1. RT-TRACS A daptive 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

2. 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

3. 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

4. Control Layers in VFC-OPAC

5. 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

6. VFC-OPAC Network Module

7. 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

8. 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)

9. Decision Variables Terminate the current phase in ring 1 (Yes or No) Terminate the current phase in ring 2 (Yes or No)

10. State Variables Signal status Elapsed time since last signal status change Standing queues Cumulative delay Cumulative stops

11. 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

12. 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).

13. How Are Flow Profiles Developed? Upstream detectors can provide an actual history for a short portion of the profile.

14. 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

15. Offset Optimization Options: Leave current offset ( zero change) Move right one interval (+2 sec) Move left one interval (-2 sec)

16. 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

17. MOE’s Volume, occupancy, speed by detector and phase. Estimated measure of queue, delay, and stops by phase.

18. 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

19. 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)

20. 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

21. Communication Requirements Communications with Central: OPAC status is polled Communications with Signal Control Software Peer-to-peer communications

22. 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.

23. 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

24. 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

25. 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 )