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A Simplified Method for Computing VSL-Bottleneck

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Control Parameters

A Simplified Method for Computing VSL-Bottleneck

TL qL

Control Boundaries

Target VSL speed

Number of VSL signs

a

a

a

qvk

c

c

qv

Step 1

Identify the bottleneck capacity: ; and key parameters:

,c cq vck

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Identify the Maximum queue length under no control scenario .

Compute the approaching traffic flow characteristics

Estimate the target control density:

A Simplified Method for Computing VSL-Bottleneck

Step 2

qL

Step 3

, , .a a aq v k

Step 4

(1 )VSL a ck k kα α= + −

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Compute the target VSL speed :

Compute the transition length :

Compute the NO. of VSL signs:

A Simplified Method for Computing VSL-Bottleneck

Step 5

v∗

Step 6

TL

Step 7

10

a

mph

v v∗−

c

VSL

qvk

∗ =

( , )a aTL f v v v∗= −

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Local Ramp Metering Control

Gang-Len Chang

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Basic Ramp Metering Concept

• Pre-timed local ramp control: Required Information - Offline flow rate on the upstream and downstream segments of

the target ramp. - Capacity on the upstream and downstream freeway segments of

the target ramp. - Maximum merging rate from the on-ramp. - Maximum allowable queue length.

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• Basic concept Metering rate for time interval k (5-15 mins)

• Deficiencies - Uncertainty in demand - Capacity ? - Maximum queue length factor (waiting time) - Unknown lane distribution - Flow rate does not represent the congestion level

Metering Rate

Equivalent rate

Downstream flow rate+ ≤

Capacity at the merging

point

From mainline flow

(For any preselected time interval)

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• Basic concept Metering rate for time interval k (5-15 mins)

• Deficiencies - Uncertainty in demand - Capacity ? - Maximum queue length factor (waiting time) - Unknown lane distribution - Flow rate does not represent the congestion level

Metering Rate

Equivalent rate

Downstream flow rate+ ≤

Capacity at the merging

point

From mainline flow

(For any preselected time interval)

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F1VOL MCAP

FVOL FCAP

MR

O

O

Q

Q

I

I

Stop line

Ramp Metering Signal

Advance Ramp Control Warning Sign

Demand Detector

Passage Detector

Queue DetectorLocal Pretimed Ramp Metering

MR+FVOL ≤FCAPFVOL≤DF MR≤DR

600

500

450

300

1507:00 AM 7:10 7:20 7:30 7:40 7:50 8:00

Time

5-M

inut

e V

olum

es

FCAP=500

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Metering Flow

Conversion Factor

Mainline flow rate+ ≤ Merging

capacity

Local Responsive control Information: Use the detectors (on the freeway mainline segment) to determine: - Mainline flow rate, occupancy in the immediate vicinity of the merge area - Ave. ramp demand - Ave. ramp queue and max. queue

(flow-in from ramp)

(Convert from occupancy/detected)

(One can set control objective here)

• Congestion in the downstream segment → feedback system •No congestion in the downstream segment → feed forward control

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Local Traffic Responsive Ramp Metering

P

D

Q

Q

D

M

Stop line

Ramp Metering Signal

Advance Ramp Control Warning Sign With Flashing Beacons

Merge Detector (Optional)

Demand Detector (Required)

Queue Detector (Optional)

VF

Freeway

M

Frontage road or surface street

Passage Detector (Optional)P

Freeway merge flowFFreeway mainline flowV

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Adaptive Local Responsive Ramp Metering Information: - Volume and occupancy data on both the freeway upstream and downstream segments - Ramp demand and ramp queue Core concept: • Compare the upstream and downstream congestion level to determine the metering rate • The congestion level is monitored by freeway detectors • The downstream detectors can also be used to monitor the max flow rate and merging flow rate • One can set control objectives on the target level of operations

Deficiencies: • Demand uncertainties and queue time • Local optimum → vs. system optimum → at the cost of waiting time for drivers at other ramps. • Point detectors → point congestion • Mainline flow variation • Same deficiencies as local signal control

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Adaptive Local Traffic Responsive Ramp Metering

½ MILE

P

D

Q

Q

D

M

Stop line

Ramp Metering Signal

Advance Ramp Control Warning Sign With Flashing Beacons

Merge Detector (Optional)

Demand Detector (Required)

Queue Detector (Optional)

VF

Freeway

M

Frontage road or surface street

Passage Detector (Optional)P

Freeway merge flowFFreeway mainline flowV

V

V VV V

FV

V VV

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Outline • Basic ALINEA (Traffic Modeling &

Control Algorithm)

• “use density or occupancy, but not speed or flow rate for control.

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Related Literature • ALINEA: A Local Feedback Control Law For On-

Ramp Metering. Markos Papageorgiou, Habib Hadj-Salem, Jean-Marc Blossville. Transportation Research Record, 1320 (1991), pp. 58-64

• ALINEA Local Ramp Metering-Summary of Field Results. M. Papageorgiou, H. Hadj-Salem, F. Middelham. Transportation Research Record, 1603 (1997), pp. 90-98

• A flow-maximizing adaptive local ramp metering strategy. Emmanouil Smaragdis, Markos Papageorgiou, Elias Kosmatopoulos. Transportation Research Part B, 38 (2004), pp. 251-270

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Traffic Modeling (1)

[ ( ) ( ) ( )]( ) (1)in outq t r t q ttρ δ+ −=

1) Flow-Density Relationship

Location Site

upstream traffic volume

on-ramp traffic volume

downstream traffic volume

stretch length

traffic density

( )tρ

inrEq-1 shows the density change over time

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Responsive ramp metering control

ˆ( ) ( 1) ( ( ))R outr k r k K o o k= − + −

2) Replace density with Occupancy

100

outoρ αµα λ

=

=

number of lanes of the mainstream

mean effective vehicle length

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3) Assume as a nonlinear function of ( )outq t ( )outo t

( ) [ ( )]out outq t Q o t=

downstream traffic volume downstream occupancy

( ) [ ( ) ( ) ( ( ))] / (2)out in outo t q t r t Q o t δα= + −

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One can also use downstream speed as a supplement

control indicator

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T H A N K

Y U!