Fast ForwardRamp Meter Design forMetro Atlanta
Taylor H. Stukes, PE
Gresham, Smith and Partners
2325 Lakeview Parkway, Suite 400,
Alpharetta, Georgia
678-518-3685
ITE Tennessee / ITS Georgia Annual Meeting 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
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 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, PEGresham, Smith and Partners
2325 Lakeview Parkway, Suite 400Alpharetta, GA 30004