1. GDOT’s Metro Atlanta Ramp Meters
Marc Plotkin
Traffic Engineer II :Regional Traffic Operations

2. Topics What, and Why Safety Benefits Design Considerations
History in Atlanta
Implementation
Operations
Results and Findings
I’m going to give a brief explanation or what ramp meters are and why they were implemented
Then talk about the safety analysis done in Minnesota and the benefits behind ramp metering.
After that talk about the implementation of ramp meters in metro Atlanta, how we as operations manage them from day to day and share some results.

3. 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 meters are a part of Georgia DOT’s large computer operated Intelligent Transportation System, housed and managed at the TMC. Meter detection loops are embedded in the pavement throughout metro Atlanta that feed information about traffic volumes and speed on the interstates and ramps to central software.
Ramp Meters are essentially “traffic lights” positioned on interstate entrance ramps. They are designed to control cars entering the freeway, allowing less disruption to mainline traffic.

4. Ramp Meter Locations
Here is a map of some other cities that currently have a ramp metering system
Minneapolis St. Paul, Portland, Seattle, Phoenix, San Jose, Dallas, Atlanta, and many others

5. 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
Without metering, groups of closely-spaced vehicles all enter the Interstate together.
At the merge point, they force their way into travel lanes, causing congestion- especially in the right lanes.
In already heavy traffic, there is a total breakdown of free-flow near the on-ramps. This has a ripple effect for many miles.
Even with no incidents, heavy on-ramp traffic causes congestion that builds and lasts through the rush-hour
Ramp meters are a cost effective tool to help manage traffic

6. 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
In 2000 Minnesota DOT issued a system wide shutdown of their ramp meters for 6 weeks.
As can be seen there was a large increase in interstate crashes during this period.
During this 6 weeks there was a 9% reduction in freeway volume however there was a 22% increase in travel time, and 26% increase in crashes
There was an estimated Annual Savings of $18.2 Million when using ramp metering.

7. Reduction in Crashes 43% 20% 38% 26% 15% Portland, OR Los Angeles, CA
Minneapolis, MN
Los Angeles, CA
Seattle, WA
Portland, OR
Long Island, NY
43%
20%
38%
26%
Crash Reduction with ramp meter implementation in Major Cities
15%

8. Benefits of Ramp Meters
PREPARE
TO STOP
Improved traffic flow from surface street to freeway
Faster travel times
Reduced merging accidents
Reduced fuel consumption
Reduced vehicle emissions
Ramp meters are designed to alleviate back-ups on interstate entrance ramps. Our central computers can then adjust the rate at which the meters operate based on plan thresholds, allowing traffic to flow more freely when entrance ramps get crowded.
During high peak times, drivers tend to compete for position and to merge all at once into mainline traffic. Ramp meters have been proven to reduce the number of accidents associated with rear-ending and merging by 30%.
The average wait at a ramp meter usually does not exceed 2 minutes with a maximum of 5 minutes.

9. 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
With the initial roll out of ramp meters, no geometric changes were allowed and only some striping changes could be made.

10. 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
Phase 2 of ramp metering started because of the increase in congestion leading up to the olympics.
5 ramp meters were selected on I-75 N inside the perimeter where ramps had lower volumes and all entrance ramps were single lanes.

11. Downtown Atlanta 1967 – Atlanta History Center
One of the first ramp meters in the city of Atlanta in This is the exit for the Atlanta History Center which at that time was located downtown.

12. 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
As said previously, 5 ramps were chosen for the initial pilot test.
All meters were turned on at 3:45PM and rates were adjusted based on storage space on each individual ramp.
Being the pilot test, thresholds were modified during peak hours.

13. History of Ramp Meters in Atlanta
Phase III – the ‘Fast Forward’ years ( )
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
During Phase 3, GDOT received funding from the Governors Fast Forward program to add 165 more ramp meter locations.
Installation would be done one corridor stretch at a time.

14. Meters on as of January 2009 GA 400 I-85 I-75 I-20 I-20 I-75 I-85
87 Ramp Meters
I-75
I-85

15. Meters on as of January 2010 GA 400 GA 400 I-85 I-85 I-75 I-75 I-20
Another 62 ramp meters were constructed totling 149 Ramp Meters
I-75
I-75
I-85
I-85

16. Georgia Ramp Meter System Today
GA 400
I-75
I-85
185 Ramp Meters with Construction projects pushing West on I-20 to add over 200 Ramp Meters in the next 2 years
I-20
I-85
I-75

17. 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
Since the original 5 ramp meter locations on I-75 NB inside the perimeter, 180 additional ramp meters have been installed with more under construction.

18. 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
Our operational goal is to provide the best possible travel time to the public while staying consistent.
To do this we constantly adjust metering thresholds to improve gaps for merging vehicles.
This results in more mobility and improved safety.

19. 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)
On a day to day basis there is a handful of employees on the operations floor and dedicated employees in the Regional Traffic Operations division that make sure all adjustments to thresholds are made properly, detectors and functioning and mainline readings are calibrated.
This is done using Central software and Navigator 2

20. Queue Management WITHOUT … WITH …
Quick simulation of how proper ramp metering can supply a needed gap to eliminate congestion in the right lanes.

21. Travel Time reduced 6 Minutes
Results
285 Westbound – PM peak – from Chamblee Dunwoody to I-75 (9 Miles)
Travel Time (Min)
# of Stops
Avg Speed(mph)
Total Delay(min)
Totals
Before
17.19
6.3
33.9
5.62
After
11.22
1.4
51.9
1.02
Change
-5.97
-4.9
18.0
-4.61
Data from TMC floor study regarding travel times before and after turn on.
On average travel time was reduced 6 minutes
Travel Time reduced 6 Minutes

22. Travel Time reduced 5 Minutes
Results
285 Eastbound – PM peak from Roswell Rd to I-85 (8 Miles)
Travel Time (Min)
# of Stops
Avg Speed(mph)
Total Delay(min)
Totals
Before
16.12
6.3
33.9
6.92
After
11.45
1.4
51.9
2.56
Change
-4.67
-4.9
18.0
-4.36
On average Travel time was reduces 5 minutes
Travel Time reduced 5 Minutes

23. 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%
Overall travel time and total delay saw significant reductions throughout the whole system

24. Result Summary Carbon Monoxide (g) reductions ranged from:
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%)
Emissions data was collected as well.
Not all Corridors showed improvement but overall the results were very promising

25. I-285 Westbound PM Peak
Detection Data studied 3 weeks before and 3 weeks after ramp meter implementation on I-285 Westbound during the PM peak

26. Comparing september of 2007 to september of 2008 on I-285 near Riverside Dr, 62% of days were moderately to severely congested before metering and only 28% moderately or severly congested after metering implemented.

27. I-75 NB in the AM hours Comparing October 2007 to October 2008, 86% of days were moderately to severely congested before metering and only 39% moderately congested with no severely congested days after metering implemented.

28. Lastly I-85 NB near Beaver Ruin comparing October 2007 to October 2008, 100% of days were moderately to severely congested before metering and only 9% moderately or severely congested after metering implemented.

29. Thank you
Marc Plotkin
Traffic Engineer II