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