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

678-518-3685taylor_stukes@gspnet.com