RT-TRACS Adaptive Control Algorithms

VFC-OPAC

Farhad Pooran

PB Farradyne Inc.

TRB A3A18 Mid-Year Meeting andAdaptive Control Workshop

July 12-14, 1998Pacific 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

Netw orkSynchronization

Layer

Coordination Layer

Intersectionn

L a y er 3

L a y er 2

L ayer 1Intersection

2Intersection

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

P SFS FS

FS

FS

D 4

D 2

D 1

D 3

P S = P rincipa l S igna lFS = Feeder S igna lD = D etector

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 detectors can provide an actual history for a short portion of the profile.

Past Future

1

1 0

1 0 1

1 0 1 1

1 0 1 1 0

1 0 1 1 0 0

H ypo the tica l a rriva lpa tte rn ove r the de tec to r

used by success iveite ra tions o f the O P A Cin te rsec tion s im u la tionand tim ing op tim iza tion

a lgo rithm s. E ach squarerep resen ts one s tep (2 -3

seconds) in tim e .

1 0 1 1 0 0 1 0 1 0 0 1 0 1 1 1 0 0 1 1 0 0 0 1

0 1 1 0 0 1 0 1 0 0 1 1 1 1 1 0 0 1 1 0 0 0 1 1

T im e

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 )