gdot’s metro atlanta ramp meters marc plotkin traffic engineer ii :regional traffic operations
TRANSCRIPT
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GDOT’s Metro AtlantaRamp Meters
Marc PlotkinTraffic Engineer II :Regional Traffic
Operations
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Topics
1. What, and Why 2. Safety3. Benefits4. Design Considerations5. History in Atlanta6. Implementation7. Operations8. Results and Findings
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What Are Ramp Meters
• Part of NaviGAtor, Georgia DOT’s Intelligent Transportation System (ITS)
• “Traffic lights” on interstate entrance ramps designed to control traffic flow onto the interstate
• Proven to relieve traffic congestion in over 20 U.S. cities for over 20 years
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Ramp Meter Locations
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Why?• Reduces crashes at merge points• Increases freeway productivity• Reduces stop-and-go traffic• Reduces fuel consumption• Cost-effective traffic management tool• Improves trip predictability
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Safety Analysis Minnesota
• Ramp Meter shutdown test– With Metering 261 crashes– Without metering 476
crashes
• Annual Savings from metering– Property damage only
• $4.8 million– Injuries
• $6.8 million– Fatalities
• $6.6 million
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Reduction in Crashes
Minneapolis, MNMinneapolis, MN
Los Angeles, CALos Angeles, CA
Seattle, WASeattle, WA
Portland, ORPortland, OR
Long Island, NYLong Island, NY
20%
43%
38%
26%
15%
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Benefits of Ramp Meters
• Improved traffic flow from surface street to freeway
• Faster travel times
• Reduced merging accidents
• Reduced fuel consumption
• Reduced vehicle emissions
PREPARETO STOP
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Design Considerations
• Some ramps dropped out of consideration during design phase– “slip” ramps – such as I-85 frontage road system– Ramps with very short storage– C/D ramps
• No “geometrical” changes allowed– No widening– Some striping changes allowed if shoulders maintained
• Acceleration distances– AASHTO Green Book compliance maintained
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History of Ramp Meters in Atlanta
Begin Phase II –the Modern Years
• Preparation for Olympics in 1996• Congestion was back, relief needed and capacity was fixed• Pilot project – 5 ramps selected• Meters began operation December 1996• Low impact ramps were selected for the pilot:
– No widening/extending– Single lanes– Not a big residential area– Relatively low volumes
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Downtown Atlanta 1967 – Atlanta History Center
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Ramp Meter Pilot I-75 NB
• Meters programmed to turn ON at 3:45 PM weekdays (TMC Planning)
• Loop Detection with 3 second gap
• Max rate set on the fly• Minimize delay on ramp (adjust
rate)• Longer ramps = Adjust rate up• Shorter ramps = Adjust rate
down• Meter ramps as needed on
individual basis• Base rates on various time of
day schedule
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History of Ramp Meters in Atlanta
Phase III – the ‘Fast Forward’ years (2006-2012)
• GDOT elected to go “all in”
• Funding mechanism, Governors’ “Fast Forward” program– 18 year worth of congestion-relief projects in 6 years
• Included 165 more ramp meters
• Staged installation, one freeway at a time
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Meters on as of January 2009
I-20
I-20
I-85
I-85
I-75
GA 400
I-75
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Meters on as of January 2010
I-20
I-20
I-85
I-85
I-75
GA 400
I-75
I-20
I-20
I-85
I-85
I-75
GA 400
I-75
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Georgia Ramp Meter System Today
I-75
I-20
I-75
I-85
I-85
GA 400
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Current Ramp Meter Locations• 185 Ramp Meters:
• Original 5 on I-75 NB, Midtown to Cumberland Mall (1996)• 27 Locations on I-20 • 51 Locations on I-285• 8 Locations on I-575• 40 Locations on I-75 North and South of Atlanta• 15 Locations on the 75/85 Connector• 19 Locations on I-85• 2 Locations on the Buford Connector• 15 Locations on GA 400• 8 Locations on US 78
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Operations- GDOT MindsetGDOT’s goal: partner with locals to provide the best possible travel time for the public.
best = more consistent and reliable
Ramp meter’s objective: Aid the mainline while limiting the impact from arterial networks supplying demand.
How do we do that?• Providing consistent flow for merging vehicles
Resulting in improved• Mobility • Safety
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Operations – Day to Day
Queue Management
• Making sure that arterials aren’t negatively impacted
How do we do that?
• Remote monitoring – during peaks– Navigator 2– Centrally connected system
• Threshold adjustments– Speed up metering– Shut down
• Ramp • Mainline (Testing)
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Queue Management
WITHOUT … WITH …
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Results
Travel Time (Min) # of Stops Avg
Speed(mph)Total
Delay(min)
TotalsBefore 17.19 6.3 33.9 5.62After 11.22 1.4 51.9 1.02
Change -5.97 -4.9 18.0 -4.61
Travel Time reduced 6 Minutes
285 Westbound – PM peak – from Chamblee Dunwoody to I-75 (9 Miles)
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Results
Travel Time (Min) # of Stops Avg
Speed(mph)Total
Delay(min)
TotalsBefore 16.12 6.3 33.9 6.92After 11.45 1.4 51.9 2.56
Change -4.67 -4.9 18.0 -4.36
Travel Time reduced 5 Minutes
285 Eastbound – PM peak from Roswell Rd to I-85 (8 Miles)
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Result Summary
• Travel time reductions ranged from:– 50 seconds to 6 minutes– 8 – 35%
• # of stop reductions ranged from:– 0.7 to 5.3
• Total delay reductions ranged from:– 30 seconds to 5 minutes– 11 to 82%
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Result Summary
• Emissions data was also collected– Hydrocarbon (g) reductions ranged from:
5 to 31%
– Oxides of Nitrogen (g) reductions ranged from: 5 to 38% One corridor increased 6%
• Carbon Monoxide (g) reductions ranged from: 1 to 15% Two corridors had increases (1% and 13%)
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I-285 Westbound PM Peak
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