GDOT’s Metro AtlantaRamp Meters

Marc PlotkinTraffic Engineer II :Regional Traffic

Operations

Topics

1. What, and Why 2. Safety3. Benefits4. Design Considerations5. History in Atlanta6. Implementation7. Operations8. Results and Findings

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

Ramp Meter Locations

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

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

Minneapolis, MNMinneapolis, MN

Los Angeles, CALos Angeles, CA

Seattle, WASeattle, WA

Portland, ORPortland, OR

Long Island, NYLong Island, NY

20%

43%

38%

26%

15%

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

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

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

Downtown Atlanta 1967 – Atlanta History Center

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

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

I-20

I-20

I-85

I-85

I-75

GA 400

I-75

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

Georgia Ramp Meter System Today

I-75

I-20

I-75

I-85

I-85

GA 400

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

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

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

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)

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)

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%

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%)

I-285 Westbound PM Peak

Thank you

Marc Plotkin

Traffic Engineer IImplotkin@dot.ga.gov