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U.S. Department of TransportationFederal Highway Administration
ACS-LiteFHWA Adaptive Signal
Control Systems
Raj S. Ghaman, P.E.Team Leader, Office of Operations RD & T
Traffic Signal & Operations Working Group March 26, 2008
Washington D.C., USA
U.S. Department of TransportationFederal Highway Administration
Slide 2
Outline
• Goals
• System architecture
• Adaptive approach– Cyclic performance measures
• Field trials
U.S. Department of TransportationFederal Highway Administration
Slide 3
Adaptive in the U.S. (FHWA)
• 1970s-1980s: UTCS– Second by second central
• 1990s: Predictive control (ACS)– FHWA ACS: RHODES, OPAC– Second by second distributed
• 2002: Controller-based Adaptive– FHWA ACS “Lite”: Siemens ITS– Leverage existing hardware– Update controller parameters every five minutes
U.S. Department of TransportationFederal Highway Administration
Slide 4
FHWA Goals for ACS-Lite
• Low cost design
• Leverage existing infrastructure• Standard US-style actuated controllers (rings,
phases, splits, barriers)• Standard fully-actuated detector layouts• Standard NTCIP Communications
• “Retro-fit” with major US signal system vendors
U.S. Department of TransportationFederal Highway Administration
Slide 5
Project Team
U.S. Department of TransportationFederal Highway Administration
Slide 6
System Architecture
Vendor
Field Master
Protocol Translation
9600bps, up to 12 controllers
NTCIP + ACS-Lite firmware upgrade
Vendor Specific or NTCIP
NTCIP
ACS-LiteOptional
Optional
Field Processor
U.S. Department of TransportationFederal Highway Administration
Slide 7
ACS-Lite Detection Layout
Flow ProfileDetectors
Phase Utilization Detectors
Need detectors at stop-bar of coordinated phases
U.S. Department of TransportationFederal Highway Administration
Slide 8
21
ACS-Lite adaptive control philosophy
• Data-driven parameter tuning
• Limited/no traffic modeling
• Recent past predicts the near future• Splits
– Phase Utilization
• Offsets– Statistical Flow Profiles
U.S. Department of TransportationFederal Highway Administration
Slide 9
ACS-Lite NTCIP firmware upgrade
• Phase Timing Status Object
• Detector Status Object
• Configuration Objects• Polled once per minute
– Second-by-second accuracy– Bandwidth efficient
• Minute-by-minute polls are “stitched” together for cycle-by-cycle performance assessment
1
2
3
U.S. Department of TransportationFederal Highway Administration
Slide 10
Occupancy per phase interval
• Occupancy values per second
• Correlated to Red/Green/Yellow
37s 4s49s
Second-by-secondOccupancy
37s 4s32s
Second-by-secondOccupancy
Cycle 1
Cycle 2
17s
U.S. Department of TransportationFederal Highway Administration
Slide 11
Cycle-by-cycle Data
Phase Timing Volume/Occupancy
U.S. Department of TransportationFederal Highway Administration
Slide 12
Occupancy per interval split tuning
57s4s29s
Phase 2AverageOccupancy
Unoccupied
Averaging
U.S. Department of TransportationFederal Highway Administration
Slide 13
Green occupancy Phase Utilization
U.S. Department of TransportationFederal Highway Administration
Slide 14
Cyclic occupancy profiles Statistical profile
“statistical” flow profile
Example shows need to move offset so green
corresponds with traffic earlier in cycle
U.S. Department of TransportationFederal Highway Administration
Slide 15
Progression Performance Offset tuning
• Performance measure for offsets “capture efficiency”
• Shift offsets small amount
• Constrain changes within user-configurable bounds
Inbound
Outbound
U.S. Department of TransportationFederal Highway Administration
Slide 16
Field trials
PEEKSt. Petersburg/Tampa, Florida
EconoliteColumbus, Ohio
Eagle/SiemensHouston, Texas
McCainSan Diego, California
U.S. Department of TransportationFederal Highway Administration
Slide 17
Field trial – Columbus, Ohio
• Early “lessons learned”– Communications integrity– Detector configuration
• Separate channels per lane
– Remote configuration capability
– Details, details
High School
Freeway
3km
Major road
Major road
Construction zone
U.S. Department of TransportationFederal Highway Administration
Slide 18
Columbus, Ohio - Hamilton Road
Study Area N
U.S. Department of TransportationFederal Highway Administration
Slide 19
Columbus, Ohio – Hamilton Road (con’t)
U.S. Department of TransportationFederal Highway Administration
Slide 20
ACS-Lite Field trial – Houston, Texas State Route 6
Study AreaN
U.S. Department of TransportationFederal Highway Administration
Slide 21
Houston, Texas – State Route 6 (con’t)
U.S. Department of TransportationFederal Highway Administration
Slide 22
ACS-Lite Field trial – Tampa, Florida State Route 70
Study Area
N
U.S. Department of TransportationFederal Highway Administration
Slide 23
Tampa, Florida – State Route 70 (con’t)
U.S. Department of TransportationFederal Highway Administration
Slide 24
ACS-Lite Field trial – San Diego, California Main Street
N
Study Area
U.S. Department of TransportationFederal Highway Administration
Slide 25
San Diego, California – Main Street (con’t)
U.S. Department of TransportationFederal Highway Administration
Slide 26
Future
• Algorithms enhancements (2008):– Long-term parameter
adjustment • Seasonal baseline parameters• TOD schedule switch points
– Cycle time tuning– Selection of transition
method– Better Graphical User
Interface (GUI)
U.S. Department of TransportationFederal Highway Administration
Slide 27
Questions?