Fast Forward Ramp Meter Design for Metro Atlanta Taylor H. Stukes, PE Gresham, Smith and Partners 2325 Lakeview Parkway, Suite 400, Alpharetta, Georgia

ITE Tennessee / ITS Georgia Annual Meeting1 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 Meeting2 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 Meeting3 Four Generations of Atlanta Ramp Meters Olympic Era: 4 sites (1996) GDOT Testing: 4 sites (2005) State Road 400: 8 sites (2006) Fast Forward: 160 sites (2007) This map is 70 miles in diameter!

ITE Tennessee / ITS Georgia Annual Meeting4 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 Meeting5 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 Meeting6 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 Meeting7 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 Meeting8 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 Meeting9 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 Meeting10 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 Meeting11 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 Meeting12 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 Meeting13 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 Meeting14 On Schedule? Questions? Taylor H. Stukes, PE Gresham, Smith and Partners 2325 Lakeview Parkway, Suite 400 Alpharetta, GA