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Congestion Mitigation

Congestion Mitigation. Michael Cassidy Anthony D. Patire. Expressway traffic management. Main Themes Innovative control strategies Equitable approach Ameliorate capacity drop. Capacity Drop. Queue. Discharge Drop. Cumulative Vehicle Count. A(t ). m. 0.9m. Added Delay. D(t ). Time.

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Congestion Mitigation

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  1. Congestion Mitigation Michael Cassidy Anthony D. Patire

  2. Expressway traffic management • Main Themes • Innovative control strategies • Equitable approach • Ameliorate capacity drop

  3. Capacity Drop Queue Discharge Drop Cumulative Vehicle Count A(t) m 0.9m Added Delay D(t) Time

  4. Move queue to ramp Change in Discharge? Meter Conventional Strategies • Traffic Signals • Restrict flow onto freeway • Add queues to city streets • On-ramp metering • Long queue spillover • Inequitable transfer of delay

  5. Sustainability Context • Problem: Congestion will never really “go away” • Goal: Efficient management of existing resources • Save time and gasoline • Equitable solutions • Method: Understand mechanism of capacity drop and reverse it to maintain high discharge flow

  6. Earlier Work X1 • Capacity Drop Mechanism at an Isolated Merge Bottleneck • Started with a sharp rise in shoulder lane accumulation X1 X3 • Induced drivers to maneuver into adjacent freeway lanes (lane changing rates doubled) X3 -- Rudjanakanoknad and Cassidy, UC Berkeley

  7. Variable Message Signs & Variable Speed Limits New bN cap = B>A bN cap = A • Higher Outflow • Reduction in “disruptive” lane changes • Many Open Questions • Requires a “full accounting” VMS: “Onramp Congestion Ahead” Meter

  8. Camera Loop VMS Yokohama-Machida Bottleneck Camera 13 22.73KP Camera 3 21.57KP +2.38% -1.87% -0.52% -0.23% Traffic Direction 21KP 23KP 22KP 20KP

  9. Loop Data Dec 23, 2005

  10. Manual Counts Dec 23,2005 On this day 12 & 13 mostly superimposed

  11. Key Features of Bottleneck • Scattered braking at camera 13 • Excess accumulation not sustained • Excess accumulation between cam 11 & 12 • Coincident with flow drops • But the head-of-queue moves upstream • Cumulative curves for cameras 12 and 13 mostly superimposed • Waves appear to be forward moving • Freeflow speed-drop on uphill segment

  12. Speculation On the grade, freeflow velocity may be a function of flow Flow [veh/hr] Triangular Fundamental Diagram Fundamental Diagram on the grade Velocity Density [veh/km]

  13. Freeflow-Speed Adjusted Counts 4700 Slopes in vehicles per hour 5100

  14. Freeflow-Speed Adjusted Counts 4700 Slopes in vehicles per hour 5100

  15. A closer look

  16. Final Thoughts • Freeway is not homogeneous due to the upward grade • On the grade, freeflow speed diminishes with flow • Conditions not FIFO • Queue begins in rightmost lane • We are optimistic that we can study the mechanism even if it happens at camera 13

  17. Future Work • Analyze more data on different days • Top-of-hill vs. Bottom-of-hill • Data after 7am • Understand capacity drop mechanism • Disaggregate lanes • Measure density profile • Invent and field-test capacity-drop mitigation schemes

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