GDOT’s Metro Atlanta
Ramp Meters
Marc Plotkin
Traffic Engineer II :Regional Traffic Operations
Topics
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What, and Why
Safety
Benefits
Design Considerations
History in Atlanta
Implementation
Operations
Results and Findings
What Are Ramp Meters
• Part of NaviGAtor, Georgia DOT’s Intelligent Transportation System
(ITS)
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“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
Ramp Meter Locations
Why?
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Reduces crashes at merge points
Increases freeway productivity
Reduces stop-and-go traffic
Reduces fuel consumption
Cost-effective traffic management tool
Improves trip predictability
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
Reduction in Crashes
Portland, OR
Los Angeles, CA
43%
20%
Seattle, WA
38%
26%
Minneapolis, MN
Long Island, NY
15%
PREPARE
TO STOP
Benefits of Ramp Meters
• Improved traffic flow from
surface street to freeway
• Faster travel times
• Reduced merging accidents
• Reduced fuel consumption
• Reduced vehicle emissions
Design Considerations
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Some ramps dropped out of consideration during design phase
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No “geometrical” changes allowed
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Acceleration distances
– “slip” ramps – such as I-85 frontage road system
– Ramps with very short storage
– C/D ramps
– No widening
– Some striping changes allowed if shoulders maintained
– AASHTO Green Book compliance maintained
History of Ramp Meters in Atlanta
Begin Phase II –the Modern Years
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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:
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No widening/extending
Single lanes
Not a big residential area
Relatively low volumes
Downtown Atlanta 1967 – Atlanta History Center
Ramp Meter Pilot I-75 NB
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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
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
Meters on as of January 2009
GA 400
I-85
I-75
I-20
I-20
I-85
I-75
Meters on as of January 2010
GA 400
I-85
I-85
I-75
I-75
I-20
I-20
I-20
I-20
I-85
I-85
I-75
I-75
Georgia Ramp Meter System Today
GA 400
I-75
I-85
I-20
I-85
I-75
Current Ramp Meter Locations
• 185 Ramp Meters:
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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
Operations- GDOT Mindset
GDOT’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
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)
Queue Management
WITHOUT …
WITH …
Results
285 Westbound – PM peak – from Chamblee Dunwoody to I-75 (9 Miles)
Totals
Before
After
Change
Travel Time
(Min)
17.19
11.22
-5.97
Travel Time
reduced 6 Minutes
# of Stops
6.3
1.4
-4.9
Avg
Speed(mph)
33.9
51.9
18.0
Total
Delay(min)
5.62
1.02
-4.61
Results
285 Eastbound – PM peak from Roswell Rd to I-85 (8 Miles)
Totals
Before
After
Change
Travel Time
(Min)
16.12
11.45
-4.67
Travel Time
reduced 5 Minutes
# of Stops
6.3
1.4
-4.9
Avg
Speed(mph)
33.9
51.9
18.0
Total
Delay(min)
6.92
2.56
-4.36
Result Summary
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Travel time reductions ranged from:
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# of stop reductions ranged from:
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Total delay reductions ranged from:
– 50 seconds to 6 minutes
– 8 – 35%
– 0.7 to 5.3
– 30 seconds to 5 minutes
– 11 to 82%
Result Summary
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Emissions data was also collected
– Hydrocarbon (g) reductions ranged from:
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5 to 31%
– Oxides of Nitrogen (g) reductions ranged from:
 5 to 38%
 One corridor increased 6%
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Carbon Monoxide (g) reductions ranged from:
 1 to 15%
 Two corridors had increases (1% and 13%)
I-285 Westbound PM Peak
Thank you
Marc Plotkin
Traffic Engineer II
mplotkin@dot.ga.gov