Scoot Trb2001 Petermartin

7/28/2019 Scoot Trb2001 Petermartin

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SCOOT, an overviewSCOOT, an overview

Peter T. Martin

University of UtahTraffic Laboratory


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SCOOTSCOOT

Split

Cycle Offset

Optimization

Technique


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SCOOT InstallationsSCOOT InstallationsUK

70+ locations (London to Aberdeen)

Heathrow Airport

Worldwide Bahrain, Beijing, Dalian, Cape Town,

Karachi, Larnica, Limassol, Madrid,Nicosia, Santiago, Dubai

North America Oxnard, Toronto, Red Deer, Minnesota,

San Diego, Anaheim, Alexandria,Arlington VA, Orlando FL


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Presentation SummaryPresentation Summary

Philosophy

The MethodOptimizers

Control mechanism

SCOOT Virtues & Vices


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PhilosophyPhilosophyPhilosophy


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SCOOT isSCOOT is modelmode lbasedbased

on-line TRANSYT

pedigree 20 year development

marketed

signal companies

Kernel


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DevelopmentDevelopment 1975 research version Glasgow

(Scotland)

1979 1st installation Coventry(England)

1991 v 2.4

First US installation


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EvaluationEvaluation

6 UK cities

overall 12% savings[+ age (3%/year) over good fixedtime plans]

Anaheim, Minneapolis


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The SCOOT PhilosophyThe SCOOT Philosophy optimizes in real time

one central computer

used to have back-up

no plans

although needs start-upseed

needs fall-back


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Philosophy cont...Philosophy cont...

"elastic" coordination (incremental)

minimizes transients

responds quickly

responds accurately small prediction times = accurate

estimates on-line measurement of cyclic flow

profiles (CFP)


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Cyclic Flow ProfileCyclic Flow Profile

enables estimation of

# veh approaching red (ie queuelength)

time to clear queue

offset adjustment impact

split adjustment impact


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The SCOOT MethodThe SCOOT Method


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The MethodThe Method

basic time unit - 1 second

calculates TRANSYTtypePerformance Index links can be weighted

alternative MOEs can be weighted

provides real-time data

good queue prediction


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Model ParametersModel Parameters

delay

congestion queue lengths

# stops

occupancy(proportion of cycletime detector occupied) -congestion measure


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Cyclic Flow Profile

Time (s)

Flow

(pcu/h

)

1 cycle

0 10 20 30 40 50


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0 m

30 m

120 m

210 m

300 m

Consider the southerly flow


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measured arrival patterns

0 10 20 30 40 50 60

0 10 20 30 40 50 60

0 10 20 30 40 50 60

0 10 20 30 40 50 60

Time (s)

Flow

(pcu/h)

1800

1800

1800

1800

0 m

30 m

120 m

210 m

300 m

0

0

0

0


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measured arrival patterns

predicted arrivalpatterns0 10 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 50 60

0 10 20 30 40 50 60

0 10 20 30 40 50 60

Time (s)

1800

1800

1800

0 10 20 30 40 50 60

0 10 20 30 40 50 60

Time (s)

Flow

(pcu/h)

1800

1800

1800

1800

0 m

30 m

120 m

210 m

300 m

0

0

0

0

0

0

0


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CYCLE TIMESfixed

SPLIT fixed

OFFSETfixedmorning peak

plan

0730

0930

overnight plan

off peak day plan

Fixed Time Plan Control


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CYCLE TIMEvaries

SPLIT varies

no distinct

plansOFF

SETvaries

SCOOT

Control


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7 8 9 10 11 12 13 14 15 16 17 1 8 19 2 0 21

DemandResponsive

SCOOT

7 8 9 10 11 12 13 14 15 16 17 18 19 2 0 21

FIXEDTIME

PLANS

Fixed

cycletime

Fixedsplits

Variablecycle

time

Variablesplits

Time Of Day

Flow


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50

0

50

08:00 12:00 16:00

50

0

50

Green time per cycle (s)

End of

green atsignal 'A'Signal 'A'

Signal 'B'

Red time per cycle (s)

Time relative

to start ofgreen at

'A'(s)

Time datum for'A'and 'B' is start of

green at Signal 'A'

Start of previous

red at signal 'A'

End of greenat signal 'B'

'Offset' isstart of green

at 'B' relative

to 'A'

Start ofprevious red atsignal 'B'

Time during the day (h)

Cycle time

Two Coordinated Signals During One Day of SCOOT Control

Source:TRL Report LR1014


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DetectionDetection

immediately down stream of theprevious intersection

(well upstream of the stop line)

early prediction of arrivals atstop line

recognizes faulty detectors

identifies blocking back queue


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A B

A

B

A

BA

B

detector

SCOOTFlowDetection

Up StreamDetectors

C


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RegionsRegions

Network subdivided into Regions each region has homogenous flow

characteristics Each region subdivided into links

and nodes

For each region, calculates degree ofsaturation for all nodes: x=q/s ratio of detected flow to saturation flow


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Critical NodesCritical Nodes

Identifies most critical node foreach region

degree of saturation highest

(not always the same nodes)

Activates Cycle Time Optimizer Co


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The OptimizersThe Optimizers


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Cycle OptimizerCycle Optimizer Optimizes cycle time

Calculates optimum cycle time forcritical node: Co

Applies common cycle timethroughout region

Regions are operated on a

common cycle maintains coordination

regional TRANSYTapproach but

double cycling


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Cycle AdjustmentsCycle Adjustments

increments from 1 to 4 seconds (+/- )

in 1 second units

intervals of not less than 2.5 minutes

congestion measured for each link

each region varied independently

V 4.2 offers greater cycle adjustment


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Cycle OptimizerCycle Optimizer

seeks to ensure most heavily loaded intersections

operates 90% degree of sat

double cycling facility (asTRANSYT)

dominates other optimizers modifies split and offset optimizers


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Split OptimizerSplit Optimizer

a few seconds before eachphase change SPLIT optimizer

decides advance

postpone

or leave alone from 1 to 9 seconds (+/- )


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Split OptimizerSplit Optimizer

minimizes the maximum degree ofsaturation on approaches to criticalnode

seeks to

balance degree of sat on allapproaches

avoids blocking-back

split calculation based on CFPpredictions

works in tandem with offsetoptimizer

subordinate to c cle o timizer


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Offset OptimizerOffset Optimizer operates on each node pairing, eachcycle

CFP enables measurement of impact

upstream detection enables prediction (time)

seeks to improve traffic progression

only looks up & down one node at atime

common cycle time ensuresprogression


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Control MechanismsControl Mechanisms


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Performance Index ControlPerformance Index Control

facilitiesfacilities

offset weighting

green wavesgreen wavescan be imposed split weighting

fixed and biased offsets

link weightings


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Signal StatusSignal Status

for low flow conditions

recognizes & models locallycalled demand dependentphases

recognizes & models emergency

vehicle override 5-10% delay reduction


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Congestion ManagementCongestion Management

FacilitiesFacilities

multi link recognition

pre-specified offsets imposed forqueue identification beyondupstream detector

gating (close cousin tometering)


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GatingGating

split optimizer

'bottle neck' critical link 'gating' storage link - U/S & D/S

signal holding

changeable message signs


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Optimizer ControlsOptimizer Controls Fixed Offset Logic

split or cycle optimizer controlled

public transportation route favor Filter turn

modeled separately

Bike logic for high bike flows(developed in Beijing)


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Automatic SaturationAutomatic Saturation

Occupancy DeterminationOccupancy Determination(saturation flow/occupancy hybrid)

easier installation & calibration

through detected sat flows elimination of validation for some

links

responsive to temporaryobstructions reducing sat flowvalues


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Information ManagementInformation Management

SCOOT Messages

detector data

model output

On-Line Data Base

Air quality estimates


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MessagesMessages

% degree of saturation

% congestion occupancy

max q

exit blockage Q clear time


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SCOOT on line Data BaseSCOOT on line Data Base

Automatic SCOOT TrafficInformation Database

(ASTRID)

stores and analyzes traffic data

Can substitute historical flow inplace of defective detector


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SCOOT Virtues and VicesSCOOT Virtues and Vices


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SCOOT VirtuesSCOOT Virtues founded on a rigorous model

sound theoretical basis

large installation base not always a good thing!

very good at coping with

heavy flows, close to saturation complex flow patterns

unpredictable variations


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SCOOT Virtues cont.SCOOT Virtues cont. provides copious data

never originally intended

tends to favor the "Main Roads"just as TRANSYT does

flexible and controllable double cycling

PI weighting factors operates with most types of controller


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InstallationInstallation

local knowledge minimal

does not require intimateknowledge of the network

becoming more self validating


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Virtues: The SCOOTVirtues: The SCOOT

Personal i tyPersonal i ty

Not as highly personneldependent as some systems

non hysterical copes with large flow change

gently

sophisticated so many facilities


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SCOOT VicesSCOOT Vices

detectors

scope sophistication


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DetectorsDetectors Detector dependent

(as are all adaptive systems)

Detector Failure up to 15% detector failure

accommodated

performance degrades back to a fixed

time plan if faults not rectified Lane detection


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ScopeScope

Still essentially tactical

Regional boundaries

Unable to accommodate over-saturation (no system can)

Urban Freeway interaction unknown


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SophisticationSophistication

intimate knowledge of networknot necessary, but

expertise now needed on options

impenetrable kernel

(unless $150,000 for license)


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Now for SCATSNow for SCATS

Scoot Trb2001 Petermartin

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