Operational Analysis Overview - Kittelson & Associates,...
Transcript of Operational Analysis Overview - Kittelson & Associates,...
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Operational Analysis OverviewRoundabout Traffic Operations AnalysisShort Course
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Operational AnalysisOperational Analysis
Basics of roundabout operationsMeasures of effectivenessModeling techniques
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Basics of Roundabout Operations: Gap AcceptanceBasics of Roundabout Operations: Gap Acceptance
Drivers make their own decisions about when to enter
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Characteristics that Affect Roundabout PerformanceCharacteristics that Affect Roundabout Performance
The driver making the decision to enterThe stream of conflicting trafficGeometry
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NCHRP Report 572: Roundabouts in the United StatesNCHRP Report 572: Roundabouts in the United States
Most comprehensive study of U.S. roundabout performance to date
NCHRP Project 3-65
Published in 2007
Anchors new HCM 2010 procedure
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NCHRP Report 572 (cont.)NCHRP Report 572 (cont.)
U.S. capacities lower than observed in other countries
Capacity clearly sensitive to geometry in the aggregate (number of lanes)
Secondary effects of geometry on capacity (e.g., lane width, diameter) masked by variations in driver behavior
Lane-by-lane analysis needed
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NCHRP Report 572 (cont.):Possible Reasons for Lower U.S. CapacitiesNCHRP Report 572 (cont.):Possible Reasons for Lower U.S. Capacities
Driver unfamiliarity with roundabouts
Larger vehicles
Prevalence of stop control
Lack of use of turn signals on exits
Suboptimal geometry affects lane use at multilane roundabouts
Trends may change over time or by region
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NCHRP Report 572 (cont.):Capacity CurvesNCHRP Report 572 (cont.):Capacity Curves
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Conflicting Flow (pcu/hr)
Max
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All RdbtsCritical LaneSingle LaneCritical Lane RegressionSingle Lane RegressionExtropolated RegressionExtropolated Regression
y=1130e-0.001x
y=1130e-0.0007x
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Need for Continuing ResearchNeed for Continuing Research
More roundabouts in operation today (~2000 in 2010 versus ~300 in 2000)
More multilane roundabouts today
Longer adaptation period by drivers
HCM 2010 procedure has calibration tools to allow procedure to be adapted to empirical, local conditions
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Operational AnalysisOperational Analysis
Basics of roundabout operationsMeasures of effectivenessModeling techniques
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Degree of Saturation (Volume-to-Capacity Ratio)Degree of Saturation (Volume-to-Capacity Ratio)
Degree of saturation = volume / capacityTypical desirable maximum = 0.85Consider context of location in determining appropriate thresholds for maximum
Higher degrees of saturation may be ok in less critical areas where impacts of adding capacity exceeds benefitMore care may be appropriate in areas where queuing is more sensitive (e.g., closely spaced intersections, interchange off-ramps)
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DelayDelay
Control delayIncludes initial deceleration delay, queue move-up time, stopped delay, and final acceleration delay
Geometric delayDelay experienced by a single vehicle with no conflicting flowsCaused by geometric features
Total delay = Control + GeometricTypical measure used: control delay
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Other Performance MeasuresOther Performance Measures
Operational measuresQueuesStops
Environmental measures derived from operational measuresFuel economyEmissions
Other time framesDailyAnnual
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Level of ServiceLevel of Service
Based on control delayLOS assigned to each lane, approach, and intersectionDelay thresholds same as for TWSC and AWSC intersections
Similar delay formulationDrivers must select gaps – no guarantee of service
Research to affirm existing thresholds or support new thresholds desired
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Level of Service (cont.)Level of Service (cont.)
LOSControl Delay
(s/veh)
A 0 − 10
B > 10 − 15
C > 15 − 25
D > 25 − 35
E > 35 − 50
F > 50
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Operational AnalysisOperational Analysis
Basics of roundabout operationsMeasures of effectivenessModeling techniques
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Modeling TechniquesModeling Techniques
Variety of modeling techniques used for all types of transportation facilities
No one method inherently superior to any other – they are only as good as their calibration to reality
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How to Model Capacity and Performance?How to Model Capacity and Performance?
Geometry, traffic
volumes
CapacityEmpirical Regression Method
Field
Aggregate gap acceptance behavior
Analytical MethodField
Traffic flow theory
Performance Measures
SimulationTraffic flow theory
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Gap Acceptance ParametersGap Acceptance Parameters
tc (critical headway)Accepts gap →
Accepts new gap → tc (critical headway)
OR within the same gap → tf (follow-up headway)
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Priority Stream
Non Priority Stream
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User behavior characteristicsUser behavior characteristics
Roundabout performance depends on the availability of gaps and the willingness of drivers to accept those gaps
Considerable variation possible from driver to driver, so performance is typically based on the mean observed performance
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Geometric CharacteristicsGeometric Characteristics
Roundabout operations are affected by the geometry of the intersection
Number of lanesLane use assignment (e.g., left, left-through, etc.)Usable length of lanesLane width, entry angle, and other relatively minor geometric parameters
Models capture these characteristics to varying degrees
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Characteristics of the Surrounding SystemCharacteristics of the Surrounding System
Effects from driveways, pedestrian crossings, upstream signals, railroad crossingsAdvanced modeling may be needed
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Flow Types at a Roundabout: Aggregations of Turning MovementsFlow Types at a Roundabout: Aggregations of Turning Movements
Entering flow (ve)Circulating flow (vc)Exiting flow (vex)
HCM 2010 Exhibit 21-2
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?
Example: Simple Volume ConversionExample: Simple Volume Conversion
Turning movements
Roundabout volumes
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16510673
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Example Step 1: Calculate Entry VolumeExample Step 1: Calculate Entry Volume
Entry volume = sum of entering turning movements
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? 344
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Example Step 2: Calculate Exit VolumeExample Step 2: Calculate Exit Volume
Exit volume = sum of turning movements as shown
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Example Step 3: Calculate Circulatory VolumeExample Step 3: Calculate Circulatory Volume
Circulatory volume = sum of turning movements as shown
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Example: SolutionExample: Solution
Turning movements
Roundabout volumes
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HCM 2010 Flow Rate AdjustmentsHCM 2010 Flow Rate Adjustments
Use of 15-minute flows or Peak Hour Factor (PHF) adjustmentsAdjustments for heavy vehiclesAdjustments for lane use
Turning movement patternsDesignated lane useGeometry (e.g., lane alignment)Driver behavior
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Conflicting Flow Rate (pc/h)
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Dashed regression extrapolated beyond the data
Capacity of one-lane entry or right lane of two-lane entry against two conflicting lanes
Capacity of left lane of two-lane entry against two conflicting lanes
Capacity of one-lane or either lane of two-lane entry against one conflicting lane
HCM 2010 Capacity AnalysisHCM 2010 Capacity Analysis
HCM 2010, Exhibit 21-7
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Cap
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Dashed regression extrapolated beyond the data
Capacity of one-lane entry or right lane of two-lane entry against two conflicting lanes
Capacity of left lane of two-lane entry against two conflicting lanes
Capacity of one-lane or either lane of two-lane entry against one conflicting lane
Capacity: 1 laneCapacity: 1 lane
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Conflicting Flow Rate (pc/h)
Cap
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c/h
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Dashed regression extrapolated beyond the data
Capacity of one-lane entry or right lane of two-lane entry against two conflicting lanes
Capacity of left lane of two-lane entry against two conflicting lanes
Capacity of one-lane or either lane of two-lane entry against one conflicting lane
Capacity: 2x1 laneCapacity: 2x1 lane
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Cap
acit
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Dashed regression extrapolated beyond the data
Capacity of one-lane entry or right lane of two-lane entry against two conflicting lanes
Capacity of left lane of two-lane entry against two conflicting lanes
Capacity of one-lane or either lane of two-lane entry against one conflicting lane
Capacity: 1x2 laneCapacity: 1x2 lane
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Conflicting Flow Rate (pc/h)
Cap
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Dashed regression extrapolated beyond the data
Capacity of one-lane entry or right lane of two-lane entry against two conflicting lanes
Capacity of left lane of two-lane entry against two conflicting lanes
Capacity of one-lane or either lane of two-lane entry against one conflicting lane
Capacity: 2x2 laneCapacity: 2x2 lane
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Calibration of CapacityCalibration of Capacity
Need for calibration to local data (preferred if available) or national averagesAll models—HCM 2010 and all types of software—need to be calibrated
HCM 2010 is anchored to NCHRP Report 572 data (average of US conditions observed in 2003)Form of empirical regression model allows for direct calibration to local field conditions
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Example of HCM 2010 Model CalibrationExample of HCM 2010 Model Calibration
Single-Lane Roundabouts
NCHRP 572 (2003 data)
California(Tian et al,
2006)
Bend, Oregon (KAI, 2009)
Critical Headway 5.1 s 4.8 s 4.1 sFollow-up Headway
3.2 s 2.5 s 2.7 s
Higher single-lane capacity in these examplesDrivers more aggressive than national average?Driver history and familiarity?Use of turn signals? (police enforcement/signing)
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Alternative ToolsAlternative Tools
HCM 2010 explicitly recognizes that HCM procedures are not the only way to analyze problemsApplicability to roundabouts
Geometric configurations not included in modelOversaturated conditions requiring multiple-period analysisInteraction effects with other intersections