incident detection, on-line saturation
occupancy measurement, and vehicle emissions estimates are part
of the features of SCOOT MC3 systems.

17. 17
ACS Lite
• Examination by FHWA of the barriers to deployment of
adaptive control led to the development of ACS-Lite, a
cooperative effort with Siemens, McCain, Peek and
Econolite.
• Its approach, aims to improve the quality of
coordinated control while retaining existing systems
with on-street masters, without the installation of large
numbers of detectors or need for central server and
communication network.
• Its algorithm gradually adjusts the background TOD
plans to adapt to gradual changes in traffic conditions,
but does not make real-time adjustments as traffic
volumes change.

18. 18
RHODES
• RHODES was developed by researchers at the University of
Arizona. It currently operates in Pinellas County, FL, and at several
others that are being used as test-beds for further development. It
continues to be used in research supported by FHWA.
• RHODES, departs from the traditional cycle length, splits and offset
approach. It determines when to change state based on current
demand at an intersection and predictions of future arrivals at that
intersection.
• It was installed on SR 522 as a test base under FHWA’s contract.

19. 19
SynchroGreen
• Synchro is being used by numerous Traffic Engineers around the
country as a simple user friendly package for intersection OPS.
• Trafficware and Naztec now offer SynchroGreen which optimizes
traffic signals, considering side-street and pedestrian traffic, as well
as Transit Priority, in addition to mainline traffic.
• The primary objective of the SynchroGreen algorithm is to minimize
total network delay, while providing reasonable mainline
progression bandwidth.
• After optimization of splits at intersections, it steps back and
analyses the whole network prior to assigning individual timing to
intersections.
• Flexible Modes: Balanced, Progression,
and Critical Movement.

20. 20
InSync
• Rhythm Engineering released InSync in 2009 and it has been
installed and tested in several locations, including Sammamish and
Puyallup in WA.
• The underlying philosophy of InSync abandons the concepts of
cycle length and phase sequence. It continually evaluates whether a
signal should remain in its current state or move to a different state,
based on the known demand of traffic at the intersection and
predicted arrivals of platoons from other intersections.
• It’s installation philosophy is to retain the existing traffic signal
controller and other equipment, and install additional hardware that
does the adaptive calculations and commands the controller.
• Uses topology of communicating individual intersections with the
cloud via wireless networks.

21. Purdue University Traffic Signal Performance Measures
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Purdue MOEs
Hi-Resolution Data at 1/10
Second Resolution:
• Phase Termination
• Detector Data Diagram
• Pedestrian Actuation
• Vehicle AOG - Purdue
Coordination Diagram
Most arrivals are during Red!

22. Purdue University Traffic Signal Performance Measures
• Purdue Coordination Diagram – Plots multiple data points for each signal cycle on
a single graph. Graphs only cover a single phase and plot the time of day the cycle
began along the x-axis with the time within the cycle plotted on the y-axis. Data
points include vehicle arrivals, start of green, start of yellow and start of red splits.
Start of green band for instance can be seen as the green line in the above figure.
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Purdue MOEs
Hi-Resolution Data at 1/10
Second Resolution:
• Phase Termination
• Detector Data Diagram
• Pedestrian Actuation
• Vehicle AOG - Purdue
Coordination Diagram
Most arrivals are during Green!

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Traffic Signal Performance Measures
Split Failures
Number of split failures during a
defined period that occur on
each phase.
Percentage of Phases with
Pedestrians
Percentage of signal cycles in a
period that have a pedestrian
activation.

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Intelight & MaxAdapt
• MaxAdapt operates in a distributed architecture running on Intelight
ATC controllers and using peer-to-peer communications.
• There is no requirement for a central system module to support the
adaptive operations.
• The arterial based adaptive algorithm incorporates the high
resolution data collected by the controller and is capable of adjusting
cycle length, splits and offsets.
Requirements:
• Communications - IP based to support the peer-to-peer
communications.
• Detection - MaxAdapt requires mainline detection approximately
400-600 feet from the stop bar at each location.
• MaxAdapt will also require stop bar detection for each approach in
order to optimize splits.

25. 25
V2V and V2i Systems!

26. 26
Moving Forward
• Although most adaptive algorithms belong to the past, embrace
new technology, consider open source.
– Think out of the box, what does it really mean to say that we want a system
that is open source?
• Consider the Client/Server relation - Thin or Thick.
• Consider the scalability and flexibility.
• Focus on Performance Measures as described by Purdue U.
• Don’t get locked into proprietary products.
• Attention to detail - most vendors are good but not most
products are.

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Moving Forward
• Use Adaptive where it is appropriate.
• Select a location where there is a know issue that can be
addressed with adaptive.
• Assess, evaluate, and validate the outcome.
• Be aware of staff capabilities and expectations, turn overs, and
kind of support we need from the vendor to be able to deliver.
• Effective signal timing is an expensive asset which requires
resources to develop and maintain.
• Highly technical subjects such as adaptive signal control are
unmaintainable with loss of “institutional knowledge” as we
gradually lose capable staff.

28. Questions?
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29. State Traffic Engineers Meeting - May 2016
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