Adaptive Signal Control
Southern District ITE
Mark Rogers – Southeast Regional Sales Manager
© Siemens 2009. All rights reserved.
What are the Ground Rules of Adaptive Control ?
Adaptive Control DOES
 Reduce or Eliminate the Need to Retime Signals
 Respond to Stochastic Changes in Traffic
 Help Delay Onset of Saturation
 Help Exit Saturation Sooner than Without Adaptive Control
 Reduce Delay
 Require Detection
Adaptive Control DOES NOT
 Increase Capacity
 Eliminate Saturation if Roadway is Over Capacity
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June 11
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The State of Traffic Signal Operations
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June 11
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Traffic Signals Compete for Resources
Page 4
June 11
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Traffic Signal Control Evolution
Late 1960s
Open Loop System
With Traffic
Detection
Centralized Control
UTCS
Central Control
Interval or Phase Control
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June 11
Mid to Late
1980s
Mid 1990s
2000
Closed Loop Control
Closed Loop
Adaptive Control
Central
Timing Plan selection by
Field Master
Traffic Responsive /
Adaptive Control
SCATS
SCOOT
ATCS
Timing Plan selection by
Field Master (ACS-Lite)
Adaptive Control
RHODES
OPAC
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Traffic Adaptive Signal Control Evolution (A Few
Highlights)
Traffic Responsive (Started in UTCS Type Systems)
 Started in UTCS Systems
 Used Time Hysteresis to Avoid Constant Transition
 Used % Better for Determining Plan Change Conditions
 Required Significant Configuration
 Still Requires Signal Timing Optimization
SCAT and SCOOT
 SCAT = Sydney Coordinated Adaptive Traffic
 SCOOT = Split Cycle Offset Optimization Technique
 Both Are Well Established and Have Been Studied Extensively
 Both Process Data at the Central Computer Level
RT-TRACS (Real-Time – Traffic Adaptive Signal Control System
 RHODES – Realtime Hierarchical Optimized Distributed Effective System
 OPAC – Optimized Policies for Adaptive Control
 Both process data at the intersection level
ACS Lite (Adaptive Control Software)
 Currently Does not Do Cycle Adjustment
 Does Split and Offset
Page 6
June 11
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Fixed Time Cycles and Splits
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June 11
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SCOOT Variable Cycles and Splits
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June 11
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SCOOT Principles
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June 11
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SCOOT Demand Profiles
Cyclic Flow
at the
Detector
Dispersion Model
Journey (Travel) Time
Stopline Demand
Page 10
June 11
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SCOOT Queue Model
Flow
Rate
Time now
Cyclic Flow Profile
Saturation
flow rate
Cruise
speed
ACTUAL
QUEUE
Flow adds to
back of queue
Modelled
queue at
time’now’
Time ‘now’
Stop Line
Red time
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June 11
Green time
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Optimizers
Optimiser
Split
Frequency
Change values
(seconds)
Every phase change
+4, 0, -4 (temporary)
+1, 0, -1 (permanent)
(typical)
Page 12
Offset
Once per cycle
+4, 0, -4
Cycle time
Every 5 or
2.5 minutes
+4, 0, -4 (32-64)
+8, 0, -8 (64-128)
+16, 0, -16 (128-240)
June 11
(typical)
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SCOOT Split / Cycle / Offset Optimizer (What is the
approach?)
Split Approach
 Balance saturation and congestion
 Considers each approach in turn
Cycle Approach
 Minimise overall delay
 Considers each SCOOT region individually
Offset Approach
 Minimise stops, delay and congestion
 Considers one node at a time
Page 13
June 11
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Monday through Friday Split Data
GA400 SB Ram p SCOOT an d TOD Spl i t Ti m e
Ph ase 4 - Mon day t h r ou gh Fr i day i n Decem ber
Split Time (Seconds)
80
70
60
50
40
30
20
10
0
12:00 AM 2:24 AM 4:48 AM 7:12 AM 9:36 AM 12:00 PM 2:24 PM 4:48 PM 7:12 PM 9:36 PM 12:00 AM
Time of Day
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June 11
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Monday Through Friday Average Split Data
GA 40 SB Ramp SCOT and TOD Split Time
Phase 4 – Monday through Friday ver
A
age in December
Page 15
June 11
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ACS Lite System Architecture
 ACS Lite Plan Changes
 Split and Offset
 Cycle After Phase II
 ACS Lite processor
 Field master, or
 Central server
 User Interface (UI)
 Web-based
 Easy configuration
 Upload most data
 Just known facts
 No calibration
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June 11
Laptop/Central
ACS Lite
ACS-Lite User Interface
May run as field master, in cabinet.
or on a server at a central operations facility
Local Controllers
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ACS Lite Measuring Demand
Phase Timing
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June 11
Volume/Occupancy
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ACS Lite Detector Data During Green
 Occupancy during green is distinguished from occupancy during red
(this is slightly simplified for clarity)
Cycle 1
Second-by-second
Occupancy
37s
49s
37s
32s
4s
Cycle 2
Second-by-second
Occupancy
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June 11
4s
17s
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ACS Lite Averages Demand Over Last Few Cycles
Averaging
Unoccupied
Phase 2
Average
Occupancy
29s
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June 11
4s
57s
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ACS Lite Example : (Before Adjustment – 100%
Saturation of a Phase)
 Balance degree of saturation across phases
 Bias to allocate “extra” green to progression phases
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ACS Lite Example : (After adjustment –
Rebalanced with no over-saturation)
 Balance degree of saturation across phases
 Bias to allocate “extra” green to progression phases
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Wreck on GA 400 With Detour on Old Milton Pkwy
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June 11
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Wreck on GA 400 With Detour on Old Milton Pkwy
Page 23
June 11
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Benefits of SCOOT (Before / After Studies in North
America and Around the World)
Benefits (% reduction)
City
Year
Field trial /
Simulation
(Agency)
Compared
to
Fixed-time
(TRANSYT)
London, UK
1985
Field Trial
(Greater London Council)
Worchester, UK
1986
Fixed-time
Field Trial
(Transport Planning Assoc.) (TRANSYT)
Beijing, China
Field Trial
1989 (Beijing Res. Inst. of Traffic
Engineering)
Santiago, Chile
1993
Field Trial
(Univ, Catolica de Chile)
Toronto, ON
1993
Field Trial
(Toronto Metro Transport.)
Salt Lake City, UT 2003
CORSIM-Simulation
(Univ. of Utah)
Delay
Stops
Travel
time
8%
19%
5%
7-20%
2-16%
3-11%
19-32%
Emission
(Fuel,
Hydrocarb,
CarbonMon.)
0-6% Fuel
Savings
83.000 veh-hour/year
GBP 360.000
31%
0.98- 126.4 - 210.4
FYRR ($benefits / $
investment)
22%
Fixed-time
(actuated/coord.,
fully act.)
17%
8%
6% Fuel
4% HC
5%CO
11-14%
 SCOOT works best in undersaturated conditions
 SCOOT delays and reduces the onset of congestion
 Once saturation is reached SCOOT behaves similarly to fixed-plan
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Benefits of SCOOT
(Corridor vs. Network Performance)
Simulation-Based Studies in Salt Lake City (Univ. of Utah, 2003)
Corridor vs. Network
Network
Type
Simulator
16-int. network
vs.
4-int. Corridor
CORSIM
Compared
to
SYNCHRO fixed-time
Benefits: delay reduction
Network
Corridor
21%
13%
 SCOOT performs better than optimized fixed-time in both corridors and complex
networks
 However in networks SCOOT provides greater benefits
Page 25
June 11
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Benefits of SCOOT
(Performance with Incidents)
Simulation-Based Studies in Salt Lake City (Univ. of Utah, 2003)
Incidents
Network
Type
- 28-int (SLC CBD)
and
- 15-int. (Fort Union)
Simulator
CORSIM
Compared
to
SYNCHRO fixed-time
Benefits: (reduction)
Incident
Duration Delay Stops Travel time Queue length
15 min.
28%
23%
31%
24%
30 min.
28%
23%
31%
24%
45 min.
28%
23%
31%
24%
 During incidents and special events, SCOOT provides a significant increase in
benefits (delay, stops, travel time, queue length)
 Benefits increase with the increase of the incident complexity
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Benefits of SCOOT
(Performance with Transit Priority)
Simulation-Based Studies in Salt Lake City (Univ. of Utah, 2003)
Transit Priority
Benefits: (delay reduction)
Network
Type
Simulator
Compared
to
Incident
Duration
With Bus-Priority
Without Bus-Priority
Non-Bus Delay Bus Delay Non-Bus Delay Bus Delay
reduction
reduction
reduction
reduction
9-int. SLC
corridor
VISSIM
SYNCHRO fixedtime
(actuatedcoordinated)
45 min.
16%
27%
21%
5%
 SCOOT reduces transit delay with minimal impact to other traffic
 With transit priority, delay reductions for both transit and non-transit vehicles are
even higher
Page 27
June 11
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SCOOT - On-street Performance
Metro Toronto’s Adaptive Traffic Control System - the first
SCOOT implementation in a major metropolitan area in
North America.
The results were impressive, with
consistent decreases averaging ...
8%
for Travel
time
22%
for Vehicle
stops
17%
for Vehicle
delays
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SCOOT - Reducing Air Pollution
On-street evaluation of Metro Toronto’s SCOOT system
showed that over the network of 75 intersections a total of ...
260,000 gallons of gasoline were saved
More importantly, these decreases in fuel consumption were
established along with annual reductions of
11.2 tons of hydro-carbons (HC)
72.1 tons of carbon monoxide (CO)
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Industry sector, Mobility division, US, Traffic Solutions
Thank You
Mark Rogers
Regional Sales Manager
Traffic Solutions
Industry
Mobility Division
Siemens Energy and Automation, Inc.
5405 Metric Place
Norcross, GA 30092
USA
Mobile 678.296.7481
Rogers.mark@siemens.com
www.itssiemens.com
Page 30
June 11
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Industry sector, Mobility division, US, Traffic Solutions