Ramp Metering

JMU

Ramp Metering
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Getting Started

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

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.)

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

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

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