Fast Forward

Ramp Meter Design for Metro Atlanta

Taylor H. Stukes, PE Gresham, Smith and Partners 2325 Lakeview Parkway, Suite 400, Alpharetta, Georgia 678-518-3685

Ramp Meter Operational Concepts

• Ramp meters preserve freeway capacity by limiting the

amount of traffic entering the mainline flow – typically at ramps with recurring congestion

• Fixed or variable metering rates • Time-Of-Day schedule (TOD) or based on freeway volumes/speed • Break up platoons on entrance ramps, easing congestion • Metered flow should make merges easier and safer

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Fast Forward Ramp Meter Operational Concept

• Modified SWARM algorithm: controls entrance ramp meters based on mainline congestion upstream of ramp • SWARM is “System Wide Adaptive Ramp Metering,” and will control a group of ramps based on where congestion is occurring • Mainline volume and speed values are used to decide when freeway becomes congested • GDOT is measuring outside 4 lanes with video detection, between 50 and 500 feet upstream of merge point

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Four Generations of Atlanta Ramp Meters

This map is 70 miles in diameter!

Olympic Era: 4 sites (1996) GDOT Testing: 4 sites (2005) State Road 400: 8 sites (2006) Fast Forward: 160 sites (2007) ITE Tennessee / ITS Georgia Annual Meeting 3

Olympic Era Ramp Meter

• I-75 Northbound only, for Olympic venues north of the City • 8-inch lens on lower signal; inductive loops on ramp • Connected to NaviGAtor; TOD operations with no freeway detection

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GDOT Testing Ramp Meter

• I-75/I-85 Downtown Connector, Southbound only • Test effectiveness of ramp meters • Video detection, multi-lane ramps, connected to NaviGAtor • Time-Of-Day schedule with “early-on” if freeway volumes are high

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State Road 400 Ramp Meters

• Not yet operational; installed during bus-on-shoulder project • Pedestal-mount signals on left side (both sides for multilane ramps) • Loop detectors on ramp • Not connected to NaviGAtor • Operates on Time-Of-Day only with no freeway detection

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Fast Forward Ramp Meters - Primary Design Criteria

• STOP BAR LOCATION – Provide minimum AASHTO acceleration length for posted speed – Provide maximum vehicle storage – Provide physical separation from mainline to prevent cheating • TWO-LANE RAMP or SINGLE-LANE RAMP?

– Travel lanes: 12 feet wide – Inside shoulder: 4 feet wide – Outside shoulder: 10 feet wide –

or obtain FHWA design exception

• No meters on freeway-to-freeway ramps or on ramps entering C-D roads

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Signals and Wig-Wag Signs

• FHWA mandated two displays per lane – Upper & lower on pedestal – Four heads on two-lane mast arm • Wig-Wag signs, one per lane, warn drivers “PREPARE TO STOP” with flashers • Pedestals and sign posts are breakaway • Poles and cabinets are outside Clear Zone or behind guardrail

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Video Detection and Video Monitoring

• Mainline video detection accomplished through off-the-shelf IVDS units (Intersection Video Detection System) directly into Ramp Meter controller • Required CCTV coverage: stop bar and discharge area • Desired CCTV coverage: entire ramp • Existing CCTV cameras are checked for suitability by actually positioning them, using the zoom, and capturing the best image

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Detection for the Ramp Meter

• “Passage” loops just downstream of stop bar (6x6) • “Presence” loops just upstream of stop bar (6x40 quadrupoles) • “Queue” loops located with wig-wag near crossing street (6x6) • Queue loops detect occupancy, and will maximize metering rate or turn signals off

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Fiber Connection with NaviGAtor Network

• Demand for fiber exceeded availability in downtown area and along northern side of Perimeter Highway • Substantial GDOT investment of staff to test and identify available fibers • Some projects installed new trunk fiber • GDOT will be using “pre-terminated” fiber connectors

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CORSIM and Other Traffic Analysis

• Vehicles In versus Vehicles Out estimated queue lengths for each hour of the 4-hour peak period • Detailed CORSIM analysis of ramp, but not adjacent signals or arterial • CORSIM estimates how long until queue loops are occupied

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Suggestions for Next Time …

In our case, the Governor challenged GDOT to get it done, and they got it done!

• Evaluate ramp capacity and queue storage prior to design phase of project, and widen / lengthen ramps to accommodate longer queues • Establish design criteria to ensure consistent design (easier to build and easier to maintain) • Involve all departments of DOT during planning phase (roadway, traffic, construction, maintenance) • Begin verifying existing fiber infrastructure during planning phase

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On Schedule?

Questions?

Taylor H. Stukes, PE Gresham, Smith and Partners 2325 Lakeview Parkway, Suite 400 Alpharetta, GA 30004

678-518-3685 [email protected]

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