Presentation on theme: "GDOT’s Metro Atlanta Ramp Meters"— Presentation transcript:
1 GDOT’s Metro Atlanta Ramp Meters Marc PlotkinTraffic Engineer II :Regional Traffic Operations
2 Topics What, and Why Safety Benefits Design Considerations History in AtlantaImplementationOperationsResults and FindingsI’m going to give a brief explanation or what ramp meters are and why they were implementedThen 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 MetersPart of NaviGAtor, Georgia DOT’s Intelligent Transportation System (ITS)“Traffic lights” on interstate entrance ramps designed to control traffic flow onto the interstateProven to relieve traffic congestion in over 20 U.S. cities for over 20 yearsRamp 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 LocationsHere is a map of some other cities that currently have a ramp metering systemMinneapolis 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 trafficReduces fuel consumptionCost-effective traffic management toolImproves trip predictabilityWithout 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-hourRamp meters are a cost effective tool to help manage traffic
6 Safety Analysis Minnesota Ramp Meter shutdown testWith Metering 261 crashesWithout metering 476 crashesAnnual Savings from meteringProperty damage only$4.8 millionInjuries$6.8 millionFatalities$6.6 millionIn 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 crashesThere 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, MNLos Angeles, CASeattle, WAPortland, ORLong Island, NY43%20%38%26%Crash Reduction with ramp meter implementation in Major Cities15%
8 Benefits of Ramp Meters PREPARETO STOPImproved traffic flow from surface street to freewayFaster travel timesReduced merging accidentsReduced fuel consumptionReduced vehicle emissionsRamp 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 systemRamps with very short storageC/D rampsNo “geometrical” changes allowedNo wideningSome striping changes allowed if shoulders maintainedAcceleration distancesAASHTO Green Book compliance maintainedWith 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 YearsPreparation for Olympics in 1996Congestion was back, relief needed and capacity was fixedPilot project – 5 ramps selectedMeters began operation December 1996Low impact ramps were selected for the pilot:No widening/extendingSingle lanesNot a big residential areaRelatively low volumesPhase 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 NBMeters programmed to turn ON at 3:45 PM weekdays (TMC Planning)Loop Detection with 3 second gapMax rate set on the flyMinimize delay on ramp (adjust rate)Longer ramps = Adjust rate upShorter ramps = Adjust rate downMeter ramps as needed on individual basisBase rates on various time of day scheduleAs 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” program18 year worth of congestion-relief projects in 6 yearsIncluded 165 more ramp metersStaged installation, one freeway at a timeDuring 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 MetersI-75I-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 MetersI-75I-75I-85I-85
16 Georgia Ramp Meter System Today GA 400I-75I-85185 Ramp Meters with Construction projects pushing West on I-20 to add over 200 Ramp Meters in the next 2 yearsI-20I-85I-75
17 Current Ramp Meter Locations 185 Ramp Meters:Original 5 on I-75 NB, Midtown to Cumberland Mall (1996)27 Locations on I-2051 Locations on I-2858 Locations on I-57540 Locations on I-75 North and South of Atlanta15 Locations on the 75/85 Connector19 Locations on I-852 Locations on the Buford Connector15 Locations on GA 4008 Locations on US 78Since 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 reliableRamp 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 vehiclesResulting in improvedMobilitySafetyOur 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 impactedHow do we do that?Remote monitoring – during peaksNavigator 2Centrally connected systemThreshold adjustmentsSpeed up meteringShut downRampMainline (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 Results285 Westbound – PM peak – from Chamblee Dunwoody to I-75 (9 Miles)Travel Time (Min)# of StopsAvg Speed(mph)Total Delay(min)TotalsBefore17.196.333.95.62After11.221.451.91.02Change-5.97-4.918.0-4.61Data from TMC floor study regarding travel times before and after turn on.On average travel time was reduced 6 minutesTravel Time reduced 6 Minutes
22 Travel Time reduced 5 Minutes Results285 Eastbound – PM peak from Roswell Rd to I-85 (8 Miles)Travel Time (Min)# of StopsAvg Speed(mph)Total Delay(min)TotalsBefore16.126.333.96.92After11.451.451.92.56Change-4.67-4.918.0-4.36On average Travel time was reduces 5 minutesTravel Time reduced 5 Minutes
23 Result Summary Travel time reductions ranged from: 50 seconds to 6 minutes8 – 35%# of stop reductions ranged from:0.7 to 5.3Total delay reductions ranged from:30 seconds to 5 minutes11 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 collectedHydrocarbon (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 PeakDetection 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.