Transcript RT-TRACS: Development of the Real

RT-TRACS Adaptive Control
Algorithms
VFC-OPAC
Farhad Pooran
PB Farradyne Inc.
TRB A3A18 Mid-Year Meeting and
Adaptive Control Workshop
July 12-14, 1998
Pacific Grove, CA
VFC-OPAC
(Virtual Fixed Cycle OPAC)
• Real-time, traffic adaptive control of signals in a
network
• Distributed optimization based on the OPAC
(Optimization Policies for Adaptive Control) smart
controller
• Multi-layer network control architecture
• Variable cycle in time and in Space
VFC-OPAC Development History
• OPAC I: Dynamic Programming optimization
– infinite horizon (single intersection)
• OPAC II: optimal sequential constrained search
procedure
–
finite projection horizon length
• OPAC III: rolling horizon approach
– real-time implementation
• OPAC IV (VFC-OPAC): network model for real-
time
–
traffic-adaptive control
Control Layers in VFC-OPAC
Intersection
1
Network
Synchronization
Layer
Layer 3
Coordination Layer
Layer 2
Intersection
2
Intersection
n
Layer 1
Control Layers in VFC-OPAC
• Layer 1: Local Intersection Control Layer
(phase length) - Optimal switching sequences
for projection horizon, subject to virtual fixed
cycle constraints
• Layer 2: Coordination Layer - Real-time
optimization of offsets at each intersection
• Layer 3: Signal synchronization - network
wide calculation of virtual fixed cycle
VFC-OPAC
Network Module
FS
D1
D2
FS
PS
FS
D4
D3
FS
PS = Principal Signal
FS = Feeder Signal
D = Detector
Data Requirements
• Ideal detector location is about 10 seconds
upstream of stop line (at free flow speed) or
upstream of the worst queue on each lane of all
through phases.
• One count detector in each lane of left turn
pockets as far upstream as possible
• Automatic compensation for ‘bad’ detectors
• Volume, occupancy, and speed measured in the
field
Control Variables
• OPAC optimizes (minimizes) a weighted
performance function of total intersection stopped
delay and stops subject to minimum and
maximum green times
• Under coordination, signal timings are also
constrained by the current cycle length
• Current Counts, Occupancy, and Speed (measured
or calculated)
Decision Variables
• Terminate the current phase in ring 1
(Yes or No)
• Terminate the current phase in ring 2
(Yes or No)
State Variables
• Signal status
• Elapsed time since last signal status change
• Standing queues
• Cumulative delay
• Cumulative stops
Constraints on Decision
Variables
• Phase interval timings (minimum green,
maximum green, yellow, all red, walk and
don’t walk)
• Opposing demand (vehicle and pedestrian
calls)
• Cycle length constraints
• Offset adjustments
How Are Flow Profiles
Developed?
• Upstream detectors can provide an actual
history for a short portion of the profile.
• Smoothed volume can be used for uniform
profiles.
• Platoon identification and smoothing can be
used for cyclic profiles.
• Adjustments can be made to eliminate double
counting (left turn phases).
How Are Flow Profiles
Developed?
• Upstream
Past
Future
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Hypothetical arrival
pattern over the detector
used by successive
iterations of the OPAC
intersection simulation
and timing optimization
algorithms. Each square
represents one step (2-3
seconds) in time.
Time
detectors can
provide an actual
history for a
short portion of
the profile.
Cycle Length Optimization
• Meet phase switching timing determined
by local conditions, while maintaining a
capability for coordination with adjacent
intersections
• Using a cycle length constraint, the cycle
length can start or terminate only within a
prescribed range
• All VFC-OPAC controlled intersections can
oscillate with a common frequency
Offset Optimization
Options:
• Leave current offset ( zero change)
• Move right one interval (+2 sec)
• Move left one interval (-2 sec)
Data Sampling
• Develops a flow profile for each phase using a user-
specified time interval
• Head of the profile is actual counts from the recent
past.
• The tail of the profile is projected for the future using
smoothed volume
• Smoothed data: volume, occupancy, speed, platoon
headways, flow profiles, and phase duration
MOE’s
• Volume, occupancy, speed by detector and
phase.
• Estimated measure of queue, delay, and
stops by phase.
Phasing Flexibility
• Supports 8 phases in a dual ring configuration
• Does not explicitly control phase sequence
• Can recognize and adapt to changes in
sequence immediately
System Architecture
• Isolated intersection control - fully distributed
• Coordinated system control - basically distributed
except for the following tasks:
cycle length determination is made at central and
communicated periodically to the intersection controller
– peer-to-peer information is communicated through central
on a periodic basis (if adjacent intersection controllers are
not linked physically)
–
Hardware Requirements
• Local Controller:
–
a computer board with a floating point processor
and 4 MB memory (e.g., 68040 or 68060 boards)
• Central:
–
3 to 4 PC’s for OI, Server, dB, Device Drivers and
Communications with at least 2 GB of HD and 64
MB RAM
Communication Requirements
• Communications with Central: OPAC status is
polled
• Communications with Signal Control
Software
• Peer-to-peer communications
Network Type
• For coordinated signal control, cycle lengths are
calculated for user-specified groups (sections)
of signals (arterials or networks)
• The cycle is calculated using the critical v/c
ratios of the critical intersection in the section
• The field computer optimizes offsets with its
neighbors, not the entire section.
Special Features
• Preemption:
–
–
–
Preemption will always take priority over OPAC.
Prioritizes transit and emergency vehicles if they are
restricted to particular lanes
Recovers from a preemption immediately
Special Features
• Oversaturated Conditions:
–
–
Isolated intersection control - OPAC will provide
maximum green to the affected phase(s) if occupancy on
the OPAC detectors exceeds a user-specified threshold.
Coordinated control
•
•
Provide maximum green to congested phases, subject to the current
cycle length
Adjust cycle lengths in response to increasing congestion
Field Installations
• 1986 - Isolated OPAC in Arlington, Virginia
and Tucson, Arizona (Single intersection
control)
• 1996 - Isolated OPAC at a Route 18 site in
New Jersey (15-intersection arterial)
• 1998 - Coordinated OPAC at Reston Pkwy
site, in Reston, Virginia (16-intersection
arterial )