I13 Bullock Preempt

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    Emergency VehiclePreemption & Evaluation

    Procedures

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    Background Standing in for Juan Morales on

    presenting FHWA TReL study onPreemption in Northern, VA.

    Added state of the practice in signalpreemption/priority to talk.

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    Outline Proceed with assumption that NTCIP

    Preemption objects represent a genericstate of the practice functionality.

    Discuss features/limitations of NTCIPObject

    Summarize/recap recent evaluationwork.

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    State of the Practice - NTCIP NTCIP TS 3.5 represents

    A basic agreed upon terminology andparameters that agencies can specify.

    A vendor neutral set of definitions. A framework for system operation

    An open architecture for expanding thestate of practice.

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    TS 3.5 PreemptionConformance Group

    maxPreempts (TS 3.5, 2.7.1) preemptTable (TS 3.5, 2.7.2)

    Following slides based upon my interpretationof specification - I have not had any first handexperience exercising a controller withthese features.

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    Table of Preempt Parameters Number Control **

    Link ** Delay MinDuration

    MinGreen MinWalk EnterPedClear TrackGreen

    (min)DwellGreen MaxPresense

    Octets TrackPhase DwellPhase

    DwellPed ExitPhaseStatus Info State **

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    2.7.2.2 Preempt ControlVariable containing following flags Lock/Non Locking Calls Determine if a preempt overrides an

    automatic flash Determine if a higher numbered (active)

    preempt should be overridden. Phases listed in DwellPhase to flash

    yellow during Dwell phase (others flash

    red)

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    2.7.2.3 Preempt LinkObject provides a means to define a higherpriority preempt to be combined (linked) withthis preempt. At the end of Dwell time, thelinked preempt shall receive an automaticcall which shall be maintained as long as thedemand for this preempt is active.

    Provides a procedure for constructing amore complex sequence then TrkClr/Dwell

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    2.7.2.16 Preempt State no active notActive(but)WithCall

    entryStarted trackService dwell

    linkActive exitStarted maxPresence other (not defined)

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    Where are we? Base line definition of prioritized

    preemption (vendor neutral, so manynew and innovative features such asbus-priority have not been fully defined)

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    Future Existing TS 3.5 objects do not provide

    less aggressive manipulation ofcontroller needed for transit priority,they need to be defined (Balke, Head).

    NTCIP Working Group and the TransitStandards Consortium on Traffic SignalPriority will draft new NTCIP objects.

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    Example Opportunities forEnhancement

    Procedures for allocating extra time fora cycle or two to a particular phase afterpreemption terminates.

    1 (18) 2 (56) 3 4

    5 (20) 6 (54) (23) (23)

    1 2 (56) 3 4

    5 (20) 6 (54) (23)

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    Evaluating the Impact ofPreemption?

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    Problem Definition Analyze the impact emergency vehicle

    preemption has on the operation of acoordinated-actuated signal system.

    Not a steady state problem traditionalanalytical models can not be used.

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    Concerns Frequent preemtion can impose

    significant delays on preemptedapproaches

    One or two signals out of coordinationcan have a significant and lasting

    impact on an arterials performance

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    Case Study I

    H

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    ROUTE 7 - Loundoun, Virginia

    To Leesburg

    To Reston

    R o u t e 7

    XEROX BLVD.

    LANDSDOWNE BLVD.

    ASHBURN VILLAGE RD.

    P o t o m a c R i v e r

    H

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    Evaluation Equipment ConfigurationRoute 7 Signal Preemption Project

    CORSIM

    H

    N Obtainedcounts, andgeometry

    Modelednetwork

    Obtainedtimings

    Configured170s

    EvaluatedPerf.

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    Hardware in the LoopSimulation

    Signal States

    Detector States

    Simulated trafficactuates detectorsand responds tophase indications

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    Evaluation Environment

    CIDs

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    Typical Emergency Vehicle PathRoute 7 - Loundoun, Virginia

    H

    Xerox Blvd.

    Landsdowne Blvd.

    AshburnVillage Rd.

    N

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    Observed/Tabulated in TReL

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    One Preemption in 40Travel TimeIntersections& PhasesPrempted

    PathWestbound

    TravelTime(sec)

    EastboundTravelTime(sec)

    Base caseno preemptions 197.3 208.6

    4 (4) H 198.1 212.1

    5 (3),4 (2 & 5)

    H 197.3 215.9

    4 (not preempted ),3 (2 & 5)

    H 195.6 206.7

    4 (not preempted )3 (4)

    H 194.8 207.6

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    Two preemptions in 40Travel TimeIntersections

    & PhasesPrempted

    PathWestbound

    TravelTime(sec)

    EastboundTravelTime(sec)

    Base caseno preemptions

    197.3 208.6

    4 (4) H 199.8 213.7

    5 (2 & 5)4 (2 & 5)

    H

    199.9 212.0

    4 (not preempted ),3 (2 & 5)

    H 194.7 207.1

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    No significant impact to arterial or sidestreets.

    In this study, no more then 2 controllersare preempted at once.

    Relatively long intersection spacing -platoon dispersion may reduce theimpact of coordination.

    Observation/cautions

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    Second Preemption Study Applied evaluation protocol to an arterial

    with 4 relatively closely spacedintersections (700, 780, 1400).

    Evaluated both mid-day and afternoonpeak conditions.

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    Study Location - SR 26

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    Evaluation Equipment

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    Preemption Paths

    N

    N

    N

    N

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    Preemption Paths(Continued)

    N N

    N

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    TrafVu Graphic

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    Eastbound Travel(1 - Preempt in 22 min).

    N

    CUMULATIVE TRAVEL TIME (MIDDAY RUSH)EASTBOUND ROUTE 26 (PROGRESS DRIVE TO MEIJER ENTRANCE) - THRU VEHICLES

    > 1 PREEMPT(S) AT 60 SEC ( PATH_ID - 101,1,2,3,4,111) 1 PREEMPT(S) AT 60 SEC ( PATH_ID - 101,1,2,3,4,111) 3 PREEMPT(S) AT 60 SEC, 150 SEC AND 700 SEC (PATH_ID - 101,1,2,3,4,111) 3 PREEMPT(S) AT 60 SEC, 150 SEC AND 700 SEC (PATH_ID - 101,1,2,3,4,111) 3 PREEMPT(S) AT 60 SEC, 150 SEC AND 700 SEC (PATH_ID - 101,1,2,3,4,111) 3 PREEMPT(S) AT 60 SEC, 150 SEC AND 700 SEC (PATH_ID - 101,1,2,3,4,111) 0(s/v)

    >10(s/v)

    >15(s/v)

    >20(s/v)

    >0(s/v)

    >10(s/v)

    >15(s/v)

    >20(s/v)

    1 / 1 WB1 / 2 EB1 / 3 WB1 / 4 EB1 / 5 WB EB WB1 / 6 EB1 / 7 EB

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    2 Preempt in 22 MinutesStatistically Significant?

    MIDDAY PEAK AFTERNOON PEAKScenario /

    PathArterial direction that has a

    significant statistical differencein travel time

    with different margins.

    Arterial direction that has asignificant statistical difference

    in travel time

    with different margins.>0(s/v)

    >10(s/v)

    >15(s/v)

    >20(s/v)

    >0(s/v)

    >10(s/v)

    >15(s/v)

    >20(s/v)

    2 / 1 WB WB2 / 2 EB EB EB EB2 / 3 WB WB2 / 4 EB EB EB EB2 / 5 EB WB EB WB2 / 6 EB WB EB WB EB2 / 7 EB EB WB EB

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    3 Preempt in 22 MinutesStatistically Significant?

    MIDDAY PEAK AFTERNOON PEAKScenario /

    PathArterial direction that has a

    significant statistical differencein travel time

    with different margins.

    Arterial direction that has asignificant statistical difference

    in travel time

    with different margins.>0(s/v)

    >10(s/v)

    >15(s/v)

    >20(s/v)

    >0(s/v)

    >10(s/v)

    >15(s/v)

    >20(s/v)

    3 / 1 WB WB3 / 2 EB WB EB WB EB EB EB3 / 3 WB WB3 / 4 EB EB WB EB EB EB3 / 5 EB WB WB EB WB EB WB3 / 6 EB WB EB WB EB EB EB3 / 7 EB WB EB WB EB EB EB

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    Observations Preemption does not have a major

    impact on under-saturated corridors. Dwell is the only transition algorithm

    that consistently performed badly. The stolen green time is the main

    source of problems near saturation. There may be some advantage to using

    add-only transition near saturation.

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    Outline/ReCap Discussed vendor neutral preemption

    capabilities. Reviewed recently developed

    evaluation procedures - presentedsome case study results - upper bound

    on collateral impact of transit priority. Results are documented in 1999 ITSA

    Paper and Draft TRB 2000 Paper.

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    Questions