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Ramp Metering
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Getting Started
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  • What Are Ramp Meters?
    • Actuated traffic signals installed on on-ramps to control the frequency at which vehicles enter the mainline
  • History:
    • First deployed on the Eisenhower Expressway (Chicago) in the 1960s
  • Goals:
    • Increase traffic speed
    • Decrease travel time
    • Reduce collisions
    • Reduce emissions
Rationale
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  • Normal On-Ramp Behavior:
    • Vehicles merge in "platoons"
  • Impact on the Mainline:
    • Drivers slow (or stop) to allow vehicles to enter
    • The slower speeds cascade (e.g., because of the driver's rule of thumb)
Rationale (cont.)
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  • Metered On-Ramp Behavior:
    • "Platoons" are broken up
    • Individual vehicles can merge more smoothly
  • System-Wide Impacts:
    • Meters can help keep entrance demand near the capacity of the mainline
Components
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  • Signals:
    • Typically two-section (i.e., with red and green indicators)
  • Detector(s):
    • At the stop line
    • Sometimes also upstream (to detect queues)
  • Signage:
    • At the start of the ramp (to prepare the driver)
    • At the signal
Challenges
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  • Existing Ramp Geometry:
    • Inadequate acceleration length
    • Closely spaced ramps
    • Limited sight distances
  • Heavy Ramp Volumes:
    • Insufficient space for queues can cause backup onto other roads
There's Always More to Learn
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