Fast Forward Ramp Meter Design for Metro Atlanta

1. Fast ForwardRamp Meter Design forMetro Atlanta Taylor H. Stukes, PEGresham, Smith and Partners2325 Lakeview Parkway, Suite 400,Alpharetta, Georgia678-518-3685

2. 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 ITE Tennessee / ITS Georgia Annual Meeting

3. 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 ITE Tennessee / ITS Georgia Annual Meeting

4. 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

5. 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 ITE Tennessee / ITS Georgia Annual Meeting

6. 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 ITE Tennessee / ITS Georgia Annual Meeting

7. 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 ITE Tennessee / ITS Georgia Annual Meeting

8. 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 ITE Tennessee / ITS Georgia Annual Meeting

9. 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 ITE Tennessee / ITS Georgia Annual Meeting

10. 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 ITE Tennessee / ITS Georgia Annual Meeting

11. 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 ITE Tennessee / ITS Georgia Annual Meeting

12. 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 ITE Tennessee / ITS Georgia Annual Meeting

13. 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 ITE Tennessee / ITS Georgia Annual Meeting

14. 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 ITE Tennessee / ITS Georgia Annual Meeting

15. On Schedule? Questions? Taylor H. Stukes, PE Gresham, Smith and Partners 2325 Lakeview Parkway, Suite 400 Alpharetta, GA 30004 678-518-3685 taylor_stukes@gspnet.com ITE Tennessee / ITS Georgia Annual Meeting