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7/31/2019 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