LECTURE 2. FREEWAY CONTROL AS · 10.09.2015 · Ramp Metering: Objectives Control the entry of...
Transcript of LECTURE 2. FREEWAY CONTROL AS · 10.09.2015 · Ramp Metering: Objectives Control the entry of...
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IPAM Workshop
II. Freeway ControlAlex Skabardonis
UC BerkeleyLos Angeles, CA
September 10, 2015
Mathematical Approaches To Traffic Flow Management
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Bottlenecks Characteristics
Queue present upstream of the bottleneckTraffic discharges at “capacity” at bottleneck location“Free-flow” downstreamActivation time and location reproducible over typical weekdays
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Ramp Metering: Objectives
Control the entry of on-ramp vehicles so downstream freeway capacity is not exceeded Improve safety—break up merging platoons
Example Ramp Metering Rate:Downstream capacity – upstream demand5400 vph – 5100 vph = 300 vph5 veh/min ( 1 veh/12 sec)
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Why Ramp Metering: Example Control the entry of on-ramp vehicles so downstream
capacity is not exceeded Maximize freeway throughput, minimize time spent Preserve freeway capacity
Fwy mainline: no metering Fwy mainline: metering
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Ramp Metering Implementation
CV: Sensors for traffic responsive control
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Types of Metering Number of Metered Lanes
Approximate Range of Metering Rates
(v/hr)
Comments
Single vehicle entry per green interval
1 240 – 900 (4) Full stop at the meter usually not achieved at 900 v/hr metering rate
Tandem Metering Single vehicle entry per green interval per lane
2 400 – 1700 Applies when required metering rate exceeds 900 v/hr
Requires two lanes for vehicle storage
Vehicles may be released from each lane simultaneously or sequentially
Platoon Metering Single lane multiple vehicle entry per green interval geometrics
1 240 – 1100 (4) Platoon lengths permit passage of 1 to 3 vehicles per green interval
Principally used to increase metered volumes when geometrics do not permit use of more than one metered lane
Requires changeable sign indicating permitted number of vehicles in green interval
MUTCD requires yellow interval after green
Ramp Metering Rates
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Ramp Metering Strategies
Pretimed (Fixed-Time) Metering-- Historical dataTime-of-day (TOD) control
Traffic Responsive Metering-- Surveillance dataLocal traffic responsive
• Demand-Capacity (open loop, upstream detection)• ALINEA (closed loop, downstream detection)
System-wide traffic responsive• ZONE• Bottleneck• SWARM• HEROS
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Ramp Metering: Fixed Time--TOD
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System-wide Pretimed Metering (1)
InputGeometrics(Capacities)
DemandsO-D table
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System-wide Pretimed Metering (1)Solution
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Example: Fixed-Time Metering (1)1. Existing Conditions—Freeway
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Fixed-Time Metering – No ramp constraints
Ramp Queues
Freeway Mainline
Example: Fixed-Time Metering (2)
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Example: Fixed-Time Metering (3)Fixed-Time Metering – Ramp constraints
Freeway Mainline
Ramp Queues
Trade-off:
Mainline Congestion vs. Ramp Queue
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Ramp Metering: Issues
Ramp Queues and DelaysRamp storageSpillback to local street networkExcessive delaysHOV by-pass
Diversion Short tripsAlternate ramps
Equity Short trips vs. long commute
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Ramp Metering: Local Traffic Responsive
Demand-Capacity Metering
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Implemenation
OCCUPANCY METERING(%) RATE
(veh/min)< 10 12
11-16 1017-22 823-28 629-34 4>34 3
Demand-Capacity Metering
Fwy mainline upstream
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ALINEA Algorithm
r(k) = r(k-1) + KR[Oc –Oout(k)]
r(k) is the metering rate in time step k;r(k-1) is the metering rate in time step k-1KR is the regulator parameter (constant);Oout(k) is the current occupancy measurement
Local traffic-responsive strategy –closed loop
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5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 110
200
400
600
Time (Hour)
Que
ue L
engt
h (m
)
Queue Override
5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 110
200
400
600
Time (Hour)
Que
ue L
engt
h (m
)
Queue Override
5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 110
200
400
600
Que
ue L
engt
h (m
)
Queue Estimation and Control
5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 110
200
400
600
Que
ue L
engt
h (m
)
Queue Estimation and Control
Queue Override failed to limit the
queue within the limits
large variation in queue length
On-Ramp Queue Control Regulator (1)Queue Override
Queue Estimation & Control
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Los Angeles I-210W Results
Existing
6% Travel Time Reduction
16% Delay Reduction
Proposed
On-Ramp Queue Control Regulator (2)
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Minneapolis/St. Paul area along I-35 East in 1970 Balance the volume entering & leaving the zone Each zone:
3-6 miles longupstream boundary : free-flow areadownstream boundary : bottleneck
SBXMUA
Zone Algorithm (1)
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where
S: the spare capacity available within the zone(estimated from the current and free-flow density)
U: Un-metered volume (example: fwy-to-fwy connector)
)()( UABXM
Maximum allowable volume:
Metering rate:
MfR rr rf : Ramp factor
Zone Algorithm (2)
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Two level formulation:(1) Local traffic responsive
(2) Global volume adjustment Determine total volume reduction based on section bottleneck capacityAdjust metering rate = volume reduction weighting factor
Bottleneck Algorithm
Implement the most restrictive metering rate
Implemented on I-5 in Seattle by WSDOT
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SWARM Algorithm (1)
SWARM consists of swarm1 and swarm2 Swarm2 is a local traffic responsive algorithm--
currently replaced by ALINEA
Swarm1 is a forecasting global apportioning algorithm
Implement the more restrictive metering rate
Developed by Delcan (NET) for Caltrans
Implementations: California (Orange County, Los Angeles), Oregon (Portland) & Georgia (Atlanta)
System-wide Adaptive Ramp Metering
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SWARM Algorithm (2)
Tcrit = 7-10 min (prediction horizon)
Saturation Density
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SWARM Algorithm (3)
Target density =(current density) – (1/Tcrit) * (excess density)
Volume reduction =(local density – target density) * (# lanes)* (distance to next station )
Ramp reduction = volume reduction * weighting factor
Predicted density = current density + trend * Tcrit
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HERO (HEuristic Ramp metering cOordination)
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Gap Acceptance Ramp Control HISTORY
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Moving Merge System HISTORY