Congestion Mitigation Michael Cassidy Anthony D. Patire

Expressway traffic management Main Themes –Innovative control strategies –Equitable approach –Ameliorate capacity drop

Capacity Drop Cumulative Vehicle Count A(t) D(t) Time  Added Delay  Queue Discharge Drop

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

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 Capacity Drop Mechanism at an Isolated Merge Bottleneck X1X1 X3X3 X1X1 X3X3 Started with a sharp rise in shoulder lane accumulation Induced drivers to maneuver into adjacent freeway lanes (lane changing rates doubled) -- Rudjanakanoknad and Cassidy, UC Berkeley

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

Yokohama-Machida Bottleneck -0.23% +2.38% 23KP22KP 21KP 20KP -1.87% -0.52% Camera Loop VMS Camera KP Camera KP Traffic Direction

Loop Data Dec 23, 2005

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

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

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

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

A closer look

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 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