Congestion mitigation
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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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Congestion mitigation

Congestion Mitigation

Michael Cassidy

Anthony D. Patire


Expressway traffic management

Expressway traffic management

  • Main Themes

    • Innovative control strategies

    • Equitable approach

    • Ameliorate capacity drop


Capacity drop

Capacity Drop

Queue

Discharge Drop

Cumulative Vehicle Count

A(t)

m

0.9m

Added Delay

D(t)

Time


Conventional strategies

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


Sustainability context

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


Earlier work

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


Variable message signs variable speed limits

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


Yokohama machida bottleneck

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


Loop data dec 23 2005

Loop Data Dec 23, 2005


Manual counts dec 23 2005

Manual Counts Dec 23,2005

On this day 12 & 13 mostly superimposed


Key features of bottleneck

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


Speculation

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]


Freeflow speed adjusted counts

Freeflow-Speed Adjusted Counts

4700

Slopes in vehicles per hour

5100


Freeflow speed adjusted counts1

Freeflow-Speed Adjusted Counts

4700

Slopes in vehicles per hour

5100


A closer look

A closer look


Final thoughts

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


Future work

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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