Transcript Click to add title - Missouri Department of Transportation

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Ramp Meters
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What are Ramp Meters?
• Part of NaviGAtor, Georgia DOT’s Intelligent
Transportation System (ITS)
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Also includes electronic signs, cameras, website, and 511 system
• “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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Why Ramp Meters?
PPI
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Why Ramp Meters?
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Why Ramp Meters?
• Without metering, groups of closely-spaced vehicles
(sometimes 15-30 at a time) all enter the Interstate
together.
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At the merge point, they force their way into travel lanes,
causing congestion- especially in the right lanes.
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In already heavy traffic, there is a total breakdown of
free-flow near the on-ramps. This has a ripple effect for
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many miles.
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Even with no incidents, heavy on-ramp traffic causes
congestion that builds and lasts through the rush-hour.
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How Do Ramp Meters Work?
• Similar to traffic signals with red and green lights
• Most effective when turned on prior to the onset of
rush-hour
• Cycle from red to green every 3-5 seconds,
allowing one vehicle at a time to merge onto the
freeway.
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• Yellow is not used, except on the very first cycle
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Benefits of Ramp Meters
• Reduced congestion on the Interstate
• Faster overall travel times
• Reduced merging accidents
• Reduced fuel consumption
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Reduced vehicle emissions
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Current Ramp Meter Locations
• 4 on I-75 NB between Midtown and W Paces Ferry
(1996)
• 4 on the Downtown Connector SB
(2005)
• 130+ turned on during last 9 months
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About 30 more meters will be phased
in within the
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next 6 months, concluding the program
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Two-lane Ramp Meter Design
On two-lane ramps, the
meter operates in a ‘leftlane’, ‘right-lane’, ‘left lane’
manner.
.
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. PREPARE
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. . TO STOP
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What if . . .?
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If too many cars start to back up on the ramp,
automated sensors detect this and adjust the cycle to
allow vehicles to move through faster.
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If cameras show ramp traffic impeding surface street
flow, the meters can be turned off completely.
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There will be a short learning curve period in the first
few days for each corridor as the public adapts and
GDOT makes necessary adjustments.Project
PPI
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There is no “magic bullet” solution to eliminate
congestion. Ramp meters are just one of several tools
that can help fight it.
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Fears / Actual Outcome
 “The public won’t understand what to do at ramp
meters”
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Fairly intensive PR campaign in advance of turn-on
Motorists understand concept of red/stop; green/go
 “There will be lots of accidents on the ramp”
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Did not occur
“Prepare to stop” signs warn approaching traffic
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Fears / Actual Outcome
 “Ramp meters won’t help”
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Meters have “de-congested” several perennially congested
segments of freeway
Duration of congestion is reduced
 “They’ll just shift the problem from the freeway to
the surface streets”
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Most of the storage of vehicles occurs on the ramps, not the
surface streets
In cases where traffic spilled onto surface streets, special “flush”
patterns were developed to temporarily turn meters off
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Results Summary
 Travel Time Reductions ranged from:
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50 to 358 seconds
7.9 – 34.8 %
 # of stop reductions ranged from:
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0.7 to 5.3 (one corridor had a 0.7 increase)
 Total Delay Reductions ranged from:
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13.7 to 276 seconds
11.4 to 81.8 %
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Results Summary, cont.
 Emissions data also collected
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Hydrocarbon (g) reductions ranged from:
 4.6 to 31.4 %
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Oxides of Nitrogen (g) reductions ranged
from:
 4.8 to 38 %
 One corridor increased 5.8%
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Carbon Monixide (g) reductions ranged from:
 0.8 to 14.9 %
 Two corridors had increases (0.8% and 13.3%)
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Duration of congestion
 NaviGAtor detection data studied for 3 weeks
before and after ramp meters
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Before Ramp Meters
After Ramp Meters
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Duration of congestion
Figure 19. Duration of Congestion: Wednesday (PM Peak – I-285 Westbound)
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Duration of congestion
Figure 6. Duration of Congestion: Friday (AM Peak – I-285 Eastbound)
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